Redpolls and other winter songbird survivors

Redpoll (by Arnstein Rønning on wikimedia)
Redpoll (by Arnstein Rønning on wikimedia)

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Chel Anderson is a botanist and plant ecologist. She lives here in Cook County and joins us periodically to talk about phenology or what’s going on in the woods right now. Welcome back, Chel.

Anderson: Hello!

Well, we have, from time to time, talked about how birds cope under various circumstances. We’ve had sub-zero cold, wind and snow so far, so how do birds adapt to this severe weather?

Anderson: Great question. And, we could ask ourselves, how do we adapt?

Sometimes I do.

Anderson: Because it would give us some clues as to how birds adapt, but they do have some extra-special adaptations that are worth remarking on for sure, because they really are amazing in some ways. Birds have actually a lot of resistance to cold, and the obvious one, of course, is their nice, down coat. And we’ve talked before about how they can fluff those up, put air up in among their feathers just like you fluff up your down comforter when the night is going to be particularly cold and they do that and over the course of the day watching at your bird feeder or if you can watch a bird in the woods for the day or a good part of the day and the weather changes and you’ll see the bird change. You’ll see it looking really poufy, Michelin Man sort of style of figure, you know, early in the morning or when the temperatures are coldest and then as temperatures moderate during the day, you won’t see them looking like that so much. If they stop and rest for awhile in one place, then you might see them eventually kind of fluff out again to regulate their temperature, but that’s definitely a key thing, but it’s not all. We’ve also talked about how they eat high-energy food. They’re going after the highest energy food that they are adapted to eat and that they can find, and that’s because they need that energy-rich food to keep their high metabolism in full swing.

I was just going to ask about their metabolism. Do you also happen to know anything about body temperature?

Anderson: I can’t tell you exactly what body temperature any given bird is, but it’s much higher than our temperature, and importantly, in terms of this high metabolism, they have about two times the glucose level in their blood as we do. So, that’s how they keep that furnace going.

Song birds are pretty small, most of them. What song birds can tolerate cold the most?

Anderson: Well, from what I understand, common and hoary redpolls, which we do see her some years, maybe most years even if we’re lucky. They apparently have the highest cold tolerance of any songbird and apparently one of the ways, along with the ways that we’ve already talked about, they have a specially adapted pouch, either kind of part of or near their esophagus and they can actually fill that with food as it gets close to nighttime. Birch seeds would be a good example. They would focus on feeding on those in the latter part of the day especially, and they can stash a lot of those seeds in that pouch and then use that during the night to help them maintain their furnaces, to help them going strong. Other birds like Evening Grosbeaks and some other northern finches have a crop and they can store seeds in their crop and use those to help them maintain overnight. But, apparently, redpolls have set the record in terms of maintaining overnight. But, most birds utilize other adaptations to protect themselves overnight besides those that have the opportunity to cache some food internally and use it. Some birds, temporarily, when they’re at rest at night or other times of the day in response to cold might shiver. OK, shivering is a way to boost your heat. But, of course, you can’t do that indefinitely, because it takes energy to do it. But, that’s a temporary relief from cold that a lot of birds will use when they’re at rest and at other times of the day. Small birds are at a disadvantage compared to large birds because their surface to mass ratio is greater. So, they have an adaptation of having more feathers per unit of bodyweight that helps them compensate some for that disadvantage that they have. Redpolls have one particular special adaptations, the finches have another, jays have yet another. So, there are multiple ways that these issues of how do you maintain your body temperature overnight in particular that birds have evolved to do that.

Well, one more thing. What can we do as bird feeders, what’s the best thing to do to help them have this high-energy food that they need this time of year?

Anderson: Well, right, focus on the highest energy, putting out high-energy food. So, the oft-repeated thing is that suet, whether you make your own or buy it is really great, anything with a lot of fat in it can be suet, it doesn’t have to be animal fat. So, some people make up suet balls that incorporate peanut butter and things like that. So, high fat. Obviously, seeds that have the highest fat content, so black oil sunflower seeds are kind of a seed that many species can eat and are very high in fat, so that’s a good choice.

I’ve never seen redpolls at suet feeders. Am I just not seeing that or don’t they generally do that?

Anderson: Finches are not going to show up at suet feeders. The birds that are going to show up at your suet feeder are the ones with the pointy, narrower beaks, because they’re the ones that are going to be able to get that, scrap it off and peck it out. Finches are really all about seeds and fruit when it comes to food. And, of course, insects, when they’re feeding, trying to feed their young. But, in the winter, they’re going to be about seeds and fruit. But, if you’ve been feeding birds, started early and are feeding birds right along, you’re very-local-to-your-home-place birds are becoming somewhat reliant on that food. So, if you’re going to be gone, you need to either have someone stocking your feeders or you need to slowly wean your birds off the amount of food that you’re putting out because they’re not anticipating that that’s just going to disappear.

Chel Anderson, botanist and plant ecologist. Thanks for helping us understand birds in winter.

Anderson: You’re very welcome.


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