Digestive Tract:

• beak & tongue: obtaining food.  Tongue supported by hyoid apparatus; may be long, extensible
• esophagus:
• lubricated for easy passage of food swallowed whole
• crop: enlargement in middle of esophagus in most groups (lacking in Gruiformes.)
• food storage
• Columbiformes: produces crop milk for young
• stomach: two-part
• proventriculus: digestive part of stomach; produces enzymes, HCl
• gizzard: continued digestions, muscular grinding of food.  Species may eat gravel, grit to store in gizzard to improve grinding
• intestines: chemical digestion, absorption of nutrients (small intestines), water (large intestines)
• cecum (pl: cecae): extensions off of intestines; may house bacteria for digestion of cellulose (plant cell wall material; not digestible by animals)
• cloaca: sac the stores output from digestive, excretory, reproductive systems
• vent: opening of cloaca to outside

Animal/ insect matter: most nestlings; many adults.

• adaptations to predation:
• bird, mammal prey: hooked bills, sharp claws, acute vision.
• fish prey (slippery): hooked or serrated bills, backward slanting projections in mouth parts (can be on beak or tongue), spines on undersides of toes
• hard shelled prey: dropping prey on rocks (gulls)
• insect prey:
• bark insects - strong claws, tail; chiseled or thin decurved bills; extensible barbed tongues on long hyoid apparatus (woodpeckers -- Piciformes).
• flying insects - high speed (if pursue in air: swallows (Passeriformes), Swifts (Apodiformes), nighthawks (Caprimulgiformes)) or elliptical (if flycatch) wings, large gapes; well developed rictal bristles
• leaf insects - thin bills
• wax (produced by bees); digestive tract bacteria, guiding (honeyguides (Piciformes: Indicatoridae) & mammals, including humans)

• seeds - muscular gizzards (ex: pheasants) thick bills (ex: finches, cardinals, sparrows)
• leaves/needles - large cecae with bacteria.  Ex. many grouse.
• fruit - short small intestines, non-muscular gizzards, large liver to detoxify any toxins in the fruit.
• nectar - long, thin bills; fringed extensible tongues (long hyoid apparatus)