[gentle music]
- Lisa Brooks: Hello, everyone, and welcome.
Thank you for coming to today's Badger Talk.
This talk is brought to you
by the Friends of Monona Senior Center.
And today, I am Lisa Brooks.
I am the program coordinator for the Monona 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 pleased to introduce today's guest,
Dr. Lauren Riters,
a professor in the Department of Biology at UW-Madison.
Dr. Riters received her undergraduate degree
from psychology--
from the Miami University in Ohio
to pursue a long-standing fascination for birds.
Her first study was how homing pigeons return
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 Liège in Antwerp in Belgium,
followed by postdoctoral studies at Johns Hopkins University.
Please help me in welcoming Dr. Riters.
[applause]
- Lauren Riters: Thank you so much, Lisa,
for that wonderful introduction.
And thank you to the Monona Naturalists 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 birders.
But most of my research is on European starlings.
[audience laughs] 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 gonna 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 moos 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 bird
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 our vocal--
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 buntings, 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 gonna hear many birds singing.
It's gonna 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 birdsong.
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 am gonna say that if you were walking outside
and you are a birder, you are familiar with the fact
that cardinals sing cardinal song,
that indigo buntings will sing indigo bunting song,
and that meadowlarks will produce meadowlark 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.
[cardinal sings]
Okay, does anyone know what songbird that was?
Yes, okay, cardinal, right?
And you know that's a cardinal because you've heard
cardinals sing in your backyard,
and you're familiar with this species-specific song,
but you're also familiar--
Okay, so, songbirds produce these songs,
but you're 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've got woodpeckers like this flicker.
They are not songbirds, but they do produce noises.
So, the sounds that these animals are producing,
they're 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's 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's males.
They're 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's 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'll say, "chickadee."
And interestingly,
if the chickadee perceives you to be very threatening,
it will add more "dees" to the end of its call.
So, I always think that's kind of cool.
If I startle chickadee and it just produces one "dee,"
it doesn't think of me as an extreme threat,
but if it adds a lot of "dees,"
it means it considers you to be quite the threat.
Yeah.
So, in contrast to the more complex chickadee vocalization,
the call, the chickadee song is the "fee-bee."
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 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.
Okay, so... [all laugh]
...both birds are oriented in the direction--
It's 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 wanna 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.
Okay, 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.
Okay, so a 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 gonna 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, okay,
to repel typically males who are competing for their females.
And then we'll also explore the possibility that,
at least in some contexts, 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 gonna talk about some of the scientific evidence
that actually supports that.
All right, so let's start with song learning and 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 gonna focus here
on the 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.
They'll 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 birdsong,
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 sparrow 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 sparrow 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 repertoires
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 they're 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 wanna get a feel for this,
you can go to YouTube, you can look up starlings,
and you can hear them mimicking human speech or R2-D2.
I mean, they're really amazing mimics.
And finally, I wanna 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 songs,
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 sparrow song,
and it doesn't sound anything like white-crowned sparrow 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 sparrow song.
It looks quite different from white-crowned sparrow song.
It also sounds quite different.
And so, when white-crowned sparrows were raised
hearing song sparrow song, when they became adults,
they produced abnormal song.
It does not look like song sparrow song--
it might have some elements--
and it doesn't look anything like
white-crowned sparrow 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.
[white-crowned sparrow sings]
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 another,
and they recorded songs.
And so, when they recorded bird songs from Donner Pass,
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 Donner Pass
and then you move over here and record birds from Carson Pass,
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 Pass, 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 upcoming section.
But some males have been found to change their song
so that it matches female preferences.
All right, so I'm gonna talk about that here.
And so, before I introduce this idea,
I need to introduce you to cowbirds.
Okay, 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 songbird 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 his brown head,
the brown-headed cowbird.
Females do not sing in this species.
Males sing, and that will 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 nests 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.
But 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, right?
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 gonna start
to like South Dakota song."
But instead, what happened is the South Dakota males
started to produce Indiana song.
[audience exclaims] All 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 song
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 cowbird.
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 just 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.
[audience laughs] So...
- Attendee: Yeah, so true.
- Lauren: All right, okay.
So, that wraps up what I wanted to say
about song learning and practice.
Now, we're gonna 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 the 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, right?
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 in fall and 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 goes into-- 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--
that's famous for, you know, 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 this light 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, okay?
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.
All right, 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 mates.
So, that's one reason females sing.
But most of the research focused--
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.
Okay, so she hears the male song, stimulates her ovaries,
and the estradiol then goes to her brain
and increases sexual motivation, right?
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 a song and it causes them to approach.
For other females, when they have high estradiol,
they will actually enter a mating posture, okay?
They'll perform a copulation solicitation display.
So, that's something you may see if you are looking at spring
and see birds mating.
Okay.
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 they--
It's energetically costly to reproduce.
They have to invest energy in producing these large eggs.
And both males and females in songbirds
tend to take care of the eggs,
but just producing the eggs is costly,
so females wanna 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 was plenty of food available,
plenty of water available.
It's not-- You know, it doesn't have any parasites.
It's not a sick bird.
Okay, 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 practices 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 gonna 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 hasn't 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.
All right, 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 nest 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, okay?
And then their chicks, you know,
they would then prefer the same features of song,
and this led to survival.
So, this is why females prefer-- tend to prefer these long,
complex regional dialects.
All right, so we're 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.
I'm 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. [audience laughs]
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, okay?
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, songbirds 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 wanna 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 this 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 has-- is attacking that speaker to--
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 wanna say that now we have these apps on our phone
and we can play birdsong, 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 wanna know who is invading their territory.
But the problem is, you go back inside,
and for two weeks at least,
those birds are gonna keep monitoring their territory.
They're gonna sing vigorously.
They are not gonna 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 dawn song early in the morning.
They're producing "fee-bee, fee-bee."
And let's say this male is mated with this female.
They have pair bonded, they have a nest together,
they're gonna raise offspring.
So, the female is listening to her male.
And if he is a high-ranking dominant male,
when he produces his "fee-bee,"
this other bird will not interrupt.
He will not interrupt.
But if he's being challenged by another male,
this male will produce his "fee-bee."
This male will interrupt, so he starts to produce "fee"
and then another one just jumps in, "fee-bee."
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 "fee-bees"
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 "fee-bee" song.
And over here, you have researchers
playing back recordings in dark.
So, you hear "fee-bee" 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 "fee-bee,"
and he's interrupted by the researchers.
And so, experimenters observe-- You know,
they perform these, 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 mated 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 wanna 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 gonna focus a little bit
on the European starlings,
and hopefully you'll 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 'cause that makes them vulnerable to predators.
So, they have to be surrounded by flockmates.
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.
"Play is a repeatedly-- is 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, you know, 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 maybe even have seen this.
They'll go over a waterfall.
They'll walk back up to it, get back in the water,
go down the waterfall.
There are examples of swans swimming.
Here, we have kea 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.
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?
'Cause 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 Burghardt,
he's written a 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 a mating context.
It's sloppy, it's not rigid, it's not fully functional.
Okay, so I'm not gonna read through this list.
We're just gonna march through it step by step
as I provide some evidence that suggests
that song in flocks does meet these criteria.
So first, I've already said that song in flocks
plays no immediate function.
Birds don't attract a mate, they don't repel an intruder.
We also see that song in flocks is initiated
when free from stress
because they stop singing if a predator shows up.
All right, 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 in songbirds 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 stereotypy, so song stereotypy 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 songs.
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, right?
So, this suggests it's consistent with the idea
that maybe singing is a form of play behavior, right?
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 gonna 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 that are called
conditioned place preference, okay?
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 often 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
conditioned place preference, right?
So, this means I find some-- you know, this--
Previously I had a rewarding experience in this place.
All right, 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 flock song, so they're singing in flocks.
So, here's a male, let's focus 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 it's decorated in yellow materials,
half of it's decorated in green materials.
The bird has 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,
okay, in this particular case.
Okay, so we just record the amount of time
the male spends on the green side
where he, you know, 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,
developed 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.
All right, 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, "Whoa, 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.
All right, so here's the final list.
Why do birds sing?
Learning and practice, to attract a mate,
to defend a territory, or repel a competitor,
and perhaps, at least in some contexts,
also because it's rewarding.
It feels good to sing.
All right, so with that, I'm happy to take questions.
I thank you, and I did wanna highlight
a few of the sources that I kind of alluded to.
So, xeno-canto 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.
All right, so with that, I'm happy to take any questions.
Thank you for your attention.
[audience applauds]