Thumbnail image: Grace Oliver/Macaulay Library
[Chelsea Benson] Welcome. If you want to keep sharing where you’re from in the Chat, that’s great. But we’re going to get started.
So today’s webinar is brought to you by the Cornell Lab of Ornithology. We’re going to be discussing hummingbirds and how they use energy, plus taking all your questions.
My name is Chelsea Benson I’m on the Visitor Center team at the Cornell Lab. And I’m going to be facilitating today’s conversation. Before we get started, I want to recognize the lands on which Cornell University is located by reading the land acknowledgment statement.
“Cornell University is located on the traditional homelands of the Gayogoho:no– the Cayuga Nation. The Gayogoho:no are members of the holding of the Haudenosaunee Confederacy, an alliance of six sovereign nations with a historic and contemporary presence on this land. The confederacy precedes the establishment of Cornell University, New York state, and the United States of America. And we acknowledge the painful history of the Gayogoho:no dispossession, and honor the ongoing connection of Gayogoho:no people, past and present, to these lands and waters.”
Cornell Lab of Ornithology is home to a community of researchers and supporters from around the world who appreciate birds and the integral roles they play in our ecosystems. And our mission is to advance leading edge research, education, and citizen science that help solve pressing conservation challenges. With us today we have Anusha Shankar, a postdoctoral fellow at the Cornell Lab of Ornithology. Anusha, thanks for joining us.
[Anusha Shankar] Thank you so much for having me.
[Chelsea Benson] Yeah, so excited. And our second panelist is Erich Eberts. He is an ecology and evolutionary biology PhD candidate at the University of Toronto at Scarborough. So hey, Erich.
[Erich Eberts] Hey. Thanks so much for having us.
[Chelsea Benson] I’m really excited. And thank you both for taking the time to be with us and our audience today. We’re going to be hearing a lot from Anusha and Erich over the next hour. But before we go to that direction, I have a few more quick announcements.
For our Zoom audience, live captioning is provided. Select the Live Transcript button at the bottom of your screen to turn them on or turn them off. I’m going to be asking our panelists a few questions. But we also want to take questions from you. So if you have a question for Anusha and Erich, please enter into the Q&A button– into the Q&A, which is located at the bottom of your screen. We’re going to be answering some questions verbally. And for others, we’re going to be typing in responses, which you can see in the Answered column.
We also have the Chat going. We’re going to only use the Chat for technical support and to share information with you. And I have colleagues behind the scenes helping to answer the Q&A in the Chat. So thanks so much to them.
We’re also streaming live to Facebook. So if you’re on Facebook, welcome. Happy to have you as part of our audience. We are going to take your questions in the Comments box in Facebook. Please be aware there’s been some spam attempts. So don’t click any links unless they’re from us.
OK, that was a laundry list of announcements. So thank you for being with me.
So right now, it’s summer. It’s field season, which is a very exciting time to be a researcher. I know you both have been really busy collecting data on hummingbirds. So I’d love if you could start off by introducing yourself, sharing where you are in the world, what birds you’re studying, and what you’re hoping to learn. So Anusha, could you kick us off, and then Erich?
[Anusha Shankar] Yeah. Hi, everyone. I am right now speaking to you from Oregon. I’m in a town called Newberg. And I’m collaborating with a researcher at George Fox University. And we’re studying hummingbirds and how they use torpor, which is an energy-saving strategy that we will be speaking a lot about in this webinar. And what I’m hoping to learn is how animals use torpor and what– how their body temperature changes together with that energy expenditure, and what order do those go in, and how do they come out of it. Yeah.
And I’m Erich. And I’m up here in Newmarket, Canada, about 45 minutes north of Toronto, at a field station. I’m studying Ruby-throated Hummingbirds. Of course, they’re the only hummingbird that breeds in eastern North America.
And again, I’m sort of interested in the how and ways of how hummingbirds use torpor. And specifically, I’m interested in how torpor use changes between the breeding period in the summer and later in the summer as the birds fatten up and migrate southward. So, yeah, I’m generally sort of interested in what these– how torpor is allowing these hummingbirds to do what they do.
[Chelsea Benson] That’s great. And I love that we have a little representation from East to West Coast of the United States here. And I think I can speak for everyone in our audience on the East Coast that we’re very jealous, Anusha, of all the hummingbirds you get to see out West.
Erich and I are stuck here just looking at ruby-throats, which are amazing. But I’d love to see a few more.
So before we dig deeper into your current research, I’d first love to know why hummingbirds, and if you’ve always studied hummingbirds, and what drew you to the species? So Erich, if you could kick us off?
Yeah, sure. So I guess I’ve loved birds in general since before I could remember. My grandmother loved birds, and specifically hummingbirds. And she used to have a whole bunch of bird statues. One, apparently when I was really young. I don’t remember.
But I was obsessed with this statue of a green heron. And years, years later, 15, 20 years later, when I’m starting to do some bird research in university, I ended up finding this statue at my house– my mom’s house. And it just was a great reminder of the fact that I’ve loved birds for longer than I can remember.
And at that time, I was working with this group, doing some conservation work with least terns and crows. And working with that group, I ended up being able to go down to Costa Rica on a study abroad trip. And for my independent project, I ended up putting up feeders and cameras all around Costa Rica, wherever we would stop, and filming their activity, just checking out what hummingbirds were around and what they were doing.
And I enjoyed that so much that I went back to my university in Los Angeles and continued the same kind of thing, different species obviously. But I was still really interested in the crazy antics of all these hummingbirds. And that– one thing sort of led to another. And I ended up being able to go to Ecuador, where I met Anusha, to help with some of her research for a few weeks.
And there I learned about torpor. And just was intrigued by this extreme, short-term change in physiology. They’re just going up and down in metabolism and body temperature. And I was just really interested in that.
So when I went back to my university, I was able to get a research fellowship for a year or so, and continued to look at hummingbirds, and found a whole bunch of hummingbird nests on campus. And then Anusha and I went to a conference, talked with some collaborators that do thermal imaging.
And so sort of one thing led to another. We got a bunch of thermal cameras and filmed these birds that were nesting, without having to ever touch them. And we were seeing if the birds were using torpor. It turns out, nesting birds really don’t use torpor very much. But they can.
So in that whole project, I started thinking that I wanted to do a PhD in this stuff because I was so interested, and dive really, really deep into it. And that’s how I sort of ended up here in Toronto, in the Welch Lab. And we study hummingbirds and hummingbird metabolism. And that’s sort of where I’m at this point.
That’s fun, how it all kind of snowballs, right. You started with that little interest in your grandma’s statue. And then now its become this really big passion in your life. What about you, Anusha? How did you get your beginnings and why hummingbirds?
[Anusha Shankar] Why hummingbirds? Well, I started by loving being outside, and loving snakes and insects that I really was into, animals that other people were terrified by or creeped out by. I think I really like noncharismatic animals in general. But birds were everywhere. I thought they were really mainstream. And I didn’t want to study them. But then here I am, 12 years into studying birds.
And I think they’re just– they can move. They can fly. They can– their metabolism is crazy. And hummingbirds are so widespread. And they’re so diverse.
And they’re present in the tropics. And they’re in the desert. And they’re in the mountains. And they’re in the Amazon. And it’s just like these tiny little things that can survive so many different habitats and use such dramatically different strategies during the day versus at night. I think they can help us answer a lot of questions. And that’s why I’m so fascinated by them.
[Chelsea Benson] So I have to ask you this. And maybe you can’t really answer because it’s like saying what your favorite kid is. But do you have a favorite hummingbird species?
[Anusha Shankar] My favorite is the Booted Racket-tails, I think. At least that’s the answer I’ve been giving for years. People are asking me. I have to re-evaluate.
But the Booted Racket-tail has tiny little boots on its legs. And it has this racket-tail, which is a long, thin piece of feather, like the staff of the feather. And then it has a little feathered tip at the end.
But it’s just so tiny. And it buzzes in to the feeders and out of the feeders. And I saw amazing display by a male, or a female, that was– the male was dive-bombing the female deep in the middle of the cloud forest. And I think I was in love.
[Erich Eberts] My favorite I think is the Shining Sunbeam, which is– I find it to be a rather unique hummingbird because typically when you imagine a hummingbird, at least when I do, I imagine this flashing throat, this gorget. But the Shining Sunbeam is a little bit more inconspicuous, even the males.
And so they’re a lot more sort of drab looking, sort of coppery colored. But on their back, they hide this extremely vibrant, iridescent, rainbow stripe right down their back. So beside– and also, this is one of the first birds that I could work with, Anusha. So that’s one of the first birds that I held. So that’s the species that I hold near and dear to my heart.
[Chelsea Benson] Well, it sounds lovely.
So we’ve been saying the word “torpor” a lot, already. So let’s kind of talk a little bit more about what that word is. Anusha, could you share what is torpor and how is it different than hibernation and sleep?
[Anusha Shankar] Yes, one of my favorite questions. Hibernation is something many people are familiar with, like bears can do it; some squirrels– ground squirrel species– can do it. And it’s where animals, in a low-energy time of the year, for example, can save energy by lowering their body temperature, and lowering their metabolism, and requiring less energy because they’re spending less energy.
And so hibernation is a form of torpor. So torpor can be multi-day or multi-week, which is when it’s called hibernation. Or it can be daily torpor, which is what hummingbirds do. But they just do it for a night to save energy overnight. And then they can get up in the morning and find food again.
And then torpor is very different from sleep because we think that, at least from studies on mammals that when animals are in torpor they’re not getting the benefits of sleep. They’re not regenerating the stuff that– they’re not getting rid of the toxins in their brain, they’re not resting really. They’re not repairing stuff in their brain, and so it’s not sleep, it’s energy saving, which is way, way deeper than sleep. So when an animal or a hummingbird is in torpor it’s using only 10% to 20% of the energy that it would use if it were to asleep. And so the functions are really shut down when they are in torpor.
[Chelsea Benson] And for Erich, does torpor only occur at night if we’re talking about hummingbirds? It sounds like the way Anusha described it, torpor in a big general sense always happen at night because if we’re talking about ground squirrels or bears, obviously that’s really what can be for long periods of time. But for hummingbirds is it just a night phenomenon when they’re dropping that body temperature so low.
[Erich Eberts] Yeah, primarily. So during the daytime the birds can pretty much always find food. So in the nighttime that’s when they’re really challenged because they can’t find that food. So they have to rely on those sort of endogenous body fat stores of energy.
And so, yeah. The vast majority of hummingbirds, at least in a natural context, are going to be using torpor at nighttime. I do suppose that theoretically, if there was a sick bird an injured bird that couldn’t get to any food that they might enter torpor, but that would be more of a pathological kind of unhealthy way to use torpor where the bird might not even have enough energy at that point to be able to wake up from that torpor.
So in general, at least if we’re talking natural torpor what a bird is doing in the wild that’s almost always a night. And then like you said, there’s other forms of daily torpor like for example bats, they’re nocturnal in comparison with the hummingbirds that are diurnal. So the bats, the time that they can’t feed is during the daytime, and that’s typically when those bats are going to be using torpor.
[Chelsea Benson] So the way you’ve just presented it to our audience is that torpor can happen across different animal species like we just mentioned. Bats, and bears, and squirrels, and it doesn’t also sound like it’s dependent on size. So what is the factor that drives animals of all different beings to go into torpor? It’s just about energy savings?
[Erich Eberts] I would say it’s both about energy savings and sort of size in terms of two interesting things. So larger animals have more fat that they can store while doing their normal activities, but smaller animals just because of the biomechanics of it for example hummingbirds, they can’t be really agile in the air and do their courtship displays if they’re really fat. And so in that sense, smaller animals end up– we see torpor being used probably more often in smaller animals compared to larger animals at least for daily torpor that is.
And then there’s another interesting point just looking at hummingbirds. Some studies done by Anusha’s PhD advisor, I think, actually saw that some larger species of hummingbirds end up using torpor less often both because they can probably have more fat on them and do their normal thing, but also because they’re more dominant at feeders, and they chase off the smaller hummingbirds. So those larger hummingbirds have more secure access to food resources compared to those smaller hummingbirds which might be a little bit more challenged at getting enough energy to be able to make it through the night. And so those smaller species end up using torpor a little bit more often than those larger species.
[Chelsea Benson] And I just saw a question pop into the Q&A that I think is really relevant to what we’re talking about right now. Well, somebody had asked if a hummingbird will use torpor as a strategy if it’s unseasonably cold or rainy. If you could talk about that a little bit.
[Erich Eberts] Yes. So I mean, this is right along the lines of what I’m doing. In general, there’s a hypothesis that there’s a decent amount of support for at this point. And I’ll show you a slide that, again, pretty convincingly supports this hypothesis where the birds are going to be entering torpor if they hit a critically low amount of fat stores at whatever point in the night.
So in terms of if a cold front comes in and it gets really, really chilly at night, the bird might not say, oh it’s cold, I’m going to enter torpor, but the more indirect mechanism might be that the cold affects the level of fat that the birds have at whatever time of night it is. And then at some point the birds will be using that energy up rather quickly, and at some point they’re going to hit that critically low threshold and that’s probably going to initiate the physiological signals that start torpor entry.
[Chelsea Benson] Right. That’s a really good clarifying point. Thank you for that. So Anusha, I know you had said you love thinking about and studying torpor because it opens up so many other research possibilities. So could you tell us more about what you can learn by researching torpor.
[Anusha Shankar] So imagine the abnormal body temperature is like 98 Fahrenheit or 37 something degrees Celsius. Imagine if you could cool your body down on your own to like 10 degrees Celsius or in the 40s or 50s Fahrenheit, and warm yourself back up without damaging your heart or your liver or your brain or anything else. And then go about functioning with the highest metabolism of all the animals on the planet the next day. That’s what hummingbirds are doing, and that’s why it is incredible to me.
And so some of the implications of this like some medical researchers are trying to cool human brains and hearts, for example, down. Like with stroke patients or with cardiac patients, they’re trying to cool them down to prevent damage while they do the surgery because if you cool a human body down or any animal’s body down, its enzyme function slows down, all its physiological processes slow down.
And we can’t get too low yet with humans safely because then we cause damage. So if we’re able to learn how other animals do this, cooling their bodies down, slowing the metabolism down and warming back up safely, then maybe we could make advances in human surgeries as well. And then like the really sci-fi version is we could hibernate and do space travel.
[Chelsea Benson] Let’s go to the future.
Now, that’s fascinating. That is so cool that by studying torpor and hummingbird’s and other species, there potentially has this human connection and medical research component, and I think that’s just really cool to be able to make that jump. So thank you for sharing that. I’d love to take the next few minutes if each of you could share more about the specific studies that you’re doing with energy usage and torpor. And so Erich if you would lead us off and then Anusha kind of follow up. That’d be great.
[Erich Eberts] OK. Sure. So I think I’ll start with a quick video. So I’ll share my screen really quick. So I mentioned earlier that we did a– whoops, there we go. We did a study looking at whether nesting hummingbirds were using torpor. So on the 108 nights that we recorded of I think about 10 nests, only one bird on two nights use torpor and this is one of those nights.
So this is a time lapse video so it might be a little bit laggy, but it follows this graph here on the left. And on the graph, this is the eye temperature on the y-axis across the time of night. So I’ll play this video here and it goes a little bit quickly. But I’ll sort of walk you through it. At about in the next couple of seconds, you’ll see the bird sort of get really wet and that’s a period of rain. The bird is still normothermic here, but the surface temperature is just cooling off because it’s a little bit wet.
And then the bird is about to enter torpor here. There he goes or she goes, sorry. And you can see she just blends right into the background and then arouses rather quickly in the morning.
So that’s just sort of a quick example of how drastic torpor can be in these nesting birds. And then my research here– the bulk of my research in Toronto like I mentioned earlier, is looking at how torpor use changes between the seasons at least in the summer. So Ruby-throated Hummingbirds, of course, are this hummingbird that breeds in Eastern North America during the summertime and then migrate South as far as Central America in the late summer.
And during the breeding season in the summertime, the birds generally want to maintain a rather low body mass so that they can have nice aerial agility to be able to do things like courtship displays and settle territorial disputes. But then in the late summer, much like many, many other long-distance migrants they bulk up their energy reserves and they fatten up right before migration so that they can fuel that really expensive and long journey southward.
So in terms of torpor use in the summertime, the birds gain energy during the daytime. So their energy levels increase during the daytime. And then at nighttime, they essentially reduce their energy levels until they hit this sort of threshold where they enter torpor. And by doing that every night, they can go up and down. And up and down, and up and down and maintain a relatively stable body mass.
And instead, in the migration period that sort of changes and their strategy essentially sort of changes so that they can just essentially go up and up and up without ever having to go down. And so to sort of describe this, here’s this graph of the amount of fat that the birds had on them at the time that they entered torpor. So I did some rather noninvasive studies and experiments to be able to calculate this level. So I measured this level in a whole bunch of different birds throughout the entire summer. And so here, again, on this graph we have the time of night on the x-axis. And then that amount of fat that the birds had on them at the time that they entered torpor on the y-axis.
So first here in the summertime we see that the birds entered torpor at really consistent amounts of fat at whatever time that they hit this sort of threshold, they entered torpor. And that was about 6% body fat. And so this is pretty compelling support for that threshold hypothesis that I mentioned earlier where if they hit 6% at whatever time of night, they’re going to enter torpor. But then in the migration season when they fatten up they completely abandon that threshold strategy where that threshold strategy allows them to survive these energy emergencies. These critically low fat threshold, fat amounts. But then in the summertime they– sorry, in the migration time they fatten up and they’re not in any danger of running out of energy, but they still use torpor.
And so some other data that I don’t have too much time to show you now, but this other data support the hypothesis that these birds are using torpor to not go down and not maintain that really stable body mass, but end up eating a whole bunch during the daytime, not using that much energy at night. And then eating a whole bunch during the next day and a couple days of repeating that pattern allows them to fatten up really quickly and quite substantially so that they can fuel their long journey.
So overall, I’m finding this fundamental shift in the way that hummingbirds are using torpor and the strategies that torpor is playing a role in terms of how these hummingbirds are managing their energy budget in terms of their energy demands of that particular season. And that’s all I got for now.
[Chelsea Benson] Much. So I see some follow-up questions in the Q&A, and then we’ll jump to Anusha. So some people are asking how long does it take for a bird to go into torpor and to come out of torpor? So your time lapse video, it made it look like the bird roused pretty quickly, but I’m not sure what that time frame actually looked like going in and out.
[Erich Eberts] Yes. So the nesting birds are a little bit different because they have the insulation of the nest so they’re going to enter torpor and arouse from a little bit longer than a bird just sitting out on the perch. But in general, the birds can enter torpor in about a half hour depending on the ambient temperature as well. And then at that same sort of ambient temperature, I often see birds arousing in less than 10 minutes. So it’s really, really fast. Yeah it’s pretty drastic there.
[Anusha Shankar] But it can take up like 90 minutes, it really varies. And it depends on the individual. Like I think in Ecuador, we found 20 minutes to 90 minutes for arousal. So it really depends.
[Erich Eberts] Yeah. And that again probably depends a lot on ambient temperature. If it’s colder and they’re having to get from 10 degrees all the way up to 40 degrees Celsius, that’s going to take a lot longer than if they’re just trying to get from 20 to 40 or so.
[Chelsea Benson] Another question is about how do you actually measure the temperature of the birds?
[Erich Eberts] Yeah. There’s tons of different ways. So in the images that I showed you there, We were using thermal imaging and that’s measuring the surface temperature of the bird. So it’s not quite their core temperature, but with such small animals the core temperature is pretty closely related to the surface temperature. And then there’s other ways of measuring their metabolism and their body temperature by using thermocouples and putting it under their wing, and that again gets to the surface temperature.
And there’s some general methods where you’ll insert a thermocouple into the cloaca, but that sort of stuff is a little bit more invasive and sort of messes with the bird’s behavior a little bit more. So at least in my research where I don’t want to be introducing extra confounding variables and things, I tend to try to use the thermal imaging because it’s really nice and not invasive.
[Chelsea Benson] Yeah. Especially when you’re looking at birds during the nesting season when it’s a really critical time. And then another question which I have a feeling it’s going to have a lot of variability, and Anusha you can probably weigh in here too, is people are wondering what is the quote unquote, “normal” temperature range for a hummingbird versus a torpor temperature.
[Anusha Shankar] Yeah. So the normal range is really hard to know exactly because they’re quite variable but it’s around 40 degrees Celsius. I have no idea what that is in Fahrenheit. I’m so bad at converting. About 100 Fahrenheit and then when they’re in torpor– how torpor works is it’s not an active cooling process. They’re becoming like lizards, they’re becoming ectotherms meaning that they’re allowing the outside air to decide what their body temperature is.
And so normally, humans, we’re endotherms. We can generate our own body heat and we maintain a high, stable temperature. So we’re homeotherms, same temperature all the time. But hummingbirds can go from being endothermic homeotherms generating heat, maintaining a high body temperature to becoming like lizards at night. And so they’re allowing the outside air to decide what their body temperature is. And so it depends on what the outside air temperature is. Like if it’s 10 degrees Celsius, they can often get down to 10 degrees Celsius.
One species in Peru, I think, was found to get down to 3 degrees Celsius when the outside was that cold, but usually when it gets really, really cold, hummingbirds increase their energy expenditure a bit to maintain some minimum tolerable body temperature in torpor, and they try not to let their bodies go below that.
[Chelsea Benson] Something that’s popping up a lot is because they’re so cold, and they can’t rouse very quickly it makes them susceptible to predation. Is that true?
[Anusha Shankar] There’s two ways to look at it. One is that, yes they can be susceptible to predation, but they’re really small, and they might be hard to find. Among the scientists that have published papers on hummingbirds torpor, we know of one who studying hummingbirds in cave who was able to find hummingbirds in torpor.
And one more in the 1970s, where they found one hummingbird in the wild in torpor. So they’re really hard to find at least by humans. And the other side of it is that for something like a heat sensing snake that was trying to find a hummingbird at night, a cold humming bird is much harder to find that a warm hummingbird, and so torpor might help them avoid predation from things like heat sensing snakes.
[Chelsea Benson] Very cool. All right one last question, Erich. Because you were looking at temperature and body fat, how do you measure body fat on hummingbird?
[Erich Eberts] Yeah good question. Good question. So recently there’s been some new technology that’s come out called quantitative magnetic resonance, and essentially what this does is it’s really, really similar to MRI, magnetic resonance imaging, but instead of pumping out an image of your knee or whatever, it gives you the amount of fat, the amount of lean mass so like muscle and other sort of non energetic tissue and the amount of water mass in this bird. And it’s really nice because it’s just this rather small machine. It’s really expensive, but you just insert the bird into this tube. The bird just has to be immobilized. It doesn’t have to be anesthetized, it’s fully alive and awake. And the scan just takes two to three minutes or so. And it’s really, really accurate.
So that’s essentially how I measure the body composition and get the amount of fat. And then to specifically get that amount of fat at the time that the bird enters torpor at, and I do the QMR, the quantitative magnetic resonance, measure their body composition in the evening. And then I use a method called respirometry which measures the oxygen and the carbon dioxide that the bird is consuming and producing. And from that we can estimate the amount of energy that the bird is using throughout the night. And so using those data, I can calculate that level at the point of the night that the bird enters torpor at that level of fat.
[Chelsea Benson] That’s fascinating and very high tech. How cool.
All right, Anusha let’s take some time to talk more about the work that you’re doing. And Thanks Erich for sharing.
[Anusha Shankar] Sorry, lag a little bit. So yeah I will share my screen in a minute. But for my PhD I studied a few different things about hummingbirds broader than torpor and then I got really into torpor, but I was studying broadly how they manage their energy in a natural landscape.
And so we were funded by this NASA grant to look at how hummingbird energetics interact with the energy availability on a landscape like the flowers and how they’re distributed, and how does hummingbird’s energy budgeting change as the landscape changes. And so we found some pretty cool stuff by working with hummingbirds in Arizona. And I also spent about a year in Ecuador trying to collect data on things like this.
And we found that they’re really flexible in how they use their energy. If the flowers in their landscape are super clumped, this was one species in Arizona. But if the flowers in their landscape are super clamped, they can sit in one place and not spend much energy, and keep feeding, and not spend much time hovering and flying. But if the flowers are really sparse and dispersed in their landscape then they can spend a lot of time and energy trying to get between flowers and forage for food.
And so we’re able to see how they manage that energy in relation to the changes in the landscape. And then I also really got interested in torpor use. And we studied torpor in about 12 species in Ecuador and in Arizona. And I’ve gotten much more into that. So going from the whole animal to what’s happening inside the body is what I’m really interested in.
So I’ll share my screen and show you. Someone asked for pictures of the hummingbirds that we were talking about. And I’ll show the one that Erich was talking about because I found this pic. This is the Shining Sunbeam that he fell in love with in Ecuador. It has that beautiful rainbow color on his back. And you wouldn’t see this when the hummingbird is just floating from the front. It just looks like a brown hummingbird.
And this is a male with a full coloration on his back. So this is a hummingbird, I also use thermal imaging and I also use the respirometry because those are really convenient ways of studying things that are otherwise really secret and hidden about these animals. And so this is a video of a hummingbird that’s asleep. It’s maintaining a high body temperature. This is its eye which is– I don’t know if you can see my– this is its eye which is really warm, and this is its tail, and this is its beak. And it’s using up energy pretty quickly. And then this is a hummingbird in deep torpor where like Erich showed, it’s really, really cool.
Its whole body is down to some 16 degrees Celsius, which is like maybe 50s or 60s Fahrenheit, and it’s saving a bunch of energy by doing that. And so now what I’m focusing on is measuring this gives us the body temperature or the surface temperature. But, measuring it together with their metabolic rates to see what exactly– What’s the trigger? Which one goes first? Does the body cool first or does their metabolism slow down first, and then what happens to help them get out of it.
[Chelsea Benson] Sweet. Thank you so much. I’m just scanning over in the Q&A to see if there was a follow-up question. I don’t see one exactly for what we’re talking about. Some people are wondering so when they’re in torpor like you showed and you said, how do they maintain– can they perch? Can they grip? Are they immobile? What is a bird in torpor look like.
[Anusha Shankar] Yeah. I think that addresses a lot of the other questions that some people were asking about seeing at bird at a feeder, is it in torpor or not. When a bird is in torpor, it’s cold. It’s not really responsive to what’s happening outside. It’s heart rate and it’s breathing can really slow down, so I’ve watched these hummingbirds, when they’re in torpor they don’t take a breath for like 10 seconds sometimes and then they take four deep gasping breaths, and that is a: [imitates gasping rapidly]
And then they don’t breathe for a while. So their metabolism is just so different. And so they’re not doing that in the three or four minutes that you see them being inactive at a feeder. But they are able to still grip somehow. The muscles in their legs have this ability to grip onto things no matter what, and so even when they’re in deep torpor, they will be holding on to the branch. Because otherwise they’ll just fall and die probably. Which is not good.
[Chelsea Benson] No. Not so much. Not a good strategy for survival. So another thing that people are asking is, is there like that video is pretty dark with the bird in torpor. Is there a visual cue of when a bird rouses itself? Does it actually shiver? Can you see a rustling of feathers? And then that rewarming must use a lot of energy, is that correct?
[Anusha Shankar] It does. It’s not as much energy as being at a high body temperature but it’s definitely more energy than in torpor than they need. So if they’re– in the morning if you see a hummingbird at a feeder that’s not moving, its eyes are closed. It’s sitting in this hunched position with its beak up, and its metabolism is slow, its body is cold, it’s torpor and probably doesn’t have the energy to get out of it. But they do kind of shiver and shake and they move their heads and they sometimes start doing what in my mother tongue is called [non-English speech] which is like: [imitates smacking lips]
I don’t know if there’s a word for that in English. They just kind of suck on that. They just do that a bit. Yeah. So there’s definitely these signs and they start, they go from– You can see the puffiness change. So in the beginning of the evening, the feathers are very flat. And then as it gets colder at night, they start shivering and puffing up. And then they get puffier, and puffier, and puffier. And in torpor, they’re just like these puffy balls sitting like this. And then when they warm up they’re coming back to not being puffy.
[Chelsea Benson] Yeah–
[Erich Eberts] I’ll also just mention that we don’t know what triggers arousal, that’s one of the big questions that’s still outstanding. And yeah it’s a really interesting question. And it’s similar to what is starting entry? Does the metabolism spike first or does the body temperature have to get up a little bit before the metabolism can start spiking?
Another sort of interesting thing that I’ve seen only a couple of times when I’m looking at the bird in the morning arousing well, I’ve seen the bird actually just start sort of shaking back and forth and it looks like it’s shivering and trying to generate some metabolic heat so that it can get up rather quickly. So yeah. Again, the arousal question is still an interesting outstanding one.
[Anusha Shankar] But they often arose like an hour before sunrise, so I think it has something to do with the circadian, with the light cue because they somehow know when– Even animals in hibernation, it’s amazing how do you keep track of time when you’re barely functioning. I can’t even keep track of time when I’m fully functioning. It’s insane that they are be able to know when to get up. That’s something that’s telling them in their brain get up now because it’s going to be light out.
[Chelsea Benson] That’s right. Some people are asking about other energy saving strategies that hummingbirds might have. So one thing that’s coming to mind, Eric is that Ruby-throated hummingbirds can migrate across the Gulf of Mexico, which is a really long way. And so what kind of energy demand is that? Is there any way that they can save energy, maintain energy. What does that look like? Not only during migration but also like daily seasonally.
[Erich Eberts] Yes. So of course hummingbirds, they have some of the highest mass specific metabolisms of any vertebrate and when we say that, it’s we’re really talking about hovering metabolism. And typically in the daytime when the birds are hovering around, they have access to food.
So the sort of supply demand equation is a little bit sort of balanced during that daytime. But then at night the sort of equation gets a little bit more uneven where the birds still have relatively high metabolic rates to maintain normothermy versus they can’t eat at all. So torpor can allow them to balance out that equation and those energy demand versus supply things a little bit better.
But then of course you have these seasonal periods like molting which is really energetically expensive, and, say, migration where they have to really fatten up. And they’re experiencing really, really high energy demands. But again, torpor at least in the migration period can help them sort of prepare for that migration and bulk up those fat reserves. And back to what Anusha was talking about, about their flexibility and some other energy saving mechanisms. Is simply just to go chill out instead of flying around all day. If for example a storm comes through and there’s not really too much food available, maybe the birds instead of flying around, doing their courtship displays will just hang out and be able to feet a little bit less.
And then in regards to flying over the Gulf of Mexico. It’s a sort of a really interesting question that I don’t believe has been really explicitly proven yet. Unfortunately, the Ruby throats are just too small to be able to put radio tags on to be able to track them throughout their whole journey.
Some researchers around the Gulf of Mexico though, were able to tag juveniles. So they tracked the juveniles all the way around the Gulf of Mexico. So this sort of makes us question– like they weren’t able to tag the adults. So we don’t know exactly where the adults go. There is a hypothesis that the adults have this experience where they know that there’s something else on the other side of the Gulf of Mexico.
So they know that it’s OK to fly straight across versus the juveniles don’t really know what they’re getting into. So maybe they start flying, they get a mile offshore and they’re like Oh oh, am I going to be able to make it? And they turn around and just go around the Gulf and do this more of a fly and forage strategy where they’re flying a little bit, eating a little bit flying a little bit, eating a little bit. Rather than eating a whole bunch, bulking up a whole bunch of energy stores and then just making one direct flight.
And then there’s also some other– if that is what the adults or at least some of the adults are doing is going straight across the Gulf of Mexico. I’ve talked with some of my collaborators, just ideas and hypotheses that there’s a possibility that while the birds are in forward flight, and for that long period of time, they could theoretically shut off some of their metabolism that’s not really important for that forward flight. So this might be similar to some I think Dolphins shut off half their brain when they’re sleeping. So we’ve talked about some ideas. Maybe hummingbirds could somehow reduce their metabolism even while they’re still flying which could be really, really cool. I don’t know of anyone who’s really explicitly starting to look into that, but some interesting ideas.
[Chelsea Benson] It’s fascinating. The One thing I love about science and research is there are always more questions. There’s always something new to learn that sparks another question, and as you’re talking, all these changes in technology can really help us ask even more interesting questions. Oh something that I saw and I just wanted to clarify is we often think of hummingbirds and their food source as like the nectar at the feeders. But I think we should just be real clear that hummingbirds have a lot of different food types. So Anusha, what are some of the hummingbirds’ favorite foods?
[Anusha Shankar] There’s something called the hummingbird pollinated syndrome in plants where the more red or bright orange, pink flowers are the ones that they tend to visit, and the flowers that they feed on usually have longish corollas, or a flower shape is more long than broad and wide. And so. Yeah, bee balm is a really common one. Salvia species are really common.
There’s so many in South America, but I think the hummingbird– you should look within your region what’s the most common hummingbird family of flowers are. And that’s a really great– they seem to prefer flowers or feeders in general. So if you can do that in your garden, rather than having feeders, that would be amazing. Otherwise, I keep wondering if there’s feeders all the time, why don’t they just sit there the whole day and not go to flowers. I think it’s because they prefer flowers.
[Chelsea Benson] And insects too, insects can be a big part of some hummingbirds’ diet. So in addition to planting flowering plants for your hummingbirds, also promoting insects within your garden can be really beneficial because those are a great food source because they have a lot of protein.
So when we’re talking about fattening up, this is a good thing to have bugs and the nectar and of course our sugar feeders that we put out. I’ve seen a few questions related to climate and impacts that it can have on climate as in climate change, sorry. And the impacts it can have on hummingbirds. So we know that there has been gradual shifts in things like insect emergence, plant growth, in temperatures, but there also are like big storms, forest fires that we see that are more dramatic examples of climate change.
And so, Anusha, I was wondering if you could share a little bit about how climate change, whether it’s more gradual examples or large scale examples has impacted hummingbird species, that I know of. I know this is not directly related to both of your research but I think it’s a question that a lot of people are curious about.
[Anusha Shankar] I think it’s a complicated one, anything climate change-related, there’s a lot that’s going on. But so I think that they’re really flexible energetically. They’re able to respond to a lot of different changes in the environment at least in the short term pretty easily like I saw in that study with the flowers changing in Arizona and how the hummingbird was able to change its date and how it used its time depending on that.
But in the long term, I think the plants might shift with climate change. I just got a question from a reporter by email a few days ago saying she lives in Los Angeles, and the flowers are flowering a few months earlier. And so you can imagine that if the plants in the landscape change their timing, then hummingbirds would be affected because the flowers that they feed on will change.
So I think temperatures could change that could directly affect their physiology, yes. But they could be flexible enough to deal with it in the short term. But the other changes in their landscape like habitat availability, and flower availability, and nesting habitat and things like that could change and affect them much more drastically in the shorter term. And warming temperatures could affect the torpor use. It could make being not in torpor at night, being asleep at night more expensive because– or less expensive. But then torpor would become less energy saving. Really, it depends on where they live and what temperatures they’re experiencing. It’s not a straightforward question.
[Chelsea Benson] And as you pointed out at the beginning of the webinar, hummingbirds are an incredibly flexible species. They live in all different types of habitats and can shift quite– and I wouldn’t say easily I don’t think that’s the right word, but they have the ability to make changes. Not that that shouldn’t diminish the importance of climate change, but at least with hummingbirds in the short term they do have flexibility. Erich, did you have anything you wanted to add on to that? I wasn’t sure.
[Erich Eberts] No. Not really. I mean, I think Anusha summed it up pretty good, pretty well. They’re one thing, yeah if those flower abundances let’s say in one particular area go down and the birds are on a short term timescale able to adjust and be flexible with that by using torpor more often, you might see some other downstream effects of sleep deprivation and other impaired immune function and stuff like that. So again, it’s a really complicated question but important.
[Chelsea Benson] Yeah. So we have a few minutes left. I’d love to learn more about what you’re looking forward to with your research. What are you hoping to learn next? Is there anything we should look forward to? Anusha, if want to want to start us off, and then Erich.
[Anusha Shankar] My longer term goal is to go back to India and apply for faculty positions to be able to work at a University there. And we don’t have hummingbirds in India, unfortunately, but we have a convergent species, a group of species called the sunbirds. So they’re not evolutionarily branched off from hummingbirds at all, they were split way long ago in the evolutionary tree. But they’re both nectarivore groups, so they feed on nectar from plants. And I would really like to study a range of birds in India and their metabolism, and whether torpor is a thing among Indian birds, we don’t know that. And we have a lot of birds. So that’s my longer term goal.
[Chelsea Benson] It’s exciting.
[Erich Eberts] And I’m not exactly sure what I want to do, but along the lines of hummingbirds, I still think it’s really important to be able to figure out what completely free living hummingbirds are doing. Of course, most of what we know about torpor in hummingbirds is coming from laboratory studies, or at least semi-captive studies. And I mentioned radio tags earlier are a way to track hummingbirds.
And Ruby-throats are too small still to be able to do that with, but larger species in the tropics, we might be able to radio tag those guys, follow them around, find where they sleep and then set up thermal cameras so that we can be extremely non-invasive or totally non-invasive, and still be able to see how often the birds are using torpor under these completely natural contexts. I think that would be really cool and really interesting.
[Chelsea Benson] That’s awesome. Let’s see, a few more questions coming in. Well, I shouldn’t say a few. A lot! So thanks to our audience for all these really amazing and thoughtful questions. Some people are wondering about hummingbirds and migratory hummingbirds. Do they come back to the same yards, areas every year? You guys what have you learned from–
[Anusha Shankar] Some do, because people who band hummingbirds to put little aluminum-numbered bands on their legs to track individuals have found them running multiple years in a row. Erich is much more knowledgeable about migration in general, but these–
[Erich Eberts] These are the bands. They’re tiny.
[Chelsea Benson] Oh, it’s so tiny. So–
[Erich Eberts] Less than a millimeter wide.
[Chelsea Benson] So that’s on a safety pin, it looks like. Oh my gosh.
[Erich Eberts] Yeah exactly. They’re really, really tiny. But, yeah exactly. So here at my field station, we’ve been banding hummingbirds for, I don’t know, about 10 years or so. And we frequently get birds that have come back year after year. I think earlier this summer, I caught a bird that we banded six years ago or something like that. So yeah they definitely are coming back to the same areas. That said, we also get new hummingbirds that are coming in from other areas as well. They have extremely good spatial memory.
[Chelsea Benson] So for everybody who’s like my hummingbird came back, it could be.
It’s possible. What’s the lifespan for a typical hummingbird like on an Anna’s Hummingbird or a Ruby-throat?
[Anusha Shankar] The average used to be about seven years and the longest a banded bird was recaptured after it was 12, that’s pretty long. The smallest of the perching birds or the passerine birds, would live only two or three years. And hummingbirds are able to live way longer. And I think it might be because they’re able to use torpor and save energy and not be functioning normally during the night. But no one has tested that yet as far as I know.
[Chelsea Benson] Are there other birds that use torpor besides hummingbirds? Like you said you want to study sunbirds, Anusha, but are there other birds that are known to use torpor regularly like hummingbirds do?
[Anusha Shankar] Sunbirds don’t seem to use torpor like hummingbirds do as far as we know, but so it’s only been studied in less than 1% of all bird species whether torpor occurs in those birds and there’s 10,000 bird species. So there’s not that many studies on torpor in birds in general, but it’s been known– OK, so torpor can be many things. It can be a lowering of body temperature that’s just a little bit or a lot.
And the bird species, the groups that can lower their body temperature by more than 20 degrees Celsius that’s only three, the nightjars, the hummingbirds and mousebirds. The others can maybe– like even pigeons can sometimes lower their body temperature five or six degrees Celsius and save a little bit of energy, in shallow torpor but not, yeah not deep torpor as often.
[Chelsea Benson] Another reason we should just love and appreciate hummingbirds. So fascinating. Do you– I wanted to give Erich and Anusha, I didn’t know if you saw any questions pop in that you wanted to address before we wrap up.
[Anusha] I saw one: When do they sleep, if they’re using torpor at night? And I think that gets to a lot of the questions about sleep versus torpor. I think in the beginning of the night and in the end of the night when they get the amount of torpor about an hour before sunrise on average. And I think that might be the time when they sleep, but yeah I don’t know the answer fully to that question. They definitely don’t get that eight hours of sleep like average humans do.
[Erich Eberts] And it’s also important to recognize that they’re not going into torpor every single night for the entire night. So on a day, a particularly good day where they had a whole bunch to eat and they stored a whole bunch of fat, and maybe they start the evening with really high amount of fat and don’t actually ever have to end up using torpor that’s probably their optimal goal for each individual day.
And then torpor, if they don’t quite get to their optimal level of evening fat, torpor can hold them over for the rest of the night after they hit that threshold. So if they start the night with 10% fat and they hit their threshold at halfway through the night, they’re still sleeping for half of the night. So that’s probably also some time that they can get some snoozes.
[Chelsea Benson] Great. Thank you. So thanks to our audience for asking such great questions. This was really fascinating to just scroll through and see all the ways that you’re thinking about hummingbirds, and the energy they use and it’s just really great. And Anusha and Erich, thank you so much for sharing your knowledge with us today. I hope that you guys had as much fun as I did, and I know our audience is really engaged. So thank you so much for your time.
[Erich Eberts] You’re welcome.
[Chelsea Benson] So I’m going to be– sorry.
[Erich Eberts] No, I was just saying thank you.
[Chelsea Benson] The classic Zoom cut off.
So I’m going to be emailing all our Zoom attendees with the recorded webinar and some of the links to Anusha and Erich’s research. He also has a really great video about his research which I’ll add to that. And also I have a downloadable poster of hummingbirds of North America, so you can get a copy of that poster that was illustrated by an artist at the Lab of Ornithology. So if you’re watching for Facebook or if you’re watching on Facebook, check the comments for the links and the resources. And for the Zoom audience, I’ll be sending out that email tomorrow.
This webinar is part of a series. We’ve been spotlighting programs and research from around the Cornell Lab and beyond. So thanks to the University of Toronto Scarborough for letting us borrow you for a couple hours here, Erich.
And we’re now learning about birds not only in our backyards, but around the world. And this work, including today’s webinar is funded primarily by people like you, our audience who choose to become a member. So if you enjoyed today’s webinar, I hope you’ll consider becoming a member and you can visit birds.cornell.edu to do that. That is all today. Thanks again, Anusha and Erich. And–
[Anusha Shankar] Thank you–
[Erich Eberts] Thank you.
[Anusha Shankar] –you are a wonderful host.
[Chelsea Benson] –thanks to our audience. Yes, so fun. And yeah, thanks again. Have a great afternoon, everyone. I hope everybody gets out and looks for some hummingbirds.
All right bye.End of transcript
Hummingbirds delight with their brilliant colors and dizzying flight. But all that nonstop activity comes at a high energy cost, so how do hummers meet their calorie needs? Join researchers Anusha Shankar from the Cornell Lab of Ornithology and Erich Eberts from the University of Toronto Scarborough as they share what they’ve learned about how hummingbirds use energy. Discover the demands of migration, the nesting season, and even just getting through the night; plus learn how sleep differs from torpor. We’ll also spend time answering your questions about these flying jewels during live Q&A.