WHEN COLD WEATHER approaches, we humans usually have it easy. We can retreat to the shelter of central heating, or pile on more layers of clothing. The path to survival is a lot more complicated for birds, of course, and a new book delves into how they have adapted to face the challenges of cold and scarcity of food that winter represents.
The book is “The Courage of Birds and the Often Surprising Ways They Survive Winter” (affiliate link), and one of its co-creators, David Sibley, talked to me about some of the impressive suite of tactics that different species have developed to live to see another spring.
“The Courage of Birds” is written by Pete Dunne, author of more than 20 books about birds, and illustrated by today’s guest, David Sibley, one of whose indispensable Sibley Guides I suspect may be on your bookshelf, or even beside your binoculars. Their new book looks at strategies North American birds have evolved to meet winter head on, and I was glad to learn about some of those as winter heads our way, too.
Plus: Comment in the box near the bottom of the page to enter to win a copy of their new book.
Read along as you listen to the Nov. 11, 2024 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify (and browse my archive of podcasts here).
birds in winter, with david sibley
Margaret Roach: I guess we haven’t spoken since about 2020 when your wonderful book, “What It’s Like to Be a Bird” was published. And actually I just gave a copy of that to a new birder, a young friend, the other day. It’s a wonderful book that explains what they’re all doing out there. And that’s I guess what this book does, too.
David Sibley: Yeah, great. Thank you. Yeah, a lot of the things that Pete wrote about in this book I had written about in “What It’s Like to Be a Bird.”
Margaret: Exactly. So this isn’t your first collaboration with Pete between the two of you, I think, and at least one entire shelf in my bookcase is stuffed, full of your books because you two are both so prolific. And I think it was like 2012, maybe, the revised edition of “Hawks in Flight;” I think maybe you collaborated on that as well. Is that a memory?
David: Yeah. Well, I first met Pete at Cape May in my first year. Well, when I arrived there, he hired me to help with the hawk watch in 1980 when all that was just getting started. And pretty quickly we developed a collaboration and I got involved with working on “Hawks in Flight” that Pete and Clay Sutton were working on.
Margaret: Right.
David: The first edition didn’t come out until 1988. And then around that time also, I illustrated Pete’s book, his collection of essays, “Tales of a Low-Rent Birder” [affiliate link]. And there were a couple of other projects in there as well.
Margaret: Yeah. Well, I have most of those and more. So as he writes in the new book,
“The Courage of Birds,” it’s not just penguins in Antarctica who had to figure out how to be tough in the face of cold. Birds in many regions have to sort of have a line of defense against winter, and feathers, I guess, are the first line of defense. So I thought maybe we could start by talking a little bit about feathers and what they do.
David: Yeah, well, I’ll say feathers are what we see of a bird. When you look at a bird out there in the wild, basically all you see is feathers. They’re streamlining, waterproofing, wind proofing, insulation, coloration, all those things. And just incredibly evolved and perfectly adapted to that. And the down feathers that birds have, that the fluffy, soft feathers that really provide a lot of the insulation, are still the most effective insulation known. Nothing synthetic surpasses them. Their own feathers by weight are the most efficient insulation that’s known, and that’s what birds have.
Margaret: Right. And of course, mankind keeps trying to mimic it and make synthetic versions, down substitutes, so to speak, for our pillows or our blankets or whatever, our winter coats. Honoring that effective stroke of genius of down. And speaking of a couple of the tactics, the strategies that birds use, if they didn’t have feathers they couldn’t do things, tactics against winter’s cold like head tucking [below] and fluffing up the feathers to be even warmer, I guess. So the feathers in winter do a lot of jobs as well.
David: Yeah, the birds can move the feathers. They have these tiny muscles where the feather attaches in the skin, and they can actually raise and lower the feathers on the body. So just by raising all of the feathers up so they stand up a little taller, increases the thickness of their insulating layer. It’s like putting on an extra jacket or getting into a sleeping bag. And they fluff up in a, basically they look like a round, fuzzy ball, a fluffy ball, when they’re sleeping. They’re fluffed up into a sphere and they tuck their head into the feathers of their backs so that their bill… A bird’s bill is not insulated, it’s exposed, and there is some blood flow in there. And they’re breathing of course, also. So by turning their head around and sticking their bill into the feathers of their back, then their bill is insulated, and their breath cycles through the insulation of their feathers. And they don’t lose that heat either.
Margaret: Right. Very efficient.
David: Yeah.
Margaret: So besides head tucking [above] and fluffing that you were just kind of talking about, in the book, Pete mentions other anti-cold strategies like sunning, and cuddling, and shivering, and flocking, and burrowing and torpor. I didn’t know that any birds were able to use the state of torpor as an anti-cold device. The chickadees and titmice maybe, do I remember that right?
David: Yeah. And hummingbirds. And hummingbirds don’t stay around in the winter, but they do it just in any colder conditions. But yeah, there’s one species that actually hibernates called poorwill, that goes into an extended state of torpor, and their body temperature drops way down and breathing slows, heart rate slows. But birds like chickadees can do that just overnight. And their body temperature drops to a 50 degrees or so. And then when they need to wake up in the morning, they shiver, their muscles vibrate, twitch, to generate heat and just the metabolism generates heat and warms them up and they get going again.
Margaret: Yeah. And a couple of other strategies are roosting and feeding, of course, as a stay warm strategy. And when one is going to go to roost, one does so with a full crop. Yes, with a stash of food.
David: Yeah. And I was surprised to learn that well, birds can sense an approaching storm. They sense presumably the dropping air pressure, and they instinctively read the signs in the sky so they know that a storm is coming, like a snowstorm. And anyone who’s listening or who lives in a place that has real winter probably notices this, that your bird feeder becomes much more active in the 12 hours before a snowstorm starts, right up to the moment the snowfall begins. And that’s the bird’s primary response to an approaching storm in the winter, is just to eat more [laughter]. They fuel up and then they can go find a nice sheltered spot out of the wind and out of the precipitation, and hunker down and maybe stay a day or two if they have to, but just living off of the extra food that they took in.
Margaret: So migration, I’m so old that this topic always makes me think of that song by the Clash. I think it was in the early 1980s, “Should I Stay or Should I Go?” [Laughter.] And that’s the question for a species of birds and even individuals within some species that are partial migrants: should I stay or should I go? What are the benefits of either decision? Yeah, so that’s another tactic for survival.
David: Yeah. And one of the things that I liked about Pete’s approach to this book is that he considers migration and going to the tropics part of a bird’s strategy for surviving winter, which obviously it is. But some birds in winter go to the tropics. And birds that live on insects, like swallows and flycatchers and most of the warblers, they have to go south, and they have to go south before the first frost. So their migration is timed. The evolutionary calendar that they have developed is to migrate south before there’s any real threat of a frost and a lack of insects. So they’ll be moving south in August from the far north. And getting south, they don’t want to be caught by a strong cold front and a cold snap, and suddenly all the insects are gone. And then they still have to fuel up to fly 2,000 miles. So they have evolved a system to get a calendar that gets them out of the north before there’s any decline of insects.
And then other species like sparrows that eat seeds, or robins that eat fruit, they’ll stay later and move south in October.
So every species has its own strategy depending on what it eats and where it’s going, what direction it’s headed. There’s different migration strategies for every species.
Margaret: Right. I think in the book he says that 70 percent of species that are North American breeding birds, birds that breed in Canada or the U.S. including Alaska, I think migrate at least short distances. And it’s interesting because you just mentioned robins. Everyone thinks robins are this sign of spring. “Oh, the robins are back.” But the robins are here [laughter]. There are robins in Newfoundland, he says in the book, in Southern Alaska in winter. Yes?
David: Yeah. And when I was growing up in Connecticut in the 1970s, robins were actually really rare in the winter then. And it’s kind of a new phenomenon in the last few decades that robins are staying farther north. And I think a lot of it has to do with the plantings and invasive plants that produce a lot of berries. So plants like Euonymus and buckthorn and bittersweet here in the Northeast. There’s a lot of fruit out there now and through the winter, so robins can actually survive here.
And robins are what we would call more of a facultative migrant, that’s the technical term for that. They’re not truly migratory where they go north and south on a schedule, they move in response to food and weather. And they can move like if they find a lot of fruit somewhere, they’ll stick around. And when that fruit is all eaten up, they’ll move somewhere else. Or if there’s a big snowstorm or an ice storm that makes the food hard to get, they’ll move. And they might move east or west or even north if they feel like there’s some chance of finding food there. So they just kind of wander all winter. They drift southward, but then they just move around wherever they can find food.
Margaret: Right. Well, and speaking of following the food or finding the food, and again, in the book Pete talks about irruptions, years where I think he describes it as abandoning food impoverished regions for food rich ones. In some years when there’s no crop in the boreal forests or whatever of a given thing, the birds that are dependent on that crop will move farther south and look for sustenance elsewhere.; the so-called winter finches. I remember maybe 15 years ago having a big group of pine grosbeaks spend the winter here with me. And when I first reported it through the Cornell Lab of Ornithology system, which I think maybe even then was not even digital at that time. I can’t remember whether it was eBird or whether it was manual, how we did it at the time. But however I did it [laughter], emailed it in or did it in eBird.org. They wrote back and said, “No, that’s not right.” Because it was really odd.
It was really early, and they just spent the whole winter here. And they just were so beautiful. And they’re charismatic and they’re gregarious birds. They’re not scaredy-cats. Yeah, it was fun. It was fun to be with them.
David: Yeah. And those irruptions, and it’s not like a volcanic erruption [laughter], it’s a different spelling.
Margaret: With the letter I, not E.
David: Yeah. And there’s two factors in that. One is if there’s a very good breeding season and a large number of young birds are produced, then there isn’t enough space and enough food in the North to support all of them, and some have to move south. But also if it’s combined with a good breeding season and a lot of young produced, and then a lack of food to support them through the winter, then big numbers will move south.
Well, actually a lot of those species they’ll move east and west as well, like the robins. And very few birds have a truly north-south migration. We say birds go south for the winter, but most of them are migrating southeast or southwest or a lot of different directions.
Margaret: Right. I’ve mentioned this on the show before, but I’ll tell you this because it was so unusual. Last winter, in December, a Wilson’s warbler male showed up at my feeders.
David: Wow.
Margaret: And I’m just across the border; you’re in Massachusetts in I think Central Massachusetts, and I’m just across the border from the Berkshires in Columbia County, New York, and cold [laughter]. And I have water. And I think that’s an important thing to say is that it’s not just food, water is critical all 12 months of the year. And I have a substantial amount of unfrozen water. And so this bird, who probably got thrown off, of course in stormy times during migration or who knows what, he came, and I don’t know how in the world this little creature even adapted to eating seeds. And he didn’t go on the perches of the feeders, but he ate beneath the feeders and kind of integrated into the group. It was the strangest, strangest thing. And it went on for weeks and weeks.
And I don’t know what became of him, obviously. So there’s these things that we feel privileged as humans to see, but it’s also kind of upsetting, kind of terrifying, like the idea of a creature being thrown so far off course, that they’re outside where they’re safe, where they would’ve chosen to go.
David: Yeah, if you put yourself in their shoes, so to speak, it’s a scary prospect. But it’s also from an evolutionary sense, those are the pioneers. And if that bird survives… It’s gone off course but if it ends up in a place that works for it, where it survives the winter and makes its way back to its breeding grounds in a healthy condition, it could pass on that knowledge genetically of that migration pattern. And develop a new wintering area for the species, that kind of diversity of strategies is really good for the long-term survival of the species. These are the pioneers and-
Margaret: Yeah. Well, and sort of speaking of that in a longer term, since in the book Pete Dunne writes about having to do with the relationship with seeds. Like 370 million years ago, plants began encasing their seeds in protective shells. And then 250 million years later, birds began to use those seeds for winter food. And that was a big change, this adaptation to seed eating, allowed birds to remain in northern areas when there were no insects, some species to do so.
David: Yeah.
Margaret: Yeah. So the co-evolution between plants and of course then the birds moved the seeds around, so they helped the plants and this relationship that developed.
David: Yeah, there’s a lot of birds and fruit. The fruit attracts the birds. The birds eat it. And they carry the seeds and deposit them all across the globe.
Margaret: Yeah. I love some species cache the seeds. They sort of make little stashes of it. Yes?
David: Yeah. And some species they start early in the summer storing food that they will use in the winter. The Canada Jays, which is one that Pete writes about in the book and I did an illustration of, that’s one of the real champions of food caching. They live in the North Woods in Canada mostly, as the name implies. And they start in the early summer hiding food, just finding insects, seeds, fruit, anything edible and stashing it. And some studies on other species like Clark’s nutcracker and chickadees [above] are two other species that stash food, they can remember tens of thousands of hiding places. They have, I guess, a little map in their head of all the places that they’ve put little bits of food and they can go back and find them all.
Margaret: It is astonishing. That’s the part that you just never get over the sense of awe of nature. Do you?
David: Yeah. There’s so much going on that we don’t appreciate until we begin to kind of figure out what’s going on, but there so much more that we don’t even know about.
Margaret: Yeah. I wanted to take a few minutes to just talk about another source of seeds, and it’s written about in the book as well. We’ve become a nation of bird feeders [laughter]. We feed birds in large numbers. And how has that impacted birds in winter? How has that changed things?
David: The studies that have been done on bird feeding show no real effects, some slight increase in survival of birds getting through real bottlenecks, like ice storms. But birds, they don’t become reliant on the feeders. Even after one study, a feeder that had been operating continuously for several decades was taken down, and the birds that had been using it were watched to see how they fared without the feeders after generations of birds had used these feeders. And there was no real effect.
And even though you’ll see birds continuously visiting your feeders, but they’re still getting at least half of their food in the wild in nature. And if you stop feeding, if you leave your feeder empty for a week while you go on vacation, those birds they’ll go back to natural food sources with no problem. It probably has helped some of the species like red bellied woodpecker and Carolina wrens that have expanded their range north in the last few decades. Tough-
Margaret: [Laughter.] I’m laughing about Carolina wrens because I have some very bossy ones here that of course, years ago they weren’t here. I didn’t see them. And now I have them year-round, and they’re quite… a lot of personality.
David: Yeah. And those species, they’re at the northern limit of their range here in New England and upstate New York. And the bird feeders probably helped them colonize this area and help them survive. But it’s probably not really having a huge impact on bird populations. It’s just a nice bonus for the birds that use it.
Margaret: And hopefully it brings more people into contact with nature in a way that makes them more aware of these relationships, and hopefully care more about animal species and so forth. That would be my hope.
David: Yeah, I think that’s my best point about bird feeding. The thing I tell people is that it’s just a great way for us to interact with the birds.
Margaret: Yeah, make a connection. So I just wanted to ask, speaking of bird feeding and having bird feeders in the yard, it’s that time of year people when are putting them out and so forth. Safety: One of the things that I saw on your Facebook page this fall I know at least once. And you’ve reminded people about it a number of times over the years I’ve been reading your stuff about window strikes and how they kill, what? A billion birds a year, I think. So any tips on that on what we should be not doing or doing to minimize that danger?
David: Yeah, it’s a challenge because it’s so dispersed. Each window might only have one or two bird strikes a year, but when you multiply that by the number of windows it’s a huge number. The most effective and the best way to prevent it is to put some markings or tape on the outside of the window in vertical strips. No more than 3 inches apart, I think is the recommendation. So it creates a barrier that the birds can see and that they see it and they think they probably can’t fly through it.
Birds are seeing the reflection of the world around them in the window and thinking that it’s a space they can fly into, and then they crash into the glass. So putting vertical lines across that makes it clear to the birds that there’s some kind of barrier there and they probably can’t fly through it. And that will reduce, nearly eliminate window strikes. And the American Bird Conservancy has a lot of information about this, and they sell the tape and some other solutions.
Margaret: I’ll give a link to that. And I noticed on your Facebook page you had something from U.S. Fish and Wildlife service from a department within there that had some good tips, too. I’m so glad to speak to you again, and congratulations on the new book. Please share my good wishes with Pete Dunne and my appreciation. And I hope I’ll talk to you again soon.
(Illustrations by David Sibley from ” The Courage of Birds.”)
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 15th year in March 2024. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the Nov. 11, 2024 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify (and browse my archive of podcasts here).
