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Avian Physiology

Avian Physiology. Sonia M. Hernandez. Objectives. Understand the metabolic adaptations of birds to deal with speed and endurance Trace a molecule of air as it travels through a bird’s respiratory system What are advantages of air sacs?

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Avian Physiology

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  1. Avian Physiology Sonia M. Hernandez

  2. Objectives • Understand the metabolic adaptations of birds to deal with speed and endurance • Trace a molecule of air as it travels through a bird’s respiratory system • What are advantages of air sacs? • What are peculiarities of circulatory system that allow for high metabolism? • How does a bird control body temperature? • Pay attention to underlined terms

  3. Temperature and Thermoregulation • Birds are endotherms • What is the advantage of high body temp?

  4. Endothermy is expensive • Energy input • Birds consume 20-30X more energy than reptile • Overheating….

  5. Birds are athletes • Speed • Endurance • BOTH require • High energy inputs • Efficient O2 delivery system • Efficient metabolic waste product removal

  6. Respiratory System • Small, dense, spongy lungs • Very vascular • Unidirectional flow • No diaphragm • How does air move in/out?

  7. Follow one molecular of air…. • Molecule enters nares • Travels down trachea • Across syrinx and into primary bronchi • Into air sacs • Across lung surfaces

  8. Respiration in 2 cycles, 4 steps • First breath: • Step 1 • Inhaled air from primary bronchi to posterior (caudal thoracic and abdominal) air sacs • Step 2 • Exhalation; air moves from posterior air sacs to lungs • Gas exchange

  9. Continued… • Second breath: • Step 3 • inhalation; Oxygen-spent air moves from lungs to anterior air sacs (cranial thoracic, cervical, clavicular) • Step 4 • Exhalation; CO2-rich air moves from anterior air sacs back out

  10. http://www.youtube.com/watch?v=LbJU0ocOKdo

  11. Why? • Maximizing contact of fresh air with surfaces of lung • All of air in lungs is replaced with each breath • No residual air in lungs • Thus:

  12. Air sacs • Number varies • Most have 9 • Thin-walled • Extend into coelomic cavity, bones

  13. Air sacs • Other functions? • Heat removal • Voice • Courtship display • Protect organs

  14. How do birds deal with high altitude? • Low O2 tensions • What do you do when you go up in altitude? • Increase respiratory rate

  15. Circulatory system • High metabolismrapid circulation of blood • Fast delivery of O2, removal of CO2, glucose and nutrients • 4 chambered heart • 41% larger than mammals of same size • Normal heart rate? • Cardiac output=heart rate X stroke volume (vol of blood pumped/contraction)

  16. Even at rest…. • Cardiac output is higher at rest (bc of larger stroke vol) • Ventricles empty completely, fill more • More muscle fibers, thinner • High performancehigh arterial blood pressure (300-400 mm Hg) • What is human blood pressure?

  17. Basal and Active metabolism • Resting (BMR) • Much higher than most vertebrates • Active • Increases 25-80% • Swimming mallard3.2 X BMR up to 5.7 X BMR

  18. Aerobic scope of birds • Sustain high levels (10-25 x BMR)

  19. Thermoregulation • Internal heat production balanced vs heat lost • Insulation increases if heat needs to be reserved

  20. How to adjust heat loss • Down • Fluffing, tucking head under wing, raise feathers to expose darker feathers

  21. Scholander’s model of endothermy Lower critical Temp Upper critical Temp

  22. Thermoneutral zone • This zone is result of adaptations for average environmental temp in which bird lives • Snow buntings do no shiver until temp drops below 10C but N cardinals start at 18C

  23. Acclimatization • Winter acclimatized goldfinches • Withstand extreme cold (-70C) for 6-8 hrs • Ramp up of BMR and short-term heat production

  24. Global warming • Expected to change the distribution of birds • Current projected pace is too fast • Major reallocations across states and within regions

  25. Other ways to deal with cold… • Microclimates • Huddling

  26. Hypothermia • Facultative hypothermiabody temp drops below normal • Normal fluctuation of a few degrees

  27. Torpor • Pronounced hypothermiasignificant decreases • Hummingbirds, Common poorwill • Unresponsive to stimulus • Todidae, coliidae, trochilidae, apodidae, caprimulgidae, columbidae Mousebirds

  28. Torpor

  29. Waking up…. • Hummingbirds require 1 hr to raise body temp and metabolism sufficiently for normal activity

  30. Heat stress • Control hyperthermia • Allow body temp to get closer to environmental temp decreases evaporative losses

  31. Heat stress • Behavioral adaptations….

  32. Heat loss and circulation • Long legged birds • Countercurrent system of vessels

  33. Keep your head cool… • Maintaining brain temp 1C cooler than body

  34. Bergmann’s Rule • Increase in body size with cooler temperatures • Smaller body=higher surface area • Heat loss lowest in hot climates small birds lose more heat

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