In this episode, you’ll hear about:

• How many caches chickadees actually make

• Why birds from harsher climates often have larger hippocampi

• How flexible brain structure really can be within an individual’s lifetime (we’re busting some myths here!)

• Studying these little geniuses in the lab vs. the wild

• 00:49 - Exploring the Nature of Obsession

• 01:46 - The Memory of Chickadees

• 11:00 - The Cognitive Abilities of Chickadees

• 14:22 - The Impact of Environment on Chickadee Brain Structure

• 20:55 - The Intersection of Genetics and Behavior in Chickadees

Timestamp Disclosure
These timestamps were generated using AI and may contain errors or omissions. They are provided for accessibility and reference purposes only and may not perfectly reflect the original audio.

Dr. Scott Taylor
We found genes that in humans have been related to obsessive compulsive disorder. And in humans, we label OCD as something that requires maybe treatment.

But if you think about chickadees in Alaska, if all they have to do is find and hide seeds, that's an interesting thing to think about too, that these things we characterize as conditions in humans, under the right conditions could be really, really beneficial. You know that moment when you walk into a room and instantly forget why you're there? Or when your phone vanishes, only to turn up in the fridge?

That's me. A couple of years ago, my memory failed me in a more brutal way. I wear a ring my dad and stepmom gave me when I finished my PhD.

The band was my grandfather's, and they replaced the stone with opal and ironstone. Opal is my birthstone. After a picnic in the park with friends, this ring was just gone. Nowhere. Not in the house, the car, the cooler.

I remembered fidgeting with it, but had zero memory of taking it off. Eventually, I had to accept that this ring was gone. Fast forward more than a year later, my partner texts me a photo and it's this ring.

He'd found it in a closet in a bag of cords and charging cables. I have absolutely no memory of putting it there. None. But imagine if my survival depended on not doing stuff like that.

If misplacing just a few snacks meant I might not make it through the winter. That's basically the daily reality for a chickadee. Which brings us to today's question. Okay, but how do chickadees never forget?

To help us unpack that, I'm talking with Dr. Vladimir Pravosudov, a professor in the Department of Biology at the University of Nevada, Reno, who has spent decades chasing these little geniuses through forests and right into the lab. These tiny, charismatic puffballs, the ones you hear with that cheery chickadee Dee Dee, are professional hoarders.

In late summer and fall, they hide seeds all over their territories. Not dozens of spots, thousands little caches wedged under moss, behind bark, tucked into cracks so narrow you'd need tweezers.

Weeks later, in sub zero temperatures, they go back and find them. Not somewhere over there, the exact spot. Imagine remembering the location of thousands of identical post it notes you scatter throughout a forest.

That's a typical Tuesday for a chickadee, all with a brain a little bigger than a chickpea. So what's going on here?

How are chickadees running one of the most precise filing systems in the animal kingdom while the rest of us can't even remember our Netflix passwords. For chickadees, forgetting isn't just inconvenient. It can be life or death. Natural selection has pushed their memory to superhero levels.

And this isn't just about practice. Their brains literally differ.

The hippocampus, the part of the brain linked to spatial memory, is physically larger in chickadees from colder, tougher climates than than in those from milder areas or lower elevations. Same species, same song, same look, but different brains tuned to different winters. For chickadees, memory isn't just a skill.

It's a survival strategy written into anatomy.

Because chickadees live across such a broad range, from relatively gentle southern forests to brutal northern winters, they've become this natural experiment in climate, cognition and adaptation. They're not just adorable feeder birds, although they are among the most adorable.

There are case studies in how the environment literally writes itself into the brain. So the next time you see a chickadee at your feeder, imagine the invisible map it's carrying around in its head.

Each visit, it grabs a single seed, usually black oil sunflower seeds, if you're wondering, and flies off to tuck it somewhere in your yard. Seed after seed, cache after cache. Thousands of tiny coordinates stitched into that tiny brain.

After the break, we'll chat with Dr. Vladimir Pravasudov to dig into how they pull this off, what it means for understanding memory more broadly, and how that brain environment dance might change with the climate. Stay tuned. Welcome to the podcast, Vladimir. It's great to have you here.

I thought it would be fun to start off by just talking about what I remember about the first time you and I talked about spatial memory.

It was after I'd been invited by one of your previous students and one of our guests on the podcast this season, Dr. Carrie Branch, to give a talk at the University of Nevada, Reno, about some of my work exploring the genetic basis of plumage color variation in birds.

Dr. Vladimir Pravosudov
Right.

Dr. Scott Taylor
And I remember after the talk, we met and you asked me if I thought we would be able to use some of those same techniques, so sequencing whole genomes and relating variation to whole genomes to study chickadee memory. And I'm pretty sure my response was, I don't think we can do that well.

Dr. Vladimir Pravosudov
Hi.

So my recollection, I think, was we've been working on cognition for quite a while, and I had these ideas about selection and generally acting on spatial memory and food caching birds.

And we published a number of papers, but we consistently were getting criticism that we don't know if things are heritable or they don't have the genetics. And our previous attempt to find a collaborator kind of failed. Nobody really wanted to get in there saying that there's just nothing to look.

And that's how it started.

Dr. Scott Taylor
Yeah, that's how it started. I remember after the talk chatting about the possibilities and going through, well, you know, maybe this trade is too complex.

We're not going to be able to understand the genetics, but why don't we try anyways? And now we've published multiple papers about the genetics of spatial memory.

But we could only get to that point in our collaboration because of all the amazing work, as you just mentioned, that you guys had been doing for now. I mean, now it's been over a decade. But measuring something like memory or spatial memory in wild free living birds is incredibly difficult.

And it would be really awesome if you could share how you came up with the idea to do that and then actually were able to do that.

Dr. Vladimir Pravosudov
Right, right. Because when actually when I started all this work even more years ago, classically people working in the lab.

And I've done some of the initial kind of pioneer work on this by comparing birds from different populations, by bringing them in the lab. But I wasn't quite happy.

Of course, obviously A, you cannot look at fitness, you cannot look at survival of birds in the lab, and B, still testing wild animals in the lab, I still feel that they're not quite really showing what they are capable of. But of course it's hard. How do you study things in the wild?

And it's kind of also, there's a long story to this because I remember a long time ago actually when I was still at UC Davis, I was a research faculty and I met Eli Bridge, who's also a really long term collaborator who was very interested in RFID technology. And back then he asked me would I be interested in testing something with chickadees? And I said yeah.

And I had a very simple idea that I wanted to implement and that was basically using kind of standard lab design, or an animal is trained to learn one out of multiple rewarding locations and see if that we could actually bring it to the field. The beauty of chickadees is they're always hungry.

Dr. Scott Taylor
They definitely are.

Dr. Vladimir Pravosudov
They're living on the edge in the winter and they're caching, which means that they have enormous motivation to go to the feeders even when they are not hungry. Which is very different from the lab because in the lab chickadees actually wouldn't cash as much. They don't have the same motivation.

And so actually in the lab cognitive test, they lose motivation very quickly after just getting a couple of seeds of rework in the field that's not happening.

And so we kind of initially started thinking about developing things more like an orat, almost like a radial maze type of things where one of the feeder will be providing food, but the RFID will control it. So in other words, we can program only one feeder that will give food. And every feeder records locations.

So RFID is a radio frequency identification system. So it's using P tag, so it's a passive integrated transponder that is on the animal. Most people probably are familiar with this from pets. Like a dog.

You'll put a chip in your dog or in a cat, and if it gets lost, somebody will basically scan it and will immediately get the identification of the animal. The beauty of that thing is it's small, it doesn't require a power source.

So rfid, or radio frequency identification board, which is a computer board, is the one that actually is connected to the antenna, which is built into the feeder antenna and the perch. So when the bird lands on the perch, it reads immediately the individual id, which is on the leg band, kind of incorporated.

So every time bird lands, we know exactly who landed on each feeder, we know the timing, precise timing, they're all coordinated, they're connected through gps. So there's a perfect timing across all eight feeders.

We are using eight feeders and like I said, we programmed that each bird only have one rewarding feeder. And the bird don't know that obviously at the beginning.

And when they start exploring, they'll go to every theater until they hit the one that gives them food.

And then next time they come back, if they use memory, they should make fewer errors or they should visit theaters that are not rewarding fewer times. And then we just run it for four days. They literally pick a seat, take a few seconds, fly immediately away.

They cache or, or eat that seed, take several minutes, then they come back and it's a second trial. And the birds can run anywhere between 50 to sometimes 1000 trials in a four day period, depending on the winter.

And then we can estimate the reduction number of errors and we're controlling for the number of trials. And that gives us a very good estimate of their cognitive abilities.

Dr. Scott Taylor
Yeah, so you came up with this amazing system and yai tell us a little bit about that. Because it's one thing to measure a behavior, and it's another to actually understand that the behavior you're measuring is Relevant.

It's very difficult to design experiments that actually measure the thing you really care about. And that is linked to something like survival.

Dr. Vladimir Pravosudov
Right. So the first thing for us was to see if we actually see variation.

If all animals are showing differences and they do, there's a tremendous variation in how well animals do that.

Then the other interesting thing, which sometimes scientists don't necessarily do, because we're interested specifically in spatial memory, it's very critical because when people do it in the lab, they always involve controls. In other words, we want to make sure that they're using space and not something else.

In our case, in our first year, we actually rotated the entire design. Once birds learned which feeder gives them food, we rotated the whole array 180 degrees.

And that allows us to see birds are following the same feeder that they somehow can identify, or they use space. And we've confirmed they're definitely using space. Oh, cool.

The next step was to see if that variation that we are detecting is, like you said, relevant. And we looked at the survival of specifically the first year birds, the juvenile birds that hatched that year and went through their first winter.

And basically we measured this spatial cognition in as many birds we can, and then we saw how many of them actually survived until the last year. And chickadees are highly resident. They don't go anywhere. They spend their entire lives in the same places.

In our case, they don't show any altitudinal migrations at all.

And so, yeah, and then the very first study with Ben Sonnenberg, we showed that the birds that did better actually are more likely to survive, and the birds that did worse were disappearing and dying. And another really cool thing, we actually showed that the birds don't change their cognition.

The birds that were measured in the year one first winter, when we retested them after they survived, they actually showed exactly the same thing, which was confirmed later on with the paper that we published in Science this last year.

When you follow birds for multiple years, and we've shown that we are measuring something that's a property of the bird, and it's not really changing with time or experience with our race. They just shown this very flat line kind of across multiple years.

Also showed that not only the survival of juveniles is affected, but actually the entire longevity. We showed that birds with better cognition live, on average, two years longer.

Dr. Scott Taylor
Yeah. If you have between six and eight chicks a year, living two more years is quite a few more chicks to put out into the world.

Dr. Vladimir Pravosudov
Right? Right.

Dr. Scott Taylor
It's really amazing that you've been Able to figure out how to measure this trait in the wild, link it to survival, tell that there's variation in the trait. And this is all within one species.

Within mountain chickadees in the Sierra Nevada, I think chickadees are this really familiar species in North America. Whether it's mountain chickadees or black capped chickadees or Carolina chickadees, most of us live with them in our backyards.

I'm wondering, do we know within a season how many things they're caching within their territory? Given that they're caching these seeds individually, sometimes under bark, is there a way to know that?

Or do we have estimates on really how much caching an individual is doing in a given year?

Dr. Vladimir Pravosudov
We actually do because that's how the whole field kind of started. Because the very, I mean the very first studies were done by Germany, I believe by Lou De.

But the classical work on foot caching was done by Swain Hawftorne, who was kind of a big hero of scientific of mine when I was still an undergrad or from Norway, who published the very initial series of papers talking about caching circles of food and European kind of like chickadee species and willow tits, encrusted tits and coal tits. And he showed that these individual birds can catch up to hundreds, some thousand individual items per year.

Dr. Scott Taylor
Wow.

Dr. Vladimir Pravosudov
And that's kind of what initiated my initial, piqued my interest on that when I was doing my master's degree and I was working with Siberian tits and willow tits, which again kind of like chickadees and far north.

And I was basically following them with the stopwatch day in, day out for hours and hours of time and simply recording every time they catch food, how long time it takes, how much to eat. And then I kind of tried to estimate giving the amount of time that they have and the frequency with which they find food and cash food.

And I was able to estimate that over the year an individual Siberian kit can catch almost up to half a million individual food items.

Dr. Scott Taylor
Half a million. Wow, that's incredible. And they're doing this every year because.

Dr. Vladimir Pravosudov
They'Re, they're doing it every year.

Dr. Scott Taylor
They're depleting the food cache over the winter and then replenishing it every year. That's incredible.

I think even tens of things are easy to lose track of in your house, let alone 500 or 100,000 hidden individual seeds in your territory. Oh man, that's so fascinating. Before we keep going, let's take a quick break.

We haven't talked about this yet, but there's like a specific special part of the chickadee brain that really matters for their spatial memory.

And your research and others has shown that the harshness of the climate that a chickadee lives in, whether that's higher latitude or higher elevation, really does have an influence on its brain structure.

And I was wondering if you talk to us a little bit about your studies in that context and this the hippocampus and why it's so relevant for what we're talking about. Right.

Dr. Vladimir Pravosudov
So actually also again, their initial work that kind of drew attention to that whole idea and that hypothesis that was named the adaptive specialization hypothesis by John Krebs and David Cherry at Oxford. Right. And they initially compared multiple species. They basically compared species of store food, cash food, and not cash food.

And they showed that the species on a species level of cash food have significantly larger hippocampus compared to species that don't catch food.

And they're the ones that gave rise to that idea that the food caching species will evolve this adaptive specialization by evolving a much larger area of the brains called the hippocampus caching. Why it's important because it's important for them to survive the winter.

So obviously the winter is harsher, meaning colder, longer, more snow and caches are more essential. They're more important.

So if they don't get them again, if a black capped chickadee in Alaska doesn't find food cache, it doesn't have much time because the day is short. There's not very much time for them to find it. And so there should be very strong selection pressure on it.

While if the bird lives in a more relaxed environment, like for a black capped chickadee somewhere around Seattle in Washington state, it actually never gets cold. Right. And so the bird may have lots of second chances to kind of find something and survive. That's how it all started.

And so we started by comparing birds from Alaska and actually Colorado, but we use them from Fort Collins, from the low level, kind of at low elevations. And we showed that indeed Alaska birds have a lot bigger hippocampi with many more neurons. On a subground, we compared 10 populations.

We actually look at the whole range, pretty much most of the continent of North America. And we looked specifically at the climate both longitudinally and latitudinally. So we can control for day length.

Because if you go and look at Maine and Minnesota, they will have much harsher winters, much colder winters, more snow than birds in Seattle. Even the birds in Seattle will have the same day length in the Winter as birds in Minnesota for example.

And so basically when we compare 10 populations, we saw an absolutely beautiful pattern that was very clear.

So in other words, the more harsh environment, the bigger the hippocampus, the more neurons they have and actually the higher neurogenesis rates they have, which is pretty impressive. And we sample birds directly in the wild without any captivity kind of effect.

So these birds are non migratory and yet they have very different brain size or hippocampal size in different climates. And of course it could be triggered by local experiences and environment.

And we followed up by conducting a common garden experiment where again my postdoc Tim Roth went to Alaska and Colorado and actually. Oh actually in Kansas and found the nest. And we hand reared this chickadees before they even fledged from their nest. So they couldn't see anything.

And they were at the same lab, the same cages and then the difference were very big. The same difference basically were maintained.

Dr. Scott Taylor
Yeah, and that's super important in the context of the trait and whether it is genetically controlled or plastic. By doing that, by raising those birds from Alaska and other places in a common garden together, you were able to show that.

Yes, it's not an experience dependent plasticity. Could you talk a little bit about what you think the trade offs or the costs might be for having really good spatial memory?

Dr. Vladimir Pravosudov
I mean.

Dr. Scott Taylor
Right.

Dr. Vladimir Pravosudov
Well, I mean generally cost of brain maintaining brain tissues is high. We already kind of know that. Right.

So in that way any cost of generating this neural tissue and maintaining larger hippocampus could be higher trade offs. It's an interesting question because I don't think there's a very clear thing.

Our work potentially suggests that there may be trade off with flexibility.

In other words, when an individual has very strong memories, that individual may be, it may be harder for that individual to give up those memories and learn new information or exchange the memories.

Dr. Scott Taylor
Yeah, I think it's important to remember context. The environmental context within which anything is operating is super important for the value of that trait.

So like yeah, in Alaska if all you're doing is caching and, and then you survive because of that, that's great. But if you don't need to be doing that in Washington, near Seattle, then yeah, you can be more flexible.

And I think humans don't always think about context and variation and how that can change both across environments, but through evolutionary time.

Dr. Vladimir Pravosudov
Right, right. For example, we found that high elevation chickadees, which have better memory and bigger hippocampi, they're much less aggressive.

So if you actually pit them up against Each other from low elevation, they're always losing fights. Even the big bird will lose to the smallest.

Actually, on the Wanawa experiment published by Cary Branch and David Kozlowski, we had the smallest bird, smallest male from low elevation who beat everybody up.

Dr. Scott Taylor
Really. He was the most aggressive.

Dr. Vladimir Pravosudov
He was the most aggressive. And then Kerry followed this with a mirror aggression test when they were basically exposed to the mirror.

And we've confirmed that birds from high elevation also much less aggressive, which is also interesting because if these birds were to move down to low elevation, whereas milder, they actually would lose. They would lose in the dominance context. And so they may not do very well.

Dr. Scott Taylor
Is this like a bird fighting ring? How do you test the aggression of a, of a chickadee?

Which, I mean, we've all seen a defeater, But I think maybe our listeners don't know that chickadees are actually quite feisty little birds.

Dr. Vladimir Pravosudov
The way we test them, obviously you need to test them within the same sex. So we tested the males specifically. Otherwise we already know the differences.

And then for the test, we basically we put them in a room in experimental arena for a very brief time. When two birds are released simultaneously in the arena and we are watching what's happening and they settle the domino square very quickly.

And then for the mirror, we also, we're letting them in the experimental room and we have a mirror right across on the perch. And chickadees do not have. It looks like the self recognition. And they always attack mirror.

So when they see their own reflection in the mirror, they actually charge at the mirror. They go in there and then we measure how frequently they attack the mirror.

Dr. Scott Taylor
And.

Dr. Vladimir Pravosudov
And that kind of is index of aggression.

Dr. Scott Taylor
Yeah, it would be very difficult to do that in the field. Although maybe our listeners are getting ideas about Gladiator 3 featuring chickadees, but with more positive outcomes.

One of the things I thought was really interesting is that the genes we were finding related to variation in spatial memory had direct connections to axon growth and neuron development and stuff.

But the one that I don't know, I always think of in the context of these trade offs is that we found genes that in humans have been related to obsessive compulsive disorder. And in humans, we label OCD as something that requires maybe treatment.

But if you think about chickadees in Alaska, if all they have to do is find and hide seeds, that's an interesting thing to think about too, that these things we characterize as conditions in humans under the right conditions could be really, really beneficial. Okay.

So we've reached the part of the show that we call that's BS or bird stuff, where our guest gets to demystify something about birds that they think we should all know. Vladimir, what do you want to call BS On?

Dr. Vladimir Pravosudov
Well, again, it's as far as bird. It's not true bs, but it's one of those things that have taken kind of a place in public media and in literature which is overused.

And it's one of this.

There's one study a while ago which the same author did kind of replicate, but not quite the same by suggesting that chickadees grow the hippocampus every fall by 30, 40% when they're caching food, and then they shrink their brains back. And that idea was very popular and it is still very popular.

And at the initial study that actually didn't look at the same individuals, they simply sampled relatively small sample sizes of these birds. And when that study was published, initially, why? Obvious reasons, it stirred a lot of interest because that's amazing.

If they were to do this, then the lots of labs started trying to replicate these results and they couldn't.

Everything we see suggests that number one neurons is incredibly stable, which means to me at least, that it seems that that number is definitely controlled by some genetic program, that basically developmental program that kind of builds this volume itself. Volume can change because of neuronal, because of dendritic pruning expansions, but that's not the same as literally growing a bigger thing.

And I wish that media would kind of tone it down because it's not quite supportive.

Dr. Scott Taylor
I mean, it's. Yeah, it's an attractive story to tell, but without having the same measures from the same individual, which haven't been done, we can't.

We can't really address that question. And all the evidence points to that not being the case. Well, I want to thank you so much for joining us, Vladimir.

It's been really great to us join chat.

Dr. Vladimir Pravosudov
Thank you for inviting me.

Dr. Scott Taylor
This has been really fun. So good luck with the field season. Thanks for joining us.

Dr. Vladimir Pravosudov
Thank you very much.

Dr. Scott Taylor
Okay. Birds are dinosaurs. And around here we like our snacks. So we end each of our episodes with a dinosaur nugget.

Today's is about chickadee memory and how amazing it is. On an annual basis, chickadees remember the individual locations of hundreds of thousands of seeds.

And their ability to do this is directly tied to environmental harshness. In places like Alaska with really cold and snowy winters, chickadees probably remember the locations of up to 500,000 seeds.

While down here in Colorado where our winters are less harsh, it may only be only 150,000 seeds. So the next time you lose your keys, remember a chickadee would never. That's a wrap on our episode. Okay, but how did Chickadees never forget?

If you liked this episode, leave us a comment like and subscribe. We'll catch you next time. Bye. Okay, But... Birds is hosted by Scott Taylor with production and creative by Zach Karl.

Transcript Disclosure
This transcript was generated using AI-assisted transcription and may contain errors or omissions. Please refer to the audio or video episode for the most accurate representation.