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.

Digestion of BirdsDigestive system is

often subdivided into functional regions

Specialization reflects feeding behavior

Video linkhttp://people.eku.edu/r

itchisong/birddigestion.html

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

pylorusSmall intestine

Large intestine

cloaca

vent

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

pylorusSmall intestine

Large intestine

cloaca

vent

Prey CapturePrey 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

Bill AdaptationsInsectivores

Perched Feeders: typically have short, thin, pointed bills (tweezer-like) for seizing insects.

Aerial Feeders: typically have short, weak beaks and a wide gape.

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.

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.

Bill AdaptationsSeed 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.

Bill AdaptationsSeed 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

Bill AdaptationsStrainers like

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

Bill AdaptationsProbers 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.

Bill AdaptationsNectar 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.