1. Birds (Class: Aves) Birds apparently evolved from reptiles
during the Jurassic.
The oldest known bird (Archaeopteryx)
resembled reptiles in limb bones and other features.
Birds still resemble reptiles: horny beaks, scaly legs, and egg-laying.

2. Digestion of Birds
Digestive system is often subdivided into functional regions
Specialization reflects feeding behavior
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3. Digestive Tract Specializations
Crop: in most birds; provides storage (largest in seed eaters); can produce “milk” containing fat & protein, but lacks sugar of mammalian milk. Production is stimulated by prolactin as in mammals.
Buccal cavity
esophagus
crop
proventriculus
gizzard
pylorus
Small intestine
Large intestine
cloaca
vent

4. Digestive Tract Specializations
Proventriculus: contains acids and enzymes.
Gizzard: often contains small pebbles or grit and is thick and muscular for grinding food.
Buccal cavity
esophagus
crop
proventriculus
gizzard
pylorus
Small intestine
Large intestine
cloaca
vent

5. Prey Capture Prey are captured primarily with beaks and feet.
Raptors rely on talons to catch prey – not beaks!
Beaks are toothless,
preventing any
processing in the
mouth

6. Bill Adaptations Insectivores
Perched Feeders: typically have short, thin, pointed bills (tweezer-like) for seizing insects.
Aerial Feeders: typically have short, weak beaks and a wide gape.

7. Bill Adaptations
Mud Sifters like Flamingos and Dabbling Ducks use their tongues and bills for prey capture. Both structures have horny projections (lamellae) and sensory corpuscles to scoop up water & mud and filter out the prey items.

8. Bill Adaptations Carnivorous Birds like ravens
and roadrunners have heavy
beaks to kill prey.
Raptors like eagles,
owls, falcons, and
hawks use their
talons to catch prey,
but have a sharply
hooked beak to tear off chunks of flesh. In addition, falcons have a tomial tooth (sharp projection from the upper mandible matching a notch in the lower mandible.

9. Bill Adaptations Seed Crackers like cardinals have stout, heavy bills.
Fish eaters like pelicans, mergansers, and anhingas, have pouches, hooks, serrations, or spear-like bills to kill and grasp fish.

10. Bill Adaptations
Seed Pryers like crossbills use the diverging ends of their bill to pry seeds out of pine cones.
Hammering is a technique used by chickadees and woodpeckers

11. Bill Adaptations
Strainers like shovelers and spoonbills use widened bills and tongues to strain small particles out of water and mud. They are also considered mud sifters.

12. Bill Adaptations
Probers like many shore birds have extremely long thin bills. Some of them are able to flex their bills backward (skull kinesis) to grasp crabs and other invertebrates from holes in mud or sand.

13. Bill Adaptations
Nectar Drinkers like humingbirds and honeycreepers have long slender downward curving bills to fit into flowers. They also have extremely long tongues that actually coil upward over the skull (hyroid apparatus) with hair-like projections at the tip to allow nectar to adhere to it.