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26.3 Birds
KEY CONCEPT Birds have many adaptations for flight.
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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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26.3 Birds
• The oldest undisputed fossilized bird is Archaeopteryx.
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26.3 Birds
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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26.3 Birds
• Wings are structures that enable birds to fly.– airfoil shape– covered with feathers
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26.3 Birds
• Air sacs help a bird meet its oxygen demand during flight.
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26.3 Birds
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
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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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26.3 Birds
• 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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26.3 Birds
• Birds show great diversity in their foot shape.– webbed
blue-footed boobybald eagle
green woodpecker
– heavy claws– different toe location
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26.3 Birds
Feathers: Anatomy
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26.3 Birds
Feather Types
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26.3 Birds
Flight Feathers
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26.3 Birds
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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26.3 Birds
Wing shapes
Great once in the air, but first need to get launched! - Mastery of Flight beginning of video
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26.3 Birds
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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26.3 Birds
Adaptations for flight: Anatomical
• Feathers• Wing• Reproduction (internal, eggs)• Bones
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26.3 Birds
Anatomical adaptations: Bones (already mentioned)
• Lightweight, strutted or hollow• No teeth• Modified forelimb
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26.3 Birds
Anatomical adaptations: Bones
• Fused bones of pelvis, feet, hands, head• Uncinate processes on ribs• Furcula (wishbone)
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26.3 Birds
Flight Adaptations: Physiological adaptations
• Endothermic• Separate red and white muscle fibers
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26.3 Birds
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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26.3 Birds
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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26.3 Birds
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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26.3 Birds
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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26.3 Birds
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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26.3 Birds
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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26.3 Birds
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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26.3 Birds
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?
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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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26.3 Birds
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