How birds avoid
wearing sweaters.
Thermoregulation &
methods of
maintaining
homeostasis
Importance of Thermoregulation
• Mitigating
– Heat gain
– Heat loss
• Birds are endotherms = use metabolic
heat to regulate body temperature
• Thermal relationship to environment*
critical to survival
Model of Endothermy
• Dynamics of temperature regulation
• Least energy spent in thermoneutral zone
(TNZ)
• Temp in TNZ can be altered by changing:
– Feather positions
– Varying return of venous blood from skin
– Blood circulation in feet
– Exposure of extremities
Scholander’s Model of Endothermy
Scholander’s Model of Endothermy
• Metabolism ? below LCT due to shivering
(heat production)
• Metabolism ? above UCT due to panting +
evaporative cooling + direct effects of
temp on cell fcn (heat loss)
Gambel’s Quail
• Habitat – hot, dry desert
• Day
– Foraging 6.2 hrs/d
– Resting 6.7 hrs/d (under shrub cover)
– Run + fly short distances 2-3x/d
• Night
– Sleep or rest
– Temp within TNZ
• Result ? avoid heat stress, reduce metabolic
heat production
Maintaining control in the cold
Maintaining Control - Cold
• Shivering (below LCT)
• Regulating blood flow* (sit down)
• Feather coat
– Molt new plumage
– Fluff feathers
– Readjust feathers
• Move to sunny areas to absorb more heat
• Huddle with group
• Find cover
Hypothermia and Torpor
• Body temp ? below normal = facultative
hypothermia
• Pronounced hypothermia/body temp ?
normal + incapable of normal activity +
unresponsive to stimuli = torpor
• e.g. hummingbirds
– Oxygen use ? by 75%
– Respiration rate ?
– Heart rate ?
Torpor
LCT
38
17.5
Maintaining control in the heat
Maintaining Control - Heat
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Gaping – open bill
Panting – faster breathing + gular flutter
Exposing bend of wing
Feather coat
Wetting abdomen
Regulating blood flow*
Relax
Move to shade
Move to water + bathe
Soar in cool air
Regulating Blood Flow
• Birds lose most heat from legs + feet
• Use countercurrent heat exchange:
– Network of blood vessels in the leg to conserve or lose
heat
• Heating (staying warm)
– Arteries + veins intertwine at base of leg-heat carried by
blood in arteries transferred directly to blood in veins
– Vary amount of blood shunted from base of leg to foot;
can restrict blood flow to foot
• Cooling (staying cool)
– Blood can bypass the network + go to the extremities
Blood flow regulation
Summary
• What is the model of endothermy? How
does it apply to birds?
• How do birds maintain control in the
cold/heat?
• What is countercurrent heat exchange +
why is it useful?