Richard Prum on Birds, Beauty, and Finding Your Own Way (Ep. 126)

How ecology and selection drive avian evolution.

Richard Prum really cares about birds. Growing up in rural Vermont, he didn’t know anyone else interested in birding his own age. The experience taught him to rely on his own sense of curiosity and importance when deciding what questions and interests are worth studying. As a result, he has pursued many different paths of research in avian biology — such as behavioral evolution, where feathers come from, sexual selection and mate choice — many of which have led to deep implications in the field. In 2017, Tyler agreed with several prominent outlets that Prum’s book The Evolution of Beauty was one of the best books of the year, writing that it “offers an excellent and clearly written treatment of the particulars of avian evolution, signaling theory, and aesthetics, bringing together some disparate areas very effectively.”

Richard joined Tyler to discuss the infidelity of Australian birds, the debate on the origins of avian flight, how the lack of a penis explains why birds are so beautiful, why albatrosses can afford to take so many years to develop before mating, the game theory of ornithology, how flowers advertise themselves like a can of Coke, how modern technology is revolutionizing bird watching, why he’s pro-bird feeders yet anti- outdoor cats, how scarcity predicts territoriality in birds, his favorite bird artist, how Oilbirds got their name, how falcons and cormorants hunt and fish with humans, whether birds exhibit a G factor, why birds have regional accents, whether puffins will perish, why he’s not excited about the idea of trying to bring back passenger pigeons, the “dumb question” that marks a talented perspective ornithologist, and more.

Watch the full conversation

Recorded May 20th, 2021

Read the full transcript

TYLER COWEN: Hello, everyone, and welcome back to Conversations with Tyler. Today I’m talking with Richard Prum of Yale University. I spotted Richard in the field some while ago and classified him as great American ornithologist. Richard, welcome.

RICHARD PRUM: Thank you. Great to be here.

COWEN: Why is there so much infidelity in Australian birds in particular?

PRUM: [laughs] Well, I don’t think that there probably is an extraordinary amount of infidelity in Australian birds. However, there are certainly a number of classic cases of the investigation of multiple mating in Australian birds, the classic case being the fairy wrens, which have a very weird social system, including one feature, which is multiple mating.

COWEN: How well can we explain why fairy wrens are different in their mating practices? How much explanatory power does ornithology have there?

PRUM: We need to talk a little bit about what makes fairy wrens extraordinary in other ways. Fairy wrens live in cooperative groups, extended families that include multiple males and females of reproductive age. Usually, a large number of them are at least male offspring of previous years that are hanging around helping mom and dad or some adults raise their relatives.

This probably arises — and is very common in Australian birds — it probably arises because of very high habitat variability, in particular variability in rainfall, as you see already. Thinking about Australia, we think a lot about whether there’s a drought or not, right? Under those conditions, you never really know whether you’re going to have enough resources to raise kids.

Another feature is that the habitat is rich in some times of the year, and so as a result, they’re packed cheek to jowl, so there’s no real estate for the kids to go off to. They stay at home, move into the basement, and help their parents until they can inherit the back 40 or take over or bud off, if you will, into a new territory.

That means there’s a lot of reproductive opportunities between groups, but the groups are in separate territories. A lot of what happens in these cooperative species like fairy wrens, people found out, is that the females mate-multiply. That is, they can mate with other members of the group besides the mature or most dominant male. Or they can mate with other males in other groups.

COWEN: Is it variability of rainfall that makes Australian birds weirder?

PRUM: Well, there are two cool things about it. One is that, yes. People have associated cooperative breeding — this special variation in the avian family life, where you get a cooperative behavior among reproductive-age individuals with unpredictable rainfall. That’s a general phenomenon. You find it a lot in different parts of the world.

COWEN: How does the equilibrium work there? Rainfall is unpredictable, and then what happens? It’s all for the equilibrium, so to speak.

PRUM: Yes, sure. Rainfall is unpredictable, and also, the other combination is the habitat is saturated. There aren’t a lot of places to go. What that means is that it’s often more helpful or more useful for individuals to delay dispersal until their reproductive age. Then they’re hanging out, and then, of course, they do work. How they have a benefit is, it could be both helping their relatives — kin selection — or they could be gaining experience, direct benefits, like learning how to raise a family before they get a chance to do their own.

COWEN: Is it the case that birds are more modular in construction than mammals? For instance, they don’t seem to use their wings and legs so much in concert, the way mammals might. Or is that not true?

PRUM: Well, that’s a really cool thing. Actually, if you go back to the gait of a crocodile or any tetrapod, the front legs and the hind legs were really coupled. You have to do that well. Going back, probably, in the very long bipedal theropod dinosaurs — long history of bipedality in theropod dinosaurs. Those things had to be uncoupled, and it required a lot of rewiring both of the motor movement, the brain, the muscles, et cetera. That’s ancient in the lineage of birds.

Think of T. rex with its tiny little forelimbs — very decoupled. Then what birds have done in flight is actually to couple the forelimbs with the tail in flight. We have a part of the axial skeleton which now becomes, in a way, related to the flight apparatus, which are the forelimbs, the front — the wings. It basically turns out to be deep dino biology that birds are just taking advantage of in flight.

On the evolution of flight

COWEN: Here’s a very stupid question. The intermediate steps towards the evolution of flight — why are they efficient? I go through life. Let’s say I didn’t have a car. I’ve never woken up and said, “Gee, I would love to glide today.” Right? Gliding serves no purpose for me, so how is it we get to flight in between? Why did that persist?

PRUM: Yes, deep controversy there. There are lots of careers that have been thrown on the pyre of avian flight origins. In detail, there are two theories. One is the ground up, cursorial theory, that somehow you’re running, and you’re running fast enough, and you start with maybe movements that help you manipulate as you run, and then finally takeoff from the ground. The other is the arboreal theory, or the trees down, that you start with gliding and control movements of gliding, and then eventually to powered flight.

Those folks have been warring at it for almost a century but really going at it for the last few decades. Where does it sit now? The interesting thing is that it used to be that the origin of birds was like a menu where you had column A or column B. Column A was birds are not related to dinosaurs, feathers evolved for flight, and flight evolved from the trees down. Then the opposite was in column B. Birds are dinosaurs, feathers evolved for thermoregulation or for something other than flight, and flight arose or evolved from the ground.

It turns out that the dino people were correct. Feathers did not evolve for flight, and birds are dinosaurs. It turns out the column A was actually right about flight. Flight most likely evolved from the trees down, and there’s a whole bunch of reasons why, starting with gliding like a flying squirrel, and then controlling your gliding, then using those control movements to create a flight choke.

COWEN: But flying squirrels are not that plentiful, right? They’re not taking over the world. They don’t seem to do that well.

PRUM: Yeah, they sure as hell are taking over Borneo, I can tell you. When you go into Southeast Asia, there are forests where there are incredibly diverse gliding mammals of multiple families. That’s probably because the forest is made mostly of dipterocarps, which look like really, really high broccoli, 30 meters high. There’s a lot of space.

Why are they gliding? Well, to get away from predators. Or even, ultimately, they get good enough at it that they can use it to disperse from tree to tree. The idea is that that’s how it started. Of course, maybe one of the reasons why flying squirrels haven’t taken over the world is because they never got to powered flight like birds did, which obviously is going a lot further.

COWEN: Now, according to Jennifer Ackerman, duetting of song occurs in about 16 percent of bird species. How well can we explain the cross-sectional variation there?

PRUM: Well, a lot of explanation in biology is historical explanation. I don’t think that comes out in a regression line. One of the things we see is, again, social complexity in tropical birds. You’re much more likely to have pairs that endure for the whole year and resident on a territory. That long-term social relationship will support duetting.

COWEN: Is this the migratory birds that have lost duetting?

PRUM: Well, duetting is still highly concentrated in just a few groups — songbirds and a few other lineages. There’s a lot of things like gulls and penguins and shorebirds that don’t have duetting per se.

COWEN: If you were carving up how much of this universe of duetting is explained by historical persistence and path dependence as opposed to theory, what would your proportions be?

PRUM: I don’t know, but I’d have to say a large amount of it — 30 percent, 50 percent — is history because a lot of these groups originate, like Australian birds — one of the interesting things — all of songbirds are out of Australia. They persisted there for a very long time. There are a lot of lineages with lots of female song and some duetting and complexity in Australia. Then a few, a very few lineages that came out of Australia. That kind of long history in a place means that you’re likely to keep something like that, or not have the opportunity or reason to change it.

COWEN: Putting path dependence aside, if you were trying to give us the most fundamental explanation of why sexual dimorphism is different in birds compared to mammals, what would that be?

PRUM: Well, that’s actually a really big question. [laughs]

COWEN: Of course, but the most fundamental factor — what is it?

PRUM: The most fundamental factor is that most birds don’t have a penis.

COWEN: Talk me through the equilibrium there.

PRUM: [laughs] There’s a lot. That’s where we start: Most birds don’t have a penis, which means that one of the things that happens in avian evolution that’s distinct from mammals is that the kids require a lot of care. They’re growing up in the nest, they’re hatching out of an egg, but they’re very, very vulnerable until they can fly.

Birds have a very rapid period of rapid development. That means that they grow up and leave the nest, and you need two parents to do that efficiently in most diets or most kinds of ecologies. That means the dad’s got to be at the nest.

We usually thought that you have social monogamy, at least two birds helping raise the young, because the young are so needy and they have to grow up quickly. But there’s another possibility, which is that they could evolve to be so needy and grow up quickly because they managed to get males at the nest.

One of the things that happened in the phylogeny of birds — you’ve got ostriches and their relatives, and you’ve got chickens and ducks, and then you’ve got the rest of birds, and that’s a bunch. That’s the vast majority of them, and in that lineage leading to the rest of birds, the penis evolved away, and the question is why. My own theory is that female birds preferred mates that did not have a penis.

One of the ancillary benefits of that, one of the correlated benefits of that is that they were no longer subject to sexual coercion or sexual violence. They could be coerced behaviorally, but they couldn’t be forcibly fertilized. That means that they have freedom of choice, and what do they do with their freedom of choice? They choose beauty. One of the reasons why birds are so beautiful is that males don’t have a penis. They have to be subject to choice in order to effect reproduction, and also they have to invest if females require it.

One of the reasons why birds are so beautiful is that males don’t have a penis. They have to be subject to choice in order to effect reproduction, and also they have to invest if females require it.

COWEN: Now, sometimes albatrosses don’t breed until they’re 20 years old or even, on average, maybe it’s what — 10 years old. What are they doing in the meantime that’s so important?

PRUM: Well, that is a deep question. I actually have a student working on delayed maturation. What are they getting better at, right? Because life history theory tells you that there’s no upside to delaying reproduction if all things are equal, but they must be getting better at something.

A lot of people think it’s foraging. Raising that one young on an island, and foraging hundreds of miles out in the ocean and returning, and there’s the whole social relationship to raise an albatross family. It’s tough. Being efficient enough to raise may take years to develop. You’ve got to get good at foraging before you can raise a baby, and certain diets certainly require that. We have the same thing in many large gulls. It could be that they’re getting better at foraging.

On the economics of ornithology

COWEN: One thing I like about ornithology is it has a lot of game theory, just like economics does. Sometimes when I read it, it feels very familiar. Let me ask you whether you all have the same problem that we do. With economic theories of signaling, once you get past the very simplest model, typically there are many multiple equilibria that theories are hard to test. They can predict all kinds of things, and you don’t know what to do next. Does ornithology have the same problem with signaling, an extreme of multiple equilibria?

PRUM: I think so. The question is, is that a bug or is that a feature? Because nature really does look diverse. The idea that there could be multiple equilibria is not a problem for us, or at least for me. Also, you can tell from a lot of my answers, I’m really interested in history itself as interesting, explanatory powers.

The other feature, though, is that many of my colleagues in evolutionary biology have bought the economic line that communication is about efficient exchange of information. But there’s a lot of things we communicate about that isn’t about information. A lot of my work has been on ornament and sexual display.

The popular idea is that beauty and the sexual attraction in birds — and nature in general — is a kind of efficient way to communicate actionable information about mate quality. But the other possibility is that it’s merely beautiful, that it is an irrationally exuberant market bubble in a genetic mating market, and that they’re off the ranch.

I am really fascinated by those kinds of communication that are about suasion and not about information. There are some contexts where, of course, we know that signaling theory applies well, but there are plenty of others where it doesn’t.

COWEN: Here’s part of what bugs me. As an economist, I see multiple equilibria. Whether I like them or not, I feel comfortable with it. You’ve stressed in your work there’s a certain arbitrariness to a lot of aesthetic values in birds and, indeed, elsewhere.

But if you just look commonsensically at a lot of animals — including birds, including humans — it seems that markers of health and fitness and vigor are strongly correlated with sexual attraction, and that’s not arbitrary. We have these models with a lot of multiple equilibria, and then we have our common sense, which says go to the gym to get a date — and birds also. How does that all fit together? Doesn’t that mean it’s not arbitrary?

PRUM: Well, the interesting thing that I think you have there — you have multiple ways to predict that outcome. I’m going to take an aesthetic example. For example, say you went to the symphony, and there was a violin concerto or, if you prefer, a blues concert or even a rap concert. And in the middle of the cadenza or the solo or the biggest thing, the performer begins to break out in a sweat. They’re really exerting themselves.

The question is this: Do we like the music because they’re sweating? Or do they have to sweat in order to make the musical performance that the audience likes? Both of those are equal. But most people would say that this is an indicator of quality because they’re pushed to motor limits, but aesthetic processes are going to do the same. We don’t like the ballet because many amazing artists and athletes are injured in the process of producing the ballet. We like it because of the aesthetic impact of the ballet.

There are other hypotheses for why traits are extreme, and maybe at the limits — performance limits or health limits — of those individuals. How do we differentiate between those two? Well, I spend a lot of time thinking about that, and I think that the special hypothesis — the one that demands specific evidence — is that the correlation is actually a result of the relation between the signal and some other kind of benefit, other than the benefit of beauty.

COWEN: I have cardinals and blue jays in my backyard. I enjoy them greatly. I like their colors. If bird aesthetics are arbitrary to the mating processes of birds, why do I also find it beautiful? Isn’t that a funny coincidence?

PRUM: That is deeply cool. I think that’s because humans are intelligent, and we have time on our hands and excess cognition and curiosity to burn, and that leads us to become fascinated by nature.

But interspecific aesthetic regard is a fascinating thing. In the case of color and the case of song, it’s explicable in some ways because at least some of this is physics. There is an inherent wavelength relationship between various color combinations. The same for acoustics, in which we can imagine the harmonic relationship between notes in a bird song, just like we could analyze a piece of music.

The real fundamental mystery is why do flowers smell beautiful? That one does not have [laughs], at least immediately, appealing answers because, it turns out, there are no receptor genes in common between a bee and a human, and they’re responding to the same flower odors in a similar way.

I don’t think it’s because the olfactory space is just filled with all sorts of other things, and that’s where they’re left, and we learn about that. I think they are generally positive. I think there are graduate-level research questions to be pursued in interspecific aesthetic impression.

COWEN: Building on that example, what can avian evolutionary theory learn from how flowers attract pollinators through signals? It seems they use color, they use nectar, they use deceptive mimicry, but it can’t be the same kind of Fisherian co-evolution if the final result is beautiful. Doesn’t that imply it’s not Fisherian co-evolution that is generating the beauty?

PRUM: Well, certainly, one thing about pollinator and plant interactions is that they are different species. From the pollinator perspective, the pollinator is getting food, nectar, and sometimes eating the pollen. From the plant perspective, the plant is getting animal aid in dispersing their gametes to reproduce with other plants. What is the plant doing? The plant is investing in another animal. In order to do that, it has to advertise its opportunity.

This is really in the realm of advertising. What the flower really has to be is memorably rewarding. To me, that’s like going into the grocery store, and you look at a Coke can or a box of cereal, and there’s literally nothing on the can or on the box that will tell you anything about what the experience of eating or interacting with that product will be like. And that’s exactly what flowers are like.

There’s a whole realm of this field in biology, trying to emphasize co-evolution, that particular flowers and particular pollinators interact. Of course, those do occur, but the vast majority of flowers are pollinated by generalists and the vast majority of pollinators are generalist pollinators, so they have to be memorably rewarding. Some of them are like Doritos — you’ll reach over and grab one, but it’s not really what you need.

Then some products you’ll go further for because they’re really, really rewarding. This implies, actually, that bees are making choices. If bees were not making choices, then the world wouldn’t be full of beautiful flowers. All the flowers would be exploiting that one button that was the most efficient way to get that bee just to show up and feed.

But of course, all the flowers would come to look like each other, and then they wouldn’t be carrying their pollen to another one of their same species, so the whole thing would fail. Bees are making choices, and they’re making aesthetic choices based on the memorably rewarding experience of using a flower.

Of course, for a bee, a flower is like architecture plus olfaction, and actually electric. It turns out that hummingbirds and insects establish a static charge as they fly. As they approach the flower, it’s like when you rub a balloon on your hair. You can feel the balloon getting near your hair. Your hair starts to stand up or whatever.

As they approach the flower, they can actually experience this electric charge. The hairs on their body stand up, so they can tell. And of course, when the bee forages at the flower, the charge is neutralized. They can tell how recently that flower has been visited — before they even get there — by the static force acting on their hairs. This is a subjective experience that really influences their choices in the world.

What does that have to do with bird breeding, your question? Well, it has to do with the fact that we put the subjective experience of the animal at the center of our analysis. Indeed, that leads, I think, to a really accurate understanding of what’s going on in nature.

Now, you mentioned Fisher. We didn’t talk about that, but what is a Fisherian process? A Fisherian process is a self-organizing sexual selection mechanism where genes for preference — liking long or short tails — become correlated with genes for the trait — having a short tail or having a long tail. Individuals who like long tails are going to find mates with them, and anyone who likes short tails are going to find mates with those.

Those two forms of variation will start to co-vary, and that means when an individual selects on a mate, they’re also indirectly selecting on co-varying or correlated genetic variation for preference. That means the whole thing can just run itself, and of course, it does and produces a lot of diversity.

COWEN: Before we move on, let me put in a plug for your excellent and award-winning book, The Evolution of Beauty.

On birding

Now let’s go to birding. Let’s say you’re a birder with a collecting mentality. Should it count if you only hear the bird, like a nightingale in a thicket?

PRUM: Well, it definitely counts. The question is, what does it count for?


PRUM: I am one of those birders, and moving from animal subjectivity to birder subjectivity — bird-watching — what the list really is about is accounting for your subjective experience of the bird. It doesn’t just matter that there’s that bird in that tree. What matters is, did you see it or did you hear it? That’s your experience of it. Hearing a bird — for some birds — is more spectacular than seeing them, obviously.

But yes, people do make different sorts of lists. Typically, for what’s called one’s life list, people really want to see the bird. “Have I ever seen the bird?” But if it’s for a more minor list — your day list, your state list, or actually data points — then hearing it is just as good as seeing it if it’s for the purposes of data.

COWEN: Now, amateurs have so much ready access to technology: iPhones, air pods, so much more. How is this shaping the evolution of bird-watching?

PRUM: Oh, my gosh, it revolutionized it. There are two programs produced by the Lab of Ornithology at Cornell University that have really transformed birding. One is called eBird, where you can keep live checklists on your phone as you go.

Then the other is Merlin, which will actually identify photographs, using artificial intelligence of birds. They take a photograph of a bird and load it up, and it’ll tell you what it is for most parts of the world with incredible accuracy for common birds and really quite elaborate ability for even obscure birds.

What you have to say now is, in addition to an electronic camera, young folks today are birding with their phones. Their data are going up to the cloud in real time and influencing what other bird-watchers are doing and becoming the subject of science through citizen science, so it’s really been a huge revolution.

COWEN: Birding in this sense is a bit like chess, a quite unlikely winner from the rise of the internet and technology but exploding in popularity?

PRUM: I don’t know. I guess my fingers aren’t quite enough on the pulse. We went through a long time because as a kid, I grew up birding. I started at the age of 10. For me, it was all about going outside. It’s like, I’m going out after school. Screen door slams, and there you go, you’re off outside. I have been concerned for a long time about whether the way children are raised in the modern world that not enough of that is happening.

If people get back outside through their phones, I think that’s great. Still, I’m old school. I’m not keeping my checklist during the day as we go. That means my data aren’t probably as high quality either, but I think some people are.

COWEN: What’s the most important bird missing from your personal checklist? Hearing it doesn’t count, you’ve already told us.

PRUM: There are lots of different measures, but sometimes there’s no rationality to it. Well, about five, six years ago, I took a trip up to northern Norway to see Steller’s eider, a duck. If you imagine between Norway and Alaska — what is there? Way, way up there. That’s where they nest. In the winter, they only barely come down to Norway or Alaska.

I wanted to see them, and I got up there. Ten years ago, on that date, I would have seen a thousand. Five years before, I would have seen a hundred. By the time I got there, climate change was happening so rapidly in the Arctic that I got there, and there were none to be seen on that date.

I’ve been really desperate to see Steller’s eider — just because. Because you take a notion, and that’s the beautiful thing. History of life is a tree. I’ve been very interested in the phylogeny of birds. Who’s related to whom? The big tree of life and the tree of birds. You can say, “I’ve seen these and these species, but I haven’t seen these. What’s the species most unrelated to any species I’ve seen that I could . . . What would be the species that would give me the best addition to my total sample of avian diversity?”

COWEN: A moa.


PRUM: Exactly. The answer right off the bat, for most people, would probably be the hoatzin. The hoatzin is a very weird vegetarian or leaf-eating Amazonian bird. The bird probably most unrelated to any other living bird. After that, it gets a lot of specific things to what you’ve seen. The next trip you’re planning — those are the most important birds to see.

COWEN: It seems there’s been a lot of big advances on the research side lately. There’s cheap tagging, much easier radio telemetry, applying machine learning to bird song. What’s the most important thing going to come out of all these very new advances?

PRUM: You’ve only just begun to skim the surface. I’ll say this proudly, just to embarrass myself. I used to think that the chicken genome was the most uninteresting thing I could ever imagine. It turns out genomics has really been fantastically revealing for features we ultimately want to know about, like the funny features that characterize birds. Transcriptomes — taking a tissue and sequencing all of the RNA that’s being expressed at the moment, getting an idea of what expression states are in different kinds of cells — on up.

On your tagging technology, that’s been fantastic. The Max Planck Institute of Animal Behavior in Germany has put up ICARUS, a big satellite that is capturing in real time data on animal movement, individual animals. They’re getting basically the whole entire movement of a life of a wild animal.

You get enough of those, and sure enough, you got a very new view of what’s going on in the world. The interesting thing about progress is you never know what it’s going to turn up, right? That’s where the opportunities are, but figure out what’s the best way to use that technology to answer or address a cool issue in birds.

COWEN: What’s your favorite word for a group of birds? Is it a covey of quails, an unkindness of ravens, a parliament of owls? Which one?

PRUM: I don’t know, I think my favorite word for a group of birds would be the genus. [laughs] That’s a different group, a historical group.

COWEN: Should we use bird feeders in our backyards?

PRUM: I think so. I love my bird feeders. I really enjoy them. I think that there are some downsides, in particular being sites of potential infection for diseases that are moving through. They’re the opposite of social distancing. They’re social concentrating. They can be centers for conjunctivitis-like illnesses in finches recently in the United States, et cetera.

COWEN: Do they just worsen the Malthusian equilibrium? How well does the Malthusian subsistence theory predict bird populations? Are birds at the margin of subsistence, first of all?

PRUM: One of the things that Malthus didn’t take into account, or much account, was variability, the fact of an ice storm, for example. A lot of birds in the winter — if you think about birds at your feeder — they can do fine at -5, -10 degrees Fahrenheit, -20 if you get the chickadees — if they have enough food. But if they don’t have access to food, they will die in a single night. These ice storms, which could be just 32 degrees, covering all the food, the whole environment with ice for a day — can be just devastating for lots of birds.

If there weren’t feeders, their populace would really be harmed. Things like Carolina wren, which is a bird expanding — I think a big ice storm will set down Carolina wren populations at the edge of the range in New England or the Mid-Atlantic. For five years, it’ll take them to rebound after that.

COWEN: Do we have good theories of bird property rights, somehow invoking the ideas of relative scarcities to explain when birds are territorial or not territorial? Or is that just a big mess that we don’t understand?

PRUM: No, there are some good things. If you’re, say, an aerial insectivore — you’re catching insects in the air — you’ll be territorial if you catch insects that are 15 inches away from a branch. Just going out for a little sally. You could defend all those branches — that’s my territory. But if you’re a swift or a swallow, and you’re flying hundreds of meters or hundreds of feet up in the air and all of it, it’s very hard to defend that, so you give it up.

Lots of marsh birds . . . Marshes are very rich — lots of bugs. If you can grab your patch of lily pads or bulrushes or cattails, you can really do well. You want to defend that. But if you’re a puddle duck, there’s going to be lots of water there, and things somewhere 18 inches below the surface of the water — you can’t really defend that.

For the most part, it’ll vary with your body, your ecology, et cetera. We can do experiments. For example, sometimes hummingbirds will defend a floral resource, and then when it gets big enough, they’ll just give it up because there’s no reason to do it anymore.

On things under- and overrated

COWEN: Now, in all of these conversations we have a segment in the middle called underrated versus overrated. I toss out a name, an idea, a place. You tell me if you think it’s underrated or overrated. Got it?

PRUM: Okay. It could be a combination of Rorschach test too. Because what do we think of the thing that’s named? But yes, go for it.

 COWEN: Roger McGuinn.

PRUM: I don’t know who that is.

COWEN: I thought you were an expert about the Byrds. Here’s an easier one: Larry Bird.

PRUM: Larry Bird. [laughs] Larry Bird is perfectly rated.

COWEN: The birdsong music of Messiaen, the French composer.

PRUM: I think way underrated. I love that stuff.

COWEN: Charlie Parker. What’s your favorite cut by him?

PRUM: I know it when I hear it, and I actually have albums where I know which cut is which, but I don’t know . . . I haven’t looked at the liner notes in order to know —

COWEN: It has to be “Ornithology,” right?

PRUM: Yes. Underrated.

COWEN: The Alfred Hitchcock movie, The Birds.

PRUM: Overrated.


PRUM: I think there’s a lot of damage to be afraid of nature. I know people that are bird phobic, and I’m not sure whether it arises from something like that movie.

COWEN: Is the diversity of the protagonists in The Birds a kind of portent? Does that make it more terrifying?

PRUM: Or just the sinister turn that all of nature is out to get us. When I saw it — and maybe it is in black and white; I saw it in TV in black and white as a kid — I just crossed my arms, and I don’t know, I’ve never seen it since. [laughs]

COWEN: John James Audubon as an artist — overrated or underrated?

PRUM: I think we’re still underrating what he achieved.

COWEN: Who is your favorite bird artist? Is it him?

PRUM: An artist? No. George Miksch Sutton. George Sutton, who is an American watercolorist of American birds. Fantastic, fantastic renditions of birds. He really was amazing at both the art and the ornithology.

COWEN: Putting aside birds, travel in Suriname — should I go?

PRUM: I haven’t been in more than a decade, but you should definitely go. It’s a marvelous part of the world. I think it’s on hard times in recent decades. Beautiful, beautiful people and marvelous avifauna.

COWEN: Let’s say a good friend comes to you, who has a reasonable income, well educated, but not an ornithologist, not even a birder, but interested. This person says, “I have a month of my life, and I want to go around the world. I can go anywhere feasible and look at birds.” What is the perfect tour for that person? You’re in charge. Where do you send them?

PRUM: That’s fascinating. I think one of the things that can impress a person without the experience to understand that the hard work is worthwhile, or will be worthwhile, is spectacle. Things like penguin colonies in the Antarctic are just profoundly amazing. That would definitely be a possibility. Other kinds of ornithological spectacle depend on how young they were. Some people, there are some things —

COWEN: Let’s say they’re 40. They’re able-bodied, but they’re not a rock climber. Do you send them to Colombia? To Panama?

PRUM: Yes, but the problem with some of those places, of course, is that the bird-watching is hard. It really is hard work. I know, I’ve taken students who know little — well, they had had half of my ornithology course — taken them to Ecuador. We’ve seen 490 species of birds in 10 days. Usually, [laughs] their brains are fried. It’s a lot of work, but I think you need to be over a little hump before you do that, so a spectacle would be good.

One thing I did was, in 2018 in Brazil, I went to see a nesting site, a nesting colony of Lear’s macaw. It’s an aqua, bluish-green, turquoise parrot, and it nests in a cliff face where there are holes. They come out of this cliff face in the dawn. It’s a huge cliff with a cavern in front of you, and they fly around. It was unbelievably moving. It’s unbelievably beautiful. These are intelligent birds that live for decades, know each other as individuals. Unfortunately, critically endangered, but being well conserved at this site.

There are a number of things like that. An oilbird cave is another incredible thing for the right person. These are nocturnal frugivores. They live in caves in South American Andes. They fly out of the cave at night and fly dozens or even hundreds of miles out to forage on avocado and palm fruits that they bring back to the cave and feed to their babies.

They’re called oilbirds because they used to capture them and render them down for oil, and cook with it, and make candles out of it. That’s how fatty they are from the avocado oil. Going to an oilbird cave is amazing. Often, deep in the cave, you’ll see a forest of etiolated seedlings — all white, no photosynthesis. They’ve started to propagate in the guano. The guano will look like guacamole green because that’s what they’re actually eating: avocados. [laughs]

It’s the edges of ornithological experiences. For the right person, some things like that could really be the best.

COWEN: Why is it that birds such as falcons and cormorants hunt and fish with us? How did that happen?

PRUM: Domestication is a cool thing. It’s where people intercede with nature and somehow co-opt the biology.

COWEN: I want to know the “somehow.” Is it that they’re smart enough to figure out gains from trade? Has it become instinct?

PRUM: I think it’s that — mostly that you get the animal while it’s young. Traditionally, in falconry, you’d get the bird on Southern migration and capture it. You could tell it was naïve. You could fool it easier, so it’s easier to capture. Then you’d either hold it for a year over the winter and then let it go, or then later you kept with it. They haven’t become a domesticated strain, if you will, like a chicken or a dog, but you’re co-opting the capacity.

It’s like having a pet parrot. The parrot thinks it’s a human, and the way it develops in this new environment with human social partners is extraordinary indifferent. That’s how that works. The fishing with the cormorants — I don’t know if it’s still going on. It was a tradition in areas of Japan, I know, but I’ve never witnessed it or seen it happen. I think that those birds are captured from the wild. They don’t breed them, I don’t believe.

COWEN: Here’s a question from a reader, and I quote, “Osprey. They hatch early July, are flying by the last week of August. The adults leave around September 15th, heading south, and the young ones hang around for a couple of weeks bulking up on the late landlocked salmon spawns, then head south.” End quote. How exactly do they know where to go? How exactly does this bird instinct work?

PRUM: [laughs] This is great. This is actually an area where we’re learning a lot because of new technology. Now, we have these GPS transmitters that would get satellite information in real time on where those birds are. This is the work mostly, I believe, of Rob Bierregaard, who has done this in ospreys. Most ospreys spend the winter in a very narrow area of the llanos of Venezuela and Colombia. That’s where the ospreys go, or at least in this continent.

What the young ospreys do is they fly off the East Coast, wandering around in the ocean. Sometimes they hit Bermuda. Sometimes they might return to South Carolina. Then they basically mess it up, but somehow or other, eventually, they get down to the Antilles and they realize, “Oh,” and they follow the chain of the Lesser Antilles down to South America.

Then, on the way north, they realize, “Oh, we’ve got the Guajira Peninsula in northern Colombia. We pass over it, and we get to Jamaica.” Then they go boop, and they return up through Florida to the east. Then, what do they do next year? They go down to Florida, jump over to Cuba, come down the islands. So it’s a combination.

What do birds need to migrate? They need to have a magnetic compass. They also have a sun compass. They have to have a clock and an experience of the sun. They need a map, about which we don’t know much. Then they have to have a bearing, like where they’re going. Then, a sense of how far to go — from the map — whether they have reached their destination.

Then, in real life, they experience the world and then refine that with experience. They have some innate properties or capacities, and then a lot of experience. Of course, a lot of them fail to learn, and I’m sure some of those birds that wander out in the ocean fail.

COWEN: How much is there a generalized G factor for the intelligence of birds? For humans, we would call it a G factor. If you’re smart at one thing, you tend to be smart at another. If a bird is, say, good at using tools or good at playing, is the bird just smart flat out? Or are birds highly specialized in their smartness? They’re really smart at one thing, and then very stupid at another?

PRUM: That’s a great question. I think that there are lots of examples of extraordinarily specific smartness in birds that doesn’t apply. But the birds that are really smart tend to be smart at a lot of stuff. There’s a few of them that stand out with breathless smarts. I’m thinking parrots and crows, corvids and parrots. They’re the most notable. They stand out above everybody else.

Indeed, if you look at the pallial neurons, which are basically the ones with the smart connections, a parrot will have more pallial neurons than a monkey with a brain that’s four or five times as large. They’ve gone a different route in their organization of cognitive complexity, and they’re really doing it really efficiently. But there are all sorts of extraordinary intelligences that are very, very specific in birds, I think, that don’t have that property.

COWEN: Do you think ravens and crows understand death?

PRUM: Oh, wow. I don’t know.

COWEN: A lot of birds go crazy when they see other dead birds, right? They make a lot of noise. Doesn’t mean they understand death, but they know something’s gone wrong.

PRUM: No, but I do think there are examples of birds. Carl Safina has cataloged these. I don’t know that literature, but there are certainly examples of birds that appear to be mourning or understanding that their compatriots are physically present, but no longer living, [laughs] whatever that is. I wouldn’t be surprised if they do. They know each other as individuals deeply and appreciate it.

You were mentioning albatross earlier. One of the things about albatross, the big ones — they nest every other year, so in every albatross colony, there’s an even-year cohort and an odd-year cohort that returns, and they take off the other year, then come back to reproduce.

They are monogamous over decades if they live long enough. They’ll spend that year off — 9 ½ months or 12, 15 months, whatever it is — and they’ll even fly around the entire Southern continents, around Antarctica a couple of times, then return to the Farrallon or Malvinas islands, and then meet that same mate and then mate again. They recognize each other. I certainly think they would understand that that bird is not returning.

COWEN: Birds have culture, right?

PRUM: Absolutely. Just one example of culture: half the birds of the world learn their songs from other members of their species, almost always not their parents. What that means is you’ve got a decoupling from a genetic variation and the phenotype or the presentation of the animal. So, what do they do? They learn from other individuals, and they learn preferences.

The birds in the areas around Chicago, New York, and Boston sound differently, just like the people do, and for pretty much the exact same reason. It’s not because of the wind in Chicago or the baked beans in Boston. It’s isolation by distance and historical contingency and cultural change. Birds have been doing culture for tens of millions of years, which puts us to shame, certainly in terms of diversity.

Of course, we piled a lot of culture on our one little invention, and that’s notable and interesting in its own right too.

COWEN: Will puffins perish?

PRUM: Wow. The oceans are getting deeply screwed up, and climate change — both of these combinations are really affecting the Arctic or northern . . . I don’t think the puffins will go extinct on a couple-century scale, but their distributions and lives are really going to change, I think.

COWEN: Should we try to find the DNA of passenger pigeons and bring them back?

PRUM: I find this rewilding business or revivification to be really off-putting. However, and mostly because of —

COWEN: But why?

PRUM: The reason why it went extinct is that it needed continental scale, richness of chestnut and oak forests in order to survive, and there is no place in the world where that is. They were extraordinarily social. They only laid one egg a year, which means that they are very, what we call K-selected. As a result, there’s almost no place for them in the world.

Having said that, most of my criticisms are also framed by the unrealism of the technology. Okay, so we find a few genes, and we put them into a band-tailed pigeon, the sister group, the closest extant species. We put them in, and we make it a little bit more like a passenger pigeon. Wouldn’t that be cool? I’m like, “Well, no. That’s not really cool.”

If we really had the technology to really bring back passenger pigeons and do that, sure, I’d be into that, but we are very, very far from that.

COWEN: What’s the best overall framework for thinking about the actual value of avian biodiversity when we face real tradeoffs? Are we going to put in more wind power? It’s going to kill some birds, but it might help with climate change. How do we even begin to approach a question like that? Do we ask the economists? You’re not going to ask me, right?

PRUM: Actually, I’m just grading term papers right now in ornithology, and I had a term paper [laughs] in ornithology exactly on this question that was pretty good — by a political science student with interest in environmental policy, so yes. I don’t know if I’ve got the training to say that, except to understand that, yes, it is real tradeoffs. I think we’re making them all the time.

If there were enlightened policies like carbon tax, et cetera, even a little bit of it, we’d be in a much better situation to see where maybe it would solve itself, but there’s certainly a lot of reason for concern.

It’s also a lot of interesting resilience. We’re looking in New England here where I live. We used to have chestnut trees, and they disappeared. And we used to have elm trees, and they basically became irrelevant. Now, we’re looking at hemlocks disappearing because of the woolly adelgid, and now the ashes — the emerald ash borer from China has arrived.

We’re losing major trees, and yet, there still seem to be forests. We still seem to have a lot of birds in them. Now, there are fewer birds — that’s true. There seems to be some kind of resilience despite this change. I don’t know. I wish I had a better answer, but I’m still a historian rather than a predictor in my work.

COWEN: Is one billion too many sparrows?

PRUM: [laughs] No.

COWEN: Is it wrong to own a cat that you let outside?

PRUM: Yes.

COWEN: Just flat-out wrong?

PRUM: Yes.

COWEN: But if we don’t know how to make the tradeoffs, how do we know it’s wrong?

PRUM: Well, because that is really, really clear. You have concocted, created an artificial predator that you’re keeping really happy and healthy, and feeding it, and keeping it in a peak condition, so that you can have it go outside and entertain itself, and its entertainment is damaging to the world. The scale of cat death — I don’t know the numbers, but way more birds are killed by cats than are killed by all the wind power in America. It’s devastating. It’s billions of birds.

COWEN: I read an estimate recently. It did not seem to be scientifically serious, but it suggested that a billion birds die each year just by crashing into human things. Is it plausible that the number is that high?

PRUM: Sure, but I’ll tell you that the data for cats is way bigger than that. Cats kill more birds than all the skyscrapers and windmills, and these are pets, and also feral cats that are maintained by humans.

On the Richard Prum production function

COWEN: Very last segment of our chat. It’s what I call the Richard Prum production function. How did growing up in rural Vermont help influence who you are professionally and lead to your success?

PRUM: A lot of my science is deeply rooted in natural history. I am not interested in law-like properties of nature, but in the idiosyncratic instances. A lot of that view grew out of bird-watching, grew out of my childhood and being interested in birds. A lot of people do birding and then go into science, but for me, somehow that birding experience affected how I do science.

I have a minority style of mind in modern science. A lot of great scientists out there, but most of them are not thinking the way I do, and so, as a result, there just seemed to be more opportunities laid out —

COWEN: What’s that difference in how you think? How would you characterize it in its most fundamental form?

PRUM: I really care about birds.


I think that birds are really interesting. I am not necessarily worried about what the other guy . . . Here’s the deal. My favorite Onion article was titled “NSF studies show science is hard.” [laughs] Yes, science is hard.

What is people’s response to that, the fact that science is hard? A lot of people will go and say, “Well, if I’m going to expend a lot of energy, I better do something that somebody else thinks is important. What do you think is important?” They look to the sides, and they think that doing something that somebody else thinks is important is their mission.

I think about the birds, and I think, “What is the coolest thing that I could do with my time now, or this day, this next day ahead of me that would solve something?”

A lot of people will go and say, “Well, if I’m going to expend a lot of energy, I better do something that somebody else thinks is important. What do you think is important?” They look to the sides, and they think that doing something that somebody else thinks is important is their mission. I think about the birds, and I think, “What is the coolest thing that I could do with my time now, or this day, this next day ahead of me that would solve something?”

Of course, I love to connect that to big science, whether it’s where do feathers come from or how do blue birds get blue? Areas that I’ve worked on. And in many cases, they turn out to have deep implications for their field. It’s that regard for the birds. It’s what Donna Haraway calls situated knowledge. It’s not the voice from nowhere. It’s the specific instance, the view from here and where that “here” is.

I recently read a paper in an esteemed journal called The American Naturalist, which is very highly ranked but sounds like a wildflower or garden club report or something. Anyway, The American Naturalist, and you got 2,000 words into the paper before you realize that it’s about house wrens in Ohio. Now, what is going on there?

I think people are embarrassed about the position of their work. They’re so interested in the general principles of, “Oh, this is a big incisive issue that biologists need to solve.” And that generalized frame is leading us often astray to do work that’s uninspired or a lot incremental, like everybody else is doing, et cetera.

You’re pushing me in new ways. Maybe it’s being the only bird-watcher that I knew under the age of 25 as a child for a long time, led me to think, “You just got to rely on yourself to figure out what’s of value in your work.”

COWEN: Who first spotted your talent for studying birds, other than you?

PRUM: As a kid, I interacted with a number of people that were mostly garden club ladies. They were my mom’s age or older retired people. They had cars. I did not have a car in fourth grade, fifth grade, so it was a great deal. They certainly did a great deal to cultivate me, but —

COWEN: The garden club ladies are underrated. That’s what you are telling us.

PRUM: Absolutely. [laughs] That’s a big one. Then natural history — their introduction to flowers and ferns and to another way of being outdoors, which, actually, I related to much better than the Boy Scouts, which I left pretty quickly. Then I met a young Yalie, then hippie, a guy named Tom Will, who’s now just recently retired from Fish and Wildlife Service. He was a great mentor early on in birding.

COWEN: Last question. Other than the obvious, such as intelligence, hard work, how do you recognize a very talented prospective ornithologist? What is it you look for?

PRUM: You just get these responses. Luckily, I’ve had the privilege to teach lots of really amazing people, but you’re explaining something to somebody, giving them a bit of a context, and then all of a sudden, you get a shot back. You get a response back, and you’re like, “Oh, yes, they got that. This is the next thing. They got that.”

Then it pitches back, that interplay, where you link something out, and they see where you’re headed and ask you a question. And they often will say, “I don’t know if this is a dumb question, but what about blah?” It’s like, “That’s not a dumb question. That’s the fundamental focus of [laughs] where this whole field is going.”

I used to teach at the University of Kansas. In Kansas, it’s a big, very huge university, but the grad students were as good as anywhere. You would have a marvelous experience of discovering a student who was really smart and didn’t actually know it. They might have been the smartest kid in their town and coming off somewhere in West Kansas. Well, they had never had an opportunity to experience what they were capable of.

It’s really that response. Are they coming back at you with their own thoughts?

COWEN: Richard Prum, thank you very much. Again, a big plug for Richard’s book, The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World — and Us. Thank you, Richard.

PRUM: Thank you. That was really fun.

Thumbnail photo credit: Russell Kaye