27. Birds (1)
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Transcript of 27. Birds (1)
BirdsChapter 27
Class Aves – BirdsBirds (class Aves) are archosaurs but almost every
feature of their reptilian anatomy has undergone modification in their adaptation to flight.
Class Aves – BirdsBirds are found in most every habitat from forests to
deserts, even in caves. Some birds dive in the ocean to 45 m to catch prey.Birds have visited both the North & South poles.The bee hummingbird of Cuba weighs 1.8 g and is one of
the smallest vertebrate endotherms.
Derived Characters of BirdsA bird’s most obvious adaptations for flight are
its wings and feathers.Feathers are the feature that set birds apart
from other vertebrates.
Derived Characters of BirdsSome other theropod dinosaurs had feathers, but they
were not capable of supporting flight. Insulation – provides support for the idea that some
dinosaurs were endotherms.Bright colors may have been used to attract mates.
Characteristics of BirdsAll birds also have hindlimbs
adapted for walking, swimming, or perching.Foot structure in bird feet
shows considerable variation.
All have keratinized beaks.
All lay shelled amniotic eggs.
The Origin of BirdsBirds descended from theropods – a group of small,
carnivorous dinosaurs.
By 147 million years ago, feathered theropods had evolved into birds.
The Origin of BirdsArchaeopteryx
The oldest bird known.Skull similar to modern birds but with thecodont
teeth.Wings with feathers were present.
The Origin of BirdsMuch of the skeleton was
that of a theropod dinosaur.Long bony tailClawed fingersAbdominal ribsS-shaped, mobile neck
This fossil demonstrated the connection between theropods & birds.
The Origin of Birds
Archaeopteryx arose from the theropod lineage.
Closely related to Dromaeosaurs.More shared
derived characters.
Many had feathers used for insulation and/or social display.
Living BirdsThe ratites, superorder
Paleognathae, are all flightless.Primitive archosaur
palate.Ostriches, emus, rheas,
kiwis, tinamous.Flat sternum, poorly
developed pectoral muscles.
Living BirdsAll other birds are superorder
Neognathae, having a flexible palate.
The demands of flight have rendered the general body form of many flying birds similar to one another.
Flying birds have a keeled sternum with well developed pectoral muscles.
Living BirdsFlightlessness has
evolved in many groups of birds.Penguins (use wings
to swim through water).
Many fossil forms including flightless owls, pigeons, parrots, cranes, ducks, & auks.
Usually occurs on islands with few predators.
Form & Function – FeathersFeathers are lightweight,
yet tough, consisting of:A hollow quill emerges
from the skin.This becomes the shaft
which bears numerous barbs that form a flat, webbed surface, the vane.Each barb contains many
barbules.
Form & Function – FeathersContour feathers are vaned
feathers that cover and streamline a bird’s body. Called flight feathers if they
extend beyond the body.
Down feathers are soft and have no hooks on barbules.
Filoplume feathers are hair-like – function unknown.
Powder-down feathers disintegrate as they grow, releasing powder that aids in waterproofing.
Form & Function – FeathersFeathers are homologous to reptiles’ scales.
It develops from an epidermal elevation overlying a nourishing dermal core. In reptiles, this elevation flattens into a scale. In birds, it rolls into a cylinder and sinks into the follicle
from which it will grow.
Form & Function – FeathersAs a feather nears the
end of its growth, keratin is deposited to make some of the structures hard.
The protective sheath surrounding the new feather splits open, and the feather unfurls.
Form & Function – FeathersWhen fully grown, feathers are dead – like mammalian
hair.
Birds molt to replace worn out feathers.Usually feathers are discarded gradually to avoid bare
spots.Flight feathers & tail feathers are lost in pairs to maintain
balance.Many water birds lose all their primary feathers at once
and are grounded during the molt.
Form & Function – FeathersColors in birds may be pigmentary or structural.
Red, orange, & yellow are colored by pigments called lipochromes.
Black, brown, & gray are produced by the pigment melanin.
Blue is created structurally by the scattering of shorter wavelengths of light by particles within the feather.
Form & Function – SkeletonA light, yet still strong skeleton is a requirement for
flight.Bird bones are laced with air cavities.
Form & Function – SkeletonBirds are archosaurs, and had ancestors with diapsid
skulls.Bird skulls are highly specialized – mostly fused into one
piece.
Leg bones in birds are heavier – this helps lower the center of gravity giving aerodynamic stability.
Form & Function – SkeletonModern birds are toothless.
Instead they have a keratinized beak.
Most birds have kinetic skulls.They have a wide gape.Upper jaw is attached loosely increasing the gape.
Form & Function – SkeletonAll birds that can fly
have a large, thin keel on their sternum that provides area for the large flight muscles to attach.
Food & FeedingEarly birds were carnivorous, feeding mostly on
insects.Many birds are still insectivores.Other foods include nectar, seeds, berries, worms,
crustaceans, molluscs, fish, frogs, small birds & mammals.
Food & FeedingSome birds are generalists, feeding on a wide range
of food items.Perhaps more competition for food, but less danger of
something happening to the food source.
Others are specialists, only feeding on one type of food.Less competition, more danger of losing the food source.
Food & FeedingThe beaks of birds are strongly adapted to
specialized food habits.
DigestionAt the end of the esophagus of many birds is the crop.
Used for storage.
DigestionThe stomach has two compartments:
The first secretes gastric juices.The second, the gizzard, is lined with keratinized plates
that serve as millstones for grinding food.Birds swallow small stones to help this process.
DigestionOwls can’t digest the bones & fur or feathers of their
prey.These materials are bundled together and ejected
through the mouth.Owl pellets can be used to determine what the owls in a
particular area have been eating.
Circulatory SystemBirds have a four-chambered heart.
Separate systemic and respiratory circulations.
Fast heartbeat – faster in smaller birds.
Red blood cells are nucleated and biconvex.Mammals are enucleated and biconcave.
Respiratory SystemThe highly adapted respiratory system of birds is
adapted for the high metabolic demands of flight.The finest branches of the bronchi are developed as
tubelike parabronchi through which air can flow continuously – instead of ending in saclike alveoli as in mammals.
Respiratory SystemThere is an
extensive system of nine interconnecting air sacs that connect to the lungs.
Air flows to the posterior air sacs, to the lung, then to the anterior air sacs and out.
Respiratory SystemThe result is that there is an almost continuous stream
of oxygenated air passing through the highly vascularized parabronchi.
Excretory SystemUrine is formed in large, paired metanephric kidneys.
There is no urinary bladder.Nitrogenous wastes are secreted as uric acid rather than
urea.Bird kidneys can only concentrate solutes to 4-8 times
that of blood concentration.
Excretory SystemSome birds,
including marine birds, have a salt gland to help rid the body of excess salts.Salt solution is
excreted from the nostrils.
Nervous SystemBirds have well
developed cerebral hemispheres, cerebellum (important for coordinating movement & balance), and optic lobes.
SensesBirds usually have poor sense of smell & taste.
Some, carnivores, waterfowl, flightless birds have well developed sense of smell & taste.
Birds have the keenest eyesight in the animal kingdom and also very good hearing.A hawk can clearly see a crouching rabbit a mile away!
FlightTo fly, birds must generate lift forces greater than their
own mass and they must provide propulsion to move forward.
Bird wings are designed to provide lift.
Flight - Wings are Specialized for Particular Kinds of Flight
Elliptical wings are good for maneuvering in forests.
High speed wings are used by birds that feed during flight or that make long migrations.
Dynamic soaring wings are used by oceanic birds that exploit the reliable sea winds.
High lift wings are found in predators that carry heavy loads. Soaring over land with variable air currents.
MigrationMany species of birds
undergo long migrations using well established routes.Some species make
the trip quickly, others stop along the way to feed.
Often, they follow landmarks such as rivers and coastlines.
MigrationThe stimulus for
migration has to do with changing hormone levels brought about by a change in day length.
MigrationBirds navigate using a number of cues:
Visual cues – landmarks.Accurate sense of time.Some may use the Earth’s magnetic field.Celestial cues – sun by day, stars at night.
Social Behavior – Mating SystemsTwo types of mating
systems found in birds:
Monogamy where an individual has one mate.Rare in animals,
common in birds. Seasonal or lifelong
Social Behavior – Mating SystemsBirds have a high incidence of monogamy because
both parents are equally able to perform most aspects of parental care.Often success of the hatchlings requires care from two
parents.
Social Behavior – Mating SystemsPolygamy where an individual has more than one
mate during a breeding season.Polygyny – one male, many femalesPolyandry – one female, many males
Social Behavior – Mating SystemsThe most common
form of polygamy in birds is polygyny. In some species,
such as grouse, males gather in a display area or lek. Each male defends part of the lek and displays for the females.Only females care for
young. http://www.youtube.com/watch?v=s2_wdMmEupQ
Social Behavior – Mating SystemsAn example of polyandry occurs in spotted
sandpipers.Females defend territories and mate with several males.Each male incubates a nest of eggs in the female’s
territory and does most of the parental care.
This system may have evolved in response to high predation rates.
NestingMost birds build nests
in which to lay eggs.Often great care is
taken to hide the nest, or make it inaccessible to predators.
When the young hatch, they usually must be fed by one or both parents.
NestingPrecocial young, such as
ducks, water birds, fowl and quail are covered with down when they hatch and can run or swim as soon as their down dries.Most precocial young
must still be cared for by the parents for a time.
NestingAltricial young are naked and
unable to see or walk at hatching.They must remain in the nest
for a week or more.Parents must spend lots of
time & energy bringing food to hatchlings.
There is a continuum with the young of many species falling in between the two extremes.