07 December 2009

Adaptations to Cold

1) Plumage--a bird can increase insulating layer. Northern birds have higher densities of feathers than do southern ones. Individuals show seasonal differences. The House Sparrow molts after breeding season and the winter plumage weighs 30% more than the summer one. Thus the bird shifts LCT down to 0 degrees C. Snowy Owls have a very heavy plumage: LCT = -10 C. Emperor Penguins breed in the winter when the average daily temperature is -25 C.

2) Counter-current exchanges. Look this up in a General Biology book. Extremities are sources of heat loss, especially for herons and gulls. They remedy this by running warm arteries close to cold veins.

3) Fat storage--acts as insulation, stores energy and yields higher energy than proteins. The Emperor Penguin increases its body weight with fat --50% is burned off in 2-3 months while the MALE incubates eggs 65 days without food.

4) Shivering--spasmodic muscle contraction to release heat and seen most often in cold climates.

5) Decrease surface/volume ratio. BERGMAN'S RULE: body size increases as you go north. Birds don't really follow ALLEN's rule with smaller extremities with a gain in latitute (perhaps because relatively little heat is lost through extremities, compared to mammals), but look at penguins' small flippers and wings!

6) Behavior--birds in cold roost in cavities or under other surfaces like snow. Birds often aggressively will huddle (many textbooks have photos of creepers huddling). Birds will forage on leeward side of tree in wind and they will sunbathe.

7) Torpor--a reduced metabolic state. Torpor has been discovered in a few birds: Swifts, goatsuckers, and some swallows.  Google torpor on the Internet and see what you can come up with.

Snowy Owl

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