Hello, everyone, and welcome.
Thank you for coming to today's Badger Talk.
This talk is brought to you by the Friends of Manona Senior Center.
And today, I am Lisa Brooks.
I am the program coordinator for the Manona Senior Center.
We are open weekdays, and we provide activities, classes, and fitness programs
that enhance the lives of those 50 and better to enjoy.
I am Lisa to introduce today's guest, Dr. Lauren Readers,
a professor in the Department of Biology at UW-Madison.
Dr. Readers received her undergraduate degree from psychology
from the Miami University in Ohio
to pursue a longstanding fascination for birds.
Her first study was how homing pigeons returned from distant locations
during her PhD at Bowling Green State University.
She continued to study birds and began her research
related to why birds sing at the University of Leisure and Antwerp in Belgium,
followed by postdoctoral studies at John Hopkins University.
Please help me in welcoming Dr. Readers.
Thank you so much, Lisa, for that wonderful introduction,
and thank you to the Manona Naturalist Club
for inviting me to give a talk today.
And thank you all for coming on such a cold, snowy Wisconsin winter's day.
I really appreciate that you came out for this.
All right, so my research that I've been conducting for over 25 years
and most of my years I've spent at the University of Wisconsin
is focused on, I like to call it, why birds sing.
And I study how hormones, environmental and social factors interact
to control singing behavior in songbirds.
And I'm going to share with you the species that I study the most,
and many of you will groan, especially if you are burgers,
but most of my research is on European starlings.
All right, so I know.
The reason this will upset some of you is because starlings are invasive songbirds,
they're tremendous agricultural pests,
they kick native songbirds out of their nest sites,
and Aldo Leopold actually called them signs of a sick environment.
But they are amazing singers, so you may leave here today
with at least a small appreciation of starlings.
I'll talk a little bit about my research,
but I'm going to speak today more broadly about what it is
biologists have discovered about why birds sing.
So vocal communication is critical for successful social interactions
across a wide range of animal species.
And for most species, vocal behavior is not learned.
So we are all familiar with the fact that different species produce their different species specific songs.
Even children can tell you what sound different animals make,
so we're familiar with the fact that frogs croak, cows moo, and cats meow.
And for the vast majority of these species, these vocalizations are unlearned.
A cow does not need to listen to adult tutors, to practice its moo's,
to eventually moo appropriately as an adult.
A cow at some point during its life is going to moo.
A cat, even if it's never heard other cats meow, is going to be capable of producing a meow.
However, although it's very rare,
there are some animals that must learn at least some of their vocalizations from other animals.
Typically they learn from their parents or other adults, or they learn from tutors,
and they practice their vocalizations, and those are the vocalizations they'll produce as adults.
So this vocal learning is really rare.
We see it in only a few animals.
Elephants are vocal learners.
Songbirds, which we're going to focus on today, are also vocal learners.
And then other classes of birds that aren't technically songbirds,
but hummingbirds, parrots, they are famous for their vocal learning.
Dolphins and whales learn their vocalizations, seals learn some of their vocalizations,
humans, we're familiar with the fact that we learn our vocalizations from adult tutors,
typically our parents, also our peers shape the form of vocalization we produce.
And then there's evidence for vocal learning also in bats.
But when it comes to vocal learning and production, songbirds are in a league of their own.
So it is estimated that there are about 10,000 bird species on the planet,
and almost half of them are songbirds.
And here are some photographs of songbirds that are present in Wisconsin.
Not all of them are here right now in winter, but in spring you can see yellow warblers,
cardinals, indigo-bundings, and meadowlarks here in Wisconsin.
Right now, many of these species have migrated south, except for cardinals.
You'll always see a beautiful red cardinal out in a snowy field.
It's one of my favorite birds, just because how cheerful they make me feel.
So here are songbirds you'll see in Wisconsin.
And right now, if you go outside in winter, you're not going to hear many birds singing.
It's going to be fairly quiet.
You might hear a cardinal sing, but in spring, when birds have migrated back to the north,
back to Wisconsin, you walk outside and the sky is full of bird song.
And if you have an ear, you can listen to that song and probably identify the different songbird species.
And now if you have the Merlin bird app, you can download it on your phone, you can just hold it up.
It will listen to the birds and tell you what birds are singing.
But as some of you are birders, I'm going to say that if you were walking outside and you are a burger,
you are familiar with the fact that cardinals sing cardinal song, that indigo-bundings will sing indigo-bundings song,
and that meadowlarks will produce meadowlarks song.
You can walk around and you know what birds are around you.
Your app can also tell you what birds are around you.
And that is because each songbird species produces its own species-specific song.
Okay.
Does anyone know what songbird that was?
Yes.
Okay.
Right. And you know that is a cardinal because you have heard cardinal singing in your backyard
and you are familiar with this species-specific song.
But you are also familiar, okay, so songbirds produce these songs.
But you are also familiar with the fact that there are other birds that are not songbirds,
and that would include birds that you see here, like this red-tailed hawk, a turkey, you have woodpeckers,
like this flicker, they are not songbirds, but they do produce noises.
So the sounds that these animals are producing, they are not songbirds, okay, songbirds are named
because they produce song, but these are called calls.
So songbirds call and they sing, and other birds, non-songbirds produce calls.
So biologists distinguish between the two.
It is a little bit muddy, but in general, songs are the long, melodious, complex songs that you hear,
filling the sky in spring when songbirds are preparing to breed.
Typically it is males, they are singing to attract females.
These songs are learned.
In contrast, calls tend to be shorter and they tend to be unlearned.
So an example of a call would be an alarm call.
If you startle a bird and it squawks, that would be an example of an alarm call.
Or if you run into a turkey, it might gobble.
That would be an example of alarm call.
And it is generally thought that calls are not learned in contrast to songs.
Now there are some exceptions to what I'm saying.
Chickadees are songbirds that are very plentiful in Wisconsin.
And chickadees are named after their call, the chickadee call.
So if you startle a chickadee, it will produce this vocalization.
It will say chickadee, and interestingly, if the chickadee perceives you to be very threatening,
it will add more D's to the end of its call.
So I always think that's kind of cool.
If I startle a chickadee and it just produces one D, it doesn't think of me as an extreme threat.
If it adds a lot of D's, it means it considers you to be quite threat.
Yeah.
So in contrast to the more complex chickadee vocalization, the call,
the chickadee song is the fee-be, it's just two notes, right?
It's very simple.
So there are exceptions to the idea that song is complex, but in general,
song is this complex, melodious, learned vocalization.
All right, to support the learning and production of the song,
songbirds have evolved a very elaborate brain system.
So what I'm showing you here are cartoons on the left here of the songbird brain.
This is a zebra finch.
They're commonly studied to understand how the brain controls singing behavior.
And over here, I just have a representative non-songbird, a turkey.
And here's the turkey brain.
So both birds are oriented in the directions, the side view of the brain, right?
And you already noticed something is very different.
The songbird brain, each of these circles represents a brain region.
The arrows represent the connections between the different brain regions.
And this system of brain regions is dedicated to song learning and song production.
And turkeys and other non-songbirds don't learn vocalizations, at least not to a large extent.
And so you see they lack this dedicated system involved in vocal learning and production.
So this is unique to songbirds, and something like it also exists in parrots, something like it also exists in hummingbirds.
And in humans, we see a brain system similar to this because we're famous also for our vocal learning and production.
So one other thing I want to add about this song control system is that in birds that breed seasonally,
males will sing a lot more in spring, and at this time of year, some of these brain regions grow.
They become huge, they actually grow new neurons.
So neurogenesis occurs.
And songbirds are the first species in which it was discovered that adult animals can grow new neurons.
And I think that's good news for all of us, right?
But found discovered first in songbirds.
All right, another unique thing about birds, and this isn't specific just to songbirds, but you'll also see this in non-songbirds as well.
But they have a syrinx.
So this is their voice box.
So the syrinx is located right here, and here's kind of a blow up of the syrinx.
And what you see is that there are two sides to the syrinx, and each side can produce a distinct vocalization.
So it can sound almost like two birds are singing, and this is why birds can produce such complex songs.
We can't do this because we're restricted by our larynx.
So our larynx is our voice box.
All right, so birds have evolved these complex brain systems.
They have this amazing syrinx that can produce these elaborate vocalizations.
So song must be really important.
So why?
Why do birds sing?
There are many reasons that birds sing, and I've come up with a list of four here.
We're going to start by talking about the fact that sometimes when you hear birds sing, it's because they are learning their songs and they are practicing their songs.
Birds are probably most famous, and this would be primarily males, for singing at high rates during the breeding season to attract mates.
We're then going to talk about the fact that birds sing to defend territories, to repel typically males who are competing for their females.
And then we'll also explore the possibility that at least in some context birds may sing because it's rewarding.
Singing may be self-reinforcing.
That is, birds sometimes may sing simply because it feels good.
So we're going to talk about some of the scientific evidence that actually supports that.
All right, so let's start with song learning in practice.
Many birds start to learn songs while they are developing in the nest, and there are two types of song learners.
First, I'm going to focus here on these sensitive period learners.
So this is an adult white-crowned sparrow, and males primarily sing with white-crowned sparrows, females sing, but a little bit less.
So when a young bird is developing in the nest, and as a fledgling, it can hear its father producing song.
And so young birds will develop a template to learn what their species-specific song should sound like.
And then, as fledglings, they start to practice song, and they go through a babbling phase, which is much like human infants.
And during the babbling phase, if you have an ear for bird songs, sometimes you can hear these birds, and it sounds kind of sloppy.
We've heard it in our aviaries, in starlings. It almost sounds like they're whispering, but the song doesn't sound quite right.
It sounds a little bit like white-crowned sparrowed song, but not exactly.
And so they keep practicing the song, and it comes closer and closer to the template that they've stored in their brain,
and pretty soon they're singing a song that matches adult white-crowned sparrowed song, and in these species, song crystallizes.
And that is the song that these sparrows will sing for the rest of their lives.
So they are called sensitive period learners. They listen to the song during a sensitive period during development.
They learn the song, and then that is the song. They don't continue to learn new songs.
That's the song they'll sing for the rest of their lives.
But in other species, such as European starlings, these birds are called open-ended learners.
And that's because they can continue to learn new songs and add new elements to their vocal repertoire throughout their lives.
And one thing I think is really interesting about starlings, and also catbirds, thrashers, blue jays, mockingbirds.
They not only learn their own species-specific songs, but their vocal mimics.
And they can mimic the song of other birds. They can mimic car alarms. They can mimic dogs barking.
And they're really excellent at mimicking human speech.
And if you want to get a feel for this, you can go to YouTube. You can look up starlings.
And you can hear the mimicking human speech, or R2D2. I mean, they're really amazing mimics.
And finally, I want to say that in many species, both males and females sing.
So males are really famous for producing their courtship song to entice females to mate.
But females of many species also sing, and that hasn't been as well studied, but it's starting to receive a lot of research attention.
So I mentioned that white-crowned sparrows females sing a little bit, males sing a lot.
In starlings, males tend to sing more than females, but females do sing quite a bit.
And in cardinals, which you might be familiar with just from your backyard, males and females both sing at really high rates.
All right, so biologists discovered that song is learned, and then they wondered,
well, if song is learned, could birds learn the song of any species?
So could a cardinal learn a yellow warbler song, and could a warbler learn the song of a sparrow?
And so these are the kind of studies that scientists have been running to ask these kind of questions.
And in this case, they focused on young white-crowned sparrow song development.
And so over here, I'm showing you a sonogram. This is a pictorial representation of the song of a white-crowned sparrow.
And so it is frequency over time, and it's a pictorial representation of how the song would look, right?
And so when white-crowned sparrows are tutored when they're young, if they're hearing the song of adult white-crowned sparrows,
when they grow up, you can see that they produce what is considered normal white-crowned sparrow song,
so they learn the song of their species.
But in this study, the researchers had another group.
In this group, they raised white-crowned sparrow chicks, and they did not expose them to any song,
so they heard no song during development.
And then as adults, these white-crowned sparrows, they sang, but you can see the sonogram, the pictorial representation of song,
does not look anything like normal white-crowned sparrowed song, and it doesn't sound anything like white-crowned sparrowed song, right?
So here is this pictorial representation of this abnormal song.
All right, now for the exciting question, could white-crowned sparrows learn the song of another species?
So in this case, they focused on song sparrows, and you can see here a pictorial representation of song-sparrowed song.
It looks quite different from white-crowned sparrowed song. It also sounds quite different.
And so when white-crowned sparrows were raised hearing song-sparrowed song, when they became adults, they produced abnormal song.
It does not look like song-sparrowed song, it might have some elements, and it doesn't look anything like white-crowned sparrowed song.
So what this indicated to researchers is that song is learned, but birds are predisposed to learn the song of their own species.
All right, the next question...
That was a white-crowned sparrow.
All right, so the next question researchers had was, if birds are learning their song, could they learn, could they have accents?
So we, many of us, probably have a bit of Wisconsin accent, right?
You're familiar with a Boston accent, an Oklahoma accent, so could birds develop accents?
And the answer to that is yes.
Songbirds have been found to develop regional song dialects.
And so here I'm showing you an example of a kind of study that showed this.
So this was a study in mountain white-crowned sparrows.
The birds were living in the Sierra Nevada mountains. So here's Nevada, here's California.
And what researchers did is they went around different areas in the mountains that were quite distant from one other.
And they recorded songs. And so when they recorded bird songs from dawn or past, here is how the sonogram looked.
And so the song sounds like mountain white-crowned sparrow song.
And you can see, though, that if you record birds from dawn or past, and then you move over here and record birds from Carson past,
the sonograms look a bit different. And the songs sound a little bit different.
So your Merlin bird app, or by ear, you would recognize these birds to be singing white-crowned sparrow song.
But they have slight regional dialects. So you move all the way over here to Virginia Lakes.
You can see the song is a little bit different. Sonora past, the song's a little bit longer.
So this is considered evidence that birds do have accents. They can develop regional dialects.
And one thing that I think is really interesting, and we'll get back to this, is that, so I've mentioned a little bit,
males are singing courtship song, and it turns out females are picking males based on the kind of songs they sing,
and females prefer to mate with males that are singing local dialects.
All right, we'll talk about that a little bit in the upcoming section.
But some males have been found to change their song so that it matches female preferences.
All right, so I'm going to talk about that here. And so before I introduce this idea, I need to introduce you to cowbirds.
So I can tell from some of your faces, you're not exactly happy to hear about cowbirds.
They are another relatively unpopular, often maligned song word species, but I think they're also amazing.
And you'll probably think they're amazing, too, when I talk a little bit about them.
But the reason cowbirds aren't very popular is here on the left we have a female.
And here we have a male with this brown head, the brown-headed cowbird.
Females do not sing in this species, males sing, and that'll be relevant in a minute.
But one reason people don't love these birds is because males and females will mate,
and then the females will lay their eggs in the nest of other birds.
And the males and females do not raise their own chicks.
And that can be incredibly costly to other songbirds.
Forced to raise, this is a yellow warbler, forced to raise this giant cowbird chick.
Right, so that is energetically costly. This is why people don't always love cowbirds.
This situation actually poses a really difficult challenge for cowbirds.
Cowbirds, when they're young, they're being raised by other birds.
But this cowbird, when it grows up, it's going to sing cowbird song.
It does not grow up singing the song of its host species.
So this cowbird will not grow up to sing yellow warbler song.
And people wondered, well, how? How does that happen?
And so it seems like what happens is at some point after they fledge,
cowbirds do meet up with other cowbirds, and I can talk a little bit about that maybe later.
But they do find a way to meet up with other cowbirds.
And then they start to learn their species-specific songs.
And here is an interesting story.
So this kind of summarizes a complex body of research.
But the way I heard it is there was a research group that had male cowbirds from South Dakota.
So they had flocks of male cowbirds from South Dakota in aviaries.
And these South Dakota males are producing South Dakota song.
They have the South Dakota regional dialect.
And females in this species, they do not sing, but they had some females from Indiana.
And they put the females from Indiana into the aviaries with the South Dakota male.
And the females from Indiana, they prefer to mate with males singing Indiana song.
That's the song they know. That's their regional dialect.
And so they thought, well, over time, if we put females from Indiana with males from South Dakota,
those females from Indiana are going to start to like South Dakota song.
But instead, what happened is the South Dakota males started to produce Indiana song.
Right? So when housed with Indiana females, the males learned the Indiana song.
And I want to remind you that females don't sing.
So they actually weren't hearing the Indiana male song.
But somehow these males started to, they were shifting their songs so it sounded a little bit more like Indiana song.
And so researchers were wondering, how is this happening? What are the females doing?
And so they couldn't see it with their naked eye, but they recorded the female male interactions.
So what you're seeing on the left is this is a female, okay, she doesn't sing, here is a male cow bird.
And so the male right here, he starts to sing.
And if he sings a South Dakota song, she ignores him.
But if he sings something that sounds like Indiana song, then she responds with this really rapid wing flip.
It's very subtle. She flips her wing.
And you can see over here that the male sees that. He sees that she flipped her wing.
Yes. And now he will incorporate whatever song he was producing into his repertoire.
And so in this way, females will, her wing strokes will shape male song.
And I like to think of it. I showed you that song control brain system.
Females are the architects of the male brain.
All right. Okay, so that wraps up what I wanted to say about song learning and practice.
Now we're going to talk about probably what is the best known reason that birds sing.
And this is typically males. Males spend a lot of time singing during this breeding season in an attempt to entice females to mate.
And I should say males also sing to defend territories.
And that's to keep other males away from their mate.
And even when it's not the breeding season, some males are singing to practice their songs so that they can more effectively attract mates later during the more serious breeding season.
All right. So much about singing, at least for males, relates to mating.
And birds will time their courtship song and their mating so that chicks will hatch when resources are available.
So there's a couple different mating strategies. Some songbirds are opportunistic breeders.
Here are zebra finches. On the left is a male. On the right is a female.
Zebra finches are from Australia. They live in desert kind of arid conditions.
And if they were to lay their eggs in the middle of a drought, then the chicks would hatch.
And there would be no seeds, no plants, nothing to feed the chicks, and they would die.
And so these birds, they time their breeding to match food availability by mating when it rains.
So when it rains that activates some of those brain regions we talked about, that trigger singing behavior,
and now the male, when it rains, will sing to attract a female they'll mate,
and then their eggs will hatch when plants have grown and seeds are available to feed their offspring.
Around here, in Wisconsin, we primarily have seasonally breeding birds, and that makes sense.
If a starling or another songbird were to lay its eggs in the winter of Wisconsin, there is snow.
It is cold. Probably the chicks wouldn't survive. And if they did hatch, there's very little food available.
There's not much in terms of seeds. There are no insects available.
And so here, birds have evolved to restrict their breeding to spring.
They restrict their breeding to spring because then the chicks will hatch when food is available
and the temperatures are warm and they can survive. So how does this happen?
Well, it turns out the best predictor of when it is an optimal time to breed is the day length.
So we're familiar with the fact that day length is really short and fall in winter months
and it increases, the day length gets longer and longer as we move towards spring.
And this is something that is tracked by songbird brains.
And so I think it's really interesting. With songbirds, information as the day length increases,
as we get closer to spring, that information goes through the skull of the songbird.
It goes through the skull and it stimulates deep receptors in the brain.
And that causes the gonads to grow. These are supposed to be the gonads.
And the gonads produce a hormone called testosterone, kind of a famous hormone that's famous for regulating male sexual behavior.
And in Starlings, it does. So as the testosterone increases, it goes up to the songbird brain.
It goes to the brain regions involved in song production.
And it also goes to brain regions involved in sexual motivation.
And this causes males, now when they're presented with a female, to begin to sing high rates of courtship song.
So they don't sing much when testosterone is low and day length is short.
They coordinate everything so that they're singing when day length is long and conditions are optimal for breeding.
And I should add, the way they know that the slight is going through the skull is you could put a little cap on a bird
so that the light can't get through the skull.
And even though the sun is shining through the eyes, they don't respond.
So their testosterone wouldn't increase. That's how they know that it goes through the skull and not through the eyes.
Which I think is fascinating.
Alright, so what about females?
Well females do sing during the breeding season.
And one of the main reasons they sing seems to be to defend their mate and to defend their nest.
They defend their mate. They don't want other females mating with their mate.
So that's one reason females sing.
But most of the research that has focused on females focuses on their responses to male song.
So male song is used to attract and stimulate females.
So here we have a female starling and she is checking out a male.
There is a male in this nest box. He is singing high levels of courtship song.
And she is considering mating with this male.
And when she hears this song actually it causes her ovaries to grow.
And she releases the hormone estradiol.
So she hears the male song stimulates her ovaries and the estradiol then goes to her brain and increases sexual motivation.
So this coordinates female behavior so that she is also mating and laying her eggs at a time when her chicks are likely to survive.
So for some females like starlings they hear song and it causes them to approach.
For other females when they have high estradiol they will actually enter a mating posture.
They'll perform a copulation solicitation display.
So that's something you may see if you are looking at spring and see birds mating.
But females are choosy so they will not mate with just any male.
They listen carefully to the song and they select mates very carefully.
And the reason it's thought that females are choosy is because it's energetically costly to reproduce.
They have to invest energy in producing these large eggs and both males and females in song words tend to take care of the eggs.
But just producing the eggs is costly so females want to pick a high quality male.
So females it turns out across species that have been studied they tend to prefer males that are singing local song dialects.
They prefer males that are singing long complex songs and they also prefer to mate with males that are singing at really really high rates.
So why?
What do females get out of a male that sings a lot of highly complex song in a local song dialect?
Well it turns out that these different features of male song tell females about both a male's early condition and about his current condition.
So with respect to a male's early condition it turns out that developmental stress can interfere with song learning.
So what we're looking at here are two fledgling robins.
On the left you have a very healthy young robin.
This robin grew up where there's plenty of food available, plenty of water available.
It doesn't have any parasites, it's not a sick bird.
So here's a young bird that's raised under excellent conditions.
And here we have a songbird that was raised under impoverished conditions.
It's got parasites, it might be sick, there's not much food or water available.
It turns out that the developmental stress will interfere with song learning.
So this bird is listening to its father produce song and it's got the template but it practice a song, it never accurately matches the song template.
So in a way it has a regional dialect, it has a dialect that doesn't match the geographic region where it's developing.
And so females, when this male grows up and sings its song, it's not going to be a great song, it doesn't perfectly mimic its father's song.
Females will not prefer to mate with this male.
This male will grow up and because it has an experienced developmental stress and it's in great condition when it's young, it will produce a very accurate mimic of its father's song.
So this is how females benefit by selecting males that sing song that's very close to the regional dialect because it indicates that they're mating with a male that at least was in a great condition when it was young.
Other features of song tell females about the male's current condition, so how is he doing right now?
If she listens to a song, is he healthy right now?
So if he mimics the song really well, you know he was healthy when he was young.
But right now different features of song will tell the female if the male is healthy.
So singing is thought to be costly.
It requires energy to produce song and when birds are singing they're not doing other things, they're not eating, they're not mess building.
And it also puts them at risk for predation, they're singing, they're making themselves very visible while they're singing, so there are costs associated with singing.
And what that means is only healthy high quality males can produce high quality songs.
So low quality males, maybe males that are infested with parasites, males that aren't eating or getting enough water, these low quality males, they simply cannot cheat and sing high quality songs.
So it is said that song is an honest indicator of male quality.
So I'm not suggesting females are consciously making these decisions, but over time females that preferred males that sang high levels of song, if they mated with them, their chicks were more likely to survive.
And then their chicks, they would then prefer the same features of song and this led to survival.
And this is why females prefer, tend to prefer these long, complex regional dialects.
All right, so moving on to another reason that birds sing and that is to repel a competitor or to defend a territory.
Some of you are familiar with the fact that birds defend their territories.
They're showing you three highly territorial birds that live here in Wisconsin.
You've got the meadowlark, the cardinal.
How many people have been attacked by a red-winged blackbird show of hands?
Yeah, you walk along a pond and before you know it, something is smacking you in the back of your head.
And it's frightening, so that's a red-winged blackbird.
So meadowlarks are quite territorial, they tend to have two or maybe three nests on a territory that they defend, and they defend by singing.
Cardinals tend to be monogamous, males and females form pairs.
Sometimes they will stay together for years, the same pair.
So they tend to be monogamous and they will defend a territory.
Also, red-winged blackbirds tend to have five or even 15 nests that they are defending.
And they are quite aggressive when they're defending these territories.
Now the territorial defense primarily is meant to repel other birds that might be competing for their mates,
but you know in the case of red-winged blackbirds, they'll also attack you if you get too close to the territory.
So some birds do produce different songs when they're defending a territory and when they're trying to attract a mate,
but most of the birds, and many of the birds here in Wisconsin, they sing the same song,
and it turns out the song that is attractive to females actually repels other males.
And if you think about it, that makes sense, because if song is reflecting male quality, males wouldn't want to mess with a high-quality male.
If you are a male and you're trying to usurp somebody, knock them off their territory,
you would rather knock off an unhealthy weak bird than try to challenge a bird that's singing a great song,
because that accurately reflects the quality of that male.
Okay, and I do want to note that territorial song is not just a male thing.
Female cardinals will vigorously defend territories, sing to repel intruders.
Starlings also will sing to defend their nest site.
All right, so how do biologists know that birds sing to defend territories?
Well, one of the ways they know is they will slip out into the territory of a bird, like the song sparrow,
and they will put a speaker in the territory.
So in this case, you have a song sparrow, and this speaker is playing male song sparrow song.
This song sparrow is attacking that speaker and singing to vigorously defend its territory
from what it perceives to be another song sparrow that's invading its territory.
It's also been found that if a biologist will play song in an empty territory,
that territory is more likely to remain empty.
So these are some of the pieces of evidence and some of the ways that biologists have discovered this.
So I do want to say that now we have these apps on our phone, and we can play bird song, but it is not recommended.
And the reason for that is you could go in your backyard and play cardinal song,
and if you have a pair of nesting cardinals, they will respond.
They will come and get in your business, right?
They want to know who is invading their territory.
But the problem is you go back inside, and for two weeks at least,
those birds are going to keep monitoring their territory.
They're going to sing vigorously.
They are not going to invest energy raising their young, so it is recommended that you do not play the song
and that you just let the biologists who have permits to do this do this kind of work,
because it's certainly tempting, but not recommended by ornithologists.
Okay, so territorial song is used to repel other males from territories.
It's not used to attract females, but females are listening.
Females will eavesdrop on these territorial songs.
And so I think there's a great example of this that is in chickadees.
So here is a female chickadee, and here are two males that are singing the Don song early in the morning.
They're producing Phoebe, Phoebe, and let's say this male is mated with this female.
They have pair bonded, they have a nest together, they're going to raise offspring.
So the female is listening to her male, and if he is a high-ranking dominant male,
when he produces his Phoebe, this other bird will not interrupt.
He will not interrupt.
But if he's being challenged by another male, this male will produce his Phoebe, this male will interrupt.
So he starts to produce Phoebe, and then another one just jumps in.
Phoebe, the female listens. She does not like that.
If a female hears that her male is interrupt, she will sneak off and seek extra pair copulations.
It's scandalous, right? This is a sordid tale. She will cheat on her male.
Okay, so how do researchers know this?
They have gone out into the field, and they will, you know, listen to the Phoebe's and these kind of these male singing competitions.
And so in white here, the unfilled mark, this is the sonogram of an actual bird producing his Phoebe song,
and over here you have researchers playing back recordings in dark.
So you hear Phoebe's song, this would be the submissive playback, this guy does not overlap, okay?
And over here you have an example of an aggressive playback on the right.
So here's the actual male saying, Phoebe, and he's interrupted by the researchers.
And so experimenters observed, you know, they performed this interruption, or they didn't overlap with the song,
and then they went to the nests of the males that they were focusing on, and they said,
how many eggs in that nest are sired by other males?
How many eggs were fertilized by other males?
And they found that if the male was given this aggressive playback, if he was interrupted,
many of his eggs were fathered by other males.
So the female went out and made it with other males.
But if he wasn't interrupted, or if they did nothing, just as a control,
you see that most of the eggs in his nest belong to that male.
So I think this is just fascinating, right?
So females eavesdrop, and high-ranking males that receive an aggressive response lose paternity.
All right, so we're moving on to the final reason that birds sing, that I've added to this list,
and I just want to explore what researchers have suggested about the possibility that birds may sing
simply because it feels good, because it's rewarding, it induces a positive state.
Factors that reward singing behavior are very clear in some contexts, okay?
Factors that reinforce singing.
So here we have this red-winged blackbird.
If it sings, and another male leaves that territory, if it repels an intruder,
that can be reinforcing.
That bird is likely to sing again in that same context to repel other intruders.
In the breeding context, here we have a male starling singing from the opening of his nest hole.
He's attempting to attract a female to that nest hole, and they will mate.
And if he does that, if he attracts her, and they mate, this song will also be reinforced.
It will be rewarded.
So the reasons they're singing, the factors that reward this kind of singing are very clear.
But in some contexts, why birds sing is not clear.
And so this is where I'm going to focus a little bit on the European starlings,
and hopefully gain some appreciation for them.
But they are famous, right?
They're famous for forming these large murmurations, these huge flocks.
During the breeding season, they are in pairs, in breeding pairs.
But outside the breeding season, they become really socially tolerant.
They're highly gregarious.
They start to like other birds, and they form these flocks.
And while they're in these flocks, they sing.
They sing, and they sing, and they sing.
And this is in fall and winter months.
You don't see this during the spring breeding season.
So fall and winter, huge flocks, and they're singing.
And it's really not clear why they're singing.
So it's known that they don't sing much if they're alone, probably because that makes them vulnerable to predators.
So they have to be surrounded by flock mates.
If a predator shows up, they stop singing.
So we know this song, it's important that you've got a low stress environment.
A stressor makes them stop singing.
And when they're singing, they often are not even looking at each other.
So here's a bird singing right here.
The other birds aren't even paying attention to the other birds.
So it doesn't seem to be responded to, at least immediately by other birds.
They might be listening, but they don't seem to respond.
It doesn't attract a mate.
It doesn't repel an intruder.
In an immediate sense, it doesn't seem functional.
Like it is probably important for them to practice their song.
But in an immediate sense, nothing's happening.
They're just singing.
So there are very few behaviors that animals perform at high levels for no apparent reason.
But one exception to that is playful behaviors, okay?
So playful behavior, this is a definition from a textbook.
A play is a repeatedly, is it a repeated, seemingly non-functional behavior that differs
from more adaptive versions structurally, contextually, or developmentally.
And I would say that singing in a large fall flock, it is a repeated, seemingly non-functional behavior.
And they seem to be doing it for no reason.
So is it possible that song in these flocks of starlings and other overwintering flocks
could it be a form of play behavior?
So why do we play?
Why do animals play?
We would say you play because it's fun.
And fun is nearly synonymous with, it feels good, right?
So could birds in this context sing because it's a form of play behavior?
All right, so to put this into context, it is estimated that of the 10,000 bird species on the planet,
only 1% play.
And yet there are famous examples of play behavior.
So ducks have been found to repeatedly go over waterfalls, and some of you may even have seen this.
They'll go over waterfalls, they'll walk back up to it, get back in the water, go down the waterfall.
They're examples of swans swimming.
Here we have kia parrots, they are playing, they are considered to be the most playful bird in the world.
They live in New Zealand, in the mountains, and if you park your car, they will destroy your car.
They're not trying to be destructive, but they're so playful and so curious.
They might destroy your boots, they'll steal your camera.
They play with each other, they'll play with the snow, like they're amazing.
Here we have a bird of prey, this is a kite that is dropping, in this case he's dropping a tennis ball,
dropping the tennis ball, picking it up, flying up, dropping the tennis ball,
and birds of prey, more typically you would see bone fragments.
They'd be dropping a bone fragment and repeatedly catching it, right?
So it's an important behavior, it teaches them hunting skills, but in an immediate sense, it has no function.
Here we have a crow sledding, and then we have a magpie playing with a dog.
All right, so there are these famous examples of play, and yet only 1% of the birds of the world are thought to play.
However, it is possible, or could it be, that when they're singing in flocks, songbirds are learning their song,
could that be a form of play behavior that would be exhibited by almost half the birds on the planet?
All right, so how do you know if behavior is play behavior?
It can be difficult to know, so I'm showing you here two dogs playing, this is a puppy playing with an adult,
and if we look at this puppy playing, if you're familiar with dog behavior at all, you would recognize this as play.
Now if you were a child or not familiar with dogs, you might say, oh my gosh, they're fighting, right?
Because it's hard to know, is that puppy fighting, or is he playing?
Could he be trying to mate with the adult dog? You don't know.
And so we can tell it's play, but it's hard to know the difference.
And so Gordon Burkhardt, he's written the textbook on play behavior, and he said for behavior to be play,
it has to meet these five criterion.
And one of the things you notice right here is this behavior is kind of sloppy.
It's something you wouldn't see in a serious aggressive context, or mating context.
It's sloppy, it's not rigid, it's not fully functional.
Okay, so I'm not going to read through this list, we're just going to march through it step by step as I provide some evidence
that suggests that song and flocks does meet these criteria.
So first, I've already said that song and flocks plays no immediate function, birds don't attract a mate,
they don't repel an intruder.
We also see that song and flocks is initiated when free from stress because they stop singing if a predator shows up.
Alright, so what about these other criteria?
Let's look at these two, modified from other contexts, so modified from the reproductive context,
and is it not fully functional, and is it performed repeatedly but not rigidly, so is it sloppy?
So studies and song words suggest that each of these criteria is met.
This is an example from Starlings, and it's something you would see in other birds that sing in spring and fall.
What you typically see in spring, song is longer in Starlings, it's shorter in the fall non-breeding season when they're in flocks,
and females, remember they prefer to mate with males that sing long songs and males don't mess with males singing long songs,
so by adjusting the song structure you actually might promote cohesion in the flock,
they may be more willing to hang out because there's no aggression, there's no fighting over mates or defending territories.
If you look at song stereotopy, so song stereotopy is how well the bird reproduces its song again and again and again,
and spring during the mating context, this is when females prefer males singing high complex repeated song,
males have very stereotyped song, they repeat song the same way again and again and again,
song elements are in the same order each time, and in fall they get a little sloppy.
So this is consistent with the idea that maybe singing is a form of play behavior.
So I think we can check these boxes, that song is modified from context in which you might see the behavior,
doesn't seem fully functional, it's not attracting a mate or repelling an intruder,
it's performed repeatedly but not rigidly, so I'm going to check these boxes.
So the last question is, I said song does erupt spontaneously outside the breeding season,
but the question is, is it rewarding? Do birds sing for fun?
So how do you ask a bird if it feels good to sing?
So to do this, we borrowed methods from psychology, these are methods they're called condition place preference.
It's designed to ask rats if it feels good for example to eat rich fatty food for example.
So we adapted these methods to ask birds if it feels good to sing, and the idea is basically if something good happens to you in a certain place,
you return to that place, right? So I find in the kitchen I'm off in front of the pantry,
I don't know why I'm there, I'm just standing there, and I think it's because there are sweets in my pantry.
So I associate the pantry with something good, and so sometimes if I'm working at home I'm just there,
I'm like what am I doing here? It's because I have a condition place preference, right?
So this means I find previously I had a rewarding experience in this place.
Alright, so we use these methods in birds, and here are starlings singing in flocks, we've tested them in different contexts,
this only works for flocks on. So they're singing in flocks, so here's a male that's focused on him, he is singing.
And let's say that song is associated with a positive, affective, positive emotional state, he feels good when he's singing.
You take him, and you put him in a distinct place. So the place in this case, we have a cage, half of its decorated in yellow materials,
half of its decorated in green materials. The bird is sung, and then we take him from his flock, and we put him with his positive emotional state,
let's say, into the green side. Now this bird is associating green with a positive state, and so the next day you just take that same bird,
and you put him into this cage, and you just say, does he spend more time on the green side, or the yellow side?
And the idea is, if birds feel good when they're singing, that they should spend more time on the green side, in this particular case.
So we just record the amount of time the male spends on the green side, where he associates with something positive, and the yellow side.
And what we found in repeated studies, like we've replicated this at least four times, we see that males sing at high rates
on strong preferences for the place we put them after singing. So what you're saying is, anything above this hatch mark, in the example I gave,
means the male spent more time on the green side, anything below the hatch mark means he liked yellow.
And what you can see is birds that don't sing much, they don't have much of a preference, they'll go to the green side, they'll go to the yellow side.
But males that sing a lot, they spend almost all of their time on the green side, and it actually correlates linear with song.
The more they sing, the more time they spend on that green side, which I think is fascinating.
And it suggests that in fall, birds are singing because it feels good.
Alright, so now I think we can check this off, so we've met all five criteria, which suggests to me that singing in these flocks, when they're practicing their song, can be considered a form of playful behavior.
And we thought, well we're quite creative, no one's ever thought of this before, but it turns out about 150 years ago, Darwin suggested this.
He said, the songs of birds serve mainly as an attraction during the season of love, but male birds continue singing for their own amusement after the season for courtship is over.
So we may not have been the first to propose this, but I think we are among the first, at least, to provide some experimental support for this idea.
Alright, so here's the final list.
Why do birds sing, learning in practice, to attract a mate, to defend a territory or a repellic competitor, and perhaps, at least in some context, also because it's rewarding, it feels good to sing.
Alright, so with that, I'm happy to take questions.
I thank you, and I did want to highlight a few of the sources that I kind of alluded to.
So Zeno Kanto is a really good site if you want to hear different birds singing or upload your own songs.
You can go to Birdcast during the migration season, and it will track the millions of birds that are leaving Wisconsin and coming back to Wisconsin.
And then many of you I know are already familiar, and use the Merlin bird app.
You can just download that to your phone, and then you'll know what birds are singing around you.
Alright, so with that, I'm happy to take any questions. Thank you for your attention.
Thank you.