Avian Physiology

1. Avian Physiology Ornithology, 23 January 2007 Donald Winslow Following Gill�s Ornithology, 3rd ed., Chapter 6

2. Energy needs of birds Eat more food, Consume more oxygen, Move more rapidly, Generate more heat than other vertebrates.

3. Higher body temperature than other endotherms (i.e. mammals) Birds maintain body temperature just below the temperature at which proteins begin to denature.

4. Respiratory system Trachea, syrinx, bronchi, lungs, air sacs Primary bronchi Secondary bronchi Parabronchi Blood capillaries Air sacs

5. Two-cycle, unidirectional air flow Inspiration draws air from outside into lung and posterior air sacs. Expiration pushes air from posterior air sacs through lungs. Second inspiration draws air from lungs into anterior air sacs. Second expiration pushes air from anterior air sacs through lungs and outside.

6. Birds can hyperventilate without losing blood flow to brain. Flying at high altitudes, birds must breathe rapidly to maintain oxygen supply to flight muscles. Rapid exhalation leads to loss of carbon dioxide, raising pH. In mammals (but not birds), high blood pH prevents blood flow from reaching the brain.

7. Most birds do not smell well, but the vultures do.

8. Circulatory system 4-chambered heart, double circulatory system Two atria; two ventricles. Pulmonary circuit brings oxygenated blood to heart and removes carbon dioxide. Systemic circuit takes oxygenated blood to tissues and carbon dioxide to lungs. Mammals and crocodilians also have 4-chambered hearts.

9. Metabolic rate can be measured as oxygen consumption. As more energy is needed for cellular metabolism, more oxygen is used to burn food molecules. Active metabolic rate is higher than basal metabolic rate. Flight metabolic rate is higher than active metabolic rate.

10. Running birds (such as ratites) can raise metabolic rates high above basal rates.

11. In thermoneutral zone, birds can maintain temperature without raising metabolic rates At low ambient temperatures birds must shiver to stay warm, increasing metabolic rate. At high ambient temperatures birds must evaporate water to cool, increasing metabolic rate.

12. Energy budget can be constructed by multiplying time budget by metabolic needs of different activities.

13. Severe cold stress leads to torpor.

14. Geographic ranges are determined by heat tolerances. Global warming is leading to shifts in the geographic distribution of bird species. Terri Root�s analysis of Christmas Bird Count data. Flightless birds, such as mallee emuwren (Stipiturus mallee) of south Australia, may not be able to disperse to suitable habitat.

15. Birds of the same species at more northerly latitudes have larger body size. Surface-area-to-volume ratio is smaller, conserving body heat. Larger birds can fast longer during cold spells with snowcover.

16. House Sparrows (Passer domesticus) in North America have undergone selection for large body size.

17. Downy Woodpeckers (Picoides pubescens) are larger at higher latitudes.

18. Gulls reclaim heat from legs by countercurrent exchange.

19. Countercurrent exchange Warm blood flows in artery from body to toes. Cold blood flows in vein from toes to body. Heat from artery leaks into vein and is carried back to body. Toe temperature is maintained at lower level than body temperature.

20. Feeding and digestion Tongues Digestive tracts Foraging ecology Water economy Excretory systems

21. Birds have specialized tongues, often barbed. Woodpeckers have long tongues for extracting insects from under bark.

22. Avian digestive tract Pharynx Esophagus Crop Proventriculus Gizzard Intestine Vent

23. Doves and pigeons produce crop milk.

24. Gizzards used for grinding seeds and insects Gizzard has muscular wall. A bird will often swallow grit, which helps gizzard grind. Frugivorous birds have specialized digestive tracts that allow fruit to bypass gizzard.

25. Energy balance A bird must spend more time foraging when food sources are low quality. Fat reserves allow birds to fast. Migrant birds build up fat reserves prior to migration.

26. Birds with large body size can more easily conserve water.

27. Excretory system Kidney, ureter, intestine, vent, cloaca Male reproductive organs Testes Vas deferens Female reproductive organs One ovary One oviduct Uterus

28. Sea birds have salt glands above eyes to help with salt balance