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Okay, but does easy living make birds dumber? · Okay, But... Birds

• 0:00
  They're not really that bright.
• 0:01
  They're not the sharpest tool in the shed.
• 0:29
  Growing up, I usually had pets, zebra finches, canaries, fish, hamsters, even a chinchilla for a while.
• 0:35
  But the one I think about most was a little blue budgie named Buddy.
• 0:39
  Buddy was social, demanded Cheerios, took baths in the sink, and pushed a tiny yellow car around like it was his job.
• 0:46
  Over time, he picked up a few words, hello, pretty bird, Buddy.
• 0:50
  It wasn't a huge vocabulary, but every time he said his own name, I felt like I was witnessing something that shouldn't be possible from a brain the size of a peanut.
• 0:56
  Yeah.
• 0:58
  Buddy was, in my mind, the perfect pet.
• 1:00
  Easy to care for, easy to love, easy to keep alive.
• 1:03
  So for a long time, I assumed budgies became popular pets because they're, well, easy.
• 1:07
  But budgies don't come from anywhere easy.
• 1:10
  They come from the Australian outback, where they live in flocks of hundreds, sometimes thousands.
• 1:14
  Yeah.
• 1:15
  chasing rain across one of the most boom and bust landscapes on the planet.
• 1:19
  One year, a place is lush.
• 1:20
  The next, it's dust.
• 1:22
  Budgies have to track water, remember where our food was, communicate constantly with their flock, and decide as a group when it's time to pack up and fly somewhere else.
• 1:30
  That's not the resume of a bird that's casual.
• 1:33
  That's a bird that's paying attention.
• 1:35
  Which raises a question I didn't think to ask back when Buddy was alive.
• 1:38
  If a hard, unpredictable life seems to favor a bigger, more flexible brain, what about birds that have it easy?
• 1:44
  Are stable, predictable environments a kind of evolutionary off-ramp for cognition?
• 1:48
  Do birds get less smart when they don't have to work for it?
• 1:51
  The complication, of course, is that brains are expensive, painfully expensive.
• 1:55
  As an evolutionary biologist, I think about this trade-off all the time.
• 1:58
  Every gram of brain tissue costs more than a gram of something else.
• 2:01
  So there's a trade-off for bigger flight muscles, a longer gut, faster reproduction, or more fat for a hard winter.
• 2:08
  A bird's body is the more interesting version of a budget meeting, and the brain is always asking for a raise.
• 2:13
  Which brings us to the topic of today's episode.
• 2:15
  Okay, but does easy living make birds dumber?
• 2:18
  To help us unpack that, I'm joined by Dr. Carlos Botero, Associate Professor at the University of Texas at Austin, whose research has spent the last decade rewriting what we thought we knew about brains, environments, and the surprising directions evolution can run.
• 2:31
  After the break, Carlos walks us through the cognitive buffer hypothesis and the wild plot twist his lab uncovered when they tested it.
• 2:37
  We get into why, in the harshest places on Earth, non-migratory birds split into two camps, the geniuses and the brutes, with almost nothing in between.
• 2:46
  Stay tuned.
• 2:52
  Well, welcome back to the podcast, everyone.
• 2:54
  I'm really excited to have Carlos here today.
• 2:55
  Thanks for joining us, Carlos.
• 2:57
  Thank you very much.
• 2:58
  Thank you for having me.
• 2:59
  Of course.
• 2:59
  Yeah.
• 3:00
  And I thought we could start off thinking about, you know, this idea that we think of a hard childhood.
• 3:04
  We might think of setbacks or the idiom, what doesn't kill us makes us stronger.
• 3:08
  What does a hard life mean for a bird?
• 3:12
  Well, I think that when we talk about hard life, we need to be aware that birds, just like us, are exposed to a series of challenges, a series of things that they need to do in life, like finding food and shelter, avoiding enemies or predators, finding the right bait or navigating stuff.
• 3:29
  space, seasons, and social systems.
• 3:32
  All of those things are kind of like the challenges that universally pretty much every animal has to deal with.
• 3:38
  And when we talk about hard life, you often think about environments or situations in which some of those challenges are particularly strong.
• 3:46
  So for example, in really variable places where seasons change dramatically, say for example, places where drought and
• 3:53
  heavy precipitation happen, or when there's winter and summer, really extreme changes in temperature.
• 3:59
  Those are situations in which a lot of these challenges get to be really particularly acute.
• 4:05
  So you really need to make sure that you have enough food for the winter, or that you need to make sure that you know where the water sources are during the drought.
• 4:14
  Those kinds of situations are what we talk about when we think about hard life in birds.
• 4:20
  There's a trade-off, right, between environmental stress and cognitive investment.
• 4:23
  Can you talk a little bit about that?
• 4:25
  So the expensive tissue hypothesis was originally kind of suggested that other expensive tissues were primarily considered to be things like the gut.
• 4:33
  So you don't have really long...
• 4:36
  intestines or things that use energy because you just basically can't afford it because a lot of your energy is going to the brain.
• 4:42
  So you have like smaller, more efficient organs.
• 4:45
  But over the years, it has been developed that there are other expressions of that trade-off.
• 4:50
  So for example, in birds, we see that the flight muscles that consume oxygen,
• 4:55
  Huge amount of energy.
• 4:56
  Basically, when you produce that lift, you're using all this muscle power and you're consuming a lot of energy.
• 5:03
  It turns out that birds with bigger brains also tend to have smaller flight muscles.
• 5:07
  And that has been considered as one of those expressions of how costly it is to maintain a big brain.
• 5:14
  Yeah, and that trade-off, the flight muscles are, I mean, for people listening, the flight muscles make up a huge percentage of a bird's body mass, much more than all of our muscles combined as humans.
• 5:25
  And so it would make sense that there'd be a trade-off between that really huge investment in muscle versus brains.
• 5:31
  And yeah, I think...
• 5:32
  I don't know.
• 5:33
  I mean, it makes intuitive sense that the brain would require a lot of energy, but it's probably not something many of us spend a lot of time thinking about, that we're giving our brain so much energy compared to other organs in our bodies.
• 5:44
  Is it just costs in the context of other organs?
• 5:48
  Is it just flight muscles or are there other things too?
• 5:50
  Well, so there's things like the accumulation of fat or other kinds of specific costs, but there's also some other kind of like...
• 6:00
  indirect costs, like for example, development is much longer.
• 6:04
  So usually kind of like, and in humans, that's kind of like pretty evident.
• 6:08
  Our babies basically need a lot of time before they become independent.
• 6:13
  And like, we don't become sexually mature until like way, way...
• 6:19
  It takes much longer than other species, primarily because it takes such a long time to develop the brain to the potential that we need.
• 6:27
  And so we see the same in kind of species that like non-human animals as well.
• 6:34
  Basically, there's a lot of investment that goes into making a fully functional brain.
• 6:38
  And it is even more so when the brain is a big part of what your life strategy is.
• 6:43
  Yeah.
• 6:43
  So what are some like contrasts then for birds where like, what are some of the birds where there's this longer development time because of the brain needing more investment versus the faster development birds?
• 6:54
  Also, for example, like crows and ravens, those are highly social animals.
• 6:59
  So we're not talking about like individuals that take like...
• 7:05
  so many years as humans, but compared to other birds, they do kind of like stay together or they kind of stay in family groups and they take longer to kind of like move on to like forming their own groups or even sometimes they even stay in their groups for many, many years.
• 7:19
  So this independence takes longer to achieve in corvids.
• 7:24
  Is it generally in corvids or crows and ravens kind of highlight it more?
• 7:27
  No.
• 7:28
  Okay.
• 7:28
  So when you look at the whole corbid, it turns out that crows, so the genus corbus, those guys have much bigger brains than almost all of the members of that family.
• 7:41
  Okay.
• 7:41
  Okay.
• 7:42
  They also tend to have bigger bodies and they tend to have like this really big wings.
• 7:47
  So because of those three characteristics, they engage basically in a global radiation and over 10 million years, they basically recolonize the entire area that was previously occupied by Corbett's.
• 8:00
  And they diversified into lots of different species and changed their shapes, their behavior, their habit.
• 8:06
  That's a whole bunch of other things as an expression, basically, of that flexibility that is supported by having bigger brains.
• 8:13
  I guess in my head, it was just all corvids, but it's interesting that it's the crows specifically, like that genus of birds that has this larger brain for body size that has allowed them potentially to flexibly colonize a lot of the world.
• 8:27
  That's really cool.
• 8:28
  Your work has looked at how environmental variability kind of shapes some of these trade-offs across species and populations.
• 8:34
  And I was wondering if you could kind of talk a little bit about what you found and what patterns you found have been surprising.
• 8:40
  I guess my first surprise when I think about the work that we've done on that was the very first project that I developed when I was first starting this research program.
• 8:50
  At that time, I was really interested in understanding this idea known as the cognitive buffer hypothesis, which is
• 8:56
  The idea that having a big brain and enhanced cognition allows you to basically buffer yourself from pressures of selection.
• 9:04
  And the easiest way to think about an idea is we humans have clothing that protects us from the elements.
• 9:10
  We have houses.
• 9:13
  We even are able to live in space and to go underwater for long periods of time by basically modifying the microenvironment around us.
• 9:22
  All of that is an expression of our intelligence, the accumulated resources, our ability to cooperate and move things from one place to the other.
• 9:29
  All that is basically an expression of our brain that makes it possible for our puny phenotypes to be able to exist in almost any conditions.
• 9:39
  So I was really interested in that idea because that idea makes a lot of intuitive sense.
• 9:42
  And it's kind of like the basis of a lot of what people think about when we talk about the benefits of cognition.
• 9:50
  And so the idea, the cognitive offer hypothesis was suggested by John Allman.
• 9:55
  And the idea was that basically variable conditions, variable environments were primarily the drivers of the evolution of bigger brains and enhanced cognition.
• 10:06
  Basically, because when things are unpredictable, when you don't know what kind of pressure you're going to find, being behaviorally flexible could be very beneficial.
• 10:14
  So that idea basically has two different components.
• 10:17
  One of it is that
• 10:19
  that basically that cognition buffers you from selection.
• 10:22
  But the other one is that variable conditions drove the evolution of bigger brains.
• 10:27
  So we tried to test that by actually looking at the models that people use to estimate demographic trends in birds.
• 10:37
  And those basically involve kind of like using a whole series of different parameters to try to estimate population changes over time.
• 10:44
  And one of the model's parameters, it's like statisticians call it usually the nuisance parameter.
• 10:49
  It's like the stuff that they want to get rid of, which basically tells you how much populations oscillate over time.
• 10:55
  And that oscillation for us was really important because we were basically trying to say, like, if climatic variability is really driving those oscillations, then we should be able to see that species that have bigger brains oscillate less than species that have smaller brains.
• 11:07
  So they have more stable populations than others.
• 11:11
  And what we found was that lo and behold, that result is really strong.
• 11:15
  There's lots of evidence suggesting that indeed climate variability is linked to oscillations and brain size.
• 11:23
  But then we did a second thing, which to me was very surprising, which is that we didn't stop there.
• 11:28
  We realized that it's not necessarily, when two things are related, it's not necessarily because one causes the other.
• 11:36
  The correlation is not causation.
• 11:38
  And then we started asking the question, well, isn't that big brains, sorry, that occupying variable environments drove the evolution of big brains?
• 11:48
  Or could it be that having big brains enabled the colonization of variable environments?
• 11:54
  So after doing this analysis in many different ways so that we could account for slightly different assumptions, we discovered that pretty much in every single kind of analysis that we did, it was very clear that
• 12:09
  the evolution of big brains enabled the colonization of variable environments and not the other way around.
• 12:14
  Oh, okay.
• 12:15
  So basically, we found that even though the idea behind the cognitive buffers hypothesis works, and actually there's evidence for it, it was not the exposure to those conditions that drove the initial evolution of big brains.
• 12:27
  So to me, that was a huge, kind of like big surprise.
• 12:30
  Yeah.
• 12:31
  That basically...
• 12:33
  kick the can down the road a little bit because we still don't know exactly why the big brains evolved.
• 12:39
  But I have to say that the more I work with this, I think that it's not just a single explanation, that most likely big brains evolved for a variety of reasons.
• 12:47
  So there's many possibilities.
• 12:48
  One is that the kinds of diets that animals had, the other could be the social systems in which they live.
• 12:55
  Anyway, there's many different things that could have driven the evolution of big brains to begin with, and then that allowed the colonization of those variable environments.
• 13:02
  So I guess that was one of the big surprises at the beginning.
• 13:05
  Yeah.
• 13:05
  But there's been actually many others.
• 13:07
  I don't know if we have time, but I could tell you a couple more if you want.
• 13:10
  I would love to hear more.
• 13:11
  And I think this idea is really important, like that there are many reasons you might grow a big brain or many things that might allow you to like food that's nutrient rich or very social living.
• 13:20
  And then that can allow you later on to invade these very environments is really interesting.
• 13:25
  But yeah, tell us more about what's been interesting and exciting.
• 13:29
  So...
• 13:30
  So another surprise, for example, that's a quick one, was that when we started working on this and we kind of found really strong evidence of this relationship between climatic variability and population stability.
• 13:44
  And this idea that the cognitive overhypothesis was really well supported.
• 13:47
  We started reviewing the literature and we realized that in everything.
• 13:50
  Basically, every paper, including our papers, we were always kind of like talking about it as if these variable environments were kind of like the fertile ground for the evolution of bigger brains.
• 14:02
  But my postdoc at the time, Trevor Fristow, who's now at the University of Puerto Rico.
• 14:06
  Trevor is from Alaska, and I had been to Alaska a couple of times, and we were talking about this issue.
• 14:11
  And then we stopped from where we said, like, wait, what about the ptarmigans?
• 14:17
  The dharmigans are basically chickens and they're not really that bright.
• 14:22
  They're not the sharpest tool in the shed.
• 14:25
  And they live in the most variable places of Alaska and they're really common and they seem to be kind of like in the face telling us that cognition is not usually what they are using to survive in that environment.
• 14:37
  So when we started thinking about that, we started asking the question, well, what happens with, I mean, like, clearly not every species is doing the same thing.
• 14:45
  So we looked at it a little bit more carefully.
• 14:47
  And then we discovered that when you look at the distribution of brain sizes among birds, it follows a really nice, normally distributed pattern with like a central tendency and some variation.
• 14:57
  Yeah.
• 14:57
  But as you move to different portions of Earth, that pattern kind of like changes.
• 15:01
  So in the tropics, that pattern stays the same as the normal distribution.
• 15:05
  But as you move northward, or actually poleward, you realize that in those really variable regions, you start seeing this binomial distribution in which you only have really dumb birds and really smart ones.
• 15:18
  And all the ones in the middle disappear.
• 15:20
  Interesting.
• 15:21
  So that really, by modal pattern, made us take a second look.
• 15:23
  And then we started realizing that that was associated with very different life strategies or strategies to deal with environmental variability.
• 15:30
  Okay.
• 15:31
  So on the top end, those bright guys are basically dealing with this variability by looking at, by using kind of like their brains to find new resources, be flexible in the way that they search, remember things, cache things during the summer and use them in the winter.
• 15:49
  Those kinds of like cognitive-based strategies.
• 15:51
  But the tarmigans and the other ones that are on the other end of the spectrum, what they are doing is they're really focusing on strategies that are basically...
• 16:01
  They're basically hardy birds.
• 16:02
  It's basically brain versus brawn.
• 16:05
  And these hardy birds basically have usually bigger body size.
• 16:09
  In the case of the ptarmigan and many others, they have really big guts.
• 16:12
  And they specialize on diets that have a lot of vegetative plant material, which basically means that in the thick of winter, when things are really rough...
• 16:22
  A ptarmigan, basically the only thing that he needs to do is shake off some leaves and eat some of those branches that have like almost no energetic content.
• 16:31
  But with those huge guts, they're able to digest it and get out enough food to survive, enough energy to survive, but not enough to run a big brain.
• 16:40
  So it's basically like they specialize on resources that don't give you enough energy, but allow you to survive.
• 16:47
  And then on top of that, they've added other traits that are very important, which are things like they reproduce like crazily.
• 16:54
  Because usually when conditions are really like,
• 16:58
  So in the really bad years, a lot of ptarmigans die, but the few that survive reproduce like wildfire and the populations kind of like boom again.
• 17:07
  So it's a combination of like reproductive strategy, the energy sources that they're taking, and basically not...
• 17:14
  They have selection against pig brains.
• 17:17
  And in fact, other papers by Daniel Sola and his lab have shown that, whereas most bird groups have tended to increase their brain size as they move into variable environments, the galliforms, which is where the ptarmigans live, the galliforms have actually decreased it.
• 17:32
  So they've moved into these places by basically specializing these strategies that require...
• 17:42
  so many sacrifices.
• 17:44
  One of the sacrifices is your brain.
• 17:45
  Yeah.
• 17:49
  So, galiformes outside of these variable environments have like a different brain size to body ratio.
• 17:55
  As they move into these harsher environments that are more variable, they invest in just brute forcing it through.
• 18:01
  Yeah, like in the case of the ptarmigans, the gut.
• 18:03
  That's so cool.
• 18:04
  That's not to say that the tropical chickens are bright.
• 18:07
  That's just to say they're less problem.
• 18:10
  They have less cognitive problems than tempered ones.
• 18:13
  Yeah, yeah.
• 18:14
  It's all on a scale.
• 18:16
  Even a tropical chicken doesn't challenge a corvid, like a raven or a crow.
• 18:20
  Yes, exactly.
• 18:22
  I didn't realize that bimodality piece, that's really interesting.
• 18:25
  But like you said, the investment piece, if you have to invest a lot of energy in your brain versus in the case of the ptarmigan, they're investing...
• 18:32
  the energy that they do have into their gut, into this microbiome structure that can grow a microbiome, which for most birds, the microbiome is quite simple.
• 18:41
  But in these birds like ptarmigan and other galliformes, they have extensive guts that then the bacteria can help them break down these really low nutrient food sources.
• 18:51
  Exactly.
• 18:51
  And they're like full of cellulose and things.
• 18:53
  That is really difficult for us to break.
• 18:55
  Yeah.
• 18:55
  Yeah.
• 18:55
  I love the idea of just brute forcing it through an Alaskan winter without being creative about it at all.
• 19:00
  Just...
• 19:01
  Yeah, those guys just rough it up.
• 19:04
  Yeah, yeah.
• 19:05
  Versus ravens that are clever enough to follow wolves around and find their kills and all of this, which is such a different strategy, like you were saying.
• 19:13
  Or the caching birds, like the chickadees I work on.
• 19:19
  So other kind of related and interesting tidbits is that, for example, when you think about cognition and how flexibility allows us to do so many things,
• 19:29
  One of the kind of like very easy corollaries to take out of that is that you would expect that birds with bigger brains should be able to occupy a greater range of environments.
• 19:38
  Right.
• 19:39
  They should be so flexible.
• 19:41
  And in general, that is true at the family level.
• 19:44
  So things like the corvids really kind of like occupy the whole world.
• 19:46
  But it turns out that when you look at the species level...
• 19:50
  It tends to be that having a big brain in general is associated with having a narrower climatic niche, which for me was a huge surprise because I was expecting to see them everywhere.
• 20:02
  And it turns out that they're not.
• 20:03
  Like, they tend to be...
• 20:07
  The answer to this kind of mystery is actually like a boring one, but it just happens that these species with really big brains and enhanced cognitive capacities, they tend to occupy environments like the Arctic, which are huge in geographic space.
• 20:23
  But when you look at it in a climate space, it's actually a very narrow range of climates that they're occupying.
• 20:28
  So things like Siberia are huge areas like...
• 20:32
  biggest area, kind of like continental area that we have on Earth.
• 20:36
  But all over it, the climate is very similar.
• 20:39
  So these pieces are occupying really big regions in geographic space, but really small climate niches when you really look at it.
• 20:45
  So that for me was another kind of like interesting finding.
• 20:49
  And that goes along with other kind of like...
• 20:52
  more nerdy but also equally important things that we've discovered.
• 20:55
  Like, for example, the fact that this cognitive buffer, by weakening selection, by buffering you from selection, it basically leads to lower rates of evolution.
• 21:06
  So when we tend to think about like, hey, climate is changing and species must be adapting...
• 21:12
  The paradigm used to be that we think about slow adapters as in greater peril, as being in greater peril, because somehow they're not being able to adapt.
• 21:22
  It turns out that in species with really big brains, slow phenotypic adaptation is not a measure of increased vulnerability.
• 21:29
  It's just a measure that they're not being selected upon so strongly because they're buffering themselves against selection.
• 21:36
  So one of the examples that we've kind of like discovered was that in the last 50 years, there has been a pretty dramatic decrease in body size as the world becomes warmer.
• 21:45
  And that's kind of like an expression of something that we call, like biologists call Bergman's rule.
• 21:52
  And this idea that
• 21:54
  heat transfer is easier when you have more surface than volume.
• 21:58
  So as you become smaller, the proportion of surface to volume increases.
• 22:02
  And that allows you to more effective heat transfer.
• 22:04
  And lo and behold, as the world has warmed up,
• 22:08
  Loads of species, insects, there are several different taxons, but in birds in particular, we have really good evidence that bodies have become smaller.
• 22:16
  And when we looked at this trend, but added brain size to the picture, it turns out that, yes, everybody's becoming smaller, but birds with bigger brains are becoming smaller at like,
• 22:26
  a third of the rate that burns with smaller rates.
• 22:28
  Really?
• 22:29
  Brains.
• 22:30
  And this is even though our sample of brain size is just minute compared to the actual sample of.
• 22:36
  So we didn't explore the entire range of brain size because we didn't have data for that.
• 22:41
  But for the ones that we did, it was kind of like
• 22:43
  third of the total scale and we already see like three times difference in rates.
• 22:47
  So it's a pretty major effect.
• 22:49
  So it's buffering, release, changing rates of evolution.
• 22:51
  How does that relate to migratory behavior?
• 22:53
  Like a lot of the birds you've been mentioning that in these temperate regions are resident temperate birds like the ptarmigan or ravens and crows.
• 23:01
  Does the brain size pattern hold for migratory birds or no, because they're like moving to and away from environments that they want to be in?
• 23:11
  Yeah, so that story is actually really interesting, but also really complicated.
• 23:14
  So first, I'll start with that bimodal pattern that we talked about in really extreme environments.
• 23:18
  Yeah.
• 23:19
  That bimodal pattern happens only in residents.
• 23:23
  When you add the migrants to that community, then you see this, like, it actually turns out back into a normal thing.
• 23:30
  I fell in the middle.
• 23:30
  Okay.
• 23:31
  So basically what is happening is that all those animals with intermediate brain size have too big of a brain size to do the strategy of the ptarmigan.
• 23:38
  Right.
• 23:38
  Because they're spending too much energy for that, but not big enough to do the kinds of things that crows, ravens, and owls do with their bigger brains.
• 23:49
  So those guys are forced to leave because they can't really cope with staying with either of those two strategies.
• 23:56
  So that basically means that migrants in general tend to be like intermediate brain sizes, not too big, not too small, kind of like intermediate.
• 24:05
  And also, so when you think about, well, how does that relate with all the things that I've been talking about?
• 24:10
  And one place that we've been looking recently is kind of like looking at the effect of brain size on these migratory journeys that there's at stake.
• 24:20
  And basically what we've been looking at is we know that across the world, across the temperate regions of the world, spring is now tending to come a little bit early.
• 24:29
  So like all this, in some places actually it's coming a little bit late because of like this weirdness of all these climate patterns.
• 24:35
  But there's changes in spring that are pretty dramatic that are happening all across.
• 24:39
  Yeah.
• 24:40
  And birds basically are starting to arrive at the wrong time of the environmental cycle, which could have huge implications for the reproductive success and for their survival because...
• 24:52
  Sometimes they're going to be arriving when it's too cold and all the chicks die or they are in peril.
• 24:57
  Or sometimes they arrive too late and there's not enough food.
• 25:00
  All these phenological mismatches basically could create really huge problems.
• 25:04
  So we've been looking lately at this with one of my grad students, Angie Sue.
• 25:10
  And what we've been discovering is that basically most of the species in North America really are arriving late.
• 25:19
  The mismatch between the changes in environmental cycles and the changes in bird arrival is increasing.
• 25:26
  And brain size actually plays a role, but it plays a very different role than we used to think.
• 25:33
  It just so happens that when you look at these patterns, animals that have...
• 25:38
  So we were assuming, for example, because of this cognitive buffering,
• 25:42
  that buffering would allow animals that arrive slightly later out of synchrony with the environmental cycle to kind of like be flexible about it, find other four sources of food.
• 25:54
  We basically assumed that it would be enough to weaken selection and they would be showing more mismatch than the others because they didn't feel the consequences of that mismatch so much.
• 26:06
  It turns out that they feel it even more.
• 26:08
  And then when you look at species with bigger brains, we find actually that they tend to have to be more phenologically stable than species with smaller brains, particularly after the ones that do longer migratory distance.
• 26:22
  So there's like an interaction between the two terms.
• 26:25
  And what we think that could be going on is two different things.
• 26:28
  One is that maybe the cost of like long...
• 26:32
  flights, long journeys, get compounded by the cost of really big brains.
• 26:37
  So once you arrive to a place and there's not enough food, that's particularly problematic.
• 26:42
  But the other possibility is that in those journeys, as the animals are moving around, not all of them just go from A to B and then back.
• 26:50
  They tend to do stopovers in different places.
• 26:53
  It is possible that having a bigger brain allows you to kind of like better, like be more attuned to like the local changes in the environment and be more strategic as to when you leave those stopover places.
• 27:04
  So we don't know exactly if it's an effect of like better information gathering or stronger compounded costs.
• 27:11
  But the bottom line is that they're not behaving at all as what we thought they would at the beginning.
• 27:15
  So the bigger-brained migratory birds are better matching the phenological changes that are happening.
• 27:21
  Yes.
• 27:22
  And that is, when we talk about surprises, that's another surprising finding because normally we tend to think about phenological stability as a sign of like, oh, these species are more adaptable.
• 27:33
  Like if you're better able to adapt to what is happening, then you're better able to like match the changes in the environment.
• 27:39
  But it turns out that if you really think about it, there's another alternative, which is that there could be something that we could call as population filtering, which is that in species where selection is really strong and where individuals are just like die if they don't arrive on time, then over the years, you're going to see that the few that remain are really much more close to the optimal.
• 28:00
  but not because they've adapted, but just because the ones that are not so close get filtered out.
• 28:05
  There's just much stronger selection.
• 28:07
  Yeah, I was thinking about that in that context, especially maybe in the context of what their chicks need to grow up to be successful individuals of that species too.
• 28:17
  Like if they're not matched phenologically, and then we get back to this idea that
• 28:21
  you know, the brain is metabolically needy.
• 28:23
  Perhaps there's a cost there that you, if you're not matched, you just won't raise chicks that survive.
• 28:27
  And so there's this really strong selection that leads over time to this better matching.
• 28:32
  That's really interesting to think about.
• 28:33
  Can you tell us about how you guys measure brain size in birds?
• 28:36
  Because people might be wondering that.
• 28:38
  Yeah, so there's many different ways of doing it, but the easiest way is to take specimens in museums and empty out their cranium and then fill it out with pellets that are like little tiny little pellets of lead that we know their volume.
• 28:57
  And so you fill it out up to the specific point and then you...
• 29:01
  Pour that into a measuring cup and then you figure out the exact volume of the cranial cavity.
• 29:07
  And it turns out that because specifically of the anatomy of birds, birds are always kind of like making sure that they don't have extra things going around because they're flying and they're always in like war economy, basically.
• 29:20
  Yeah, basically.
• 29:21
  Yeah.
• 29:22
  The size of the brain is pretty much the same as the size of the cranium.
• 29:26
  There's not wiggle room there.
• 29:28
  So the size of the cranium really tells you exactly how big the brain is.
• 29:32
  So we use that volume as an indication of how big the brains are in different species.
• 29:38
  And then you can convert it also.
• 29:40
  So some species have also measured...
• 29:42
  Sorry, some researchers have also measured wet weight or...
• 29:48
  some other kinds of metrics, but you can always convert from one to the other to have kind of like samples across species.
• 29:53
  And right now we have a data set that is around 25, 2600 different species that we have brains for, brain size for.
• 30:01
  Yeah, speaks again.
• 30:02
  We had a recent episode about the importance of museum collections and I don't think anyone would have thought of, oh, and it's also important for measuring the size of bird brains and understanding how they occupy the environments they occupy.
• 30:13
  But here, here's the evidence of that.
• 30:15
  That's really cool.
• 30:17
  Yeah, and to the fact that bird bodies are so heavily shaped by flight that, yeah, they're not going to have extra anything.
• 30:27
  It's war economy all the time.
• 30:29
  All the time.
• 30:30
  People don't think about that.
• 30:31
  Birds really do live kind of on the edge of all of these metabolic and other pieces of...
• 30:38
  Yeah, kind of on the edge of everything.
• 30:41
  It's very interesting.
• 30:42
  All right, we've reached the part of the show we call That's BS or That's Bird Stuff, where we give our guests an opportunity to debunk a myth that ruffles their feathers.
• 30:49
  So, Carlos, what do you want to call BS on?
• 30:51
  We tend to think that big brains always make things better, but it turns out that because brains are costly, there are situations in which actually they can make things worse.
• 31:00
  So just like everything, we need to think about cognitive strategies as one of many dimensions of an organism's phenotypes.
• 31:08
  And it's important to understand that there are limitations and constraints involved with that as well.
• 31:15
  Yeah, it definitely puts the ptarmigan into context when you understand that it can't do both.
• 31:19
  It can't be a really cognitively flexible, heavily investing in its brain creature and persist through the winter the way that it does by eating basically sticks.
• 31:32
  Awesome.
• 31:32
  Well, thanks so much for joining us on the podcast today.
• 31:34
  This has been a really fascinating conversation.
• 31:36
  Well, thank you very much for having me.
• 31:38
  This has been really fun.
• 31:39
  Awesome.
• 31:43
  Birds are dinosaurs and around here we like our snacks, so we end each episode with a dinosaur nugget.
• 31:47
  Today's nugget is, in the harshest environments on Earth, evolution doesn't seem to produce average birds.
• 31:52
  You're either a corvid solving puzzles or a ptarmigan eating frozen twigs, with almost nothing in between.
• 31:58
  And, as the world warms and birds across the border are getting physically smaller, the bodies of the big-brained ones are shrinking at about a third the rate of the small-brained ones.
• 32:06
  Their brains aren't making them adapt faster, they're making them feel the pressure less.
• 32:10
  That's a wrap on this week's episode.
• 32:12
  Okay, but does easy living make birds dumber?
• 32:14
  If you like this episode, leave us a rating or review or like and subscribe.
• 32:17
  We'll catch you next time.
• 32:18
  Bye.
• 32:23
  Okay, but birds is hosted by Scott Taylor with production and creative by Zach Carl.