Avian Physiology Part II: Feeding and Digestion

Avian Physiology Part II: Feeding and Digestion Sonia M. Hernandez

What GI characteristics are uniquely avian? • No teeth • Little saliva, few taste buds • Mammals: chew first, chemistry second • Birds: chemistry first, grinding second

Into the mouth and… • Down the mucous-gland lined esophagus • Very distensible • Can produce “milk”

Crop • Expanded esophagus • Stores, moistens and softens food • Regulates flow • Sometimes specialized

“Stomach” • Two-chambered • Proventriculusglandular • Gastric juices, peptic enzymes • Very large in fish-eaters, carnivores • Ventriculusmuscular Shrike can digest mouse in3 hrs!

Intestine • Length varies depending on diet • Shortfruit, meat, insects • Longseeds, plants, fish • Ceca • Bacteria aid in digestion

Intestinal function • Extremely efficient • Rapid transit time • Combine active and passive transport of nutrients into enterocytes

Assimilation • Raptors 66-88% of energy • Herbivores 60-70% of young plants • Can change seasonally • American robins improve lipid assimilation when eating berries in fall

Eating for… • Birds eat to fulfill calorie requirements • Exceptions: • Willow ptarmigannitrogen and phosphorous • White-crowned sparrowamino acids

Sucrose • Songbirds cannot eat • No sucrase • Results in diarrhea • Hummingbirds • Assimilate 95-99% of nectar energy from sucrose nectar • Also absorb glucose

Energy Balance • Ideally a balance between between intake and expenditure • Before migration, need to eat more to store as fat reserves

Foraging time • Amount of time feeding decreases with increasing nectar from each flower

Fat reserves • Typically kept at a minimum • Songbirds, 10% for winter needs • Bulbuls, 5%, to make it through the night

Fat reserves and Hoarding • Large birds can survive longer without eating • 10g warbler at 1-9C will die in 1 day without food • Male emperor penguin fast for 90-120 days and lose 45% body mass

Fat reserves and Hoarding • Acorn wood pecker, shrikes, Crested tits

Water economy • High metabolisms require a lot of H2O • Particularly in warm climates • Especially bc of evaporative losses • Water acquired from food

Evaporative water loss at non-stressful ambient temps decreasing sharply with increasing size of small birds. metabolic water production (cross-hatching) offsets this loss High metabolism=more metabolic H2O than other verts

Drinking water • The drier the environment, the more need to visit surface water regularly

Excretion • Kidneys • Excrete uric acid • Twice as much nitrogen as urea • Can be excreted in semisolid form • Comparison: • Birds use 1 ml of water to excrete 370 ml of nitrogen • Mammals need 20 ml • Further concentrate uric acid in cloaca through reabsorption of water

Too much water… • Hummingbirds consume huge quantities of water • Intestines can allow water to pass through without processing by kidneys • Have highest evaporative loss

Can’t concentrate… • Loops of Henleare very short

Avian Physiology Part II: Feeding and Digestion