Happy New Year, friends! I hope you had a great holiday season. I’ve been enjoying hanging out in my tank getting to meet everybody that stopped by to check out the park with their families. At this time of year, I love hanging out under my special heated log. My coworkers keep a warm heating pad in that spot so I can stay warm and toasty even when it is chilly outside.
The other day, I was relaxing in the warmth when I noticed a bunch of noisy birds chirping and fluttering around in the Pollinator Garden. Besides the regular song sparrow and Carolina chickadee visitors, I realized that a bunch of them were little gray birds with white bellies and black beaks that I had never seen before. I asked my coworkers about it, and they told me that those birds were dark-eyed juncos. They are a kind of sparrow that breeds farther north in Canada, and they migrate to Pennsylvania for the winter. That surprised me, because how do birds stay warm in the winter here when I don’t even like to leave my cozy log?!
My coworkers told me that birds have a lot of different strategies for the winter months. They have several behaviors that keep them from losing too much warmth. Firstly, many birds will seek out the warmest spots like the sheltered interiors of forests and hedges instead of cold forest edges. They also find places that will help them shelter from bad weather, like dense brush piles, hollow trees, and even empty bird boxes. That’s why my coworkers make sure all of the park’s bird boxes are clean and empty in the fall before the cold weather arrives! Some birds, like the park’s Carolina wrens, will even huddle together overnight when the temperatures are especially low.
Besides behavioral changes, birds also have some physiological adaptations that help them retain warmth in winter. Birds are warm-blooded just like people, but their normal body temperature is around 106° F compared to humans’ 98.6° F. That’s a lot warmer than me – since I’m cold-blooded, I’m the same temperature as my tank! Many adaptations are designed to make sure the birds don’t lose too much of the heat they already have.
They have small fluffy down feathers under their outer flight feathers, which help to trap air close to their warm skin. When birds puff up their feathers, their down helps them retain up to 90% of their core heat. Their round fluffy shape also minimizes heat loss, which is a pretty cool trick!
Birds also rely on fat to help them stay warm in winter. They don’t use it the same way mammals do, though. My coworkers showed me a picture of a big bear that put on a bunch of fat to stay insulated during winter hibernation. If birds gained that much weight, they would have a really hard time flying. Instead, they store fat in deposits under their wings, on their thighs, and in their furcular hollows (wishbones) to use as an energy source for thermogenic shivering.
This kind of shivering is also very different from when mammals visibly shiver in the cold. Instead, they activate opposing muscle groups, which cause contractions without lots of shaking. The contractions put off heat as a by-product, which in turn gets trapped by their feathers and keeps them nice and toasty! Thermogenic shivering requires lots of fat to keep it going though, so many birds switch to high fat, high protein foods like nuts and seeds for the winter season.
All of these behavioral and physiological adaptations help the birds maximize the number of calories they eat while minimizing the heat they lose their surroundings. I wonder if that would work for snakes too. Maybe I can get my coworkers to give me an extra mouse on Monday, just to check!
Warmest wishes! Your friendly neighborhood corn snake,