Thumbnail image: Richard Simmonds/Macaulay Library
[Chelsea Benson] Let’s get started. So welcome to tonight’s webinar from the Cornell Lab of Ornithology. We’re going to be discussing the science of seduction, just in time for a little pre-Valentine’s Day event.
My name is Chelsea Benson. I am on the Visitor Center team at the Cornell Lab and I’m going to be facilitating tonight’s conversation. Joining us this evening are Laurel Symes. Hi, Laurel.
[Laurel Symes] Hello.
[Chelsea Benson] We also have Vanya Rohwer. We have Robyn Bailey.
[Robyn Bailey] Hi, everyone.
[Chelsea Benson] Jordan Boersma.
[Jordan Boersma] Hello.
[Chelsea Benson] And also Carrie Branch.
[Carrie Branch] Hey there.
[Chelsea Benson] Wonderful. Thank you all for joining us. They are going to be sharing a bit about science and seduction and what it takes to find and attract a mate. I want to thank you all for being with us tonight and we’re going to be hearing more from our panelists after a few quick announcements. So they’ll rejoin us in a little bit here.
Our webinar tonight is hosted from Ithaca, New York, and I’m going to read a statement acknowledging the Indigenous people as the original inhabitants of this area.
Cornell University is located on the traditional homelands of the Gayogohónǫ’, the Cayuga Nation. The Gayogohónǫ’ are members of the Haudenosaunee Confederacy and 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. We acknowledge the painful history of the Gayogohónǫ’ dispossession and honor the ongoing connection of Gayogohónǫ’ people, past and present, to these lands and waters.
For those of you who are not familiar with the Cornell Lab Ornithology, welcome. We are home to a community of researchers and supporters from around the world who appreciate birds and insects, as you’ll hear this evening, and the integral roles they play in our ecosystems.
Our mission is to advance leading edge research, education, and citizen science that helps solve pressing conservation challenges. We have a couple more tech notes before we get into the presentations tonight. Closed captioning is available on Zoom. If you want to turn those captions on or off, you’re going to click that CC button at the bottom of your Zoom screen and that will enable you to either hide them or see the captions for tonight.
Tonight’s program each of our panelists that I just introduced, they’re going to be sharing a short presentation and the final program is dedicated to a Q&A from you, the audience. For those of you on Zoom, you can click that Q&A button and type in your questions. We’re going to answer some questions live and we’ll also be typing our responses. So you can check the answered column to see those responses.
We’re going to only use the Zoom chat for technical support and to share information. And I have very wonderful colleagues behind the scenes who are helping me out. So thank you to Leo and Katherine for doing that. We’re also streaming live to Facebook.
And if you’re our Facebook audience, hello there, you can add your questions to the comment section in Facebook and they’ll get passed along to myself and the panelists. All right. All that said, let’s get started. So our first panelist is Robyn Bailey. Hey, Robyn. Welcome back.
[Robyn Bailey] Hey, Chelsea. Thank you.
[Chelsea Benson] Robin is the NestWatch project leader. NestWatch is a citizen science project here at the Cornell Lab and tonight Robyn is going to start us off by imagining what it would look like if birds use dating apps.
She’ll share what makes birds swipe right in the spring. We’ll dive into different characteristics on display and discuss the lesser known points of a standout partner. All right, Robyn. Take it away.
[Robyn Bailey] Sure, Chelsea. Let me just share my screen. Make sure I grab the right one. Turn on. OK. How is that? Give me a verdict if it’s good. OK, great. Thank you so much. All right. Thank you everyone for tuning in tonight and I wanted to just kick off our little talk about avian seduction and one of the most relatable ways that I could think of, by imagining birds as users of online dating apps.
I met my husband on match.com. So that was the inspiration behind this little endeavor and I like to imagine that in the modern world with all these apps that birds, if they have thumbs they would be swiping right and left a lot.
So many of you already know about some of the well-known bird romances like the birds-of-paradise and blue-footed boobies and of course, the showy species like peacocks. But I wanted to talk about some of the ones that are not so celebrated in their efforts at romance. So let’s take a look at some of the lesser known romantic strategies out there.
OK. Before we do that, I want to get you acquainted with some key terms when it comes to mating strategies. We’ll talk about monogamy, the most common system among birds, which is a system in which one male and one female are paired either long term or just for that season.
We’ll talk about polygamy, which is the next most common system in which one male will mate with multiple females. Polyandry, which is rather uncommon. That’s the system in which one female will have multiple male partners. And then polygynandry, which is a really rare system. We’ll talk about that a little bit later. And then leks and extra pair of fertilization.
I just wanted to preview these terms for you that I’ll use. And that last one will come up again later on in the panel so keep that in mind. Now usually with births, it is the females who choose among males. But as we’ll see with polyandry, sometimes males get more of a choice.
No system is better or worse than another but each has been refined over evolutionary time to suit the particular circumstances of each species nesting environment. For birds, it’s all about passing on genes and there is a fascinating variety of ways in which they can do that. So let’s look at a few.
We’ll start with monogamy and I chose Greater Roadrunners as an example of monogamy because they look for long term partnerships. And one of the reasons that I chose the species is that part of their courtship ritual involves long vigorous runs during which the mates chase each other around sometimes for hours.
Chelsea would know a thing or two about that, she’s a long distance runner. So I think that this is a really fun lesser known strategy. They do take breaks but they can be at it for hours and hours. Like kids chasing each other on the playground, they’re running the back roads and the brush in order to find love. So if you’re a road runner and you can’t keep up with your partner, she’s probably moving on.
Another fun thing that they do is they have a behavior where they present sticks to their intended and what is called the stick offering display. And both sexes will offer these sticks, perhaps because both can participate in nest building. So the female does most of the nest construction while the male brings her nest materials to the site.
And finally, during what is called the tail wagging display, the males will present food items such as dead lizards, snakes or grasshoppers to females. And as you can see in the photo, this is usually followed up with copulation.
Another monogamous species is the black vulture. They’re strict monogamous. They’re looking to pair for life. These pairs engage in what is called a circle display. The males will circle the females with his neck stretched high and forward, and exhales loudly into the face of the female.
So just take a moment and imagine the sensory experience of having hot vulture breath express directly into your face. That’s what romance is to a Black Vulture. Pairs also have other things they do. They have a ritualized dance in which they both face each other and engage in this up and down rapid display accompanied by some build gaping.
And in this dance as you can see in the photo, the birds will hold their wings fully spread and ultimately jump up and down in the air while emitting a yapping noise. Fun, right?
Now let’s move away from monogamy and talk about some other mating systems out there. We have Greater Prairie-Chickens are example of polygamy, and they don’t have true peer bonds. So their relationship could be characterized as short term polygamy. Again, polygamy meaning multiple females for one male.
They breed on what is called a lek. This is a communal gathering spot where the males perform their courtship displays to an audience of females. The best performers get to copulate with females, who are usually very selective. Only a fraction of the males will get to copulate. Let’s watch them perform their booming and stomping display in this quick little video.
You can see the air sacs are imprinted on the sides of throat. And if you watch carefully, you’ll see the feet doing a really rapid stomping movement there. The females are the ones without the air sacs on their neck and they’re just watching to see who they’re going to pair with.
The stomping, that’s really cute. OK. That’s enough for that. Let’s move on and talk about a different polygamist known as the Red-winged Blackbird. This bird might be more familiar to you. They do not bother with the legs, they have territories.
The males will hold a territory and multiple nesting females can nest within one male territory. The maximum known harem size as it’s called, for the number of females has been recorded at 15 females to one male’s territory. So that’s a lot of partners to keep up with.
Females too though, are not tied down and have been shown to have high rates of extra pair of paternity. Meaning that multiple males are fertilizing the eggs in one clutch of eggs. Due to this complexity in their breeding system, the parental care that the male gives to the nest is widely varying from some males giving no food to the nest at all to others being really involved and taking care of the young.
And sometimes even have an additional male feeding the young and helping to take care of it because after all, some of his offspring might be in that nest too. There’s a lot going on with your common everyday Red-winged Blackbird.
OK. We’re going to move on to polyandry and our example of that is the Spotted Sandpiper. And in this system, it is the females who fight over males and perform courtship behaviors on their territories in order to secure male mates. Now, this is a little bit different.
The female will do some aerial flying, displays, singing, ritualized nest building displays and other ground displays. The females will even fight over males on their territory. Sometimes stridently, they can be really aggressive and they will also be aggressive to males on their territory that are not receptive to them.
So there’s a lot going on there but she’s doing this because she wants to have multiple simultaneous nests with males performing most of the incubation duties in chick rearing. And in this way, they are able to maximize the genetic output of a single short breeding season. So that’s polyandry.
And then the last one I want to talk about is the very unusual one. So we’re going to move to the high arctic of Canada and Alaska to visit the Smith’s Longspur. It’s one of the most unusual breeding systems known among pastorants. The Smith’s Longspur is polygynandrous. Each female pairs and copulate with two or three males for a single clutch of eggs.
So in this photo of eggs, there might be three or four fathers siring these different eggs. And at the same time, each male pairs and copulate with two or more other females. There’s no territories being defended by the males. But instead, the males follow the females around and guard them closely and copulate with them frequently in order to reduce competition from other males.
And it’s been documented that over a period of one week in the early spring, a female longspur may copulate more than 350 times, one of the highest copulation rates of any birds. And this mating system is just chaotic. So there’s a lot of copulating going on, a lot of pairing up. So that has been your overview of different mating systems of birds and some little known facts about avian seduction. So with that, I would like to turn it back over to Chelsea.
[Chelsea Benson] Thanks, Robyn. That was fantastic. A quick question from the audience before we go to our next panelist. I think you mentioned at the beginning, but what’s the most common mating system for North American birds? Because your research and your work is focused primarily on North America. So is it monogamy, polyandry, what is it?
[Robyn Bailey] Monogamy is by far the most common, and that can mean just for this season or for the life of the bird or the life of one partner.
[Chelsea Benson] Wonderful. And that was so lovely and fun. And I’m still thinking about that vulture breath, which apparently is great for vultures but sounds disgusting to me.
[Robyn Bailey] Lesser known points of attraction.
[Chelsea Benson] Wonderful. Thank you so much for that presentation. All right. Our next panelist is Carrie Branch. Now that we have an idea of what those bird species need to swipe right, we’re going to learn more about another North American bird, the Mountain Chickadee.
And Carrie who is a rose postdoctoral fellow at the Cornell Lab is going to talk about why smart is the new sexy for chickadees. Thanks, Carrie.
[Carrie Branch] Great. Thanks so much. So I’ll be talking about one of our common birds out West actually, and how the dating apps might not be the best place for these guys. Because often on dating apps, you can’t tell how clever someone is and that seems to be very important for our little Mountain Chickadees.
So just a little background to start with, it’s been really widely demonstrated that females will actually differentially invest in their reproductive output based on how attractive the male is that they’re mated with.
And so this may be anything from morphological variation in certain traits or perhaps the complexity or variation in the song that a male may produce. So for example this barn swallow here, we know that females that are mated to males with longer tail streamers will actually invest more in their offspring as is also the case in this example of a pied flycatcher.
When females are mated to males with larger white spots on their foreheads, they’ll actually invest more in reproduction and this could be anything from laying more eggs, so having larger clutches to fledging more offspring to feeding certain individuals more often than others.
So you might be curious as to why females would choose to do this. It has to do with the type of benefits that they’re gaining from their mate. And that might be something like the trait that they’re interested in is associated with a male who is a better parent. So they might provide their offspring with more food items and come and feed the offspring more often.
Alternatively, it may be that if there’s a genetic basis or heritable basis to the trait the females choosing based on, that she wants to get those same genetic advantages for her offspring and that would be something we would call indirect benefits.
And so while we’ve seen this a lot in morphological traits as well in what we call secondary sexual traits actually, so things like plumage variation and song variation. We are actually curious about whether or not cognitive abilities matter when it comes to female mate choice.
So we asked whether females actually increase their reproductive investment when they’re mated to males with better cognitive abilities. In order to address this question, we used our long term study system, the Mountain Chickadees, which again are their non migratory birds that inhabit the Western montane regions of North America shown here. And in the purple regions, you can see the densities are much higher for these individuals.
And we study them in the Northeastern Sierra, Nevada just outside of tricky California. And these birds again because they’re not migratory, they actually choose to cach food items all over their territories when food is really abundant, so like fall and summer, to use later to actually help them survive throughout the winter when food is really scarce.
And we know that they rely on these specialized spatial memory abilities to actually recover their food stores because again, they’re scattered all throughout their territory. So it’s not just one big larger hoard like you might think a squirrel would do.
So you might be asking how we know they perform better or they have better spatial cognitive abilities. And we’ve actually moved into the wild. While a lot of work has shown enhanced cognitive abilities in the lab, if we want to think about reproductive benefits or survival benefits, then we need to take this into the field and actually see what’s going on. So that’s exactly what we’ve done.
And what you’re seeing here is one of our feeder arrays, we have four at our field site. Each feeder array has eight feeders on it and each of these feeders is equipped with a radio frequency identification antenna. And what this does is when an individual like this bird here who has a PIT tag, or a Passive Integrated Transponder tag lands on this antenna, the antenna reads the individual.
And then based on who we’ve programmed access to particular feeders will either open or not open to allow a bird access to a seed reward. So here’s what this looks like. When a bird comes to the feeder, you see that’s the correct feeder for this bird. So he access to a seed and then he flies off.
And what we do again is assign the bird to 1 feeder out of 8. And so we can actually look at their performance over time and see how they’re performing on this task. So for example, this schematic here shows a chickadee’s eye view of our feeder array system.
And let’s say, for example, we’ve assigned an individual to this feeder here highlighted. But what happens is maybe first, they go to this feeder. They don’t get a reward there. Then they go to the next feeder again, not rewarded. But then finally they go to their correct feeder. And so what we’d say is that individual made two errors in that trial. So then we just average the number of errors they make across trials and we can compare that to things like mating preferences.
And we’ve actually shown that individuals that perform better on this task are more likely to survive the winter. And so how do we address whether or not females are actually increasing their reproductive investment? It seems like this is an important trait as these birds are more likely to survive, and certainly females will want their offspring to survive.
So as Robyn was mentioning, the most common pear type in North American birds is what’s called social monogamy. So again, this means that they are paired with one individual throughout the breeding season and maybe multiple years but they will seek extra pair copulations outside of their social bond, often with neighboring birds.
They are also exhibit biparental care which means that the male and the female will both feed the chicks, although the female actually builds the nest, and she also incubates the chicks. And so the females can be quite sassy. So here’s a fun video of a display that females will do when they think of predators near.
And don’t worry, she’s not harming her eggs when she does that. And we take our information, our data very quickly and try to move on so that we minimize the amount of disruption that we cause the females when we come to their boxes.
In order to assess this difference in reproductive output, again, we collected four different measures. So we looked at the actual initial lay dates. When they laid their first egg, that’s often correlated with success of a brood.
We also looked at clutch size. So just the number of eggs that they laid. We looked at brood size, which is the number of chicks they fledge. And then we also looked at nesting mass to see how large the nestlings were. Oftentimes individuals who are larger when they fledge are more likely to survive as well.
So here’s the data for this. And you’re looking at on our x-axis is the mean number of errors of the male. So this is just the male’s response or performance on that cognitive task I showed you, where fewer errors is a better performer compared to worse errors, which are worse performance which would be more errors on our x-axis.
And then what you can see on our y-axis here is our clutch size. And if you notice, we see a significant relationship such that individuals that perform better on the test have larger clutches. But of course, it’s the females who are controlling this clutch size.
So you see that females actually invest more in their clutch and lay more eggs when they’re mated to a male who has better cognitive abilities. And what’s exciting is that this translates to brood size. So again, we’re looking at very similar results here where x-axis, we have the better performers compared to the worst performers.
And again, brood size is associated or significantly associated with better cognitive abilities of the male. So when females are mated to these males that have better cognitive abilities, they’re actually fledging more chicks.
So then the question, of course, is how are they doing this? And this brings us back to our secondary sexual traits, thinking about things like song and plumage variation. So perhaps they’re directly observing these birds caching. So this female here is watching this male cach, but that seems like it would take a lot of time, especially in terms of extra pair paternity choices.
And so we think more likely what’s going on is that females are actually using these secondary sexual traits. So variation in plumage or variation in their song, like these two males are showing here. And if you’re not familiar with the Mountain Chickadee song, it’s a bit different than our hey sweetie, Black-capped Chickadees song. It sounds a little like this. Let me slow it down.
So it’s still rather simple but there are some secret hidden complexities in there that the females can detect. And so with that, I’d like to thank a lot of my collaborators as well as Jen Lobo who was an Illustrator from the Lab of Ornithology and you for your attention.
[Chelsea Benson] Wonderful. Thank you so much, Carrie. I just want to ask a quick question that I’m seeing. So it seems like, is there any indication that males may prefer one female over another in the pair, my question just moved, where it’s typically the female that chooses the mate? So does the male ever have any role in the choosing of the mate or is it always the female for your Mountain Chikadee species?
[Carrie Branch] Yeah. So it’s really interesting. It’s a great question. We’ve got a lot of biases in terms of how we’ve addressed these kinds of questions, both in the sense of our assumption that females are the picky ones and the ones choosing the males. And I think that males absolutely have a say because they are participating in biparental care.
We don’t really know much about that in our system at this point but what was really interesting with this study is that females who performed better on our cognitive tests actually fledged larger chicks. So we didn’t see that association with males.
But that could be something that if males are cuing in to the quality of females that they may be tapping into as well. Our females don’t sing as much and there tends to be some variation in the quality of females that may be harder to detect for males. So stay tuned, but absolutely that is the case for other systems.
[Chelsea Benson] And I have one more quick question. The audience was commenting how elegant the design is for the features and just how cool it is that you have, what was it? The PIT tag that allows it to open and close and reward. Have you ever had any birds that just cannot figure it out?
[Carrie Branch] Oh, we have birds that just abandon the thing altogether. So we do go through what we would call a habituation process. So the birds for several weeks are just visiting the feeder nonstop without the moving door.
And then when we get into our testing period, we actually start where any feeder that they visit the door will open. And then eventually after a week or so of that, we assign them to a particular feeder that where they’ll gain a reward. And oftentimes when we do that, individuals just drop off and stop coming to the feeders altogether.
So either it’s not a high enough quality or we’re really relying on them to opportunistically come to our feeders and participate in this task. So, yes. I think they can figure it out but they might just be too afraid of it. And so the benefit isn’t outweighing the cost for them in that instance.
[Chelsea Benson] Well, that and they’re out in the wild. So there’s plenty of other food sources available if they get a little frustrated.
[Carrie Branch] Yes. Well, in theory. We’re usually doing this in the wintertime but they’re caching all fall and summer before we even start giving them any kind of food item. So they likely have plenty of cash. Whether or not they know that, we don’t know.
[Chelsea Benson] Right. Great. Well, thanks Carrie. We’ll have more questions for you in just a little bit.
[Carrie Branch] Great. Thanks.
[Chelsea Benson] Yeah, of course. All right. So for our next presenter, welcome Jordan. We’re going a little bit further afield. In fact, we’re going across the ocean to Australia and New Guinea to hear about fairywrens who have quite a diverse array of courtship strategy. So Jordan Boersma is joining us. He’s a post-doctoral fellow at the Cornell Lab.
And he is going to show how humans aren’t the only species to woo and mate with flowers. In fact, fairywrens are known to go courting with petals too. All right, Jordan. Thank you.
[Jordan Boersma] All right. Thanks, Chelsea. Hi, everyone. So I’m a new post-doc here at the Lab and I’ve been studying fairywrens for the last decade plus. And so this is a group of birds a family of birds that is native to Australia and New Guinea. And they are special because they are extremely colorful birds, really exhibiting every color of the rainbow.
And obviously a lot of birds are quite colorful. I’m sure a lot of you have noticed that. But the degree to which these birds are colorful is pretty absurd. And also because they’re inhabiting mostly open habitats, their bright coloration is really standing out as they’re moving around in their environment.
So they make for an ideal sort of study system to test questions about what causes these different plumage types and what that’s associated with. And so I’ve been doing this work for a number of years, in the context of these different mating systems that we heard about earlier from Robyn.
And so what I’m going to be addressing today with studies in furry friends is whether or not social monogamy equals sexual monogamy. And there’s a lot of nuance here, which I’ll be introducing with this fairywren group.
And if you find yourself really intrigued by fairywrens in particular, I want to direct you toward the Fairywren Project which was co-founded by Joe Welklin, who’s a recent graduate of the Lab of Ornithology. Just got his PhD this past year. And this is a great resource for just learning a lot more about fairywrens. There are all over social media that have a website as well. And Joe shared a couple of videos that I’ll show you in a little bit here.
So fairywrens typically are socially monogamous. And so what that means is that they will defend their territories from neighboring birds that might be trying to steal their territories or against predators. And so that’s one of the benefits for being socially monogamous, is that you tend to have a mate around you can help with these functions.
And so what I’m going to show you here is a pair of White-shouldered Fairywrens native to the island of New Guinea. They’re defending their territories against this simulated threat. So I placed these cardstock mounts on their territory and I’m playing a duet, so male and female singing together.
And this is going to elicit an aggressive response in these birds. And they might not look very aggressive because these really cute little birds but they are actually being really angry and aggressive here.
So they’re often on their territories ready to ward off threats to their environment but we also know from following around fairywrens that often the males in particular will spend a lot of time off their territories. And specifically what they’ll do is they’ll grab a flower petal and then they’ll fly, in some cases hundreds and hundreds of feet with that flower petal to go try to woo extra pair of females.
They don’t really like bringing flowers to their own social mate. They already have this pair bond intact with their social mate. They like to bring these flowers and fly considerable distances to try to attract other females to mate with them as well.
And so here’s a White-winged Fairywren in Australia with a flower petal. And so hopefully what you could see there was a blue and black bird with a blue flower petal. Now I’m going to show you a couple of Red-back Fairywrens who are petal carrying. These flower petals are a little bit smaller. They tend to bring these red and orange flower petals to neighboring females.
And so much like in humans, flowers seem to be a really crucial component of courtship in this group of birds. And we’re still learning some of the functions of these courtship displays, specifically carrying flowers around. And so I’m going to tell you about just a little bit of research I’ve done in this context in White-shouldered Fairywrens which are native to the island of New Guinea.
And so I’ve been doing a lot of work centered on the role of testosterone in these birds. And specifically for the study I’m going to tell you about today, I wanted to understand what is causing elevations in testosterone because we know testosterone has a lot of functions. It has a lot of functions in birds just like it does in humans, but also comes with a lot of cost.
So you want to surge testosterone when you really get the benefits and not surge it when you’re going to be dealing with a lot of the cost of elevating this hormone. And so what I set out to do is just test what’s causing these major elevations in testosterone.
We noticed that some of the males are really surging testosterone at high levels. And so I sampled some males. We just flushed them into mist nets while they were foraging on their territories just with their mates. And so they don’t have any sort of social stimulus here except for their social mate.
They’re just looking for katydids and caterpillars, the animals they forage on. We flush them into the net without a stimulus. Then we sample some during simulated territorial intrusion. So that’s what that STI is standing for here.
So this these trials look like what I showed you in that first video, where we place these cardstock mount pairs on the territory, play the song and elicit this aggressive response. So we catch males while they’re actively defending their territories against this threat to their territory.
And we sampled males who are actively courting females. They’re out off their territory carrying flower petals flying around, doing displays where they puff up their shoulder patches and try to attract these neighbor females.
What we found is, that is the context where males are really surging testosterone. So when they’re actively courting females, and specifically females that aren’t their social mate. So even though they’re socially monogamous, it’s when they are out and trying to attract these females that they’re not mated to, where they’re really surging testosterone.
And so what does that really tell us, this surge in testosterone? Well, for one we know from other bird species that often testosterone initiates courtship behavior. So you need to surge testosterone in order to express these behaviors.
So it could be that in order to grab a flower petal and fly considerable distances, especially when you’re just a small bird that– fairywrens don’t fly that well, they tend to just be hopping around the grass. So maybe they need testosterone to get the energy to fly all over their habitat with these flower petals.
And also by doing this, by elevating testosterone in this context, they can really get a lot of benefit because they are interacting with all these females outside of their pair bond where they can get these extra-pair matings. Carrie was just talking about this in Mountain Chickadees, extra-pair matings being matings with females that aren’t their social mate. And so it could be that this is a really beneficial time for them to be surging this hormone.
And so do we know whether or not promiscuity is actually benefiting males in this way or are we just assuming here? So to address this, now I’m going to talk about some research done by a former PhD graduate from the Lab of Ornithology, Janelle Dowling, and Mike Webster, who is my postdoc supervisor here.
And they tested that whether or not promiscuity is beneficial to males in Red-back Fairywrens, which are native to Australia. What’s interesting about Red-back Fairywrens is that the males can mate with females when they look just like the females. They can be cryptic brown and white where they’re blending in with their habitat and they can mate like this with females.
But all of the older males and some of the younger males, they’ll acquire this colorful red and black plumage. And this is the plumage that the males prefer. So these are the really attractive mates that females want. And so we know that these males are really successful in attracting mates.
We also know that they are the ones who are grabbing flower petals and they’re flying around and interacting with all these females who aren’t their social mate. And that’s leading to them siring young in the nests of neighbor females.
And so when we compare those red-black males to brown males regardless of their age, it seems like those red-black males are really the ones who are doing a great job of just siring young outside of their nest. So this seems like a benefit of being promiscuous. They’re able to spread their genes throughout the population.
However, while they’re out flying around with flower petals and they’re leaving their mate behind, there are other males who are coming around and courting those females. And those females might decide to mate with those males while their social mate is away.
And oftentimes, there’s a lot of these males around who are flying around with flower petals and that leads to a lot of the young in the nest for these red-black males are not sired by them. They’re sired by neighbor males because they’re spending so much time off their territory trying to court these extra pair of females.
And so we look at just within their own nest, those red-black males aren’t doing as well as the brown males who are just making sure the eggs are theirs. And that’s because the brown males are spending really all of their time on their territory, they’re mate-guarding their females their preening and just maintaining this pair bond with their female.
So we look across extra pair young and within pair young and do the comparison, there it ends up being just roughly equal. So whether you are a red-black male who’s flying around and courting these extra pair females or you’re a brown male who’s spending more time in their territory, it seems like it’s these are kind of equal strategies for just making sure that you are recruiting a lot of young in the population.
So maybe promiscuity isn’t really benefiting the males that much. So that leaves us to wonder, maybe it could be benefiting the females. And this is still an open question in fairywrens but as Carrie addressed in Mount Chickadees and in other systems, we know some things about whether or not females might be benefiting instead of the males.
And so a study that was published, actually just earlier this month in European Pied Flycatcher has found that when females mate with these extra pair males, these extra pair males then are helping them with warding off threats from predators like tawny owls.
So if a female is mating with multiple extra pair of males, then she has this stable of males around who are willing to help her fight off these predators to make sure that her eggs and young succeed because the males are invested in those nests. So it could be that the females are really benefiting from this promiscuity.
And so with that, what I’ll leave you with is that social monogamy does not equal sexual monogamy. In a lot of birds, we see a lot of promiscuity, especially in fairywrens, they are really good case study for this. I’d like to thank– This has been a collaborative work from a number of institutions here. And thanks for listening.
[Chelsea Benson] It was really fascinating, Jordan. It’s just that it goes to show things aren’t always as they seem. I know that some people are asking about fairywrens. They’re so bright and beautiful and one of the questions was, are males always the bright and beautiful of the pair. And what you just showed was no. In fact, the young males can be brown just like the female.
[Jordan Boersma] One of the main focal points of my research has been studying attractive females. So there are some fairywrens, where the females are the ones who are varying in coloration. And so there’s a lot of nuance to these systems.
[Chelsea Benson] And the other question that’s coming up is about your research method. Obviously you’re measuring testosterone and I’m assuming when you’re mist netting birds you’re getting a blood sample, just like in humans like you would test for hormones using a blood sample. Is that true?
[Jordan Boersma] That’s true, yeah. So we capture them quickly and take a blood sample quickly so that it doesn’t reflect the potential effect of us being around. So we make sure that the sample is taken within just a few minutes. So that it reflects the testosterone that’s reflecting the kind of social context that we were sampling them in.
[Chelsea Benson] Absolutely. Great. Wonderful. Well, thank you. I know we have so many questions coming in. So I’m excited to get back into dive into these after our next presenter. So thanks so much, Jordan.
[Jordan Boersma] Thanks.
[Chelsea Benson] All right. So we’re going to take a break from birds because at the Cornell Lab we also study bioacoustics, which goes beyond the avian world. Our next panelist is Laurel Symes. Welcome, Laurel.
[Laurel Symes] Hello.
[Chelsea Benson] Laurel is the assistant director at the K. Lisa Yang Center for Conservation Bioacoustics and Laurel is going to share how tree crickets attract mates with sound. So let’s take a listen.
[Laurel Symes] All right. So Valentine’s Day we might assume that lovebirds have all the fun but actually love knows no boundaries. And after most of our feathered friends have gone quiet, we might think that the party’s over but actually things are just heating up.
This might sound like a nice, peaceful night, but actually this is the sound of thousands of love hungry bugs. Our next suitor is not a bird, it’s a cricket. So this is a tree cricket and you can find these in backyards in Ithaca or really lots of backyards around the world.
And so for tree crickets, every day is Valentine’s Day. This is a male cricket and we’re peering at the back of him and let’s listen in as he calls for females. So what we’re seeing is his wings move back and forth, back and forth. But what’s actually going on here?
So this is another species of tree cricket and this might be an even more familiar sound. This will be the classic, cheesy romantic movie night kiss where two people are walking outside and this is what you hear.
And so this image actually shows us the sound that we’re listening to. There’s six chirps here from a cricket but if we listen closely, there’s actually something else going on. And so what I’m going to do is take this sound and slow it down. Because there’s more going on here than meets the ear.
So this is exactly the same sound that we heard before but now it’s slow enough that we can hear that within each of those chirps, there are actually a series of short little sounds. And so for example, here there are five different sounds that comprise what we hear as a chirp. And each of those five sounds is the cricket taking his wings and closing them.
So if you could look really closely at the bottom of the cricket wing, there are all these little tiny teeth that are just part of the wing. And what he’s doing is taking those teeth and rubbing it against a vein on the other wing. And that makes this big cellophane-like wings vibrate.
And so when we see five pulses here, it’s actually five times he’s closed that wing but it happens so fast that it all comes together and what we hear is one chirp. And so let’s take a listen again to the original full speech sound.
So we might ask, how do crickets here sound? They’re hearing something that’s so fast compared to what we’re able to process. And if you were to go looking for the ears on a cricket, you might start by looking at either side of their head. But actually where you need to be looking is in their front legs.
And so in the side of these red circles, you can see the ears on the cricket. And so this on the left is a really close up image and it’s almost a cellophane-like membrane that’s just embedded into that front leg that vibrates when sound hits it. And so if you want to whisper sweet nothings to a cricket, you really need to whisper into their knees and not into their ears, or not where you would normally find their ears.
So how do we take this information and learn something about the evolution and science of insect song? Essentially, how do we talk sexy to a cricket? So one of the really nice things about studying crickets is that they’re relatively simple songs compared to the elaborate bird song that many of us know and love.
And what we can do is take a computer program. So something relatively simple like this and make a fake cricket and then that gives us the ability to talk to a female cricket. So what you’re seeing on the left is a female cricket that’s sitting under a cup. And then we’re going to take one of these songs that we’ve made and play it to her.
And so you’ll see her turning back and forth and she’s trying to compare how loud the sound is in each of her ears until she can approach the speaker and find where the sound is coming from. And so this allows us to make crickets, so they’ve never existed. You can make them faster slower, higher, lower until you really understand what’s sexy to the female cricket.
And so this is an example of three different species of cricket and what females look for. So this is from Fort Worth, Texas where there are three different kinds of tree crickets that all live in the same place. And each of these dots shows one male cricket with each of the three colors showing the three different species.
So we’re going to focus on this yellow species here in the middle. And what we can do is make sounds that range all across many of these different pulse rates and measure what females like. And so we could see that for this yellow species, females are really responsive to about the average of the male population. And so let’s take a listen. This will be a really sexy cricket, right at the peak of the curve here.
And for comparison, this is a really unsexy cricket where these yellow females just aren’t responding anymore. So one more time, a sexy cricket. And an unsexy cricket. So you might think that they made a mistake and just played the same sound again and again but actually there are two different sounds there that differ by about eight pulses per second.
And so for us, those differences are almost indistinguishable. But for the cricket, that’s the difference between finding a male of your own species and showing up to a male of a different species. So this is a really critical difference for them to be able to make in their auditory system.
And so by being able to measure these sort of female responses, it gives us the ability to study all sorts of things about these populations and how they evolved. So for example, we can look for the same species in many different places and ask, do the females respond to the same thing in each? Or we can look for closely related species to understand how the male song and how the female preferences for that song have diverged.
We can also use these sounds– Oops, sorry. In conservation. So if you think about the rainforest for example, it’s actually really hard to know what insects are there in the forest. But if we think about what sounds they’re making, it’s suddenly much clearer.
So this is about two seconds of sounds where again, we have lonely insects calling for a mate. And what we can do is slow it down again so that we can hear what’s going on and take a listen. And we’re using a machine learning approach to identify the sounds as they happen.
And so this gives us the ability not just to listen to the sounds of insects are making and understand what the insects themselves like, but also to understand what insects are present in the forest, how they’re impacted by drought, by insecticides and by differences in land management. And so even though these crickets are making these sounds to attack females, we can use these sounds to do science as well. Back to you, Chelsea.
[Chelsea Benson] Well, that was so fascinating. I have so many questions that popped into my head and one of those is thinking about how you’re studying sound at such a landscape scale and how other sound like anthropomorphic sound or anthropogenic, sorry, sounds can impact. Big difference there, but how they can impact the sounds that the crickets are able to hear and to make. Have you seen any of that play out in your research?
[Laurel Symes] Yeah, so it’s a really interesting question. There’s a lot of anthropogenic sound in environments now. And it has huge impacts for species like marine mammals, for birds. We did a project a few years ago and played road noise on top of cricket songs.
And one of the interesting and surprising but also unsurprising findings of the study was that crickets are really good at finding mates even in the presence of noise. And if you think about it, they’ve evolved in a community with lots and lots of sounds. And so we’ve had this problem for a long time. It’s not to say that they can’t be impacted by human noise.
But even compared to some of the big really dominant species in the environment, they’re relatively well-suited to deal with this. Now other species and other habitats people have found some different things, but it does suggest that we should be thinking about how animals actually have lived historically to understand how they’ll be affected by contemporary human impacts.
[Chelsea Benson] And one other observation that I wanted to point out that one of our audience members made is they basically said, it’s kind of like the Merlin sound ID for insects, that spectrogram you showed where you could see the different insects that we’re calling throughout the forest.
And I just wanted to put it out there, is that something that you are interested in pursuing on a larger level as far as like having the public to be able to recognize insect calls in such a way?
[Laurel Symes] Absolutely. There’s a lot of different sounds that happen in the environment and most of those biological sounds all trace to species. So being able to understand what animals are making, which sound, just gives us a huge amount of insight, both for personal interests and also for conservation.
[Chelsea Benson] Cool. Well, thank you so much for sharing that really interesting work. We’re going to transition to our final panelist so that evening and then we’ll have a few minutes for Q&A. So our final panelist is Vanya Rohwer.
Vanya is the curator of birds and mammals at the Cornell University museum of vertebrates. And he’s going to be sharing some of the behind the scenes research methods that go into finding what makes a mate attractive and you’re not going to believe some of the bizarre lengths that go into doing that research. So Vanya, if you could share that would be lovely.
[Vanya Rohwer] All right. Well, thank you Chelsea. Bear with me. And OK. Well, so thank you Chelsea. You guys what I would like to do for this final presentation is tell you a little bit about some of the crazy things that researchers do to better understand the traits that are important for mate attraction and for reproductive success in general.
There are so many examples of creative studies that it was really difficult to choose. And so I wanted to start by just highlighting a couple. One is on long-tailed widowbirds where researchers actually elongated tails and then shorten them to see how that affected reproductive success.
In orioles, researchers have brightened males to see how that impacts mate selection and just interactions among individuals. Some work that I did on this morphologies, we did a reciprocal transplant experiments where you took nests from two different locations and you swap them between the locations and then measured reproductive success of those different nests.
And what unites all these examples is an element of creativity and an element of patience. Doing field work requires a ton of patience and I think the best way to visualize that patience is to imagine a researcher just sitting in a blind waiting and watching for birds-of-paradise to perform their displays.
So we’ve had a great introduction to some of the creativity involved in better understanding these traits from Jordan, Carrie and Laurel. And what I wanted to do is tell you guys about certain bowerbirds. This is a male, an adult male with this metallic inky plumage. And this is a female with a blue-green back and this beautiful scaled front.
But bowerbirds are really well known for these bowers, these stick constructions that they make and then these display arenas that are often decorated with blue objects. In this case, a lot of blue bottle caps for this male. And it’s in these arenas that males put on this really extravagant show to females.
And rather than talk about it, I rather just show you guys a video of one of these displays. And we are going to fast forward a little bit. OK. So here you have this male, this dark individual who is showing off to this female. And you can see that female is just standing in that bower and watching that male.
And the display that he just did where he ran across the screen and flipped up his wing, it often startles females and that’s bad for both males and females because it makes both have to work harder to find a mate. So males have to be careful about how intense of a display they do.
There was another, and now notice the female’s behavior. She’s standing towards the back end of the bower and she’s turning her head. She’s evaluating that male. And then in the end, she takes off. She’s unimpressed with this male’s display.
So the key observation that Gail Petrocelli and her co-authors made was that, OK, maybe these display arenas aren’t necessarily just males doing a display and there’s not just a one way transfer of information. Maybe females are communicating to the males as well.
So females could communicate to males through their body language and through their posture while they’re in this power. So for example, a female who is interested in a male who really likes this display, might crouch down and lean into this male’s display.
Whereas a female who was just startled and is maybe still making up her mind, a little hesitant is going to be standing upright and towards the back end of the bower.
So those are pretty complicated behaviors and you imagine that if you’re a researcher, how do you experimentally test like, OK, how does a female’s body language change a male’s display? I mean in a perfect world, you would have total control over a female and you’d be able to change her body language but that’s impossible. You can’t find that in nature.
So you guys, this is where some of the creativity comes in. What Gail and her co-authors did in this particular study is they created their own robotic female bowerbird. And they could control this female with a remote from about 6 meters away from the bower sitting in a blind.
And they could bow this female forward as though she was really interested in the male’s display or they could stand her up and make her seem really hesitant, startled and disinterested. And when I learned about this, my mind was just blown. And so rather than me talk about it, I think I’ll just show you one of Gail’s videos.
OK. I’m hopeful this works but this is one of the robotic females. OK. There she is. You can get a sense of how this bird moves. She’s leaning forward she’s opening up her wings a little bit, closing them and this is all controlled by remote. And here she is standing upright a little bit less interested.
And if you thought males might be uninterested in a robotic female, guess again. Males were more than willing to court these females. So I’ll just pause this right here and give you my takeaway of this.
And that is that many of the presentations that we’ve seen this evening and in this particular example, I’m always impressed at how creative biology really is and how creative designing experiments can be.
In this particular case, you’ve got a blend of ornithology, of experimental biology, of mechanical engineering. Gosh, and also electrical engineering and the fine art, even if it is a bit bizarre, of taxidermy all rolled into one to create these robotic females.
And so as I wrap up, I would like to really end with an emphasis on some of the creativity, even more the creativity that these researchers did with these robotic females. Show you the full range of motion that these birds were capable of. All right. And with that Chelsea, I will give it back to you.
[Chelsea Benson] I hope you’re going to dance after that. It’s all about the body language, right? That was lovely. Thanks, Vanya for sharing. Some people were wondering why the blue in the bower. Is it just they love the color or what’s happening there?
[Vanya Rohwer] They love the color. So you find the bowers that are decorated with the most blue material when they’re usually near urban settings or when they have a lot of access to a blue trash like bottle caps. But when you find bowers that are away from these urban settings, you find the occasional blue feather or often you find snail shells and that’s what that male was carrying around courting that female with.
[Chelsea Benson] That’s so fascinating. Thank you for sharing that research study and I love the fem Bob bowerbird. She’s great. I’d like to invite the rest of our panel to rejoin us. We’re just going to spend a couple of minutes because we’re already at 8 o’clock. I’m not sure how that happened already. But I want to make sure we answer a few questions that are burning in the Q&A and we also had people submit questions to us.
So Jordan, this question is maybe something that you can help us answer. For bird species, particularly for fairywrens that have these elaborate mating rituals, for the couples that, I guess we would say social monogamous couples, are they more likely or less likely to pair again throughout their lives or do they move on from season to season?
[Jordan Boersma] Yeah, they typically stay mated from one season to the next. There are some cases of divorce that happen and we don’t really know exactly what causes divorces in fairywrens but it certainly happens. But more often than not, they will stay mated both throughout the season but also from one season to the next.
[Chelsea Benson] Let’s see. Robyn, I’m thinking this question is probably suitable for you. You’re running a citizen science project where you’re asking people to observe birds that are engaging in perhaps courtship and then breeding and nesting cycles.
It’s a really sensitive time in a bird’s life. As you all just talked about, they’re investing tons and tons of energy into this and we want to minimize disturbance when we’re around birds. So do you have tips for people to one, like pick up on that might be happening? And then two, minimize their disruption of birds that might be engaging in these behaviors?
[Robyn Bailey] Yeah, that’s a really good question. So when you are out in the field birding and you encounter some behavior that you suspect might be courtship or copulation, a lot of times it is something that the birds can do right in front of you.
I know I’ve seen copulation in the field. It can be something that birds can do without being stressed by your presence but there are some sensitive species that you would want to watch out for. And a great example of that would be owls.
It can be really exciting to see an owl. I love owls. Hearing them outside in the woods is great. But what I wouldn’t want to do is just start broadcasting an sound to make that owl come closer because what they’re doing is saying, this is my territory. I’m the best, come see me.
And if there’s another owl and you play a really great loud recording, they could be scared off their territory or it could disrupt the courtship behavior that you’re witnessing. So I always consider it a privilege to witness birds doing their most intimate behaviors and try to give them space.
And obviously nesting is more sensitive than just witnessing a behavior like a song or an aerial flight. So there can be varying degrees of that. But any time you’re around a nest, just be careful to give the birds space. And heed warning calls, any kind of scolding sound is usually a pretty recognizable to us as a sound of like oh, that bird sounds angry so that could be a cue that there’s a nest nearby.
And if you do want to become a citizen scientist and a nest watcher, you can monitor a nest that you find. If you download our app or go to our website, we have a protocol and a code of conduct that you would want to observe any time you’re around a nest.
And so all of the researchers that you’ve seen here have been trained and permitted to do that kind of thing. So we wouldn’t want to do anything like that. We just want to abide by the code of conduct that we have. Yeah, great question.
[Chelsea Benson] Yeah, absolutely. And I think Carrie can attest especially because you’re monitoring clutches of birds, like very, very tiny and vulnerable. But there’s a lot of protocol in place to make sure that it’s done with the safety of birds in mind. So Laurel, question for you. We talked a lot about the insects and their calls. Are they ever calling back and forth or is it a one way? Is it a conversation?
[Laurel Symes] Yeah, so that’s a great question. And the crickets that we were talking about today, it’s the male that will sing and the female will use that sound to try to find him. But there’s another kind of insect called katydids and there’s one particular group of katydids where they actually do it.
And males will sing and then the females will make a short little sound to let them know that, yes, I’m here, I’m listening, keep singing. And in some species, the males will find the females. In some, the females will find the males. So that it might not be feathers only but there’s a lot of variation in crickets and katydid and insect mating also.
[Chelsea Benson] Wonderful. There was a ton of fairywren question. So I’m trying to scroll through and figure out which. So for the females that are approached with these lovely gestures of flower petals, do they ever do anything with the flower? Like, how do they receive these flower petals that are offered? What’s happening on the female side?
[Jordan Boersma] Yeah. I think it’s similar to what Vanya was showing us with the bowerbirds. The females don’t seem to ever do anything with what’s the what’s in the male’s bill. So they see the flowers and they I think kind of evaluate maybe the flowers in combination with the plumage coloration and make their decision based off that.
I’ve never seen them grab a flower. Sometimes males fly around with food and so males will bring this gift of food to an extra pair of female. And she’ll take that but yeah I’ve never seen them actually pick up the flowers.
[Chelsea Benson] And Vanya, you had to kind , of whittle down your talk to like one kind of crazy research strategy that was used. Is there another one that you were just dying to tell us about that just didn’t fit in your presentation? Like, what’s the wildest one that you can think of?
[Vanya Rohwer] There’s so many. The one I think that’s just so just clean and tidy is that long-tailed widowbird experiment, where they captured individuals and then they gave males longer tails by emptying feathers together where you cut these feathers and then you put a little needle in them. And then you gloom back together. It’s like, man, that’s such a tidy. Simple in a lot of ways experiment but to pull it off, how cool.
[Chelsea Benson] Yeah, that’s fascinating. And just to think as you were saying before, the creativity that goes into designing, the research that a lot of you are presented today is just astounding.
So I want to thank you all for taking time to share your work. And Robyn, just to share the different lesser known courtship strategies that are out there in the North American bird world.
This has been really fun and enlightening and our audience has been really engaged. And I’m sorry we didn’t get to more questions but we’re already over time. So Robyn, Vanya, Carrie, Jordan, Laurel, thank you so much for being with us tonight.
[Carrie Branch] Thanks, everyone.
[Vanya Rohwer] Yeah, thanks a bunch.
[Chelsea Benson] Tomorrow I’m going to be emailing our Zoom attendees with the recorded webinar and some of the links that we talked about today. And if you’re watching on Facebook, you can check the comments for those links and resources.
And today’s webinar is part of a series we’ve been spotlighting programs and research from around the Cornell Lab. And this work is funded primarily by people like you who choose to become a member.
And if you enjoyed the webinar, I hope you’ll consider becoming a member by visiting birds.cornell.edu. That’s all. Thank you to our audience for joining and to our panelists for these wonderful presentations. And to everyone, have a great evening.End of transcript
Think you know everything about the birds and the bees? Think again! Join our webinar to hear the latest buzz from researchers who study the Science of Seduction. Learn how smart is the new sexy (at least for chickadees), listen to sounds that make crickets swoon, and see how fairywrens use flowers to romance new partners. You’ll discover the diverse array of animal courtship strategies–all of which will be infused with natural history and first-hand accounts from the field.