Avian Medicine: Princilpes and Application - · PDF fileAvian Medecine : Principles and...

BRANSON W. RITCHIE, DVM, PhD Assistant Professor, Avian and Zoologic Medicine Department of Small Animal Medicine College of Veterinary Medicine University of Georgia Athens, Georgia

GREG J. HARRISON, DVM Director, The Bird Hospital Lake Worth, Florida President, Harrison’s Bird Diets Omaha, Nebraska

LINDA R. HARRISON, BS President, Wingers Publishing, Inc. Former Editor, Journal of the Association of Avian Veterinarians Lake Worth, Florida

AVIAN MEDICINE: PRINCIPLES AND APPLICATION

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asseriformes (perching and songbirds) isthe largest order of birds. It contains nearly60 percent of all bird species ranging in sizefrom the tiny Weebill (80 mm in length) to

the Superb Lyrebird (130 cm long, including a 72 cmtail). Canaries, finches, starlings and mynahs areexamples of passerine birds that are common in cap-tivity. Passerines are widely distributed throughoutthe world, and all passerines share a common aniso-dactyl foot structure with three unwebbed toespointed cranially and one caudally. The altricialyoung are usually naked when hatched and arereared in a nest.

The order is believed to have originated in Gond-wana, the ancient southern continent. Convergentevolution makes differentiating species based onmorphologic grounds difficult, and in the past, theanatomy of the syrinx has been a primary means ofclassification. Recent DNA hybridization and proteinelectrophoresis studies are modifying traditionalviews. One group of passerines is now believed tohave evolved and radiated in eastern Gondwana,proto-Australasia (these include such species as bow-erbirds, lyrebirds, birds of paradise, honeyeaters,Australian grass finches and fairy wrens). Anothergroup, the suboscines or primitive songbirds are be-lieved to be of western Gondwanan origin (current-day South America). These include such primitiveSouth American species as contingas, manikins, ant-birds and gnateaters. More advanced songbirds likeFringillidae finches, sparrows, warblers, starlings,thrushes and sunbirds may also have evolved viawestern Gondwana and migrated from this area tobecome widely distributed.10

While Passeriformes are widespread in the northernhemisphere, there are very few endemic families andmany of the species are migratory.56

PC H A P T E R

43PASSERIFORMES

Patricia Macwhirter

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Avian Medecine : Principles and Application, B.W. Ritchie, G.J Harrison and L.R. Harrison (Eds.)

Anatomy and Physiology

Passeriformes have become adapted to a wide varietyof ecological niches. The anatomic and physiologicdifferences expressed within the order reflect thesespecific evolutionary patterns (Table 43.1).

Digestive System

The basal metabolic rate (BMR) of passerine birds isgenerally about 65% greater than that of non-passer-ines, and their body temperature is about two de-grees Centigrade higher (around 42°C). While somedesert passerines such as the Zebra Finch have beenknown to survive months without drinking water,most small passerine birds drink from 250 to 300ml/kg body weight of water each day and may eat upto 30% of their body weight daily. These figures arehigher than those for most non-passerines, whichtend to be larger birds.

Most passerine species have a narrow, triangulartongue compared with the thick blunt tongue of par-rots. The tongue is rarely involved in clinical prob-lems. The tongue of passerines may become hyper-keratotic at the tip and extend rostrally through thebeak. The syndrome appears to cause few clinicalproblems, but the hyperkeratotic tissue can be slowlytrimmed back with a pair of strabismus scissors,taking care not to cut healthy mucosa. Other parts ofthe digestive tract differ depending on the species’feeding patterns. A ventriculus is present in gra-nivorous and insectivorous species such as finches,but not in species such as honeyeaters that consumenectar and soft foods. If present, cecae are generallysmall and vestigial.

Inexperienced Passeriformes breeders may presentchicks for evaluation of a “sore” or “swelling” on theneck. This clinical sign is usually determined to bethe crop distended with seeds and visible beneaththin, featherless skin.

There is no production of crop milk in passerines asthere is in pigeons, but some finches will regurgitatecrop contents to feed their young. Pathogens can betransmitted from parent to offspring during thisprocess, particularly with foster-raised chicks thatprobably did not receive yolk-derived antibodiesagainst microorganisms from their foster parents’

digestive system. For example, although Cochlosomasp. may cause inapparent infections in adult Ben-galese (Society) Finches, significant mortality mayoccur in juvenile Gouldian Finches being fostered byBengalese parents.15

Nestling Estrilid finches (eg, Gouldian and ZebraFinches) normally have characteristic luminousmouth markings. Mucosal patterns are species-spe-cific and help to guide parents to their own chickswithin the recesses of dark nests.

The spleen in most passerines is oblong, not spheri-cal, as it is in Psittaciformes.

Respiratory System

In most Passeriformes, unlike in Psittaciformes, theright and left nasal sinuses do not communicate. Inpasserine birds, separate samples for rhinal disease(bacterial, viral, chlamydial) cytology examinationshould be taken from each sinus if a bilateral nasaldischarge occurs (Figure 43.1).9

Singing ability is highly developed in many passerinespecies and is related to the complexity of thesyringeal anatomy. Some species have the capacity tosing duets with themselves by alternately using op-

FIG 43.1 Passeriformes, like this canary, have right and leftparanasal sinuses that do not communicate as they do in Psittaci-formes. If bilateral oculonasal discharge suggestive of sinusitis isoccurring, it is wise to collect samples from both the right and leftsinuses for culture and cytologic evaluation. Conjunctivitis in thiscanary was responsive to tylosin therapy (courtesy of MichaelMurray).

CHAPTER 43 PASSERIFORMES

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posite bronchi. Roller canaries are specifically bredand trained for their singing ability.

The ability to mimic the human voice is well devel-oped in some passerines, notably mynahs, starlingsand corvids (Figure 43.2). Among Australian passer-ines, lyrebirds are legendary in their ability to mimicthe calls of other bird species, and rain forest gullieswill re-echo with an apparent chorus of calls that can

be traced to a single individual bird.The American mockingbird has simi-lar abilities and may mimic thesounds of companion Psittaciformes.

Like psittacine birds but unlike rat-ites and penguins, passerine birdshave a highly developed neopul-monic and paleopulmonic parabron-chi. This allows for highly efficientoxygen exchange. In most passer-ines, the cranial thoracic air sacs arefused to the single median clavicularsac, making a total of seven air sacsas opposed to the nine air sacs ofpsittacine species.

Reproductive System

In general, only the left ovary andoviduct develop in normal femalepasserines. Occasionally a nonfunc-tional right ovary will develop in fe-male sparrows. Both testicles de-velop in males and during the breed-ing season these may reach enor-mous proportions in relation to thesize of the bird. These physiologicallyenlarged testicles should not be mis-taken for pathologic conditions.

Role of Light in ReproductionTemperate-evolved species (includ-ing canaries) are usually dependenton daylight intervals for reproduc-tive performance. Increased daylighthours trigger the release of luteiniz-ing hormone (LH) in responsive indi-viduals. The precise light intervalvaries among species but the physi-ologic control mechanism appears tobe similar. Light stimulates photore-ceptors in the brain, probably in thehypothalamus, where there is a cir-cadian rhythm of photosensitivity. If

light coincides with the period of sensitivity, luteiniz-ing hormone releasing factor (LHRF) is released andgonadotrophin secretion is increased. If light coin-cides with the insensitive phase of the rhythm thereis no response. Gonadotrophin release in turn, trig-gers the release of sex hormones.

There must be a rest period following a long lightexposure to allow the photoreceptive system to reac-

FIG 43.2 A hand-raised European starling can develop an extensive vocabulary and havea voice quality that is similar to its relative, the mynah bird (courtesy of Mark Spreyer).

TABLE 43.1 Distinguishing Features of Selected Passerine Birds

Family GeneralComposition

Approx.Number of

SpeciesCharacteristics

Emberizidae New Worldfinches, cardinals,buntings, Cubanfinch

550 Cup-shaped open nest, female incubates,diverse group, 9 primary feathers

Estrildidae African, Asianand Australianfinches, waxbills,nunias, parrotfinches

125 Palatal markings in young, monogamous,dome-shaped nest with side entrance, 10primary feathers

Fringillidae True finches,canaries,goldfinch,chaffinch

125 Cup-shaped open nest, female incubates, 9primary feathers, 12 long tail feathers

Passeridae Sparrows, finches 32 Bulky domed nest of dried grass, breed incolonies, seed-eating, finch-like birds

Ploceidae Weavers,whydahs, queleas

145 Dome-shaped, covered, woven nest, do notsing, some species parasitic

Sturnidae Starlings, mynahs 108 Dark, iridescent, or brightly colored,colonial, nest in holes, long straight bills,mimicry ability

SECTION SEVEN COMPARATIVE MEDICINE AND MANAGEMENT

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tivate and once again be responsive to increasing daylength. Stimulation of the reproductive cycle is bestaccomplished by a progressive increase (four-weekperiod) of exposure to light. In general, the maximumeffect of increasing day length will occur when apasserine individual is exposed to 10-14 hours oflight. In males, the release of testosterone may occurin less than 24 hours following exposure to appropri-ately increased daylight hours. This in turn can resultin rapid development of secondary sexual charac-teristics and breeding display (territorial calling, tes-ticular and cloacal enlargement, courtship behavior).

Courtship behavior is the culmination phase of thereproductive cycle. Response of females to increasedphotoperiod is less dramatic, and it may require thepresence of a male in breeding condition to triggerappropriate nesting and egg laying responses.60 Bygradually increasing the light exposure, a more natu-ral reproductive cycling occurs, and a male is lesslikely to brutalize a slowly responsive hen. This alsoaccounts for the common aviculture practice of sepa-rating males and females during the non-breedingseason.

Many aviculturists use a “breeder” cage with a re-movable partition that allows the male to feed thefemale through an opening. At various intervals, thepartition separating the two sexes is removed, and ifthe female “accepts” the male, they are left together.The nest is put in the male’s side of the cage alongwith a source of nest material, which he collects inthe nest as part of the courtship activity. An experi-enced canary breeder can remove the partition atprecisely the right time for the female to accept themale.

This photoresponsive mechanism is very sensitive,and some species of birds indigenous to high lati-tudes commence breeding at almost the same weekfrom one year to the next. The fact that many Psit-taciformes hens produce eggs within a one- to two-day period on an annual basis suggests a similar, welldefined control system of the reproductive cycle. Thisis obviously an advantage where suitable conditionsfor raising chicks are restricted to a very limitedseason. In indoor breeding aviaries, it is important tomimic appropriate daylight patterns in order tostimulate breeding. Appropriate daylight-hour pat-terns will vary from species to species. In canaries,14 hours of light is commonly recommended to inducereproductive behavior in a responsive bird. Longerlight periods may cause a shorter breeding period

and early molting. Molting causes an immediate ces-sation of breeding activity.

After a period of long daylight hours, birds becomerefractory to photostimulation, and plasma concen-trations of both LH and FSH begin to fall. In maleWhite-crowned Sparrows, for example, this occursafter 50 days of long daylight hour exposure. Follow-ing the molt and period of decreasing daylight hours(fall), the breeding season starts again with the increas-ing daylight hours in the late winter and early spring.Following the molt and several months of recondi-tioning, the process starts over (in the United States,this occurs in December with January breeding).

Testosterone-induced SingingMale canaries will usually sing best in the spring inresponse to the endogenous testosterone “surge.” If abird becomes ill, it may stop singing and may notrecommence vocalizations until the following spring,even though the initial illness has resolved. In con-trast, some canaries (even some females) sing yearround and birds that stop singing because of illnessre-commence singing as soon as their general condi-tion improves. Injectable testosterone has been sug-gested as a method of inducing singing in birds thathave stopped after a period of illness. This is a prac-tice that should be discouraged because the testoster-one has a negative feedback that causes shrinking ofthe testes and reduced fertility.

Avicultural Considerations

Husbandry

Dietary and husbandry requirements for passerinesare diverse. There are primarily seed-eating speciessuch as the canary and Bengalese Finches that havebeen domesticated for centuries, are easy to care forand breed well in captivity. Many varieties of thesedomesticated species bear little resemblance to theirfree-ranging ancestors. Java Finches, Zebra Finchesand Gouldian Finches have somewhat shorter histo-ries of domestication but are also bred intensively incaptivity, and many mutations have occurred.

Many Passeriformes are critically endangered be-cause of habitat destruction and human interference.By developing a better understanding of these spe-


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cies and pressuring local, national and internationalleaders to preserve all remaining natural habitat,the aviculturist and avian veterinarian can have adramatic impact on the health of the planet.

Table 43.2 lists the breeding characteristics of se-lected passerine species.

HousingAviaries for Passeriformes should provide adequateprotection from the elements, with tropical speciesrequiring the greatest degree of protection. In mildclimates, hardy species of Passeriformes do well incarefully planned, planted aviaries that provide ade-quate protection as well as visually attractive sur-

roundings (Figure 43.3). Indoor, temperature-con-trolled rooms may be necessary to raise finches inharsher climates or when artificial lighting control isnecessary to increase production.

Planted aviaries are popular for passerines becausethese birds cause less damage to vegetation thanpsittacines and the vegetation provides observers amore natural view of a bird’s behavior. Care must betaken to ensure that the plant species are nontoxic.

Some passerine birds require special materials fornesting or to stimulate display behavior. Care mustbe taken that the type of objects provided for thesebirds are safe. Any contact with fine synthetic fibersshould be avoided because these may become entan-gled around the birds’ feet, toes or other body areasand cause damage, loss of limb or death. Burlap(hessian) cut into small squares, torn strips of facialtissue or coconut fiber make suitable, safe nestingmaterials (Figure 43.4) (see Color 24).

Male Satin Bowerbirds will build intricate displaynests that they decorate with blue objects if suitablematerials are provided. At one time in Australia, blueplastic rings were used to seal milk bottle tops, andfree-ranging bowerbirds would selectively collectthese rings from rubbish dumps and elsewhere todecorate their bowers. The rings would occasionallyslip over the bowerbird’s neck with fatal results.Manufacturers changed the color of the rings fromblue to white or red, ending the strangulation deaths.

Disease ControlDisease control in planted aviariescan be challenging because of the dif-ficulties involved in controlling mi-croorganisms and in medicating in-dividual birds. Because it is difficultto eliminate infectious agents oncethey are introduced into a plantedaviary, it is critical that any newbirds be quarantined, tested andtreated for parasites and infectiousdiseases prior to introduction.

Free-ranging birds should be ex-cluded from aviaries to prevent thetransmission of microorganisms.Sparrows, for example, may trans-mit poxvirus, Plasmodium, featherlice, mites and Haemoproteus to ca-naries.

TABLE 43.2 Breeding Characteristics of Selected Passerine Birds

Eggs PerClutch

Incubation(days) Fledging

Australian Grass Finches 4-8 12-17 21-25

Birds of paradise 1-2 17-21 17-30

Bowerbirds 1-2 19-24 18-21

Bulbuls 2-5 12-14 14-18

Canaries and Frigillidfinches

3-5 12-14 11-17

Cardinals 2-5 11-14 9-15

Crows and jays 2-8 16-22 20-45

Java Finch 4-8 14-14 26-28

Sparrows and weavers 2-5 13-14 21-24

Starlings and mynahs 2-7 11-18 18-30

FIG 43.3 Depending on the climatic conditions and the durability of the species, manyPasseriformes can be maintained in attractive, planted outdoor aviaries.


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NutritionPasseriformes may be granivorous, nectivorous, fruc-tivorous, insectivorous, omnivorous or carnivorous.Some species adapt readily to commercially availablediets, while others may require live food and are thusdifficult to maintain in captivity. Some free-rangingspecies have specific dietary preferences (GouldianFinches prefer sorghum) but may adapt to diets pro-vided in captivity. Even finches that are consideredomnivorous or carnivorous can be successfully raisedon properly balanced vegetable-based diets (Figure43.5).

Recommended dietary levels of vitamins and miner-als developed for poultry are used as a base in smallpasserines. Finches may consume up to 30% of theirbody weight daily in food compared with 10% forlarger parrots. If dietary supplementation is basedon a percentage of particular ingredients in the diet,finches may be consuming greater amounts on a pergram body weight basis than larger species. Over-dosage of vitamins and minerals may occur, resultingin infertility, renal calcification, gout and generalpoor condition; thus, only diets specifically formu-lated for finches should be used.

Feather color is dietary-dependent in species withcarotenoid pigmentation. Red factor and new colorcanaries have genotypes that require exogenoussources of carotenoids or related compounds to en-able full development of yellow, orange and red pig-ments in feathers. Foods for these birds contain ca-rotenoids and xanthophylls to enable proper colordevelopment. Reduced or absent carotenoids duringfeather formation produces pale or whitish featherswhile excess carotenoids will cause a deepening ofyellow and red pigments.8 Commercial diets thatcontain algae (spirulina) should have sufficient lev-els of naturally occurring carotenoids to maintainproper feather coloration. In the United States, “col-ored” foods generally contain carotene-soaked stalebakery products and should be avoided in favor ofmore natural sources of carotenoids.

Free-ranging Green Finches may be bronze or red-dish if they are exposed to excessive carotenoids.Their natural color will return when they are placed

FIG 43.4 Only natural substitutes (burlap, coconut fiber) should beused for nesting material in Passeriformes. Synthetic fibers (par-ticularly yarn) may wrap around a digit, leg or wing causingavascular necrosis distal to the constriction. In some cases, thefibers are grossly visible, while in others, magnification is neces-sary to see and remove the constricting fibers. A 26 or 30 ga needlemakes an excellent cutting tool for removing small fibers undermagnification (courtesy of Michael Murray).

FIG 43.5 A mature canary was presented with a four-month his-tory of progressive lameness. The bird was maintained on anall-seed diet in a small enclosure and had no exposure to water forbathing or sunlight. Note the generalized edema, hyperkeratosis,dry brittle nails and poor feather quality suggestive of chronicmalnutrition.


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on a more natural diet. Cardinalsmay fade in color when fruits, ber-ries or greens that contain canthex-anthin are scarce.

Vitamin A lacks color even thoughit is related to carotenoid pigments.Birds that have yellow feathers(honeyeaters) may become pale incaptivity in spite of being given ac-cess to grated carrot and othersources of vitamin A precursors,due to the nutrient’s being bound toundigestible cellulose. Considera-tion should be given to the bird’snatural diet. Pollen, for example,may be a source of utilizable ca-rotenoids such as apocarotenol, apigment associated with golden-or-ange shades.

Seasonal Feeding PracticesIn passerines indigenous to tropi-cal or arid regions, seasonalchanges related to daylight hoursare less important to the reproduc-tive cycle than the periodic availability of food andwater. Most successful breeders of these speciesmimic natural conditions by lowering the caloric,protein and fat content of diets and maximizing thebirds’ physical condition by allowing free flight inopen aviaries during the non-breeding season. At thebeginning of the breeding season, the birds are“flushed,” or encouraged to come into a breedingcondition by increasing the plane of nutrition. Mist-ing some species with water (to mimic rainfall) andproviding green, fresh foods and foliage may stimu-late breeding, particularly those species from desertenvironments such as the Australian grass finches.Birds must not become chilled during the mistingprocess. Depending on the species, birds may betransferred in pairs to smaller breeding enclosures orleft in flights to colony breed.

Sexing Passerines

In some passerines, there are obvious or subtle mor-phologic differences between the genders. Males aregenerally brightly colored or elaborately marked,particularly during the breeding season. Differencesin singing, courtship or nesting behavior may alsoprovide clues as to gender. Males usually have amelodious song and are more active during courtship

with dancing, hopping and assuming of various un-usual postures in addition to building the nest. Thefemales usually have more of a chirp or single-notecall and are more passive in the courtship role.

In males of many species, the caudal end of theductus deferens forms a mass of convolutions calledthe seminal glomerulus. During the culminationphase of the breeding cycle, the seminal glomerulapushes the cloacal wall into a prominent projection,the cloacal promontory. This can be observed by blow-ing the feathers on the bird’s vent cranially (Figure43.6). Hens do not develop this projection and have aflatter vent. In the non-breeding season and withimmature birds, these differences are less obvious.

Laparoscopy can be used to determine gender inmonomorphic passerine birds, but the small size ofmany species may increase the risk of this procedure.Newer methods of gender determination using DNAtechnology are proving useful and will probably beused more extensively in the future. The cost of theseprocedures tends to limit their application to moreexpensive species.

Vasectomy in FinchesEstrilid finches may be vasectomized by making a 3mm bilateral incision 5 mm lateral to the cloaca. Theskin and muscle layers are incised and adipose tissue

FIG 43.6 In many male Passeriformes, the seminal glomerulus swells and pushes the cloacacaudally during the breeding season. The cloacal promontory is a) present in the male andb) absent in the female, which has a flatter vent.


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is displaced to reveal the seminal glomus. A portionof each seminal glomus is removed. The incisions areclosed with single sutures and the bird placed onantibiotics postoperatively. The procedure generallytakes less than 15 minutes.5

Combating Aggression

While passerine species may be small, some are quiteterritorial and others have well developed peckingorders. Head trauma, feather picking, other injuriesor death may occur in individuals that have beenattacked by a companion (Figure 43.7). Self-mutila-tion, poor body condition and increased susceptibilityto disease can be indirect results of such aggressionin birds that are psychologically stressed because oftheir low social position. Aggression is more likely tooccur if the birds are overcrowded in small, openenclosures where less dominant birds have few op-portunities to escape from dominant birds. Aggres-sion-related injuries can be particularly pronouncedif new birds are introduced into collections where asocial order has already been established.3

Appropriate measures to prevent combat aggressionwill vary depending on individual circumstances.Suggestive control measures include:

prevent overcrowding; the fewer birds, the betterkeep stocking densities lowclip the wings or remove particularly aggressiveindividualsprovide extra vegetation or visual barriers (burlapsheets) to provide less dominant birds with anescape areaprovide multiple perches, feeding locations andnesting sitesmaintain subdued lighting in indoor areassimultaneously introduce all birds into a new en-vironment.

Parents that become aggressive toward their chicksare preparing to lay a second clutch of eggs and thechicks should be removed.

Sick or injured birds should be housed separatelyfrom other birds to prevent them from being injuredby their healthier companions.

Successfully establishing aviaries containing psittac-ine, passerine and other bird species requires a work-ing knowledge of individual behavioral charac-teristics and interspecies tolerance. Parrots from the

genera Neophema (Bourke’s or Scarlet-chested Par-rots) or Polytelis (Princess Parrots) are usually se-date and will mix well with finches. In contrast,rosellas (except for the Western Rosella) or Psephotusparrots (Hooded or Blue Bonnet Parrots) are usuallyaggressive and will kill other birds that are in theirspace.

Cross-fostering Techniques

Species with long histories of domestication, such asBengalese (Society) Finches, will usually breed freelyin captivity without the use of specialized tech-niques. Members of this species are sometimes usedas foster parents to incubate and raise other finches.Similarly, Border Canaries may be used as fosterparents for other canary varieties. Cross-fostering ispracticed to increase the production of a particularpair of birds. Many species will breed and lay butmay require certain foods to raise the young. Manybirds will immediately re-lay when eggs are pulled tofoster, thereby increasing production.

One of the inherent problems in cross-fostering isthat it does not enable selection for good parentingability in the offspring. The problems that gave riseto the need for fostering in the first place are oftenperpetuated into future generations. Some organ-isms such as Campylobacter spp. and Cochlosomaspp. may cause inapparent infections in foster parentbirds but be transmitted to cross-fostered juvenileswhere disease may result. By comparison, using fos-ter parents may prevent some infectious diseasesthat are transmitted from infected parent to off-spring. For example, colonies of Gouldian Finchesthat are air sac mite-free have been established by

FIG 43.7 A Zebra Finch female was presented after having beeninvolved in an episode of territorial aggression in an overcrowdedenclosure. The bird had bilateral rear limb paresis with some deeppain. The finch responded to therapy that included corticosteroidsand being placed in a dark, cool (72°F) environment.


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using Society Finches, which are not susceptible toair sac mites, as foster parents.

Cross-fostering has also been used as a technique toenhance breeding populations of endangered species.The Helmeted Honeyeater, state bird of Victoria,Australia, is endangered. In an effort to save thisbird, eggs are collected from free-ranging HelmetedHoneyeaters and are incubated in captivity by theclosely related Yellow-tufted Honeyeater. This in-duces the free-ranging Helmeted Honeyeaters to pro-duce a second clutch of eggs and increase the annualproduction of chicks from a single pair. Similar tech-niques have been used to save other endangeredpasserines such as the Black Robin (fostered underChatham Island Robins). However, preservation andrehabilitation of suitable natural habitats must alsobe a priority if captive breeding and subsequent re-lease to the wild is to be effective.

ImprintingOne of the major disadvantages of fostered birds isthat they imprint on the foster parents and may beless likely to breed with their own species. Experi-mental work in Bengalese and Zebra Finches hasshown that development of sexual orientation andadult song patterns occur during a defined period inearly juvenile life. Male finches reared by foster par-ents of a different species or color variety preferen-tially choose females of the foster species as theysexually mature. If only male members of the fosterspecies were available, the cross-fostered malesformed homosexual pairs with these birds ratherthan heterosexual pairs with birds of their own vari-ety. The critical sensitive period for sexual orienta-tion from imprinting lasts from about the 15th to the40th days of life. Acquisition of adult song follows asimilar pattern: birds raised by foster parents learnthe song of the foster parent, even if this song wasaudible only some weeks prior to the young bird’sbeginning to sing.35 For species-specific imprinting tooccur, a finch should be exposed to its own speciesfrom the 15th to 40th days of life.

Parallels of the imprinting behavior that occur infinches have been defined in humans and other ani-mal species. For example, adult humans retain ac-cents acquired during childhood even when theymove to new locations. By comparison, children willquickly change an original accent and acquire theone characteristic to a new location. As an examplein other birds, Whooping Cranes in the United Statesthat were foster-raised by Sandhill Cranes did notlearn appropriate Whooping Crane courtship behav-

ior, yet were rejected by Sandhill Cranes during thebreeding season.

Finches are an inexpensive experimental animal andare being used as a model to study neurophysiologiccontrols of imprinting.

Breeding Parasitic Species of Passerines

Some finch enthusiasts relish the challenge of breed-ing parasitic species (birds that lay their eggs in thenests of other species) such as Paradise Whydahs(parasitize various species of the Pytilia family) andBroad-tailed Whydahs (parasitize Aurora Finches).Whydahs are generally bred in large planted aviarieswhere the parasitized finch species has first beenfirmly established and is breeding freely. The paral-lels between the appearance and behavior of thewhydah chicks and the finch chicks that they mimicare striking even though the adults of the two speciesare very different.

If male and female whydahs do not originate from thesame geographic area, they may not enter breedingcondition simultaneously, preventing successful re-production. The male whydah develops a long, flow-ing tail during the breeding season.

Special Considerationsin Managing PasserinePatients

Passeriformes are increasingly presented for veteri-nary evaluation as aviculturists recognize that suc-cessful medical and surgical treatment can be per-formed, even in tiny patients. However, ownerfinancial constraints and difficulties in collectingsamples from small birds may limit diagnostic andtreatment options. Veterinary care in these species isfrequently directed toward appropriate preventivehusbandry measures and approaching medical prob-lems from a flock perspective. As importation of wild-caught Passeriformes (eg, African finches) ceases,the cost of acquiring pairs warrants further financialinvestment in their care.


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Restraint and Handling

A “lights out/perches out” approach to capture isoften useful for small active birds. Birds will gener-ally not move in a dark room and can easily beremoved from an enclosure with minimal stress.Once out of the enclosure, the bird can be restrainedby placing the head between two fingers so that thebody rests in the palm of the hand, or it can berestrained by holding the head gently between thethumb and first finger. The latter can be difficult toexecute (Figure 43.8).

Blood Collection TechniquesThe right jugular vein is generally the best site forcollecting blood or giving intravenous fluids. It issurprisingly large even in very small birds. A nailclip, medial metatarsal vein or cutaneous ulnar veinare alternative blood collection sites but they fre-quently provide insufficient sample volumes. A skinprick technique from these sites or from the externalthoracic vein (which courses on either side of the ribcage just behind the shoulder) can be used. The bloodis collected directly from the skin into a micro-collec-tion tube.71

The lymphocyte is the predominant white cell in mostpasserine species, and lymphocytes rather than hetero-phils tend to increase in stress-related conditions.

Treatment Techniques

TherapeuticsAlthough the right jugular vein can be used for ad-ministering intravenous fluids, intraosseouscatheterization using a 26 ga needle is a practicalmeans of fluid administration in a finch.

Hemorrhage may be a problem following intramus-cular injections into the pectoral muscles in smallbirds. To minimize risk, the injection site should belocated in the caudal third of the chest muscles, anda fine gauge needle should be used (25 ga or less).Aspiration should be performed prior to injecting anydrug to ensure that a blood vessel has not beencannulated. After the needle has been removed thesite should be observed for hemorrhage, and pressureshould be applied digitally if bleeding does occur.

Drug dosing in small patients must be based on anexact weight (as determined by a gram scale) andshould be delivered with precise microliter or insulinsyringes to avoid overdose. There is little room for adosing error in a small bird.

FIG 43.8 Passeriformes can be restrained by a) placing the headbetween the second and third fingers and letting the body rest inthe palm of the hand, or b) by holding the head between the thumband first finger. Note the clean, dry nostril and perinasal area,relatively smooth beak, dry sleek feathers and clear bright eyesuggestive of a healthy Gouldian Finch.


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Fiber RemovalIt is common to see canaries and finches with finefibers (cotton or synthetics) wrapped around theirfeet or legs. Swellings associated with the feet andlegs should be examined using magnification to de-termine if fibers are involved. Individual digits or thewhole foot may be lost from untreated or chronicvascular constriction (see Figure 43.4) (see Color 24).

If there are only a few fibers, it may be possible toremove them using magnification and gentle teasingwith fine scissors, a needle and forceps under magni-fication. If numerous fibers are present, it is best tocut through all the fibers down to the skin, keepingthe incision parallel to the long axis of the leg or digit.The incision should be made on the lateral side of theappendage or wherever the fibers are least imbed-ded. Pulling on deeply imbedded fibers can causethem to further constrict vascular structures. Onceall the fibers have been severed, they may be re-moved with reduced risk of iatrogenic damage.

SplintingIn small birds, lower limb fractures can often berepaired with a sandwich adhesive or masking tapesplint (see Figure 16.3). The limb should be posi-tioned in moderate flexion to enable the bird to moveand to prevent bending that may occur if the leg issplinted straight. Several layers of tape may beneeded. This type of splint is also used to providesupport to weakened or damaged bones following theremoval of tight leg bands.

Diseases

Table 43.3 lists the most common diseases of captivePasseriformes that are likely to be seen by avianpractitioners.

Mutations and Genetic Diseases

Some passserines, such as Gouldian Finches, newcolor canaries and Zebra Finches, are bred for theircolor mutations. Other varieties (eg, Norwich, Glous-ter and Yorkshire canaries) are bred for morphologiccharacteristics. Some of these mutations may be as-sociated with genetic disease (Figure 43.9).

Feather Cysts (Hypopteronosis Cystica)Heavily feathered canaries, particularly those with“double buff” soft feathers, may develop feather cysts.Norwich, Crested, Crest-bred and dimorphic new

FIG 43.9 Linebreeding and inbreeding to achieve color or morphologicmutations produce a weaker bird with greater potential for geneticabnormalities. This color mutation Gouldian Finch will have areduced life-span in comparison to its wild-type conspecifics.

FIG 43.10 Feather cyst formation is believed to be hereditaryalthough infectious agents have not been ruled out as an etiology.Severe localized feather cysts, like this one in a canary, generallyrequire surgery to remove the cyst and all affected feather follicles.Less aggressive therapy generally results in recurrence of cystformation with subsequent molts (courtesy of Michael Murray).


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color canaries are most frequently af-fected with this condition but it mayoccur in other varieties as well. Thecondition is believed to be hereditarybut the mode of inheritance is notsimple, and other factors apart fromgenetics may play a role in the devel-opment of the condition. The possibil-ity of a vertically transmitted virusinfection causing folliculitis with sec-ondary cyst formation has been sug-gested.

Feather cysts may occur as isolatedor multiple lumps. Often they affectthe wings, back or chest. They may bebilaterally symmetrical or occur ran-domly on the body (Figure 43.10).Badly affected birds have irregularlydirected feathers all over their bodies(see Color 24). The cysts may involveone or more feather follicles, and oc-casionally whole feather tracts areaffected. The texture of the materialwithin the cyst will vary dependingon the stage of molt. Actively growingfeather cysts will have vascular wallsand contain blood and gelatinous ma-terial. Mature cysts will contain drierkeratinous material, and the cystwall may be more expansive, thick-ened and reduced in vascularity (seeColor 24).

Medical treatment for feather cysts isgenerally unrewarding. Some canarybreeders believe that iodine given at0.1 ml to 50 ml drinking water willhasten the maturation of feathercysts and allow some to desiccate andslough naturally. Controlled trials toverify this mode of therapy have notbeen performed, and some feathercysts will heal without treatment.Once mature, the material can be ex-pressed from small cysts but theproblem will recur with the sub-sequent molt.

Surgical options for feather cysts include excision ofindividual cysts, removal of complete feather tractsor lancing and curetting individual cysts (Figure43.11). Excision will remove the affected follicle andmay be useful for solitary cysts, particularly those

located on the body. This therapy is not practical ifthere are numerous cysts and will not prevent newcysts from developing at remote sites. In birds withnumerous cysts it may be more practical to remove acomplete feather tract2 (see Color 24).

The author’s preference for treating feather cysts isto place hemostats at the base of the cyst and remove

TABLE 43.3 Common Clinical Presentations and Diagnoses in Companion Passerines

Clinical Presentation Common Diagnoses

Canaries

Open-mouthed breathing,moist rales

Air sac mites, upper respiratory tract infections (bacteria,mycoplasma), inhalant toxins, lymphoproliferative disease

Masses on head Pox, caseated sinus abscesses, mycoplasma

Masses on wings and body Feather cysts

Masses on legs and feet Pox, insect bites, swelling from strangulating fibers,Knemidokoptes mites

Digit necrosis Strangulating fibers, Staphylococcus infections

Scale on legs, swollen feet Knemidokoptes mites, genetic, nutritional, associated withaging in some birds

Diarrhea in nestlings Bacterial infections, Isospora, atoxoplasmosis

Black spot (enlarged, darkliver visible through skin)

Atoxoplasmosis, bacteremias, Plasmodium

Deaths in adults (both sexes) Bacterial septicemias (especially colibacillosis and yersiniosis)

Abdominal enlargement Egg binding, leukosis

Deaths in breeding hens Egg peritonitis (often due to E. coli)

Feather loss from head Feather mites, male baldness, aggression, malnutrition

Torticollis Paramyxovirus, listeriosis, cerebral vascular accident

Finches

Open-mouthed breathing,moist rales

Air sac mites (Gouldian Finches), upper respiratory tractinfections

Masses on legs and feet Knemidokoptes (esp. European Goldfinches), swelling fromstrangulating fibers, insect bites

Scale on legs Knemidokoptes (may also be genetic/nutritional in somebirds)

Diarrhea in nestlings Bacterial infections, coccidiosis, atoxoplasmosis,polyomavirus (in Gouldians), Cochlosoma (in Gouldianscross-fostered on Bengalese)

Voluminous white droppings Campylobacteriosis, pancreatic insufficiency

Seed in droppings Cochlosoma infections, vitamin E or selenium deficiency,enteritis, lack of grit

Deaths in adults (both sexes) Bacterial septicemias (especially colibacillosis andyersiniosis); tapeworms or gizzard worms (in insectivorousfinches); mycobacteriosis (esp. siskins); avian malaria (parrotfinches)

Feather loss from head Feather mites, aggression from enclosure mates

Mynahs (and other Sturnidae)

Ascites, dyspnea Iron storage disease, hepatic cirrhosis or neoplasia,congestive heart failure

Seizures Epilepsy

Nasal discharge, sinusswelling, rales

Bacterial upper respiratory tract infections, malnutrition

Chronic weight loss, dyspnea Aspergillosis, mycobacteriosis


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all tissue to the base of the hemostats with a radio-surgical unit. With this technique, the contents of thecyst are removed along with the skin that forms thewall of the cyst but the cyst is not totally excised. Thehemostats are removed, and any remaining kerati-nous material is curetted from the base of the cyst.The small remaining part of the interior lining iscauterized with the radiosurgical unit. An elasticadhesive bandage is used to control minor bleeding.The advantages to this technique are that it is quick,economical and can be performed without anesthe-sia. Stitches are generally not required. The cosmeticeffect is preferred to what occurs when cysts aresimply lanced, and damage to surrounding tissue isless than with total excision. If the base of the cysthas been adequately cauterized, there is generally norecurrence at that site.

Birds with feather cysts should not be used for breed-ing. Unfortunately, cysts may not develop in a birduntil after it is reproductively active.

Crested CanariesCrested varieties of Norwich or Glouster canaries areoccasionally kept for show or pets. Depending on thevariety, birds with crests are referred to as “coronas”or “crested” while those of the same conformation butwithout crests are referred to as “consorts” or “crest-bred.” The desirable crested phenotype is heterozy-gous for the autosomal crested gene. Birds that arehomozygous for the crested gene die. Crested canar-ies are produced by breeding crested birds (coronas)with non-crested (consorts or crest-bred) canaries.This mating will result in 50% crested birds (Cc) and50% non-crested birds (CC). If crested birds aremated to crested birds, normal Mendelian geneticswill result in 25% non-crested, 50% crested and 25%dead chicks.

Dominant White Lethal FactorCanaries that are homozygous for the dominantwhite gene die, while heterozygous individuals arewhite. Two dominant white birds should not bemated or all the chicks will die. If white birds aremated with other color varieties, 50% of the chickswill be heterozygote-dominant white and 50% of thechicks will be other colors.

Straw Feathers Canaries and Zebra Finches occasionally show reten-tion of the feather sheath and incomplete develop-ment of the barbs and barbules. The disease mayaffect first-molt fledglings or adult birds in a sym-metrical fashion; it is believed to be genetically deter-mined (see Color 24).18,58

CataractsCataracts are occasionally seen in canaries, particu-larly in Norwich and Yorkshires. Affected birds willoften be found on the bottom of the cage or aviary,possibly avoiding flight after a previously misjudgedlanding. Histologically, there may be disorganizationof lens cortex, fragmentation of fibers, globule forma-tion and lens resorption. Cataracts are reported to becaused by a recessive gene in Yorkshire and Norwichcanaries. They may be removed surgically.36,67

Viral Diseases

PoxvirusClinical Presentation: The clinical appearance ofpoxvirus in passerine birds varies with the virulenceof the strain, the mode of transmission and suscepti-bility of the host. Canaries and House Sparrows areparticularly susceptible and may show the cutane-ous, septicemic or diphtheroid forms of the disease(Figure 43.12). The cutaneous form of poxvirus hasalso been reported in a variety of free-ranging Pas-seriformes, eg, starlings, juncos, silvereyes and Aus-tralian magpies.26,57 Poxvirus infections are usuallyself-limiting in free-ranging birds.

Poxvirus may be transmitted from free-ranging star-lings to other members of the Sturnidae family. Inone instance, all of a group of Rothschild’s Mynahsexposed to infected starlings died. In Greater HillMynahs, poxvirus has been associated with low mor-talities, but chronic eye, wattle and oral lesions occur.These include proliferative lymphocytic conjunctivi-tis, keratitis, chronic corneal ulcers, lid depigmenta-tion, cataracts, eyelid distortion and scar tissue withfeather loss on the head.37

FIG 43.11 Surgically removed feather cyst from a canary (courtesyof John Cooper).


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Mortalities of up to 100% have occurred in someoutbreaks of canary pox. Acutely affected birds mayshow lethargy, ruffled feathers, open-mouthedbreathing and death in two to three days. In lessacute cases, birds may show conjunctivitis, blephari-tis and lacrimation before the appearance of charac-teristic proliferative lesions around the eyes andmouth. Death may result if these lesions cause pha-ryngeal obstruction. On necropsy, birds dying acutelymay show cloudy air sacs and pneumonia with prolif-erative necrotizing bronchitis, while those dyinglater in the course of the disease are more likely toshow proliferative skin lesions and typical intracyto-plasmic inclusions in the epidermis and respiratoryepithelium. The skin lesions should be differentiatedfrom mosquito bite abscesses, which result in dis-crete lumps that contain caseous material when

lanced.18,40 An uncomplicated pox lesion is a con-tained fibrous reaction without a necrotic, express-ible center.

A much milder form of cutaneous canary pox is alsoseen in southeastern Australia and California. Peri-odically more virulent strains erupt and high mor-talities occur, particularly in birds kept in outdooraviaries in areas with dense mosquito populations.

While birds affected with poxvirus will typicallyshow intracytoplasmic Bollinger bodies, intranuclearinclusions have been demonstrated in the junco. Con-current infections with other viruses have also beennoted. Retrovirus-like particles have been found inthe brains of some poxvirus-infected canaries.11 Ade-nomatous tumors in the lungs have occurred as asequel to poxvirus infections.

Serologic cross-reactions between strains of poxvirusin Passeriformes have not been demonstrated, butsome strains will affect more than one passerinespecies. For example, in one outbreak, canaries andHouse Sparrows were the only species to show clini-cal signs of poxvirus or mortality even though tenspecies of passerine birds were present in the aviary(see Chapter 32).

Treatment and Control: There is no specific treat-ment for poxvirus. Antibiotics may be useful to con-trol secondary infections, and vitamin A or its naturalprecursor may aid in the healing process. Scarifyingindividual pox lesions may result in spontaneousremission. Topical application of astringent solutionssuch as mercurochrome or alcohol may be useful.Adenine arabinoside ointmenta has also been recom-mended. Mild baby shampoo may be gently appliedto any lesions around the eyes to remove scabs. Im-mune stimulants such as PEP-Eb and echinacea maybe of possible value.

Avian poxviruses can be transmitted by mosquitoes,mites or by contact through damaged epithelial sur-faces. Bird rooms should be mosquito-proofed andtreated with insecticides to eliminate vectors, andaffected birds should be isolated until fully recov-ered. Recovered birds generally have lasting immu-nity to the disease but may become carriers and shedthe virus. A modified live virus canary pox vaccinec isavailable in some countries.15,18

HerpesvirusHerpesviruses have been isolated from Estrildidfinches, Ploceid finches (weavers and whydahs) andcanaries, but in most cases they have not been asso-

FIG 43.12 Poxvirus infections are common in canaries that aremaintained outdoors in areas with high densities of mosquitoes.Depending on the species of bird and virulence of the virus, eithercutaneous, diphtheritic or septicemic forms of the disease mayoccur. Cutaneous lesions are common on a) the face or b) feet andlegs (courtesy of Michael Murray).


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ciated with disease. Outbreaks of conjunctivitis inGouldian Finches associated with herpesvirus-likeparticles have been reported in Europe.64

CytomegalovirusAn epidemic of conjunctivitis with respiratory dis-tress and a 70% mortality rate was reported in Aus-tralian grass finches maintained in Europe. Baso-philic intranuclear inclusions were seen inkaryomegalic epithelial cells of conjunctiva, esopha-gus and trachea. Cytomegalovirus-like particleswere identified by electron microscopy.12

PolyomavirusPolyomavirus-like infections have been associatedwith several clinical presentations in passerinebirds. Sporadic deaths have occurred in adult finchesof various species, particularly in birds that havebeen stressed by transport or other factors. Ventricu-lar mycosis has been reported as occurring concur-rently with polyomavirus in many of these birds.40

In color mutation Gouldian Finches, polyomavirus-like infections have been reported to cause acutemortality in two- to three-day-old babies, and poorgrowth, dirty feathering and late fledging in oldernestlings. Many affected birds had an abnormallower mandible that was long and tubular (Figure43.13). Nonspecific illness and mortality occurred inslightly older birds. Concurrent Candida infectionswere common.46

In a separate report, deaths in fledgling and imma-ture Gouldian Finches occurred without any concur-rent feathering or beak defects. The most consistentgross lesion was a swollen, pale liver.22 Currentlythere is no effective treatment for polyomavirus.Controversy exists as to whether it is best to depopu-late, rest breeding stock or to continue to breed withthe expectation that birds will develop immunity (seeChapter 32).

While polyomavirus-like intranuclear inclusion bod-ies have been described in finches in North America,Europe and Australia, the virus has not yet beencultured from passerine species. Gross lesions thathave been associated with polyomavirus infections infinches include perirenal hemorrhage, serosal or sub-serosal intestinal hemorrhage, splenomegaly, andswollen or mottled liver. Histologically, amphophilicintranuclear inclusion bodies are typically seen inthe kidneys, heart, spleen, gastrointestinal tract orliver. Cellular necrosis may occur in the bone mar-row, gastrointestinal tract, spleen or hepatocytes.

Diagnosis is based on the histologic presence of large,clear-to-amphophilic, intranuclear inclusion bodiesin one or more organs. Fluorescence should occurusing polyclonal antibody FITC-labelled conjugatespecific for polyomavirus antigen. Electron micros-copy should reveal polyomavirus-like particles.75

PapillomavirusAvian papillomavirus has been demonstrated in as-sociation with papillomas on the legs of wild Euro-pean chaffinches. Three hundred and thirty birds outof approximately 25,000 birds examined were af-fected. The virus was purified and its physicochemi-cal properties characterized.42,51

Viral papillomatosis has also been described in ca-naries from Argentina. The disease occurred season-ally during late summer and autumn over a three-year period, and the outbreaks were controlled usinghygienic measures and an autogenous vaccine.45

ParamyxovirusPasserines are known to harbor paramyxoviruses ofgroups 1,2 and 3.26

Group 1 (Newcastle Disease Virus): Many weaverfinches are susceptible and show conjunctivitis,pseudomembrane formation in the larynx and death.Neurologic signs are rare. Canaries rarely developclinical signs, and infected birds should be consideredasymptomatic carriers. Because species susceptibil-ity varies, mortality patterns in an aviary may besporadic and an infectious agent may not be consid-ered as the cause.

FIG 43.13 Long, tubular lower beaks have been reported inGouldian Finches with polyomavirus-like infections.


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Group 2: Free-ranging passerines, particularlyweaver finches in North Africa, are considered to becarriers of this virus. Many infected birds are asymp-tomatic but others may die following a period ofemaciation and pneumonia.

Group 3: This virus has been isolated from a varietyof passerines including canaries, Gouldian Finchesand weaver finches. It is generally associated with anoverall poor condition and central nervous systemsigns (tremor, paralysis or torticollis).

LeukosisSporadic deaths associated with enlarged pale liversand spleens and histopathologic lesions suggestive ofleukosis have been reported in canaries in Europe,Australia and North America. A viral etiology hasbeen proposed but has not been confirmed.1,15,18

Treatment with prednisolone may slow the progres-sion of the disease.

Chlamydia Infections

Passeriformes are less susceptible to chlamydiosisthan Psittaciformes. Chlamydia has been isolatedfrom the droppings of clinically normal finches inhouseholds in which clinical cases of chlamydiosisoccurred in psittacine species. Active disease out-breaks are intermittent, and infection rates of lessthan ten percent of the at-risk population are typi-cal.16 Chlamydiosis should be suspected in passer-ines with recurrent respiratory disease especially ifthey are exposed to psittacine birds.

Mycoplasma

Mycoplasma spp. have been isolated from canarieswith wheezing, respiratory signs including tail-bob-bing and conjunctivitis. Many cases of conjunctivitisand upper respiratory disease in canaries are respon-sive to tylosin. However, there has been no conclusiveexperimental work proving that mycoplasma is asso-ciated with this syndrome25 (see Figure 43.1).

Tetracyclines are believed to be effective againstmany mycoplasma isolates as well as chlamydia.Both of these infectious agents are difficult to iden-tify in a live bird, and a therapeutic trial withtetracyclines may be appropriate if they are sus-pected of being part of a disease complex. Tylosin ortiamutilin are other drugs that may be considered ifmycoplasmal disease is suspected.

Bacterial Infections

Some investigators believe that bacteria and othermicroorganisms should seldom be found in stainedfecal smears from normal canaries and finches. Oth-ers believe that low levels of gram-positive rods orcocci are considered normal. There is generally nobacterial growth on routine aerobic microbiologicalcultures taken from passerine birds.15,21

The general principles for treating and controllingbacterial infections in passerines are similar to thosediscussed in psittacines (see Chapters 17, 33). Pas-serines are frequently maintained in planted aviar-ies and medicating individuals can be extremely im-practical. If a decision is made to use water-basedmedication, frequently used drugs include tri-metho-prim and sulfamethoxale, amoxicillin, chlor-am-phenicol, tetracyclines and enrofloxacin. Some pas-serines are particularly sensitive to certainantimicrobial agents (dimetridazole, furacin) andcare should be exercised when administering anymedication to a finch or canary (see Chapter 18).

Gram-positive FloraStaphylococcus spp. are normal inhabitants of thegastrointestinal tract and the skin but occasionallyvirulent strains may cause disease in susceptiblehosts (see Chapter 33). Staphylococcal infections arecommonly associated with the occurrence of thrombiin arterioles. This lesion can be particularly danger-ous in small birds because collateral circulation ismore limited than with larger birds. Digit necrosis,gangrenous dermatitis and pododermatitis are likelyoutcomes. Other clinical syndromes that have beenassociated with staphylococcus infections in passer-ines include high embryonic mortality, omphalitis,septicemia and arthritis.27

Streptococcal infections have also been associatedwith embryonic mortality, omphalitis, septicemiaand arthritis in passerines, although, like staphylo-coccus, these bacteria are often part of the normalautochthonous flora.

Enterococcus fecalis (formerly Streptococcus fecalis)has been associated with chronic tracheitis, pneumo-nia and air sac infections in canaries. Experimentalinfections are possible following subcutaneous or in-trathoracic air sac injections but not by simple aero-sol administration. Clinically affected birds haveharsh respiratory sounds, voice changes and dysp-nea. These changes are similar to those caused by thetracheal mite Sternostoma tracheacolum. Concurrentinfections are possible.13


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Mycobacterium avium: Passerines are susceptible toMycobacterium avium and may show nonspecificsigns similar to those seen in other avian species:chronic wasting, diarrhea, polyuria, anemia, dullplumage and leukocytosis. Classic tubercles rarelydevelop, and gross necropsy findings usually revealminimal changes. Two histopathologic conditionshave been noted: small focal granulomas may befound in the lungs or high numbers of acid-fast bac-teria may be noted in the lamina propria of theintestine.27,47,61

Red-hooded Siskins may be particularly susceptibleto tuberculosis. Treatment of companion birds forMycobacterium spp. is not recommended because ofthe public health concerns.

Erysipelothrix rhusiopathiae may cause disease inpasserines as it does in other avian species but infec-tions are not common.

Listeria monocytogenes is a ubiquitous organismthat may be transmitted by the oral route. Canariesare particularly susceptible to listeriosis and flockoutbreaks may occur. Clinical signs include torticol-lis, tremors, stupor, paresis or paralysis. A markedmonocytosis may occur. Tetracyclines may be usefultherapy in the early stages of the disease but treat-ment is usually ineffective in birds with CNS signs.21

Clostridium perfringens was isolated from a canarythat died after eating contaminated food. Other re-ports of clostridial infections in Passeriformes arescarce but there is no reason to believe that birds ofthis order would not be susceptible.31

Megabacterium: A large, rod-shaped, gram-positivebacteria that was difficult to culture and was associ-ated with a proliferative, inflammatory reaction inthe proventriculus of canaries was described inEurope. In affected birds, the proventriculus had anincreased pH and altered synthesis of mucopolysac-charides. The koilin lining of the ventriculus wasthinner in affected canaries than in a control group,possibly as a result of the increased pH in the proven-triculus. The organism identified in these birds ap-peared to be very similar, if not identical, to theorganism defined as “megabacterium” in psittacinebirds (see Color 14).69

Enterobacteriaceae and OtherGram-negative Bacteria

Enterobacteriaceae are generally considered secon-dary pathogens. The predisposing factors that al-lowed organisms to colonize the bird should be iden-

tified and corrected. Oral neomycin or spectinomycinmay be useful for infections localized to the gastroin-testinal tract.

Escherichia coli has been associated with a varietyof disease problems in passerine birds including di-arrhea, septicemia and ascending oviduct infections.Ascending oviduct infections are usually rare; how-ever, E. coli-induced egg-related peritonitis andmetritis have been associated with high mortality insome canary flocks in southeastern Australia. Juve-niles and cock birds on the same premises were notaffected. Mortalities stopped when the birds wereplaced on appropriate antibiotics (as indicated bysensitivity testing). Interestingly, bacteria isolatedfrom Australian birds are frequently sensitive to awider range of antibiotics than are commonly re-ported with similar organisms in the United States.44

Salmonella typhimurium var copenhagen is com-monly isolated from finches in Europe that develop acharacteristic granulomatous ingluvitis, which canbe confused with crop candidiasis or capillariasis.Histologic lesions are nonspecific and include intesti-nal inflammation and focal necrosis in the heart,lung, liver, spleen and kidney. Granulomas may oc-cur in chronic cases. Salmonella spp. have also beenisolated from cases of osteomyelitis and subcutane-ous granulomas in canaries.54,62

Citrobacter sp. is commonly found as a secondaryinvader in weaver finches and waxbills. It has alsobeen associated with acute septicemia and death.21

Yersinia pseudotuberculosis is a common cause ofperacute mortality in finch and canary aviaries aswell as causing general ill health, diarrhea and dysp-nea. The organism is believed to have originated inEurope with worldwide dissemination occurringthrough rodents on ships. Yersiniosis is a widespreadproblem in Australian aviaries where rodent controlis poor. Infections occasionally occur in free-rangingbirds. Enteritis and pinpoint or large abscessesthroughout the liver and spleen are characteristicgross findings. Affected birds are often too sick torespond to therapy but treatment of exposed birdswith antibiotics based on sensitivity testing will usu-ally stop an outbreak. Decontaminating the aviaryand rodent-proofing food and water supplies shouldaccompany any antibiotic therapy.27,44

Klebsiella, Pasteurella and Haemophilus spp. a r eoccasionally isolated from Passeriformes. Pas-teurella is often associated with fatal septicemiasfollowing cat bite wounds. Even if injuries seem mi-


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nor, birds that have been bitten or scratched by catsshould receive antibiotics immediately.

Campylobacter fetus var. jejuni has been associ-ated with pale, voluminous droppings (“popcornpoohs”) in canaries and finches of a variety of spe-cies (particularly Gouldian Finches). European in-vestigators have suggested that adding animal pro-tein, minerals and vitamins (soft food) to the dietmay strengthen the bird’s immune system and pro-tect against repeated infections. Antibiotics (par-ticularly erythromycin and tetracyclines) may alsobe useful.70

Pseudomonas sp. infections may originate from theconsumption of contaminated drinking water, mist-ing bottles or inappropriately prepared soaked seed.The organism may cause foul-smelling diarrhea ormucopurulent pneumonia and air sacculitis. Treat-ment should be based on sensitivity testing, as thebacteria is often resistant to routinely used antibiot-ics. Steps should be taken to identify and removeenvironmental sources of contamination.

Aeromonas sp. has been isolated from Europeanrooks and House Sparrows.29

Fungal Infections

Candida albicansIdentifying candida in fecal swabs from passerinesshould be evaluated with caution. Many passerinespecies are fed bread products that are made withyeast. Yeast blastospores may pass through the gas-trointestinal tract unchanged and appear in largenumbers in the feces. These organisms do not reflectdisease. Small numbers of candida blastospores mayalso be present as a part of autochthonous flora.

Candida albicans is occasionally associated with up-per gastrointestinal tract infections in passerines,particularly in immunosuppressed or hand-fed neo-nates. Vomiting, anorexia, weight loss and diarrheaare characteristic findings. The lining of the cropmay be thickened and covered with whitish “turkishtowel” coating (see Color 14). Yeast blastospores orhyphae may be identified on Gram’s stain of materialfrom a crop wash. Systemic candidiasis has also beenreported in canaries.17 Nystatin or ketoconazole maybe useful in infections confined to the gastrointesti-nal tract (see Chapter 15).

Aspergillus spp.Aspergillosis may cause weight loss, respiratory dis-tress, anorexia, vomiting or diarrhea in infected pas-

serines. Immunosuppression, usually from malnutri-tion, along with contaminated environmental condi-tions are primary factors in the development of thedisease. Captured free-ranging birds are oftenstressed, suffering from poor nutrition and kept inunclean surroundings with decaying organic mate-rial. It is not surprising that aspergillosis occursunder these conditions. Aspergillosis is also a com-mon postmortem finding in sporadic deaths in free-ranging passerine birds. A granulomatous form ofthis disease occurs in which nodules varying in colorfrom yellow to white may be seen in the liver, lungs,kidneys, muscles and subcutaneous tissues. MostPasseriformes should be considered susceptible.57

Aspergillosis was a major cause of mortality inhatchling Helmeted Honeyeaters. Mortality was con-trolled by nebulizing the birds with amphotericin B.

Captive mynahs are reported to be particularly sus-ceptible to aspergillosis, possibly because of theirmoist, messy droppings and the tendency for thesebirds to be maintained in small enclosures39,63 (seeChapter 35).

Cryptococcus neoformans var. neoformansRespiratory or systemic cryptococcosis has beenrarely diagnosed in passerine birds, even though theorganism has been isolated from seed and droppingsof canaries. It has been suggested that the fungusmight persist from year to year on the wood of poorlycleaned enclosures. The organism has been associ-ated with deaths in munia finches53 (see Chapter 35).

Zygomycosis (Mucormycosis)Multiple fungal granulomas have been identified inthe lung, liver or brain in canaries and GouldianFinches fed damp, germinated seeds (sprouts). His-tologically, fungal hyphae are frequently associatedwith blood vessel walls.

Superficial MycosesDermatomycoses are occasionally reported in passer-ines and generally cause as alopecia (especially of thehead and neck) or hyperkeratosis. Microsporumgallinae and Trichophyton spp. are the most commonetiologic agents, but other saprophytic fungi mayalso be involved. Whole body dermatomycosis hasoccasionally been seen in free-ranging Red Wattlebirds (a type of honeyeater) presented at the author’spractice. In one case, the client also developed der-matomycosis. Treatment with ketoconazole andgriseofulvin provided some improvement but did noteliminate the infection. Topical baths with chlor-


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hexidine and tamed iodine washes were irritatingbut they did lead to some improvement. One birddied when the owner attempted home treatment byapplying a propylene glycol-based product over ex-tensive areas of the bird’s body.

Protozoa

CochlosomaCochlosoma spp. are flagellates that inhabit the gas-trointestinal tract of some finches. BengaleseFinches may be inapparent carriers of this organism;when they are used to foster species of Australianfinches (such as Gouldians), they may pass the or-ganism on to juveniles, causing high mortality innestlings. Typical clinical signs include debility, de-hydration and passing whole seeds in the droppings.At necropsy the intestine may be filled with a yellowsuspension or whole undigested seeds. Most affectedbirds are six to twelve weeks of age.

The organism may be identified by direct wet prepa-ration of fresh warm droppings or at necropsy usingintestinal contents. Cochlosoma has six anterior fla-gella with a helicoidal, anterior ventral sucker.38

Treatment with ronidazole at 400 mg/kg in egg foodand 400 mg/liter of drinking water for five days hasbeen suggested. After a two-day rest period, thetreatment is repeated. Dimetridazole may also beused at no more than 100 mg of active ingredient perliter of water for five days. Water containers shouldbe disinfected and rinsed clean (the organism is sen-sitive to most common disinfectants) and the aviaryshould be kept clean and dry.15

TrichomonasTrichomonas spp. infections are occasionally seen infinches, particularly those housed near infectedbudgerigars. Clinical symptoms include gagging,neck stretching, regurgitation, respiratory distress,nasal discharge, green diarrhea and emaciation. Di-agnosis is made by identifying the flagellate on a wetsmear prepared from a crop wash. At necropsy,caseous material may be seen lining the crop andesophagus, and flagellates may be identified fromthis material provided that it is fresh.

GiardiaGiardia sp. has also been reported to be associatedoccasionally with gastrointestinal tract infections infinches. Treatment is the same as for cochlosomiasis.

Coccidiosis

Coccidia infections in passerine birds may be asymp-tomatic or associated with diarrheal syndromes(sometimes with blood in the droppings), emaciation,general ill health and systemic disease. Systemicprotozoal disease is occasionally diagnosed in avianspecies, but it is difficult to classify the causativeorganism based solely on histologic appearance.Fresh tissues for transmission studies, blood for se-rology and hematology and feces for parasitologicevaluation should be saved from patients where pro-tozoal disease is suspected.

Coccidia in the Eimeriidae family have a single host.Development of the endogenous stages occurs withinhost cells to produce a resistant oocyst. Sporulationof oocysts usually takes place outside the host andoocysts of different genera have a characteristicnumber of sporocysts, each with one or more sporo-zoites68 (see Chapter 36).

Eimeriidae genera affecting passerines include:Eimeria (oocysts with four sporocysts each con-taining two sporozoites)Isospora (oocysts with two sporocysts each withfour sporozoites)Dorisiella (oocysts with two sporocysts each witheight sporozoites)Wenyonella (oocysts with four sporocysts eachwith four sporozoites)Sarcocystis (oocysts with four sporozoites)Toxoplasma and Cryptosporidium (same as Iso-spora, but sporocysts are usually found individu-ally instead of inside membrane-like oocyst wall)

When examining fresh fecal material, it is often notpossible to classify coccidial oocysts because sporula-tion may take several days to occur (see Chapter 36).

Atoxoplasmatidae are single-host coccidia withmerogony in the blood and intestinal cells, gameto-geny in the intestinal cells of the same individual andsporulation outside the host. This family contains asingle genus, Atoxoplasma. Early work suggestedthat Atoxoplasma spp. could be transmitted betweendifferent bird species, particularly between HouseSparrows and canaries, by an arthropod transporthost (particularly the red mite Dermanyssus gali-nae). More recent investigations have shown thatthese findings were incorrect, and that the parasiteis transmitted directly via oocysts in the feces andthat it is host-specific.21,38,43,68


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Coccidia in CanariesOocysts from Atoxoplasma or Isospora spp. may befound in the feces of infected canaries. Isospora is lesspathogenic and completes its life cycle within theintestines while atoxoplasma develops asexually inmononuclear blood cells and spreads hemato-genously to other organs including the liver, spleenand lungs.

Canaries with atoxoplasmosis may be defined ashaving “black spot,” referring to the enlarged, darkliver that is visible beneath the skin. Diarrhea, non-specific illness and death sometimes occur. The or-ganism can be diagnosed by identifying sporozoiteson Giemsa-stained impression smears of the spleen,liver or buffy coat. The sporozoites are found in thecytoplasm of lymphoid-macrophage cells and appearas oval structures containing pink-staining chroma-tin. Indentation of the host nucleus often occurs (seeChapter 36). Table 43.4 is useful for differentiatingbetween these two species.20

Sulpha drugs or amprolium are usually effective forIsospora sp. but Atoxoplasma sp. is resistant to treat-ment. Maintaining clean surroundings to reduce thebirds’ exposure to the infective oocysts may helpcontrol infections, but will probably not eradicate theorganism from an aviary.

Coccidia in Other Passerine SpeciesMorphologically similar Isospora species of coccidiahave been identified in over 50 species of passerinespecies throughout the world. This species has beennamed Isospora lacazei although it represents morethan a single species. Many other morphologicallydistinct species of Isospora have also been identified.Life cycles are believed to be similar to Isosporacanaria.68

Eimeria spp. generally follow the same pattern asIsospora and complete their life cycle in the intesti-nal tract. One species, Eimeria grallinida, has beendescribed in a wild-ranging Australian Magpie-Larkin which the parasite was found in the liver. Theaffected bird had been found in a moribund state anddied shortly thereafter. On necropsy, the bird showedmarked hepatic enlargement with small white foci.Various stages of the life cycle including schizogony,gametogony and oocysts were found in the bile ducts.Sporulated oocysts were consistent morphologicallywith Eimeria sp.60

Coccidia of the genus Dorisiella have been identifiedin a number of passerine species including munias,

avadavats, hawfinches and a Fohkein Grey-headedCrow Tit. Pathogenicity appears to be minimal. Wen-yonella sp. has been recovered from Pied Wagtails inIndia.68

SarcocystisSarcocysts are common in the skeletal muscles ofpasserines from many geographic regions. NorthAmerican cowbirds, grackles and other Passerifor-mes have been shown to be the intermediate hosts ofSarcocystis falcatula, for which opossums are thedefinitive host. In Australia, sarcocysts are inciden-tal findings at necropsy and a definitive life cycle hasnot been determined. Cysts can sometimes be ob-served through the skin.33,38

ToxoplasmosisToxoplasma gondii is occasionally identified in pas-serines and in isolated cases may cause death. In oneoutbreak, all 23 mynahs in a shipment died withvisceral toxoplasmosis. It was postulated that thebirds had been exposed to the organism at some timeprior to shipment and that the stress of transporta-tion had reactivated latent infections.14

Cats and other members of the Felidae family aredefinitive hosts for Toxoplasma gondii, and birdsmust ingest oocysts from cat droppings or visceralcysts from other animals in order to be infected.Feral cats in Australia have damaged native birdpopulations from direct killing and by spreadingToxoplasma sp. In one Tasmanian study, over 30% offree-ranging ravens were found to carry the organ-ism. Carnivorous marsupials, many of which arethreatened or endangered, are extremely susceptibleto toxoplasmosis. If a free-ranging bird infected withtoxoplasmosis is eaten by one of these species, themarsupial is likely to die. Birds infected withtoxoplasmosis may be asymptomatic or showneurologic symptoms, ophthalmitis or sudden death.Such birds are easy targets for free-ranging carni-vores. To avoid fecal contamination and the risk oftoxoplasmosis, cats should be prevented from enter-ing bird food storage areas.

TABLE 43.4 Characteristics of A. serini and I. canaria

Characteristic A. serini I. canaria

Oocyst length 20.1 (13-23) µm 24.6 (17-30) µm

Oocyst width 19.2 (13-23) µm 21.8 (17-30) µmLength:width 1.05 1.13

Prepatent period 9-10 days 4-5 days

Patency 10 ->95 d 5-18 d post-infection

Duration of infection 4 months 2-3 weeks


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CryptosporidiosisCryptosporidium sp. has been associated with acuteonset, severe diarrhea and death in a Diamond Fire-tail Finch. At necropsy the bird showed focal cuboidalmetaplasia of glandular epithelial cells of the proven-triculus and amyloid deposits at the base of theglands, as well as renal amyloidosis.6 Proventricularcryptosporidiosis has also been identified in canarieswith concomitant salmonellosis. Renal cryptosporidi-osis has been diagnosed in a Black-throated Finch.24

Cryptosporidium sp. has a direct life cycle but oocystshave not been identified in the droppings of clinicallyaffected passerines. The true clinical significance ofthe organism is not known, as it is often associatedwith other disease entities.

Blood Parasites

Blood parasites may be detected on routine screeningof apparently healthy passerines, but they are occa-sionally implicated as the primary cause of disease ordeath. Life stages of the coccidian parasiteAtoxoplasma sp. may also be seen in monocytes andlymphocytes. The occurrence of blood parasites var-ies from time to time and region to region. There issome evidence that the incidence of blood parasitesin birds has decreased in some areas as a result ofdecreased numbers of invertebrate vectors.4

Passerine families reported to be most commonlyinfected with hematozoa in one European study in-cluded Paridae (tits, 8% affected), Sylviidae (war-blers, 14% affected) and Turidae (thrushes, 10% af-fected). The most commonly encountered parasitesincluded Haemoproteus sp. (4%), Leucocytozoon sp.(1.8%), Trypanosoma (0.9%), Plasmodium (0.8%), Atoxo-plasma (0.2%) and microfilaria (0.1%). Haemoproteussp. is also the most common blood parasite encoun-tered in birds in North America and Australia.4,43

Other blood parasites that are occasionally seen inpasserines include the small tick-borne erythrocyticparasites Aegyptianella and Nuttallia spp.

PlasmodiumPlasmodium spp., the cause of avian malaria, aremosquito-borne protozoa of the family Plasmodiidethat occur worldwide. Sporogony occurs in the inver-tebrate host, schizogony occurs in erythrocytes andpigment is formed from the host cell hemoglobin.Each of the avian plasmodia has a limited host rangebut they do not appear to be particularly host-spe-cific. Plasmodium spp. have been described in free-

ranging wild tits, Fringillid finches, Old World war-blers, thrushes, starlings, sparrows and in Australianmagpies.4,43

The parasite has been associated with significantmortalities in Blue-faced Parrot Finches in theTaronga Zoo in Sydney. Free-ranging house sparrowsare believed to have been asymptomatic carriers ofthe organism. No other species of captive birds at thezoo were affected. The parrot finches showed signs oflethargy, anorexia, labored respiration and death. Adarkened, enlarged liver could be observed as a“black spot” through the skin and muscle of theabdominal wall. Treatment with chloroquine orpyrimethamine was successful in some cases but thebirds did not have any lasting immunity and weresusceptible to repeated infections. Controlling mos-quito vectors is necessary to prevent infections. Avianmalaria has also been reported to cause deaths incanaries and other species.23,71

HaemoproteusLike Plasmodium sp., Haemoproteus spp. are foundworldwide and are capable of infecting a variety ofbirds. Each species appears to have a limited hostrange but they are not particularly host-specific andgenerally cause only mild or inapparent clinicalsymptoms. Diagnosis is based on identification oftypical pigment containing gamonts in erythrocytes.For most species of Haemoproteus the intermediatehosts are hippoboscid flies, biting midges (Culicoidesspp.) or tabanids.

Passerine species in which Haemoproteus spp. havebeen reported are numerous and include mynahs,Fringillid finches, swallows, fly catchers, tits, spar-rows, weaver finches, warblers and thrushes. In oneoutbreak, canaries were believed to have been in-fected following exposure to free-ranging housesparrows.38,43,57

Schizonts have a predilection for development inskeletal and cardiac muscle, lung and spleen. Oneform of schizont is sausage-shaped and oftenbranches during development within capillary endo-thelium. Megaloschizonts may develop in the ab-sence of circulating gamonts and reach sizes of up to200 µm. Extensive myopathy and myonecrosis maybe associated with intramuscular megaloschizonts(eg, commonly seen in free-ranging infected PiedCurrawong around Sydney, Australia). These birdsshow multiple, yellow streaks in pectoral and othermuscles, and most are presented thin, weak andunable to fly.57 Treatment with antimalarial drugs


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(chloroquine at 250 mg/120 ml drinking water for oneto two weeks) may be useful. Orange juice may beadded to the drinking water to make the drug morepalatable.71

LeucocytozoonLeucocytozoon spp. occur worldwide except for SouthAmerica (where appropriate simuliid vectors are ab-sent). These parasites may infect either erythrocytesor leukocytes. Parasitized cells are so distorted bythe organism that it may be difficult to determinetheir origin. Pigment is not produced by leucocyto-zoon and schizonts do not appear in peripheral blood.Megaloschizonts can be found in brain, liver, lung,kidney, intestinal tissue and lymphoid tissue.

Most leucocytozoon infections are subclinical, al-though vague signs of illness and death were re-ported in infected Crested Oropendolas from a zoo inFlorida. These birds hemorrhaged from protozoalcysts within hepatic and renal tissue. It was thoughtthat the leucocytozoon may have been transmittedfrom free-flying black flies infected by feeding onlocal leucocytozoon-infected crows. The oropendolas,which had been trapped in South America, may havebeen particularly susceptible because of lack of pre-vious exposure to the parasite.52

Leucocytozoon-like megaloschizonts have also beendescribed in association with acute and fatal hepato-cellular necrosis in canaries in Texas. Outbreaks ofthe disease were controlled with dimetridazole.55

Some other passerine species that have been re-ported to harbor Leucocytozoon spp. include Fringilidfinches, swallows, tits, warblers, thrushes, starlings,blackbirds, canaries and lyrebirds.38,43,57

TrypanosomaTrypanosomes are found worldwide but their inci-dence is low and they may only be found duringsummer months in temperate climates. Vectors arethought to include hippoboscid flies (Ornithomyiaavicularia) , red mites (Dermanyssus gallinae),simuliids and mosquitoes. Evidence suggests thatthe parasites may be transmitted by contaminationrather than inoculative routes. Diagnosis is by find-ing the parasites on stained blood smears.38 Highprevalence levels of this parasite (8.3%) have beenreported along the coast of the Baltic Sea in Europe.72

Treatment is not warranted.

Trypanosomes have been identified in over 14 pas-serine families, including Fringillid finches and ca-naries, swallows, tits and pipits.38,43

Avian PiroplasmosisPiroplasmosis is an important tick-borne infectionthat has been identified in many species of birds inthe Mediterranean, Asia and Africa but it has not yetbeen found in Australia. Aegyptianella sp. is a rick-ettsial organism that appears as a small, signet ring-shaped structure in the cytoplasm of infected eryth-rocytes. Clinical signs of infection may includeanemia, fever, lethargy and occasionally jaundice.Some passerine species in which piroplasmosis hasbeen identified include crows, rooks, larks, sparrowsand buntings.38 Treatment with doxycycline or anti-malarial drugs may be useful.

Filarial WormsMicrofilaria and adult filiarial nematodes (Ser-ratospiculum amaculata and Diplotriaena sp.) havebeen reported at a low prevalence in a variety ofspecies of passerines such as lyrebirds, Estrilidfinches, honeyeaters, thrushes, grackles, sparrowsand corvids. Most infections have not been associatedwith any disease and the parasites have been foundincidentally in blood smears (microfilaria) or at ne-cropsy (adults). Splendidofilaria passerina may bepathogenic in sparrows. Treatment is not generallywarranted but levamisole may be useful.38,43,57

Internal Parasites

AcanthocephalansBoth adult and intermediate stages of acanthocepha-lan parasites may be found in free-ranging passer-ines. Adult worms are generally susceptible tobenzimidazole anthelmintics. Genera affecting pas-serines include Polymorphous, Plagiorhynchus,Prosthorhynchus and Centrorhynchus.

The Superb Lyrebird, the largest passerine species,is a ground-dwelling inhabitant of rain forests insoutheastern Australia. The acanthocephalan para-site Plagiorhynchus menurae has been identified inlyrebirds showing weakness, emaciation and respira-tory distress. Duodenal necrosis has been demon-strated at necropsy. Invertebrates are postulated tobe the intermediate hosts.48,50

Small cysts, 2 to 3 mm long and shaped like ricegrains, may sometimes be found in the subcutaneoustissues of the neck and thorax in a wide variety ofAustralian passerine birds. These cysts are interme-diate stages of the acanthocephalan Oncicola poma-tostomi, the adult stages of which are found in theintestines of dingos and feral cats. The initial host ispostulated to be scavenging insects.50


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CestodesBecause tapeworms require arthropods as interme-diate hosts, they are predominately a problem insoftbill and insectivorous finches. They are normallynot seen in canaries or exclusively seed-eating birds(such as Gouldian Finches), except in situationswhere parent birds feed insects to their offspring orthe insects are accidentally consumed with the seeds.

Many different tapeworms have been described inpasserines but in most cases, infectivity levels arelow, and the parasites cause no clinical disease. Ema-ciation, diarrhea, general debilitation and death mayoccur in birds that are stressed and are continuouslyexposed to infected intermediate hosts. Proglottids orhexacanth larvae may be noted on gross or micro-scopic examination of droppings, but these arepassed only intermittently. Certain finch species, eg,parrot finches and Diamond Firetails, are particu-larly prone to developing intestinal obstructionsfrom heavy Choanotaenia sp. infections. These highlevels of infectivity are common in densely plantedaviaries with compost heaps or other sources of in-fected intermediate hosts.

Tapeworms can be avoided by limiting access to in-termediate hosts and by using insect-proof screen-ing. Other sources of protein (such as commerciallyavailable formulated diets, insectivore mixes, eggfood or grated cheese) may replace live invertebratesas food items. However, some birds may not acceptthese alternative foods and may die or be left suscep-tible to disease because of poor nutrition. Others willbe reluctant to breed without live food or may deserttheir nestlings.

Effective anthelmintics for passerines include praz-iquantel and oxfendazole. In cases where it is notappropriate to prevent access to intermediate hosts,a regular deworming program will lower the infec-tion rate.18

TrematodesThese parasites have complicated life cycles thattypically involve snails as initial intermediate hostsand other invertebrates as secondary intermediatehosts. It is unlikely that appropriate conditions forcompletion of the life cycle will be found, exceptpossibly in planted aviaries.

Trematodes are seen occasionally in wild-caught pas-serines.38,50 Collyriculum sp. may be found encystedin the skin of birds. C. faba forms 4 to 6 mm cysts onpasserine birds such as sparrows and starlings, as

well as gallinaceous birds. These cysts have beenreported to cause death in wood thrushes by ob-structing the cloaca.

Schistosomes are trematodes that live in blood ves-sels. Gigantobilharzia huronensis is a blood flukethat has been reported in North American gold-finches and cardinals. It has also been experimen-tally transmitted to canaries.

Prosthogonimus sp. are trematodes affecting the in-testinal tract, cloaca, bursa or oviduct. These para-sites have been found worldwide in passerine speciessuch as sparrows, corvids, starlings and thornbills.38

They are not particularly pathogenic, and if clinicalsigns occur they are generally nonspecific. Dragon-flies and snails are intermediate hosts. Praziquantelmay be useful in treating trematodes.

NematodesAscaridia: Two main types of roundworms affectpasserines: Ascaridia spp., which have direct lifecycles, and Porrocecum spp., which have indirect lifecycles with invertebrates such as earthworms as theintermediate host. Both types of roundworms may beassociated with weight loss, diarrhea, general debil-ity and sometimes neurologic symptoms. Ascaridiaspp. are uncommon in passerines.

Porrocecum spp. have been found in a variety offree-ranging passerines, for example pipits, quail-thrush, thrush, blackbirds, Australian magpies, cur-rawongs and corvids. Fibrous tumors, believed tohave been induced by larval Porrocecum spp. havebeen described in blackbirds on the peritoneal sur-face of the intestine.38,50 Fenbendazole, piperazineand levamisole are useful in treating ascarid infections.

Capillaria: Capillaria spp. are cosmopolitan intheir distribution and affect a range of passerinespecies. The life cycle is direct or may involve earth-worms as paratenic hosts. Susceptibility does notdepend on dietary preferences, and the parasite hasbeen found to cause disease in a variety of seed-eaters(such as canaries), insectivorous and omnivorous spe-cies (such as weavers, whydahs, jays and mynahs)and honeyeaters.

Birds with low numbers of capillaria may be subclini-cal. Higher parasite loads may lead to weight loss,diarrhea, general ill health and death. These wormsmay localize to a variety of sites along the gastroin-testinal tract. They may be associated with white orcream plaques in the buccal cavity or pharynx andswelling and lumen distension of the crop, proven-


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triculus, intestine or bowel. Typical bi-polar plugsmay be found by directly swabbing lesions or by fecalflotation.

Capillaria are often more difficult to treat than as-carids. Aviary hygiene and removal of earthwormsare important control measures. Levamisole, fenben-dazole and oxfendazole may be effective in somecases.

Spiruroid: Acuaria skrjabini has been associatedwith significant mortalities in Australian aviarieshousing both native and imported finches. This ven-tricular and proventricular worm parasite does notaffect psittacine birds. The parasite lives under thekoilin lining of the ventriculus, and characteristicembryonated eggs are passed in the feces. Attemptsto identify intermediate hosts in this species havebeen unsuccessful, but other species of Acuaria arebelieved to be transmitted by arthropod vectors. Theparasite is resistant to treatment with many commonanthelmintics, but oxfendazole may be effective.

Acuaria spp. have been reported in a variety of free-ranging passerines in Australia, eg, bushlarks,trillers, thrush, flycatchers, whistlers, shrike-thrush, honeyeaters, Australian magpies, curra-wongs and corvids.50

Other spiruroid worms that occur worldwide andmay be found in the proventriculus or ventriculus ofpasserine species include Dispharnyx nasuata(which has been described in the House Sparrow,starling, catbird and gallinaceous birds) and Spirop-tera incerta. These worms have been reported tocause swelling of the proventricular mucosa and mayinhibit the passage of food.74

Eye Nematodes: Oxyspirura mansoni has been re-ported in mynahs, sparrows and other passerines.The parasite is found behind the nictitating mem-brane or in the conjunctival sac or the nasolacrimalduct. The intermediate host is the cockroach. Wormsshould be mechanically removed and any inflamma-tion treated symptomatically. Ivermectin is effec-tive.36

Respiratory Nematodes: Syngamus trachea (gape-worm) affects a range of passerine species as well asbirds from other orders. Corvids, starlings and black-birds are particularly susceptible. Earthworms mayact as transport hosts. Levamisole, ivermectin andfenbendazole are effective in treating this parasite,but caution should be exercised when treating birdswith heavy infections. Tracheal obstruction may oc-

cur when the parasites are killed. Mechanical re-moval of worms and treatment with low doses ofanthelmintics over several days is an effective thera-peutic plan.

Arthropod ParasitesRespiratory Mites: Respiratory acariasis (“air sacmite infection”) caused by Sternostoma tracheacolumis a common cause of dyspnea, open-mouthed breath-ing and wheezing respiration in canaries andGouldian Finches. “Air sac mites” is a misnomergiven that these parasites are frequently found in thetrachea, particularly near the syrinx. Occasionally,the mites may be visualized by wetting the feathersof the bird’s neck with alcohol and transilluminatingthe trachea with a bright source of light. If mites arepresent, they may be visible as tiny, dark, moving,pinhead-sized spots. Failure to see the mites does notrule out their occurrence because the mites may bepresent lower in the respiratory tract.

There are several options for treating this mite. Iver-mectin may be used orally or topically. A dichlorvospest strip may be placed (according to manufac-turer’s directions) near but out of reach of the birds.Birds may also be sprayed with pyrethrin synergizedwith piperonyl-butoxide insecticide spray.

Other species of passerines apart from canaries andGouldian Finches may harbor S. trachaeacolum, butthey are less frequently affected and less likely toshow severe clinical symptoms. Other species of Ster-nostoma mites have been recorded in passerines in-cluding S. sialiphilus in Eastern Bluebirds, S. spatu-latum in Olive-backed Thrush and S. cryptohyncheumin sparrows. A nasal rhynonyssid mite Speleog-nathus sturni, which occasionally causes nasal dis-charge, has been recorded in starlings.

Cytodites nudus is another mite that has been asso-ciated with respiratory disease in free-ranging pas-serines. It is much less common than Sternostoma sp.and may be found in the abdominal cavity as well asthe respiratory system. Heavy infections have beenassociated with granulomatous pneumonia, peritoni-tis and obstruction of the respiratory passages.38

Treatment is as described for other air sac mites.

External Parasites

Skin and Feather MitesScaly Mites: Knemidokoptes pilae (and several otherless common species) tend to cause hyperkeratoticlesions on the feet in passerines. This is in contrast


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to infections in psittacine birds, which are primarilyassociated with beak lesions. Hyperkeratosis causedby scaly mite needs to be differentiated from gener-alized hyperkeratosis of the feet and legs that occurswith malnutrition and age in some canaries and otherpasserines (see Color 24). Scaly mite lesions start ascrusts on the plantar surface of the foot and graduallyget thicker. Flexion of the joints of the digits causesthe thickening keratin to split and gradually enlarge,making it difficult for the bird to perch. Scaly mitelesions in passerines are sometimes referred to as“tassel foot” because of this characteristic appearance(Figure 43.14). European goldfinches and canariesare particularly susceptible to Knemidokoptes spp.but the condition has been reported in a wide rangeof Passeriformes (Figure 43.15).

Knemidokoptes spp. may be treated with topical iver-mectin. A single dose may be effective in mild cases.A repeat dose three weeks later may be needed inmore severe cases.

Feather Mites: Dermanyssus sp. (red mites) and Or-nithonyssus sp. (fowl mites) are not host-specific andmay be found on a variety of Passeriformes includingcanaries, starlings and mynahs. These mites com-monly cause irritation and anemia. Deaths have beenreported with heavy infections in small birds. Non-pathogenic feather mites of a variety of genera (An-lages, Megninia and Rivoltasia) may also occur.Lightly dusting birds with pyrethrin or carbaryl pow-

ders may be effective. Placing the powder in a saltshaker and “lightly salting” is sufficient.

Quill mites are not particularly species-specific andmay attack both passerine and non-passerine spe-cies. Dermoglyphus, Syringophilus, Picobia and Har-pyhynchus are genera that have been reported onPasseriformes. Harpyhynchus sp. has been associ-ated with extensive dermatitis as well as cysts andskin tumors on hawfinches and a Lanceolate War-bler. Hanging a dichlorvos pest strip near birds af-fected with quill mites has eliminated the parasite insome cases. Treating the bird with ivermectin shouldbe effective.

Epidermoptic Mites, which may be carried mechani-cally by hippoboscid flies, cause a depluming derma-titis followed by scale formation (Figure 43.16). My-ialges sp. (from a Blue Tit and Pekin Robin),

FIG 43.14 A mature female canary was presented with a three-week history of anorexia and lying on the bottom of the enclosure.The proliferative hyperkeratotic lesions on this canary’s foot arecharacteristic for a Knemidokoptes sp. infection (“tassel foot”)(courtesy of Terry Campbell).

FIG 43.15 A group of several hundred robins died following theingestion of pesticide-contaminated worms. Several of the birdshad hyperkeratotic lesions on the feet and legs. These were con-firmed to be caused by Knemidokoptes sp. by demonstrating themite on skin scrapings.


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Epidermotes bilobatus (from canaries) and Mi-crolichus avus (from canaries, House Sparrows andmynahs) have been described in Passeriformes.Epidermoptic mites may be easily identified on mi-croscopic examination of skin scrapings. Trombidi-form mites of the genus Neocheyletiella have alsobeen reported to cause depluming mange in canariesand Pekin Robins. Treatment options are like thosedescribed for quill mites.38

LiceLice are more common on Passeriformes than theyare on Psittaciformes. Some of the genera of bitinglice (Amblycera) that occur on passerines includeColpocephalum, Menacanthus, Machaerilaemus,Mysidea and Rininus. These lice are not specializedfor life on particular feathers and are able to movequickly. Chewing lice (Ischnocera) are often specifi-cally adapted to a particular part of the bird’s bodyand are generally more sluggish than biting lice.Some genera that affect passerines include Bruelia(on canaries and House Sparrows), Sturnidoecus (onstarlings and other passerines), Degeeriella and Phi-lopterus. Signs of the presence of lice include restless-ness and biting, excessive preening and damage toplumage. Some cases of baldness in canaries arecaused by lice.

Lice undergo a complete life cycle on the bird, and aweekly dusting with pyrethrin is an effective methodof control.

Metabolic Diseases

Iron Storage Disease and Related EntitiesVarious Passeriformes species including Indian HillMynahs, Rothschild’s Mynahs, quetzals, Birds ofParadise, Green Cat Birds and tanagers have beenreported to be susceptible to excessive accumulationof iron in the liver.28,30,59 In a group of 11 mynah birdsthat varied from five to ten years in age, clinical signsassociated with hepatomegaly and ascites included athree-day to three-month history of listlessness, re-gurgitation, dyspnea, weight loss, diarrhea, cough-ing, wheezing and syncope. Most of the birds diedwithin several days of presentation.59

Radiographs may reveal hepatic enlargement andascites in affected birds. Liver enzymes are typicallyelevated while total serum protein is low. Diagnosisusing biopsy is discussed in Chapters 13 and 20.

At necropsy birds may show an enlarged, congestedliver which may be tan in color (see Color 20). His-tologically the distinction is made between he-mosiderosis, where there is no visible tissue altera-tion but an increased amount of hemosiderin, andhemochromatosis, where there are pathologicchanges in the hemosiderin-containing tissues. He-patic pathology may include congestion, focal ne-crosis, accumulation of inflammatory cells and fibro-sis. Iron-processing cells are absent from the spleenand the spleen does not contain iron pigments.28,30,34

Neoplasia including lymphosarcoma, hepatocellularcarcinoma and erythroblastosis has been associatedwith iron storage disease. The neoplastic cells do notcontain iron.

Iron storage disease is believed to beassociated with high dietary iron lev-els in avian species with problems inprocessing iron. Susceptible speciesshould be kept on low-iron diets suchas fresh fruit and commerciallyavailable formulated rations that arelow in iron (less than 60 parts permillion) (see Chapter 20).

AmyloidosisAmyloidosis is common in GouldianFinches and is occasionally seen inother Passeriformes species.39 A f-fected birds may be found dead, havea chronic nonspecific history of ill-ness or suffer from concurrent infec-tions (polyomavirus, cryptosporidio-FIG 43.16 A number of external parasites including quill mites, epidermoptic mites and

lice can cause skin irritation, pruritus and plumage damage.


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sis). Social stress may play a role in the developmentof the disease. The liver and kidneys may appearnormal at necropsy even though they may be se-verely affected histologically. More often they willappear pale and yellowish. A hereditary predisposi-tion is suspected.18,46

Hepatic LipidosisFatty livers are occasionally seen in Estrilid finches(Zebra Finches, parrot finches and Star Finches) andmay be associated with inadequate exercise andhigh-energy diets such as soft foods and mealworms.The liver is swollen, yellow or tan in color and mayfloat in formalin.18 The use of some formulated dietsmay help resolve or prevent hepatic lipidosis.

Toxicosis

Canaries and finches are particularly susceptible toinhalant toxins because they breathe more air pergram of body weight than larger birds, and they havea highly efficient gas exchange system (see Chapter22). Carbon monoxide exposure from any source (carexhaust, gas furnace leaks, kerosene stoves) can berapidly fatal. There may be minimal changes at ne-cropsy or the lungs and blood may appear bright red.Carbon dioxide poisoning may occur in crowded,poorly ventilated shipping boxes. Passerines, likepsittacines, are very susceptible to the gases releasedfrom overheated polytetrafluoroethylene65 ( s eeChapter 37).

Certain varieties of avocado may be toxic to somePasseriformes. Postmortem findings in intoxicatedbirds include hydropericardium and subcutaneousedema in the pectoral area.32 Deaths have occurredin American Goldfinches after consuming green al-monds, presumably from cyanide released by hy-drolysis of amygdalin, a cyanogenic glycoside.

Ethanol toxicity has been reported in free-rangingpasserines (especially Cedar Waxwings) followingthe ingestion of hawthorn pommes or other fruitsthat have frozen and then thawed allowing yeastfermentation of sugars to produce ethanol. Birds arelethargic, ataxic or may be in a stupor (“drunk”).Many intoxicated birds die from accidents that occurwhile they are “flying under the influence.” Diagno-sis is based on analyzing crop contents for ethanolconcentrations.19

Heavy metal toxicities caused by the consumption ofwire are uncommon in passerines because they havelimited capacity to damage metal objects. Lead or zinctoxicosis has occasionally been seen when galvanizedwire has been use in the construction or repair ofenclosures. Heavy metal particles may be identifiedon radiographs, but most affected birds die quickly.Removing the source of heavy metals and administra-tion of chelation therapy are recommended. The oc-currence of “new wire disease” can be reduced byscrubbing galvanized wire with a dilute acetic acidsolution and allowing it to weather before it is usedfor enclosure construction; however, even wire that iswashed may still be toxic (see Chapter 37).

Neoplastic Diseases

Passeriformes have one of the lowest incidence oftumors of any order of birds or mammals. Neoplasmsthat have been regularly reported include leukosis incanaries, adenomas associated with poxvirus, papil-lomas in finches and neoplasia associated with ironstorage disease.

Products Mentioned in the Texta. Vira-A, Parke Davis, Morris Plains, NJb. PEP-E, Phylomed, Plantation, FLc. Biomune, Inc, Lenexa, KS


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