So every tree swallow that we know of in the world is in one of these about 100 roosts around there, and so that's kind of funny behavior, right? But it means how big are the roosts? huge. There can be millions of tree swallows in them. You can actually see them on weather radar, so they circle in the evenings. They circle all around. Hi, everyone! Welcome to Blackbird Joy, the podcast where we explore birds, nature, and the amazing people who study and protect them. I'm Mason, and I love birding. In each episode, I'll take you on adventures to meet bird experts and learn cool things about the birds all around us. In this episode, I got to visit Dr. Maren at Cornell University. Dr. Maron studies tree swallows, and after seeing her field research up close, I still had lots of questions. So we got together to talk more about tree swallows, bird personalities, and baby birds. What it's like to be a bird scientist. I hope you enjoy our conversation. Hey, Mason, how are you? Good. How are you? Good. I hear you're you're thinking about writing a blog post, or maybe you are writing a blog post. Sort of both Yeah. So, how far along are you, or what are you dreaming up? More interviews and fun. Yeah. Nice. Um, I'm excited to talk to you, Doctor Maren. So, yeah, what questions do you have? How do you become interested in birds? So I think I've always been interested in animals, and also in kind of just more general science, right? How the world works in the ways that it does. And so as a kid, I was always somebody who liked to kind of record the animals I saw and read about the animals. For me, it wasn't particularly birds. I was kind of equally interested in reptiles, and well, I grew up in Hawaii, so it was mostly birds and reptiles that we had out there that were, you know, and like marine invertebrates. We didn't have very many mammals because there are no native mammals in Hawaii. So that was kind of a longstanding thing for me. The first time I studied birds was actually in college, and I had a professor who was studying purple-throated Carib hummingbirds that live in Saint Lucia. He, I got a position as a research assistant with him, and so I got to go down over the summer and study those birds. And they're really cool. I don't know how familiar you are with them, but the males and the females have differently shaped beaks. The males have these really long curved beaks, and the females have these short, straight beaks, and they drink from different flowers, and so that's why they're different. So they're really cool species. I know A bet when people discovered those, it was hard to tell them apart. Yeah, exactly right. Yeah, because that's so rare, and even rarer that it doesn't have anything to do with mating, right? It's not because the males are fighting with other males or attracting females or something. It's just that they eat different foods. Yeah. How long have you been studying tree swallows? I've Been studying tree swallows now for 13 years. So that just starts. Any other kind of swallows? I did. Yes, I studied barn swallows before I studied tree swallows, and those were fun too. A little bit harder for the kinds of work that we do than tree swallows. Yeah, they do sound a little bit hard because they don't nest in nest boxes. Exactly. Yep, they're all nesting in the same place, so that makes it hard to catch the individuals that we want. What makes tree swallows special compared to other birds? I'd say a couple things. I mean, one is that they, as you probably know, they all migrate to the Gulf of Mexico in the winter, and they're all in about 100 roosts. So every tree swallow that we know of in the world is in one of these about 100 roosts around there, and so that's kind of funny behavior, right? But it means How big are the roosts? Huge. There can be millions of tree swallows in them.You can actually see them on weather radar. So they circle in the evenings. They circle all around, and then they kind of get tighter and tighter and tighter. And then one of them will drop down into the bushes, and then they all just kind of like boom down at the same time. Oh, Woah, so you can see those on a weather map? Yeah, on weather radar. Yeah, in the mornings and in the evenings, just pretty crazy, right? Such a big force to tree swallows. Yep. I think another thing is just that they are really widespread, so they can live in really different environments, and so we have birds breeding up in pretty remote areas in Alaska and up above 10,000 feet elevation, and then also like down in Georgia and Tennessee and South Carolina. So they're pretty good at dealing with weather too. Pretty resilient birds. Yep. How do you keep track of individual birds? So we do that in a couple of ways. One is the kind of standard bird banding way, where we put a little tag on their legs that has a number, and that's great, of course, if you can recatch a bird. But tree swallows have those really short little legs, and so you can't put a color band, or you can put a color band on them, but you can't see the color band, right? Because when they're perched, you just don't see their legs. Yeah, like some birds see their white stomach. Yeah, yeah, exactly. And so we have a couple of different ways our birds wear little RFID tags on their legs, and then we have an antenna at the entrance of the nest box. And so that way we can record each individual every time they go in and out of the box, and so we can keep track of them that way. We've also done some studies where we put little backpacks on them that have trackers, and we could actually start tracking them on migration, and that's fun. It's hard to do on a large scale because the trackers are expensive. So when we do those studies, we'll put on maybe 12 trackers on 12 birds, so we can find out kind of broad things about where the tree swallows are going when they're migrating, but we can't follow every bird that way. Yeah, can birds really have personalities? I think absolutely. They, they, I would call a personality just consistent differences in how in behavior, right, and how you react to things. And birds definitely respond to things differently. Some are kind of really scared of new things. Some love new things, and some are really vocal, make a lot of noise. Others don't. Some are consistently really good parents, like really invested parents, and others not so much. And so, so yeah, I think I think they are quite different. Is there any really memorable pairs that have really different personalities than a lot of the other of pairs? I think to me, it's most well, a couple things are most noticeable. One is some of them when you catch them, just squawk and squawk and squawk, and most of the time, tree swallows are silent, but that's pretty repeatable. And the other is nest defense. Some of them are really good at defending their nests, and so every time we go and peek in a box to see what's going on, we'll get dive bombed, and sometimes they come really close to you or even touch your head. And you know, again, the same birds are like really feisty and really good at defending their nests, time after time, and others are kind of like, "All right, you're at my nest. I'll run away or fly I get other ones. away. Yeah. What's the coolest thing you've learned from studying shoot startups? That's a good question. I think one of the things that I'm most interested in right now is kind of about how experiences that happen early can affect how they're dealing with things later. So things like the cold that they, if it's cold early in life, that affects how they deal with cold conditions later in life. Or if they have access to more nutrients, have like a better diet early in life, that that can also affect kind of the ways that they behave and the ways that they own raise their own offspring later, and so those kind of connections to me are really interesting. Have you ever discovered someone that surprised you? Oh, so many things. I mean, this is maybe a silly example, but one of the things that we discovered relatively recently was that people had thought for a long time that one of the ways that that birds figured out what nests they were going to use was to do prospecting at the end of the season. So to go and look in other nest boxes and check them out, say like, would this be a good home for next year? And so Wow, that's cool over the tree swallow literature that they did this, and that was kind of a big part of what they had to do at the end of the season, and then we put a bunch of those measuring devices, those RFIDs I was telling you about, on the nest boxes at the end of the season, and found out that they don't actually do that at all. They, as soon as their babies fledge, they just they leave, and they don't poke in the other nest boxes. Their babies don't look around, and so it was really interesting thinking about how this, I guess, myth had kind of developed that this is a big important thing for these birds to do, and it looks like they're not doing it at all. Do you have any theory on how the hypothesis, or like, or like a hypothesis of how this myth developed? Yeah, it's a great question. So we know that they do that at the beginning of the season, so before they settle on a place to raise their babies, they do a lot of checking out of possible nest sites, and they actually do a lot of it through the season too. So that was another really interesting surprise that we found out from that kind of measurement is that all the way through the season, the birds are peeking in on each other's boxes. So like one parent will go visit another parent's nest box, and they'll do it over and over. So they'll just peek in and say, "Kind of how are these babies doing? Sometimes several times a day, even while they're raising their own offspring. So that was another kind of real surprise to us was that they take the time to do this when they're raising their own babies, and so that we think is partly about. Kind of checking out how their neighbors are doing, and getting some important information from that. And it may also be about checking out the site that their neighbors are breeding in, and thinking about is that a good idea for me to breed later? We actually have less evidence for that than that they're actually looking at the babies and making some decisions based on how the babies are doing. Do it in like a sneaky way or a friendly way? I that's a really good question because tree swallows are often pretty aggressive with each other when they don't have enough nest sites. The females will fight a lot about them, but that was a surprise of this because the parents don't seem to care. Visitors mostly come when parents are home, and the parents just kind of let the visitor pop in and look at the babies, and they don't get very upset about it. And seems like it's not really sneaky, and so I don't know. We call them social visits, popping in and visiting your neighbors. There's also baby tree falls when you and my mom visited. Do parent birds have favorite baits? Oh, hmm. I guess it depends on what you mean by favorite babies. They often will feed some babies more than others. So if that's how you're defining favorite, then yes. We know that that has to do in part with how much the babies beg. So the ones that beg more can kind of attract attract their parents' attention more. Can get more food. Is that the same for other birds? It is. Yeah, many of them do that. It varies a little bit. Tree swallows tend to have more like the biggest baby in their nest. The difference in size between the biggest baby and the smallest baby in a tree swallow nest is bigger than for many birds, so that suggests that maybe they play favorites a little bit more than some birds do. How much broods do tree swallows never hear? I got this question because there's some birds nest around our house, and I was like, how many broods is that gonna have? How many nest boxes? Yeah, so weirdly, tree swallows almost always only have one brood per season in this around here. Some parts of their range in the south they'll they'll fit in the second one, but they're pretty unusual because something like a barn swallow might have three broods in a year, but a tree swallow is kind of one brood and they're done, which is one of the reasons it's nice to study them because field seasons are shorter. Is there any other birds around there that nest in the nest boxes when the tree swallows are there? Like, are there any birds that try to take over the nest boxes? Not usually take over. So we have a lot of bluebirds or a handful of bluebirds in our boxes. Oh yeah, we were walking back. I remember seeing those two. Yeah, right. But the bluebirds usually nest sooner, so by the time tree swallows show up, the bluebirds have already claimed whatever boxes they're going to nest in, and so they don't really seem to get into fights about that around here. Sometimes house wrens will try to take over boxes, and so then there'll be some fighting with tree swallows. Have sparrows when we do have them at the site. We'll also do that. Oh yeah! One time I heard about there was like a dead tree swallow in nest box and it has water. Like why? There's so many nest boxes. It is so funny, isn't it? It's not well, not funny from their perspective, I'm sure, but it is odd that they'll fight over a box when there's other boxes available. What are some dangers that tree swallows face? So many. We know that a really big one for at least young birds is just temperature, particularly cold. So they're really, really sensitive to to when it's cold, even when it's just a little bit cold, the adults are better at dealing with cold. Although they can also, we do see some adults die when it gets really cold as well. Predators, like all birds, are big ones. What are some mean and very high-level predators that think tree schwans taste delicious. Minks are really common predators around here, and some of them can get into the nest boxes. So that's a. Are they that small? Yeah, which is kind of amazing, right? I've never seen a mink, so I'm trying to imagine it. But that just they're really they can stretch them together. That things like that make yeah pretty amazing. Most things like a raccoon, I'm sure, would love to eat them, but they can't. They can't make it into the boxes. That ate those. Yeah. Well, one year there was tree swallow at a program. Um, there were tree swallow nest boxes, and a tree swallow nested one, and there were five white eggs. You go over there, and then there's and then there's like the shell, like half the shell, on the ground, on the cinema. So I was like, there's no chewing, so it could have been a squirrel. How a raccoon got in there. We were thinking raccoon because sometimes. There would just be like a nest box. The door would just be open. I don't know why, but sometimes, yeah. And they can be good at that. Was the nest? Did the nest look disturbed? Like, did it look kind of torn up, or no? No, it didn't look torn up at all Mammal mammal predators usually not always, but they often tear up the nest. Whereas birds, when they eat eggs and things. They often don't. You know, they'll just come in and pick out the egg, and sometimes, sometimes also could be the house wren. Okay, yeah, crows also would love to eat eggs if or nestlings Yeah, I know that they do that cougers, but I don't really remember the nest. So it could have been a minx. I remember not being shocked by the look of the nest, so I don't think it was shredded. if they can get them, but yeah. So probably in the wild they could probably prey with the rotten wood and stuff like that. Yeah, crows, jays. What's the strangest thing that has happened while doing field search? Well, when we were working in Alaska, we had a lot of problems with bears, and the bears would come and hit our nest boxes and just knock them down, and sometimes eat the nests that were inside. Rip the door off the nest box. Maybe knocking the door to the side or the tongue, but strip the entire nest. And sometimes we would run into bears while doing our our nest checks. That was fun. That's scary. What kind of bears? Grizzly bears. What? Yeah, it was intense field work, but That does sound intense. have you ever gotten chased by animal while while studying birds? Fortunately, we weren't chased by the bears. Not while studying these birds. We were chased by a buffalo doing fieldwork in Africa. Oh, sorry, that's my cat who's trying to get in on the action thing. Hello, but that was a little scary. That that was doing other fieldwork Chased by a buffalo. Yeah, yeah. So So you were running from a buffalo? Yeah. What were you doing research in Africa on? So I was doing a field course, and it was at a research station called Impala that's in Kenya, and so we got to go out there and do a project. And so our project was looking at parasites that different ungulates had, so like zebras and gazelles and lots mostly grassland animals. Yep. So we would go. We would watch the herds, and then we would go out and pick up their poop and analyze them for different parasites. But there were a lot of animals there. It was like a smelly and cool job. Yeah. It was. It was a really neat. It was a really neat trip. And you got chased by bustle while doing it? Yeah. My fortunately for me, it was a little bit more my friend getting chased than than me. But okay, they're not very maneuverable, so she was able to kind of go around. We was while we were camping, and she was able to kind of go around the tent, and it lost interest and took off. But what's the most surprising thing you've ever seen at a nest box? Should we either add a nest box, like on top of it, or in a nest box? So sometimes we get frogs in our nest boxes, what on cold mornings, it's really funny. But they they're little tree frogs, and they like to if the mom tree swallows incubating the eggs, right? Then the eggs stay warm even when she leaves, and so then the frogs come down and they stretch across the eggs and have like a little, I don't know, froggy sauna, and so that's really funny when you see those. But a couple of times we've had a frog in the box that gets surprised when we open the box, and we'll jump right out into our faces, and so that then you get a bunch of frog gunk in your hair. Yeah, I'm really not expecting a frog to suddenly hit me in the face. I wouldn't be expecting that either. Yeah. Now I have an eye to the fact that there may be frogs in the boxes, but that was early on when I was checking in. I think I squealed pretty loud. What can people do to help tree swallow? One of the big things that tree swallows are affected by is changing amounts of insects. So, with more use of insecticides, especially in agriculture, tree swallows are probably suffering in part as a result of just not having as much food to eat, and so trying to kind of reduce the use of insecticides and help insect populations to bounce back is a really big one for tree swallows. We can use a tree swallow around, there's a lot of flies or gnats. Yep, follows also are often limited by nesting sites. So, even like putting up a bird box in your backyard can be really helpful for tree swallows. I'll think about it. Yeah, and pretty fun, fun to watch. It is It is really fun to watch. What can people do to help tree swallows? Yeah, so I think I mean, there's the insect, the sort of insect reducing reducing and pesticide piece of it, they're also really affected by temperature, and so the kind Climate change? whatever we can do, yeah, exactly by by increasing temperatures in the spring and more variable temperatures in the spring. So whatever people can do to curb emissions and and reduce climate change is also going to be really valuable for tree swallows, and like many birds, also a lot of kind of urban predators can get them, and so things like keeping cats indoors is really helpful for tree swallows and for many other birds.

Do tree swallows ever compete with other swift birds, like fast birds, like purple martins, and other animals for like nesting. Because I imagine a purple martin and tree swallow might use the same box, although purple martin yeah It seems like they would, but martins just like to nest colonially so much that we never really see them competing for nest sites. They're certainly to some extent competing for the same types of food, but that's a little bit more of an indirect competition, where they're each scrambling to eat as many insects as they can, but they're not kind of directly fighting over food. Thank you so much for joining me today and for teaching me about tree swallows. It was great to talk with you. I love your questions, and I love how passionate and excited you are by birds. Yeah, can't wait to see you again. Yeah, I would love to have you out to the field site again sometime, and also you're welcome to come visit the lab if you'd like to. No, no real birds there, but plenty of bird research goes on anyway. Yeah. All right. Well, good luck with your story, and let me know if any other questions come up, Doctor Marin. Thank you so much for talking with me today and showing me your tree swallow research project. I learned so much, and I hope everybody listening did too. If you enjoy this episode, please follow Blackbird Jordan so you don't miss future adventures. I'll be talking with bird scientists, birds, authors, and other people who love birds as much as I do. Until next time, get outside, look up, and find some joint birds. Bye.