Scott Taylor: Broadly, 2026 is shaping up to be the hottest year the United States has experienced in its 250 years. If we're lucky, we retreat into air conditioning. Birds don't have that luxury. They're outside in the heat. I personally prefer being too cold to being too hot. Maybe it's the Canadian in me. A couple of years ago, on my first sabbatical, I was working in Panama with my friend and collaborator Jay Falk. During that trip, we discovered that white-necked jacobin chicks mimic venomous caterpillars, but that's a topic for another episode. Rarely in my life have I felt panic over how hot I was, but in the rainforest of Gamboa, I got that hot. I was still sweating, which was a good sign, but I was genuinely worried about cooling down. At 100% humidity, sweating barely works. The sweat doesn't evaporate, so you don't get the benefit. You're just hot and sticky. It's the worst. Thankfully Jay's house had a pool and after our hikes we could sink into water at least a little cooler than we were. Living in Colorado now, I'm regularly too hot in the summer, but here, where humidity rarely tops 40%, sweating cools you down all the time. I still remember noticing that a cold glass of water barely sweats out here. It's just that dry. And that's the thing about sweat. It only saves us because we can make so much of it from glands all over our skin. Plenty of other mammals sweat too, but for most of them, all that fur gets in the way. So evaporating sweat off the skin isn't always the most efficient way to cool down. So what about birds? They don't sweat at all. Which brings us to the topic of today's episode. OK, but how do birds handle a heat wave? To find out, we'll talk to Dr. Blair Wolf, a professor in the Department of Biology at the University of New Mexico who spent his research career studying exactly this. After the break, Blair walks us through the impossible choice birds face between overheating and drying out, why some backyard birds sail through the heat that kills others, and what birds dying in these heat waves. Tell us about what's coming. Stay tuned.

Scott Taylor: Well, welcome back to the podcast, everyone. I'm really excited to have Blair with us today. Thanks for joining us, Blair.

Blair Wolf: Yeah, absolutely.

Scott Taylor: So when it gets, you know, over 90, I start panicking. But you know what regularly gets over 100 in many places in North America and, and the world. And so as humans, we shed layers, we sweat, we might find AC, drink some cold water, but birds can't do most of those things. So what are birds doing to keep from getting too hot?

Blair Wolf: I mean birds are sort of first of all, they're sort of preadapted to these high temperatures because they have very high body temperature. Body temperatures run anywhere from 104 is sort of the baseline or 41°C all the way up to 48 or 118° in a living bird functioning normally.

Scott Taylor: That's crazy. Humans are long dead, right?

Blair Wolf: I mean, 107 to 108, 109, you are, you're gone. You're, you're, you're dead. And and that's, that's it pretty much. And so birds have this preadaptation with high body temperatures may be associated with flight that that provides a more favorable gradient for dumping heat. The means of last resort for birds and, and humans is, is, is evaporative water loss, right? Evaporative cooling, we call it where the animal is actually evaporating water from some surface of its body to to cool its body, right. So evaporative heat loss in birds, in, in, in perching birds and songbirds, it's generally comes from panting movement of the respiratory tract, right? Like dogs, they're dumping heat by evaporating water from the surfaces of the lungs and throat that carries heat away. And so they cool that way and that reduces body temperature, reduces the heat load on that other way birds cool. Is there some birds like doves that can actually evaporate water across the skin?

Scott Taylor: Oh, really?

Blair Wolf: And that's unusual. They don't have skin glands. You know, birds have very thin skins. They don't have glands in the skin for the most part. Right?

Scott Taylor: Yeah.

Blair Wolf: And so we're not. Really, right? Just the uropygial gland, right, the preen gland so so that's the only one I know about. They somehow change the permeability, the skin and dump huge amounts of heat. And so doves are unusual in that they're able to dunch dump huge amounts of heat, doves and pigeons, right, huge amounts of heat across the skin. And that may, you know, they may be the flying cockroaches of the world as the world continues to warm, right? They'll be the only thing left here. And they're sort of a third group that uses it, a process called gular flutter: goatsuckers. The poorwills, the nighthawks, those kinds of a birds actually flutter to their throat, their hyoid apparatus. And this is a very, very efficient mechanism of dumping heat. These poorwills nest on the ground. They lay a white egg. They nest in their creosote bushes where they're sitting on the ground potentially exposed to high solar heat loads and the the ground temperatures are very high as well because absorption of solar radiation. So sitting on the on the ground and and, you know, nesting during the the spring when it's still really, really hot and so.

Scott Taylor: They're do you think they're also trying to keep their eggs cool? Then that's why the egg.

Blair Wolf: Nobody's I would think that, but nobody's demonstrating egg cooling in them. I think they also shuffle and move their egg to follow the shade. Sometimes they'll they'll shuffle the egg along I think. Nice, that's not well documented, but I think they're it's also the only bird that hibernates.

Scott Taylor: Yeah, I was just going to say, poorwills. Are these these birds that have come up now a few times on the podcast? Yeah, they're super cool. The hibernating piece is fascinating that they're the only bird that hibernates and they do this gular fluttering to stay cool so they can kind of be at both ends of this insane spectrum that would kill.

Blair Wolf: Your it's a, it's a really neat bird. It's a really cool bird.

Scott Taylor: Very cool birds. The fact that birds have such high body temperatures, I knew that, but I didn't know how high they could be and still function. Is a typical bird on a typical summer day have that really really high body temperature? Do they only raise their body temperatures to avoid having to try to cool themselves down in really high heat scenarios?

Blair Wolf: Yeah, that so most birds are running in the 40s just as their baseline. We run at 37 right as our baseline. In birds, it appears that body temperature is very labile. It can it moves up and down quite, quite easily and in in part that may be associated with flight and muscle efficiency. When birds fly, body temperatures go up typically even though they're cooling as they move through the air. So body temperatures and birds seem to be very, very labile, right? They can, they can move quite a bit. And, and one of the things that that birds do is by having body temperature rise as it becomes hotter and hotter, that provides still a more favorable gradient for dumping heat without using water, right?

Scott Taylor: Yeah.

Blair Wolf: Birds have to balance both the water and energy budgets over very short time frames. Hours to days for small birds, right?

Scott Taylor: Yeah, totally. So you can pant and cool down through evaporative water loss, but you're losing water, which is usually not a good thing, especially if you're a desert living creature. Or you can hold on to your water and potentially overheat. So how do birds transition in between these things? What drives those trade-offs and are there any particularly interesting birds in that context?

Blair Wolf: Yeah. So this is a real trade-off problem, right? And so especially for birds in deserts where they are subjected to real large heat loads for an external environment, right? If their temperature in Phoenix is 118, that's going to be above the bird's body temperature. Yet there are thousands, if not millions of birds living out there under those conditions and they have to make it every day. They don't just have a drinking fountain, they can go to and and tank up on water, right? And so they have to be mindful of their body water content, you know how dehydrated they are versus because that affects the performance, right? In humans, we use, we lose a liter of water and that actually effects our heart rate, two liters, it's significant, It actually affects your running performance, things like that. And so 1 to 2% of water loss in humans really starts to produce a deficit in function, right? And so it affects our performance. So birds have to perform every day, right? At their maximal level. Every bird is an Olympic athlete. If you had Nate center on there or Maria, they're talking these, these birds are all Olympic athletes, right? Everyone in the population is that well trained to that level of fitness, right?

Blair Wolf: And so, so this trade-off with the heat is you either evaporate water to stay cool and keep your body temperature below lethal limits, right? So you don't heat stroke out or you don't and you allow body temperature to rise. Now there are limits to that. And so any limits on body temperature like that in the heat are really going to limit the animals activity. And so you can't go flying around in that kind of heat. You can't be exposed to solar radiation and that kind of heat because exposure to solar radiation is equivalent to increasing air temperature of a room by 10 or 12°C, you know, 20°F. And so if the room is already at 120, you expose the animal solar radiation. Now it's equivalent to 140°.

Blair Wolf: And So what happens to evaporative water loss as air temperature increases? Well, evaporative water loss increases what we call exponentially. It's not a straight line, it's a curve. And so you, the animal may go from losing 1 or 2% of body mass per hour by evaporating water just to stay cool at say 40°C. At 48, it may be losing 5 or 7% of its body mass an hour for a small bird like a verdin, black-throated sparrow or something like that. And so no animal can lose 7% of his body mass per hour for very long time without becoming a little freeze dried, you know, a piece of beef jerky or something, you know, bird.

Scott Taylor: Jerky, bird jerky.

Blair Wolf: Humans, it's sweating. We can use maybe 12 liters a day, you know, 3 or 4 gallons of water a day just through evaporative E loss. So we're very, very good and effective at, at cooling, but we got to stay hydrated. So this old idea, hydrate or die is true for birds. And so both doves and quail are tied to water and so they all, they both fly to water or move to water every day basically and sometimes twice a day. And so at least doves have this huge cooling capacity and we've exposed doves to, you know, 140 a 150° and they've been just fine.

Scott Taylor: Wow, what species of dove could take 140°?

Blair Wolf: White-wings and mourning doves.

Scott Taylor: Mourning doves even wow. I think most people think mourning doves are these like common backyard boring birds, but they can persist at temperatures that high. Wow. What does that work? I mean, I think is like we have sweat glands and the sweat is released and then evaporative cooling happens. But what's the deal with dove skin? Like what's the physiological mechanism there?

Blair Wolf: That's been of interest to cosmetic companies. Birds are thin skin, so they may actually change the the lipid structure of the skin and the blood flow to the skin. OK, to make the the skin more permeable to water, but that's still an open question.

Scott Taylor: That's cool that it's still an open question, but it's clearly a very effective way to live at very high temperatures.

Blair Wolf: Right. And they only pant at when they're really heat stressed, right? And so they can pant as well. And so, but they're, again, they're losing so much water. And, and in doves, you'll often see a white-winged dove nest or a mourning dove nest. I have one in my yard where the the adult birds just sitting out in the open on top of a cactus exposed to the sun's radiation. So it's sitting out there, it's 105, yet it's got the heat load from the sun and it just sits there, not moving, not panting, not doing anything, evaporating water.

Scott Taylor: Wow.

Blair Wolf: And the doves change once a day. The adults change once a day. I forgot whether the female incubates at night and the male during the day. But, you know, and, and doves are interesting from this standpoint that they breed during the summer. They're exposed to solar radiation, and they actually cool their eggs.

Scott Taylor: Yeah. Yeah.

Blair Wolf: Because they actually evaporate water to lower their body temperature and cool their eggs. So the eggs don't exceed a lethal temperature for the embryos.

Scott Taylor: Yeah, a reverse problem to the chickadees here, here in Colorado that are just trying to keep their eggs warm.

Blair Wolf: Yeah.

Scott Taylor: When heat waves hit, what are we seeing in terms of birds survival or mortality or reproductive impacts? And what do you think we should still be looking at?

Blair Wolf: Yeah, there's both acute effects, what happens right now on a daily basis and whether birds survive through the day.

Scott Taylor: Right, right.

Blair Wolf: Yeah. And so we already know that heat waves which are increasing in frequency, so they're happening more frequently. The, the duration is longer instead of three to five days, maybe have 7 or 8 days where high pressure system stays over an area and just burns it, right. And then they're just going to become more and more frequent as well and higher in their temperatures, right? And so we're on a trajectory for warming right now. We're probably looking at 3 to 4°C by 2100.

Scott Taylor: Wow. Are we seeing mass die-offs in birds? Like what are birds telling us about heat waves, what we're about to live through? I mean, you know, France just experienced an unprecedented heat wave. We're experiencing hot weather here in North America as well. I mean, birds, the canary in the coal mine is a real metaphor because canaries would die before people would. What are we learning from birds in the context of just heat waves and their broader impacts?

Blair Wolf: I think some of it's pretty subtle, right? Because there's no idiots walking around and out in the desert when it's 120.

Scott Taylor: Yeah. So we wouldn't find them if they were dead?

Blair Wolf: Yeah. Yeah, how do you survey bird populations? You know so it's only where you have birds and large numbers that around humans that you see them and and sort of Australia sort of the poster child for this.

Scott Taylor: Yeah, right.

Blair Wolf: I've documented some die-offs and 2010 and going forward of things like budgies where there's thousands of budgies under a carport, you know, and next thing you know, there's thousands of dead budgies just from acute heat stress, meaning that they, they can't cool enough, they can't evaporate enough water to maintain their body temperature below lethal limits. So there's these acute events, these acute effects that are that are happening. And in Australia there's been quite some big ones with cockatoos and the palm cockatoo. There was one population, I think they last lost half the population in a single event. But most of the birds we don't see that are dying under these bounce because they're in low densities, they're out in the desert. And we just see maybe changes in abundance through the different survey techniques we're using. But I think it's it's subtle. You know, we've lost 30% of the birds in North America since 1970. You know, there is all these different stressors where there it's land use change or pesticides or global change or whatever it might be, right? And he was definitely one.

Scott Taylor: Yeah.

Blair Wolf: Oh God. Cats. Jesus.

Scott Taylor: Yeah, we talked about cats. We should maybe do a full episode about cats someday, if I really.

Blair Wolf: Did you have Pete Marra on to talk about cats?

Scott Taylor: No, but we've thought of it. I just know the cat episode will be extremely.

Blair Wolf: Oh, it'll be contentious.

Scott Taylor: Contentious. We'll. Get a lot of I know how I feel.

Blair Wolf: Yeah, you'll get some haters. You'll get some haters on there. When his book came out, I know Amazon reviews were brutal.

Scott Taylor: Brutal.

Blair Wolf: I know. Yeah, yeah.

Scott Taylor: But cats do kill billions of birds, so that is indisputable. Yeah. Heat is another thing we need to be thinking about. And you're totally right. I mean, we've talked about bird flu on the podcast as well. And there you can. You know, if it's a colony that dies, you see it just like if it's a roosting group of budgies that all die, it's obvious you can count them. But for the most part, birds aren't existing in these large groups. And if they're dying as individuals out when it's 110°, we're not going to see it and we're going to see it reflected, like you said, in the longer term trends in population sizes and stuff, which as we've talked about many times are declining. So I guess if you live in an area that's experiencing heat waves and you want to do something like if you want to try to help providing water is really the, the, the main thing you could do is that, right?

Blair Wolf: Yeah, I think providing water and shade, right, shaded environments, I mean these birds will, I mean, birds are very good at selecting the coolest spot in the environment rest, right. So they're looking for microsites, we call them that have the coolest microclimate. And so birds are already small, so they can be very selective and where they're sitting in the environment to try to reduce their evaporative costs, right? They can reduce evaporative loss by sitting in these cool shaded microsites for long periods of time, right. And so they they do that and then providing water. I mean, all these birds will use water. Yeah, when it's available. You know, if you live in a big urban environment, like if you're in Phoenix or even Tucson, you got a heat island effect where you know, the the asphalt is absorbing all this heat from the sun is reradiating it. It elevates their temperatures of the environment by, you know, half a dozen degrees Celsius. And so you're really looking at a, you know, at a brutal environment. Go out and walk. We walk in the evening on the street and on a hot day, Man that that reradiation of energy from the asphalt is is brutal right?

Scott Taylor: It is brutal.

Blair Wolf: Yeah.

Scott Taylor: Yeah. And in a previous episode, we talked with Olivia Sanderfoot about providing bird, you know, bird baths and things like that. And if you can, how to keep them clean and make sure that they're good and ready for your, your local bird population. One of the cutest examples I think of the seeking out the right microsite at least in your area down in the southwest is the the lovebirds in in Phoenix that seek out like the AC coolant areas of the buildings I'm pretty sure.

Blair Wolf: Yeah, yeah, that's a, that's a well-documented one. You know, one of the things we haven't talked about at all are is humidity too.

Scott Taylor: Yeah. And humid environments prevent evaporation.

Blair Wolf: Right, Exactly.

Scott Taylor: Yeah, You're not going to sweat much when it's 100% humidity.

Blair Wolf: You can't sweat at all if it's 100% humidity, right? The sweat pours off you, it drips off you. Well, it's the same with with birds. It's harder to evaporate water. And so hot, humid environments are going to be particularly devastating for both humans and birds. I mean, they're serious in the Persian Gulf now that are going to be basically, you won't be able to go outside. They will be uninhabitable for humans during periods of the day because you can't cool enough to even get rid of the heat your body's producing.

Scott Taylor: OK, so many of our listeners are watching backyard birds like robins and sparrows and chickadees. They're not necessarily desert specialists. How well do the temperate species so these ones not built for extreme heat cope when a heat wave hits? Are they as adaptable, less efficient, or what's going on with them?

Blair Wolf: So animals are adapted to their environments, right? And so animals that live in more temperate environments, cooler environments, don't have the capacity to deal with heat that desert species have. And so they reach lethal body temperatures more quickly. They can't tolerate the high heat loads. And so we're seeing, you know, die-offs at lower temperatures right in a place to look at this is it's really anecdotal now. I don't think there's been any good studies, but I've talked to people up in the Arctic. The Arctic is warming four times faster than the temperate regions. And so they have anomalies where the air temperatures 20 or more degrees above what the average air temperature should be, you know, when it's when it's 90 or 100 in Anchorage, Alaska, or 120 in British Columbia, right? There's nothing that's adapted to those kinds of air temperatures. And so especially for breeding birds like up in the Arctic, maybe like waterfowl that are sitting in a feather-lined nest exposed to high solar heat loads. And all the sudden the air temperature should be 50, but it's 90 or something, right? Or 55 or 60 and it's 90 and you got the solar heat load. So I, I think for temperate species as well, they're less tolerant of high heat loads. And so they've got a, they've got to deal with it, right? And I I think that again, that kind of chronic exposure is going to have real effects on both reproduction and and survival.

Scott Taylor: Yeah, totally.

Blair Wolf: Just population sizes for sure.

Scott Taylor: We've reached the part of the show we call that's BS. So that's bird stuff where we give our guests an opportunity to debunk a myth that ruffles their feathers. So Blair, what do you want to call BS on I.

Blair Wolf: Mean people seem to have this idea that birds are these very delicate little.

Scott Taylor: Yeah.

Blair Wolf: fluff balls of feathers, when you look at birds or if you work with birds or handle birds, you know that they're super tough and resilient as far as when you interact with them on a a minute to minute basis. I mean, they may be canaries in the coal mine or sensitivity to environmental perturbations, right? Whether it's pesticides or heat or some other thing, because they have very high metabolisms. They they, you know, use lots of energy and have high rates of respiration all that. So they're really coupled with the environment. And so any, you know, any say, insecticide in, in the food they're eating is going to accumulate very rapidly in their tissues because they have such, they bring in so much energy. But if you look at them on a day-to-day basis, I mean they're super tough.

Scott Taylor: Yeah, they're telling me, yeah.

Blair Wolf: You know, you handle a hummingbird or something like that and they just barely tolerate you. If they're a little bigger, they would attack you and try to kill you.

Scott Taylor: What's up? Hummingbird would be a dangerous beast if it was the big bird.

Blair Wolf: Birds by and large have an attitude of where you know, I, I can't be defeated. They're very resilient creatures, you know, and, and they're, they're tough, you know, they do incredible things. They're all Olympic athletes, right? If we look at human populations, there's one in a million that is an Olympic gold medal winner, whereas in birds, they're all trained Olympic athletes that perform at the highest level. And so I don't think we think of it that way because we think about our own performance and how miserable most of us are empathetic. And. Yeah, birds are all Olympic athletes and so I think that. That's it's BS that yeah, birds are fragile and delicate. They are these amazing creatures.

Scott Taylor: Yeah. And I love that. Thanks so much for joining us today. It's been really awesome to chat with you about heat. And though a bit depressing, super interesting to understand how birds are coping when we are experiencing these these high heat events that we are more frequently now. So thanks again for joining the podcast.

Blair Wolf: It's been my pleasure, it's been great, lots of fun.

Scott Taylor: Birds are dinosaurs, and around here we like our snacks, so we end each episode with a Dinosaur Nugget. Today's nugget is to start. Birds run hot. Their body temperatures often sit in the 40s Celsius, temperatures that would easily kill you or me. We start to die around 107 or 108 Fahrenheit, roughly 42 Celsius. A bird can cruise right past that. And running hot is actually a feature, not a bug. The hotter a bird is compared to the air around it, the more easily it can dump. Heat the freeway passively with less expenditure of water. So when a heat wave pushes the air up toward a bird's own blazing body temperature, that cushion vanishes and staying cool suddenly starts to cost them. That's a wrap on this week's episode. OK, but how do birds handle a heat wave? If you've ever been too hot, show us some love with a rating, because we're sweating through this one in a studio with no AC in July. Catch you next time. Byeee.

This transcript was generated using AI-assisted transcription and may contain errors or omissions. Please refer to the audio or video episode for the most accurate representation.