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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

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Avian Physiology Part II: Feeding and Digestion

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  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 Henleare very short

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