Joe (et al),
I’ll take a stab at a few just from general ornithological knowledge. I’m not
sure how much Northern-Shrike-Specific information there is on these questions.
Do you have access to the Birds of the World account on Northern Shrikes?
That’s an excellent compendium of what’s known. If you don’t have access,
email me off the list and I’ll try to help with that. OK, to the specifics:
* Does the Northern Shirkes use piloerection to increase the insulation
value of their feather?
All birds do, so yes, Northern Shrikes certainly do use piloerection when it’s
cold.
* Do shrikes enter nightly torpor to conserve energy?
I don’t know about torpor. I have not heard of shrikes using true torpor.
Almost all birds of that size do have some degree of nighttime controlled
hypothermia - they let their internal temperature drop a few degrees. But true
torpor where the bird becomes inert and unresponsive seems unlikely. Can’t say
for sure.
* Do shrikes increase their body fat before the onset of cold weather?
Again from analogy with other birds, almost no birds do this. They lay on fat
to fuel migration, but they insulate with feathers, not with a layer of fat.
Most birds in winter, even in cold climates, are no fatter than they are at
other seasons. Small birds may lay on fat *daily* to get through the long cold
night, especially really small birds like Chickadees. I suspect Northern
Shrikes wake up lighter than when they go to sleep but how much fat they burn
overnight I wouldn’t want to guess.
* Do shrikes use countercurrent heat exchange to avoid losing heat to their
unfeathered feet?
Pass.
Hope that little bit helps.
Chris Hill
Conway, SC
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