The Science of Birds - Bird Songs - Part 2

Episode Date: September 22, 2020

Episode: 6SummaryThis episode is Part 2 of 2 about Bird Songs. In the last episode, Part 1, we talked mostly about the “how” and the “who” of bird songs. We haven’t really talked about the “why,” the purpose of all these vocal sounds. This episode begins by looking at the functions of bird songs and calls.Then we get into variation in bird songs, at several levels, including among species and among geographic regions.You’ll also learn about some interesting subtopics like the dawn chorus and female songs.‍‍Research CitationsWhite-throated Sparrow viral dialect study (Otter et al. 2020. Current Biology)Links to Some Things Mentioned in this EpisodeBirdNetFemale Bird SongsAttributionsWhite-crowned Sparrow singing - Recording XC565001 on Xeno CantoWhite-crowned Sparrow singing - Recording XC99572 on Xeno CantoBlack-capped Chickadee singing - Recording XC70185 on Xeno CantoRed-tailed Hawk - Recording XC71575 on Xeno CantoNorthern Mockingbird - Recording XC538537 on Xeno CantoLink to this episode on the Science of Birds websiteSupport the show

Hello and welcome. This is the Science of Birds. I'm your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. This is part two of two on bird songs. If you haven't heard part one, I suggest you check that out first. It's episode five. In part one, we covered how. bird songs are produced, which birds learn their songs, and I describe some characteristics of songs. We talked mostly about the how and the who of bird songs. We haven't really talked about the why, the purpose of all these vocal sounds. Birds spend a lot of time and energy singing, when they might otherwise be foraging for food, tending to their nests, or writing the next

great American novel. So these songs must be pretty dang important. They are, of course, and I suspect you already know what the two main functions of songs are. One, mate attraction, and two, territorial defense. Males sing to attract females so that they can pass on their genes to the next generation. Many females also sing, but we know much more about the function of male songs, so let's focus on males for the moment. Across numerous studies, it's become clear that females are attracted by the songs of males of their own species. What exactly are these females queuing in on? It's not always clear.

Many birds seem to be able to discriminate subtleties and details in sound that elude us humans. Although this surely varies across species, there is evidence that female attraction can be influenced by the number of songs that a male sings and or his performance quality. Do these or any other characteristics of a male's song accurately reflect his health, vigor, and genetic quality as a father? Scientists might frame the question this way. Is song an honest indicator of a male's health or fitness?

Research on this has had mixed results. There are cases where there isn't any apparent correlation between a male's song and his vigor. So maybe birds, at least some of them, are sort of blowing. their own trumpets when they sing. An impressive song may not always be a sign of good health or genes. Females might be attracted to the song itself, with all of its various properties. Many male birds set up and defend breeding territories. Song is a tool for marking the boundaries, or the borders of a territory, and broadcasting this

information. When a male trespasses the territory of another male of the same species, he might be in for serious trouble. But songs can also help minimize aggression and violence, at least when the birds respect each other's space. Males often recognize the songs of the other males in their immediate neighborhood. Neighbors usually tolerate each other. The same can't be said for some shady drifter that just rode into town. Any new bird on the block might be looking to establish his own territory, and this might be seen as a threat, one that must be dealt with. Now, remember that besides these lovely and complex songs, we also have calls. Some species have a dozen or more

different sounds they make besides their so-called song. These calls can have their own distinct functions. For example, many birds have contact calls, which mated pairs or flockmates use to keep track of each other as they forage. There are calls used only in flight, perhaps to also keep tabs on each other. Males sometimes have specific calls to show aggression towards their rivals. There are also alarm calls that birds use to warn each other about predators. Some birds even have different calls for different predator types to distinguish between flying versus terrestrial predators, for example.

So calls are a sort of language, and they can serve different purposes. One of our recurring themes on this podcast is variation. Nature is ripe with variation, and we couldn't escape it if we tried. There's a lot of variation in bird songs, at several levels. There's variation among species, obviously, but there's also important variation within many species. This shows up as geographically distinct dialects. This is particularly true for birds that learn their songs. Birds that grow up in a certain area often end up sounding similar

because they learn from their parents or neighbors. This is a form of culture, just like human dialects. So I really want to, like, do some stupid impressions of New Yorkers and Californians and all that right now, but I'm not going to because I'm not good at it. White crown sparrows have been a model for the study of bird dialects. Each male of this species has pretty much one simple song, but the structure of the song varies across North America. Here's a white crown sparrow in Manitoba, Canada.

And here's one in California in the U.S. Both of these songs have a pure-toned introductory note, but with careful listening, you can tell that these are not the same song overall. The parts of a species song that get preserved across space, and time might be those that are the most attractive and important to females. So the other elements, the ones females don't care as much about, would be under less evolutionary pressure to stay the same. They'd be free to change from region to region, from generation to generation. White Crown's sparrow dialects often differ over short distances,

as in tens of meters. So this species has many local dialects. Some of these seem fairly stable over time, lasting for decades, while others evolve more rapidly. For an example from a closely related species, a recent study of white-throated sparrows in Canada describes how a particular dialect has spread from British Columbia all the way to Ontario in about 20 years. That's almost 2,000 miles or 3,000 kilometers. This is the fastest spread of a song dialect that has ever been recorded, and the researchers don't know what made this song go viral among white-throated sparrows. Now, how do we know if two dialects actually reflect two separate species, or at least subspecies? This is a good question, because sometimes two species or

subspecies that look identical to us anyway are actually genetically distinct, and their songs can reveal this cryptic diversity. Sometimes dialects are matched. Sometimes dialects are matched, by an underlying genetic difference between geographic areas. In those cases, the songs might reflect some hidden species or subspecies diversity. At small local scales, dialects seem to be more cultural and passed on as memes rather than through genes. In other words, these are learned behaviors rather than inherited. In these cases, there wouldn't be any corresponding genetic differences. But sometimes we find two or three dialects at big geographic scales, like on two halves of a continent.

These are what we call regional dialects, and they're more likely to represent some actual genetic differences that have accumulated over thousands of years, perhaps when two populations of one species were separated by huge glaciers during the last ice age. Some birds don't have regional or local dialects. The Black Cat Chickadee, for example, sings pretty much the same tune all across North America, this one. The olive-sided flycatcher also sings the same song across its range. It sounds like he's yelling, quick, three beers. Somebody get that bird at Budweiser right now.

Here's the thing, though. The black cat chickadee is a songbird, a member of the awseeing-passerine lineage. Songbirds learn their songs, and they pass them on to each other the way humans share language and culture. This is why so many songbirds have local dialects.

So why don't these chickadees have dialects? We just don't know. This is an unsolved ornithological mystery. What about that, Olive-sided flycatcher that just can't wait to chug a few bruskeys. Well, he's a sub-assine passerine, belonging to another group of perching birds. Sub-a-senes, you may recall from the last episode, don't learn their songs. They are pre-programmed by their DNA to sing their particular songs.

It's no surprise, then, that the olive-sided flycatcher has no dialects across its range. Variation is rampant at the individual level as well. Males of many species develop their own unique songs. These are adapted from the songs of their parents or, more often, their neighbors. There's good evidence that many birds can identify each other individually by their songs. If you're a morning person and or an experienced birder, you've likely heard what is called a dawn chorus. Starting before dawn and continuing for a while after the sun rises, birds of multiple species often sing loudly together. This is the summation of

individual birds starting their day with loud proclamations. Often, each species sings at a specific time of the morning, so the composition of the chorus changes as the hours pass. In the UK, for example, the dawn chorus can start as early as 3 a.m. The progression of birds, in order of who starts singing first, generally goes like this. Eurasian blackbird, European Robin, Eurasian Wren, tawny owl, chaffinch, and so on. Here's a snippet of the dawn chorus from my own backyard in Oregon in the United States. These birds are singing from the edge of a coniferous forest at about 5.30 a.m. in June. A few of the species in that chorus that we're hearing there are Swainson's thrush,

Western Tanager, Spotted Tohi, and Pacific Ren. For many species, the Dawn song has a different quality and or more frenetic energy. than songs used later in the day. Ornithologists aren't entirely sure of the reason behind this, but it's thought that male birds are driven to aggressively re-establish their presence and their territory boundaries every day, first thing in the morning. Depending on where you are in the world,

the dawn chorus can be soothing and beautiful, or it can wake you up way too early with the strident sounds of screeching, barking, and wailing birds. In any case, the dawn chorus is a fascinating, aspect of bird behavior and a wonderful part of our world's soundscape. As I mentioned, it's not just males that sing. Female birds of many species make sounds. Some are short, simple calls that closely match the calls that males make.

But females of hundreds of species produce more complex songs. This phenomenon is more common in tropical birds. And since a disproportionate amount of bird song research has focused on temperate species in Europe and America, it's not surprising that many people think that it's only male birds that sing. This is just a geographic bias. Female songs seem to serve the same functions that male songs do, primarily mate attraction and territorial defense. But there also seem to be some song functions unique to females. Some female songs seem to advertise replay. productive state. For example, when she's ready to breed, a female alpine accentor

sings to alert males across her mountain meadow habitat. Females of some species also sing to keep in contact with their fledglings. Singing males are sometimes joined by their female partners in a duet. These can be simple call-and-response exchanges, or they can be highly elaborate, tightly synchronized performances. This behavior duetting is also more common. among tropical species. Duets probably help reinforce the bond between a mated pair. Unlike many temperate species, tropical birds tend to have long-term monogamous bonds, so duetting might make more evolutionary sense for those birds of tropical lineages.

It's estimated that about 20% of the world's songbirds exhibit some level of vocal mimicry. That is, they do impressions. Of other birds, mostly, but sometimes they mimic the sounds of frogs, cows, chainsaws, or other things they hear in their environments. It's not always clear why birds do this. Sometimes they seem to do it to trick other birds. In my backyard, for example, I often hear what sounds like a red-tailed hawk. But I can usually tell when it's actually a stellar jay doing his best impression of a hawk. The crafty jay may be trying to spook other birds away from the bird feeder. Here's a red-tailed hawk call, a real one.

And here's a stellar jay mimicking a hawk. But some of the most impressive mimics don't appear to be trying to trick other species. A male northern mockingbird can have a repertoire of over 150 songs that he cycles through. Many of these songs are borrowed from other species. It's hypothesized that birds like this are mimicking in order to increase the diversity of their repertoires, because knowing lots of songs is impressive to the ladies. In the song I'm about to play for you, the mockingbird appears to be mimicking a northern flicker, an American Robin, and a California ground squirrel among other things.

Mockingbirds and thrashers are in the family mimity, which has that mime root right there in the name. The starlings, which are also amazing mimics, are in the closely related family, sternity. Using bird sounds to identify species has long been invaluable for bird watching, as well as research in ornithology. And now technology has advanced to the point where fancy computer algorithms and machine learning can help us ID birds automatically using just their sounds. Mobile apps that use images to identify birds have been around for a few years now. Check out

the Merlin app, for example. But now there are apps that ID birds buy their songs. These have come a long way. I've been playing with the BirdNet app, and it has been really impressive. Birdnet uses simulated neural networks to rapidly analyze bird sounds. Do I know how simulated neural networks work? I'm not going to lie. I don't.

Maybe you do. In any case, this kind of computational magic can do some pretty cool stuff. This sort of technology is revolutionizing some aspects of biological research, including ornithology. In this episode on Bird Songs, which is Part 2 of 2, we've covered the functions of songs, ways in which songs vary geographically, the Don Chorus, female songs, and mimicry. As usual, there are many more details I could have covered on this topic. but we'll have to do that another time because I have to go stare wistfully into the distance as I wash the dishes.

I hope these two episodes of the podcast inspire you to pay some extra attention to the vocal sounds of birds. If you're a relatively new bird watcher, I encourage you to start learning the songs and calls of some common birds in your neighborhood. When you start to recognize species by their sounds, it's really exciting and rewarding. You'll be able to know which birds are around, even when you're not. you can't see them. This opens up a whole new way of experiencing nature. Thanks so much for listening and learning with me today. With each episode, I hope to make the

Science of Birds podcast better and better. I'd love to hear any thoughts or comments you have about the show. Just let me know by sending an email to ivan at scienceofbirds.com. And hey, if you love birds and you want to learn more about their biology, please subscribe to the podcast. You can also see the show notes for this episode, which is episode 6, on the Science of Birds website, scienceofbirds.com. On the website, you can tickle me pink by subscribing to our email newsletter. So check out Scienceofbirds.com. I'm Ivan Philipson, and I will catch you next time.

Peace.