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

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

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

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

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

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

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

8. 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

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

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

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

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

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

14. 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

15. Fat reserves and Hoarding Acorn wood pecker, shrikes, Crested tits

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

17. 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

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

19. 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

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

21. Can’t concentrate… Loops of Henle are very short