miraculous bird nests (vs. wily nest predators), with brett degregorio
I AM MAD FOR birds, so much so that I’ve been looking expectantly lately at the interactive migration maps on the Birdcast.info website, and browsing reports coming in from areas to the south of me on eBird.org, wondering when my fair-weather feathered friends will be joining me and livening things up in this strangest of springs.
That got me thinking about the reunion I most look forward to: a bird who uses shed snakeskins when building its nest. Yes, it’s true. And how seeing that bird collect a snakeskin in my yard led me to Brett DeGregorio, a wildlife biologist who studies, among other things, the interaction between birds and reptiles. I’m hoping this interview about what bird parents are up against, trying to keep their eggs and nestlings safe, will encourage you all to watch more closely with awe, and ask more questions this spring when you see nature doing its wild and crazy things.
Brett is at the University of Arkansas, where he’s Fish and Wildlife Cooperative Research Unit Leader. His lab there studies wildlife behavior, interspecies interactions, and conservation biology. His special interest? Reptile and avian conservation and behavior. (That’s Brett, below, holding a model “snake” used in field research.)
We talked about all the things birds incorporate into their nests—as status symbols, or as protection against predators, which is how most eggs or baby birds are lost—and how a species’ nest style is so true to form, Brett says, that, “You don’t even have to see the bird that built the nest to know what species it belongs to.” Amazing.
Read along as you listen to the April 27, 2020 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 or Stitcher (and browse my archive of podcasts here). (Above, great crested flycatcher photo above from Wikimedia, by Andy Reago & Chrissy McClarren.)
bird nests and avoiding predators, with brett degregorio
Margaret Roach: Hi, Brett.
Brett: Hi, Margaret. Thank you very much for having me today.
Margaret: I’m one of your fan girls, you know; I’ve told you that before [laughter]. I’m one of the crazy people who reads every research report that you publish.
Brett: That’s amazing. You’re my only fan.
Margaret: It’s wacky. So just for background, I thought, tell us briefly kind of about the work you do and what your lab does. I mean, on the homepage of your lab, there’s turtles and lizards and snakes and all kinds of things.
Brett: I’ve always been a little bit all over the place [laughter], but my two loves have always been watching birds, and finding and studying snakes. And my PhD research and some of my current research finally gave me the opportunity to put those two things together. And so I now spend a lot of time working myself and with my students to figure out how snakes find bird nests and what birds can do to prevent that from happening.
Margaret: Oh, O.K. Now, you’ve said the word “snake,” and I’m sure a lot of our listeners and my readers will be like, “Aaaaah! Snakes!” because there’s that visceral thing. And I had it for a really, really long time. It took me a long time not to be afraid, not to shriek and run when I saw a snake. So, put in a good word for snakes for us, before we even get started with their interactions with other animals. Tell us why you love snakes and what’s great about snakes. [Ratsnake climbs a tree; photo by Patrick Roberts.]
Brett: I’d be happy to. And I have to admit, I have that same visceral reaction every time I see snakes. [Laughter.] And it’s nothing quite that gets your heart pumping like it does. But I shriek and I run towards the snake, instead of away from it.
But they’ve always been the animal that fascinates me the most. Just trying to understand how they interact with their environment without arms or legs. And they have much more complex and sophisticated behaviors than we give them credit for. And they’re an really important part of our ecosystem, both as predators and prey. And they’re certainly one of the most misunderstood and understudied parts of our ecosystem.
And I love trying to see the world the way that a snake sees the world. It really makes you think of things a little bit differently, because they’re so different than us and they’re so fascinating. And even though they have that kind of negative reputation and people mostly are not attracted to snakes, they’re just generally harmless to us and they’re a really important part of our environment to have around.
Margaret: They do a lot of housekeeping, don’t they?
Brett: Absolutely. They’re great at controlling rodents, and they really don’t have any negative parts to them. There are venomous snakes, but they want almost nothing to do with people. It’s just bad luck that brings people and snakes together.
Margaret: Mm-hmm. You said they’re understudied. Are they hard to study? I mean, it’s not like I can just go out and say, “Here, snake. Here, snake,” you know, call in the snakes. [Laughter.]
Brett: That’s a great point. They are wildly difficult to study. They’re incredibly secretive. They’re difficult to come across. And then once you do come across them, understanding what they’re doing is really difficult. How often do we see snakes interact with one another, or capture prey or hunt prey? So, we generally have very little idea of what snakes are doing most of the time, and what motivates them to do the things that they’re doing. So, I love that challenge. And everything we learn about snakes is so new and exciting and is really opening up a lot of doors for us to understand their role in the environment and the way that they interact with other species.
Margaret: When people ask me, gardeners ask me over the years, “What should I do about slugs eating my hostas?” or whatever garden plant. And I say, “Get a snake.” [Laughter.] And by that, I usually just mean a garter snake or something because snakes are great housekeepers, even the smaller ones, even at that level. They do a lot of good work in garden sanitation.
Brett: That’s a great point, yeah. Not many things can eat slugs, but we’ve got a number of small snakes that are happy in our gardens and do good work for us.
Margaret: Yeah. So, I alluded to it in the introduction but I should probably tell the story that led me to your doctoral work and then, subsequently over the years, to other papers you’ve published, and then to calling you up out of the blue the other day and inviting you to come talk today. And I know it’ll bore you because you’ve already heard this story.
But I’m sitting, I don’t know how many years ago, at my desk. And to my right, in my field of vision, out of their side of my right eye, is a patio and a stone wall. And in the springtime, there’s a chair out there, and there’s a bird who sits on the back of the chair. And every so often—he seems very intent on the stone wall—and every so often swoops down and seems to look for something in the stone wall. And this goes on over and over again.
And I’m thinking, “What in the world?” And the behavior is that of a flycatcher, that I kind of knew the kind of activity. But I thought like, “What’s it catching? What’s it doing?” Anyway, identified the bird. It turned out it was a great crested flycatcher [photo, top of page]. And then one time, I turned my head just at the right time, and it was picking up a shed snakeskin out of the wall. There’s a lot of garter snakes in the stone wall. They love it in there, and they wriggle out of their old skin and leave it behind. And this flycatcher apparently knew that he or she or whatever could find, I don’t know if it’s a he or she, could find snakeskins there and wanted to collect them. And I read that they use them in their nests.
So, tell us about that crazy thing. I mean, how in the world, Brett [laughter], does that bird know to do that? And why? Why does a bird do that? And do other birds do that? I mean…
Brett: It is very amazing. And that behavior was first reported on in the 1920s. So, people have known about this for a long time, but it wasn’t until 2006 that anybody tested it. And what they found out is that these great crested flycatchers, they nest in cavities in trees. And one of their main predators are flying squirrels. And one of the things that loves to eat flying squirrels, and also loves to go into those tree cavities, are snakes, particularly ratsnakes.
And it seems to be that if a flycatcher incorporates a snakeskin into its nest or displays it outside of its hole, it is much less likely that a flying squirrel is going to go into that nest hole and either take it away from the bird or actually depredate the eggs of that bird. [Above, Southern flying squirrel photo from Wikimedia by MimiMiaPhotography.]
Margaret: Wow. And I mean, my head just goes to the like, “Who told the bird this was a good idea? What bird in its ancestral line how many billion, thousands of years ago figured this out?” I mean, it’s amazing. So, it’s an anti-predation strategy that this animal has developed. And in those tests that you said in 2006, they sort of proved it? They examined enough nests to prove that it did have a positive effect?
Brett: They did. What they looked at were a bunch of artificial cavities, basically bluebird boxes, but for flycatchers. And they put a third of those nest boxes, they put nests with snakeskin inside the box; and a third of them, they hung the snakeskin right outside the box; and a third of them were just regular nests without snakeskins. And what they found is that the flying squirrels stayed right away from those nests that either displayed or incorporated those snakeskins.
Margaret: It’s amazing. Now, so, you’re into snakes. You’re into birds. This is about a relationship among snakes and birds, actually in a couple of ways. Well, the snake sometimes go up the tree, looking… They go up the tree looking for the flying squirrel, is that what goes on? Or sometimes to get into the nest cavity?
Brett: I believe that snakes, particularly those ratsnakes, they love to climb trees, and they’re always looking for a good place to hide out. And one of their favorite places to hide is in those hollows of dead trees, those tree cavities.
Margaret: I see. So, snakes and birds, and they have a common ancestry, don’t they even? I mean, I’m not so good with paleontology and sort of the phylogenetic system of grouping things according to their ancestry or whatever. Are birds and snakes related sort of? [Laughter.]
Brett: Yeah. Certainly not my strong point either. But yeah, they definitely come from a shared ancestor.
Margaret: Do other birds do this—are there other birds who go looking? And is it known whether it was the male or the female who does this? I don’t know who builds the nest in the great crested flycatcher, for instance. And I don’t know how to tell them apart necessarily. Are there other birds that do this, collect snakeskins and use them in this way?
Brett: There are. And the more that you start paying attention to bird nests, the more you see the wacky things that they incorporate. I’ve seen snakeskins in a number of different species’ nests, including blue grosbeaks do it really frequently. Robins occasionally do that. [Above, blue grosbeak photo from Wikimedia by Andy Reago & Chrissy McClarren.]
Actually I spent the day today watching some robins build a nest right outside my front door, and they’re incorporating a long piece of tape off of a cardboard box, so it looks just like a snakeskin. And I’m guessing that they’re tricked by it.
We’ve seen European birds do this as well. And there seems to be a theory that these birds, who don’t nest in cavities, but instead build big platform nests so a little cup nest, they do it as kind of a status symbol.
So, there’s one bird that’s a small hawk, called the black kite, and the more snakeskins and white pieces of plastic they incorporate into the nest, the tougher they’re telling their neighbors they are. And the birds that incorporate lots of these white pieces of plastic and snakeskins, they tend to be really dominant, and other birds will not mess with them. And the kind of subdominant or weaker birds, they’re too afraid to incorporate these ornaments into their nest because they know they can’t win those fights. So, they have really plain nests.
Margaret: [Laughter.] That’s just crazy. It’s fantastic. There’s a, forgive me for saying this, pecking order among birds.
Brett: [Laughter.] That’s great, that’s perfect, yeah.
Margaret: Oh, my goodness.
Brett: And there’s even another European bird called a great reed warbler, who’s a lot like our red-winged blackbirds. And they’ve got a very similar breeding style, where there’s one male who defends a big territory, and he has multiple females nesting within that territory. And the females are always looking for snakeskins. And the more that they can incorporate into their nest, the more dominant they are within that kind of female matriarchy, and the more attention they get from the male who owns that territory. So, it’s, again, kind of a status symbol among these reed warblers.
Margaret: Oh, it’s a currency. You said “pay attention”—you’ve been paying attention to birds nests. And last year, I almost walked right into it in the shrubbery here. I was doing some raking or whatever in the spring, and I came upon, at maybe head height in the fork of a branch of a large shrub, this cup nest. I took a picture of it [below] and I went inside and I looked up, tried to look up, the materials I could recognize: It was lined with pine needles and it had bits of birch bark and also some paper from a paper wasp’s nest, and otherwise was kind of like a woven small cup nest. And sure enough, it was the exact signature, the exact description of, “How to build a nest if you are a red-eyed vireo.”
Margaret: When you go out in the field and when you see all these amazing things like what you’ve been talking about, I mean, don’t you wonder who told them? How? Did their father and mother and grandparents teach them? Is there a blueprint? Do you know what I mean? I mean, this is coded into the genetics, isn’t it?
Brett: It’s absolutely remarkable. And they are so true to form. I mean, you don’t even have to see the bird that built the nest to know what species it belongs to. It’s a really conserved trait. And I don’t know how they learn it or how they’re able to recreate it their first try, and to redo it every year. It’s absolutely incredible.
Margaret: Well, maybe I’m going to backtrack. We talked about predation on the nests of great crested flycatcher by this squirrel, this flying squirrel, and snakes are known to be predators of certain kinds of nests. And what are birds up against in trying… I mean, it’s a pretty tough thing to rear…. besides having to get all that food to feed your nestlings so that they hopefully live long enough to fledge, there’s other predators, too, right? I mean, what are birds up against? And what are the sort of stats on how birds do?
Brett: It’s pretty incredible what birds are up against. The list of nest predators is vast. I did just a review not too long ago, and counted over 100 different species just in North America that are happy to eat bird eggs and nestlings. And so, when birds are beginning to nest, they’ve got to find just the right spot that is going to avoid notice by raccoons, by hawks, by the parasitic brown cowbird, by ratsnakes. So, somehow, birds have to gauge who the predators are in the local area and how to choose their nest site that’s going to minimize their risk of getting depredated by whoever’s around.
And it can be a really difficult thing to do. And what we see is a lot of the common birds around us, the cardinals, the mockingbirds, the catbirds, thrashers, indigo buntings, blue grosbeaks, they’re going to lose 80 percent of their nests, so…
Brett: Yeah. The numbers are against them. And so, they just need to make sure that if a predator finds their nest, they get away so that they can nest another day. And most of these birds are pretty flexible. If they lose a nest, they will immediately start re-nesting. And it’s just sort of a numbers game. You build enough nests, one of them’s going to get through.
Margaret: Wow. Now, I assume you set up some kind… I mean, you don’t live up in a tree [laughter] and wait to see all of this. And obviously, some nests are not high up in trees; they’re in different habitats. But cameras? Is that what this? Has the advancement in wildlife cameras, so to speak or whatever, is that what you’re using to do all of this exploration? [Above, one of Brett’s cameras above a nest being studied.]
Brett: That’s exactly what it is. So, we build our own cameras. What we do is we purchase little infrared surveillance cameras, the same kind that you probably see above the clerk at the gas station or the takeout restaurant. And we just splice together some various components so that we can power them out in the field with little miniature car batteries or boat batteries.
And we carry them around into the woods and camouflage them and put them on nests when we find them. And that allows us to, 24 hours a day, watch what the birds are doing and really get a feel for what they’re doing, how the adults are behaving. And then when a nest fails, we can know exactly when and who was responsible for that depredation event.
Margaret: Right. And so, right now, are you still studying this? You did a lot with the blue grosbeak to see about this snakeskin stuff. Are you doing the same work? Or are you on to new birds and their relationships or nests? [Laughter.] Or…
Brett: Right now, what one of my students and I are looking at is a small group of common birds that can nest in both urban and suburban environments, as well as natural environments. And we want to see how they alter their nesting behavior in response to what we imagine are very different predator communities. The robins and cardinals that are nesting in our backyard, they’re probably dealing with protecting their nests from gray squirrels and house cats, crows. And then we’ve got the same robins and cardinals that are nesting out in more natural areas up in the Ozarks, and they’re probably dealing with raccoons and bobcats and sharp-shinned hawk. So, we want to see how these birds change their nesting behavior based upon where they’re at and who they perceive the predators to be.
Margaret: Oh, O.K. I wanted to ask you. Gardeners are listening and reading the transcript of this show, and I’m a gardener. And so, I want to know how… You have an ability to see because you have training and experience and you’ve done this many times. So, among birds that we can see in taking a walk or in our yards and whatever, any tips on sort of how to look?
One person said to me, a birder, a keen birder around here, she said, “Well, Margaret, if you want to know where birds nest, look for the adult with stuff in its mouth, flying to and from the same spot all the time around this time of year and you’ll find the nest.” [Laughter.] But what other tips? I mean, I guess that is a tip, right?
Brett: That’s one of the main things. I think that’s what a lot of the snakes do.
Brett: So, yeah, watch for that bird behavior. If they’re carrying food or they’re carrying sticks and twigs, they’re either building a nest or they’re feeding nestlings.
And the other thing is just to pay attention. If you’re unknowingly near a nest, birds are going to let you know. So, don’t ignore those angry little chips. That’s a bird telling you that you’re close to a nest. So, start looking around and you might be surprised that you’re accidentally standing right next to a cardinal nest or indigo bunting nest.
Margaret: Once in a while, I’ll spy something, like I remember an oriole, a Baltimore oriole nest. The first time I saw one, it was hanging way up high in a tree. It was like this bag hanging down, this purse, this… I don’t know what you… pouch, I guess you’d say. So, they’re in the strangest places. And I wouldn’t have noticed that except the oriole is so brightly colored and I saw it going there, you know?
Brett: O.K, yeah.
Margaret: And you’re right. The tree swallows will tell me if I come anywhere near when they’re on the nest, when they’re in the nest box. I mean, they’ll dive-bomb me and make that strange noise and so forth like, “Get away from here, you. Don’t walk near us.”
And turtles, huh? I love turtles. I don’t have a lot. I’m in an upland site and I don’t see a lot here, but turtles. You’re working with turtles a lot too lately, yes?
Brett: I am, yeah. Turtles are close to snakes in my heart, and they’re a fascinating animal. Part of the reason I’m working with them is they’re a lot easier to work with than snakes. So, when I want to see what a turtle’s doing, I just glue a transmitter onto its shell, or I glue a temperature logger onto its shell. It’s so much easier to figure out how turtles are interacting with their environment than it is with snakes.
So, some of that’s low-hanging fruit, and some of that is that turtles in Arkansas have some unique challenges. We’re one of the last states that allow people to commercially harvest freshwater turtles and sell them for meat. And we’re in charge of figuring out is there a way to make that sustainable, and if so, how do we do that? So, that’s the main thrust of my turtle research right now. [Photo of spotted turtle with transmitter from the DeGregorio Lab website.]
Margaret: I see, O.K. Well, Brett DeGregorio, I’m glad to finally meet a little more, rather than just reading everything you publish. And I hope we’ll talk again soon. Thank you so much for sharing some of your expertise with us today.
Brett: Oh, thank you so much. It was really a pleasure to speak with you. I appreciate the opportunity.
Margaret: We’ll talk soon again.
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. 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 April 27, 2020 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).