CLASS AVESDIGESTIVE SYSTEM

Professor Rolland Merch M. Arriza

Mindanao State University – General Santos City

OverviewBirds consume high-energy foods such as insects, seeds, fruits, and nectar. The digestive system is extremely efficient in absorbing energy from small amounts of food at a rapid rate.

Figure 1: Internal Organs of a Typical Chicken

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The beak, bill, or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young

Beak

Beak

Figure 2: Types of Beaks

Beak

Beak - Cracker

Figure 3: Northern Cardinal (Cardinalis cardinalis ) Figure 4: Rose-breasted Grosbeak (Pheucticus ludovicianus)

Beak - Shredder

Figure 5: Philippine Eagle (Pithecophaga jefferyi) Figure 6: Northern Goshawk (Accipiter gentilis)

Beak - Chisel

Figure 7: Pileated Woodpecker (Dryocopus pileatus)

Figure 8: Red-bellied Woodpecker (Melanerpes carolinus)

Beak - Probe

Figure 9: Green Violetear (Colibri thalassinus) Figure 10: Rufous Hummingbird (Selasphorus rufus)

Beak - Strainer

Figure 11: Mandarin Duck (Aix galericulata) Figure 12: Filter teeth along the beak

Beak - Spear

Figure 13: Azure Kingfisher (Alcedo azurea) Figure 14: Great Blue Heron (Ardea herodias)

Beak - Tweezer

Figure 15: Wood Warbler (Phylloscopus sibilatrix) Figure 16: Willow Warbler (Phylloscopus trochilus)

Beak - Swiss Army Knife

Figure 17: Pied Crow (Corvus albus) Figure 18: Common Raven (Corvus corax)

Beak - SummaryType

Shape

Adaptation

Cracker

Seed eaters like sparrows and cardinals have short, thick conical bills for cracking seed.

Shredder

Birds of prey like hawks and owls have sharp, curved bills for tearing meat.

Chisel

Woodpeckers have bills that are long and chisel-like for boring into wood to eat insects.

Beak - SummaryType

Shape

Adaptation

ProbeHummingbird bills are long and slender for probing flowers for nectar.

StrainerSome ducks have long, flat bills that strain small plants and animals from the water.

Spear

Birds like herons and kingfishers have spear-like bills adapted for fishing.

Beak - SummaryType

Shape

Adaptation

Tweezer

Insect eaters like warblers have thin, pointed bills.

Swiss Army Knife

Crows have a multi-purpose bill that allows them to eat fruit, seeds, insects, fish, and other animals.

Most birds have tongues, though unlike ours. A bird's tongue has 5 bones in it that support and strengthen it, together they are called the 'Hyoid apparatus'. A bird's tongue is generally harder and less flexible than ours.

Tongue

Tongue

Figure 19: Great Blue Heron (Ardea herodias) Figure 20: Blue and Gold Macaw (Ara ararauna)

Tongue

Figure 21: Woodpecker tongue Figure 22: Woodpecker tongue

The esophagus is large in diameter, particularly in birds that swallow large meals. Swallowing is accomplished by esophageal peristalsis, and in most birds appears to be aided by extension of the neck.

Esophagus

EsophagusThe esophagus conducts food from the mouth to the stomach in all animals. In this case with birds it goes to the gizzard first before the proventriculus (a birds stomach).

Figure 23: Jugular part of a bird

Crop

Figure 25: Avian digestive tractFigure 24: Crop sketch

Crop

Figure 26: Budgerigar (Melopsittacus undulatus) Figure 27: Caribbean Flamingo(Phoenicopterus ruber)

Crop

Figure 28: Non-lactating crop (A) versus lactating crop (B and C)

Nearly all birds have a stomach made up of two parts. The first part of the stomach, called the proventriculus, secretes strong digestive juices. The second part of the stomach, called the gizzard, has strong muscular walls that act like teeth to grind and pulverize foods.

Stomach

Stomach

Figure 29: Avian stomach Figure 30: Proventriculus and gizzard

Proventriculus

Figure 31: Cross section of the proventriculus Figure 32: Proventriculus cross section

Ventriculus

Figure 33: Proventriculus and Gizzard Figure 34: Gizzard

Ventriculus

Figure 35: Mucosal layer of ventriculus Figure 36: Closer look of the mucosal layer

Ventriculus

Figure 37: Secretory region of ventriculus Figure 38: Pellicle material being pushed out into the lumen

Stomach

Figure 39: Particle size of material in the gizzard vs. proventriculus.

Some birds practice geophagy or the practice of eating earthy or soil-like substances such as clay. This provide grit for digestion. Because birds lack teeth, many ingest pebbles or coarse soil with which to grind food in their gut. It also helps neutralize toxins from their body.

Intestine

Small Intestine

Figure 40: Gastrointestinal tracts of a carnivorous hawk, an omnivorous chicken, and 4 herbivorous birds.

Small Intestine

Small Intestine

Figure 41: Intestine Cross-section (Nothura maculosa)

Figure 42: Intestinal microvilli

Large Intestine

Figure 43: Avian digestive tract Figure 44: Avian digestive tract

Large Intestine

Figure 45: Avian large intestine Figure 46: Avian digestive tract

Avian Geophagy

Figure 47: Scarlet Macaw (Ara macao) Figure 48: Green-rumped Parrotlet (Forpus passerinus)

Unlike other birds, owls have no crop. A crop is a loose sac in the throat that serves as storage for food for later consumption. Since an owl lacks this, food passes directly from the mouth to the gizzard.

Accessory organs

Pancreas

Figure 49: Avian pancreas Figure 50: Avian pancreas tissue

Liver

Figure 51: Accessory organs Figure 52: Avian liver

Gall bladder

Figure 53: Avian gall bladder

Unlike mammals, birds don't urinate. Their kidneys extract nitrogenous wastes from the bloodstream, but instead of excreting it as urea dissolved in urine as we do, they excrete it in the form of uric acid. Uric acid has a very low solubility in water, so it emerges as a white paste. This material, as well as the output of the intestines, emerges from the bird's cloaca. 

Cloaca

Cloaca

Figure 54: Avian cloaca

Cloaca

Figure 54: Bird poop Figure 55: Bird poop

References

References Butler, Laurence. “Bird Tongues”. Butler’s

Birds. 1 November 2011. Web. 15 July 2013. <http://butlersbirdsandthings.blogspot.com/2011/11/bird-tongues.html>

Robert E. Schmidt, Drury R. Reavill, David N. Phalen (2008). Pathology of Pet and Aviary Birds. John Wiley & Sons. Pp. 41 – 42.

Conrad, Jim. “Bird Digestion”. Backyard Nature. Web. 16 July 2013. <http://www.backyardnature.net/birdguts.htm>

Chandra, Girish. “Digestive System”. Iaszoology. 30 January 2007. Web. 15 July 2013. <http://www.iaszoology.com/digestive-system>

McLelland, John (1990). A Colour Atlas of Avian Anatomy. Aylesbury, England. Wolfe Publishing Ltd. Pp. 47 – 65.

Caceci, Thomas. “Avian Digestive System”. VetMed Veterinary Histology. Web. 15 July 2013. <http://www.vetmed.vt.edu/education/curriculum/vm8054/Labs/Lab22/lab22.htm>

Ramel, Gordon John Larkman. "The Alimentary Canal in Birds". Earth Life. 29 September 2008. Web. 15 July 2013. <http://www.earthlife.net/birds/digestion.html>

Clench, M. H. 1999. The avian cecum: update and motility review. Journal of Experimental Zoology 283: 441-447.

Jackowiak, H., W. Andrzejewski, and S. Godynicki. 2006. Light and scanning electron microscopic study of the tongue in the cormorant Phalacrocorax carbo (Phalacrocoracidae, Aves). Zoological Science 23: 161-167.

References Catroxo, M. H. B., M. A. I. Lima, and C. E. M. P.

D. M. Cappellaro. 1997. Histological aspects of the stomach (proventriculus and gizzard) of the Red-capped Cardinal (Paroaria gularis gularis). Rev. chil. anat. 15: 19-27.

Chikilian, M. and N. B. de Speroni. 1996. Comparative study of the digestive system of three species of tinamou. I. Crypturellus tataupa, Nothoprocta cinerascens, and Nothura maculosa (Aves: Tinamidae). Journal of Morphology 228: 77-88.

Silver, Rae (1984). "Prolactin and Parenting in the Pigeon Family". The Journal of Experimental Zoology 232 (3): 617–625. doi:10.1002/jez.1402320330 <http://www.columbiauniversity.org/cu/psychology/silver/publications/035Silver%201984.PDF>

Ehrlich, Paul R.; Dobkin, David S. and Wheye, Darryl (1988) Bird Milk. stanford.edu <http://www.stanford.edu/group/stanfordbirds/text/essays/Bird_Milk.html>

Duke, G.E. 1994. Anatomy and physiology of the digestive system in fowl. Pages 46-49 in Proc. 21st Annual Carolina Poultry Nutrition Conference, Dec. 7-8, Charlotte, N.C.

Fritz, J., E. Kienzle, J. Hummel, O. Wings, W. J. Streich, and M. Clauss. 2011. Gizzard vs. teeth, it's a tie: food-processing efficiency in herbivorous birds and mammals and implications for dinosaur feeding strategies. Paleobiology 37: 577-586. <http://paleobiol.geoscienceworld.org/cgi/content/abstract/37/4/577>

References Barton, N.W.H. & Houston, D.C. 1993. A

comparison of digestive efficiency in birds of prey. Ibis 135:363-372. <http://www.gla.ac.uk/researchinstitutes/bahcm/staff/davidhouston/davidhouston/digestiveefficiencyandfeedingstrategyinbirdsandmammals>

Stevens, C. E. and I. D. Hume. 1998. Contributions of Microbes in Vertebrate Gastrointestinal Tract to Production and Conservation of Nutrients. Physiological Reviews 78: 393-427. <http://physrev.physiology.org/cgi/content/full/78/2/393>

Gillespie, M. J., V. R. Haring, K. A. McColl, P. Monaghan, J. A. Donald, K. R. Nicholas, R. J. Moore, and T. M. Crowley. 2011. Histological and global gene expression analysis of the 'lactating' pigeon crop. BMC Genomics 12: 452. <http://www.biomedcentral.com/1471-2164/12/452/abstract>