26.3 Birds

KEY CONCEPT Birds have many adaptations for flight.

26.3 Birds

Birds evolved from theropod dinosaurs.

• Birds and many theropods share anatomical features.– hollow bones– fused collarbones that form V-shaped wishbone– rearranged muscles in the hips and legs – “hands” that have lost their fourth and fifth fingers– feathers

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• The oldest undisputed fossilized bird is Archaeopteryx.

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A bird’s body is specialized for flight.

• Birds have several unique features that allow them to fly.– wings to produce flight– strong flight muscles to

move the wings– active metabolism that

provides energy to the muscles

– hollow bone structure to minimize weight

– gonads active during only part of year

small intestine

largeintestine

lung

gizzard

kidney

cloaca

crop

sternum(keel) heart

liver

pectoral muscle

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• Wings are structures that enable birds to fly.– airfoil shape– covered with feathers

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• Air sacs help a bird meet its oxygen demand during flight.

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Birds have spread to many ecological niches.

• The shape of a bird’s wing reflects the way it flies.– short and broad– long and narrow

26.3 Birds

small intestine

largeintestine

lung

gizzard

kidney

cloaca

crop

sternum(keel) heart liver

pectoral muscle

– wide and broad• The shape of a bird’s wing reflects the way it flies.

– stout and tapered

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• Differences in the shape of a bird’s beak reflects how it eats.– spearlike– hooked– chisel-shaped

blue-footed booby green woodpeckerBald eagle

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• Birds show great diversity in their foot shape.– webbed

blue-footed boobybald eagle

green woodpecker

– heavy claws– different toe location

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Feathers: Anatomy

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Feather Types

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Flight Feathers

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Flight feathers and the Wing

• Primaries– Attached to hand– Asymmetrical vanes– Owls have silent flight because of

barbs on front of vane– Generate thrust (forward motion)

• Secondaries– Attached to ulna– Generate lift

• Tail feathers– Function in steering and braking

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Wing shapes

Great once in the air, but first need to get launched! - Mastery of Flight beginning of video

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Feather care

• Birds preen up to once an hour!• Some preening glands have lipids which resist keratin

eating fungi and bacteria

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Adaptations for flight: Anatomical

• Feathers• Wing• Reproduction (internal, eggs)• Bones

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Anatomical adaptations: Bones (already mentioned)

• Lightweight, strutted or hollow• No teeth• Modified forelimb

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Anatomical adaptations: Bones

• Fused bones of pelvis, feet, hands, head• Uncinate processes on ribs• Furcula (wishbone)

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Flight Adaptations: Physiological adaptations

• Endothermic• Separate red and white muscle fibers

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Flight Adaptations: Red versus White fibers• Red fibers = sustained work, ability to produce heat by

shivering• White fibers – powerful stroke but cannot be sustained

Pigeon wing and breast?

Grouse or turkey wing and breast?

Bird leg?

Humming bird wing and breast?

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Flight Adaptations: Circulatory System• High metabolic demands require rapid circulation of high

volumes of blood.– Four chambered heart

• Double circulatory system (pulmonary and systemic)

– Large heart -50-100% larger and more powerful than mammals of the same size.

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Flight Adaptations: Respiratory System• Mammals: simple but inefficient. 20% of air never

contacts a respiratory surface for exchange• Birds require 2 full breaths to move air completely

through system. More efficient w/ help of air sacs• In addition to lungs, th ey have ~9 air sacks extending

into abdomen, land toward wings

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Flight Adaptations: Urinary system

• How often do you see a bird drink?

• Sources:• High metabolism = high metabolic

water production (up to 80% of requirements)• Food: particularly birds of prey and insectivores.

• Seed eaters need the most water• Free water – streams, watering hole, raindrops, snow

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Flight Adaptations: Urinary system

• Water conservation

• Excrete uric acid – a semi-solid with 2x the nitrogen per molecule. Concentrated in cloaca up to 3000x the acid level as in blood

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Flight Adaptations: No teeth…Digestive system impact?• Crop• Proventriculus (stomach)• Ventriculus (Gizzard)• Intestines

– Caecae

If a nectar eater, is a gizzard important?What size caecae would a goose have?

What other feeding adaptations do birds have?

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Bird Adaptations: Bill Shape

• So important that this is one way birds are classified. Twenty different orders of birds are recognized

• Why are there so many different types of birds?

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Evolutionary Arms Race

• Over evolutionary time, we expect natural selection increases the efficiency with which predators detect/capture prey AND also we expect selection to increase prey ability to avoid detection and to escape!

• Who wins?

26.3 BirdsEvolutionary Arms Race

Predator adaptation

• Improved visual acuity• Search image• Limit search to abundant

areas• learning

Prey Counter-Adaptation

• Crypsis• Polymorphism• Space out• mimicry

Winners? No. Life versus dinner principle. Stronger selection on prey. Predators adapting to a variety of prey species and cannot specialize.

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Bird Adaptations: Reproductive System

• Bird Egg• One functional ovary (less weight)• Nest structure and bird behavior create microclimate for

embryo• Laying/incubating eggs

is dangerous. Need to avoid predators!– Site choice– Nest structure– Adult behavior