In this episode, you’ll hear about:

• Why birds migrate

• How birds navigate long-distance routes, and what’s instinct vs. learned

• How scientists track migration across continents and the wildest journey Nate has followed

• What happens when birds drift off course, and how climate change is reshaping routes and timing

If you enjoy this one, follow Okay, But… Birds and share it with a friend who thinks migration is as simple as just “flying south.”

• 00:37 - Understanding Bird Migration

• 03:44 - The Science of Bird Migration

• 10:09 - The Mysteries of Bird Migration

• 13:44 - Impact of Climate Change on Bird Migration

• 21:30 - Understanding Bird Migration and Its Challenges

• 23:48 - Understanding Bird Migration

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. Nate Senner (Excerpt)
Birds are burning fat as their main fuel. If you watch the Chicago Marathon, the people at the front of that race did not look really fat at the beginning and then really skinny at the end.

But that is exactly what birds like Godwitz are doing.

Dr. Scott Taylor
It's really hard to comprehend bird migration until you see familiar birds in an unfamiliar place and remember that they got there by flying. And then it's mind boggling realizing the distances that some birds travel powered by their own wings. It truly makes marathons seem quaint.

And to help us make sense of this aerial magic, we're joined by one of the researchers using satellites and cutting edge technology to track birds as they move across the globe. Today, I'll be joined by Dr. Nate Senner, the Mass.

Audubon Bertrand Chair for Ornithology in the Department of Environmental Conservation at the University of Massachusetts Amherst.

As a graduate student, I spent several months doing fieldwork on the Guano Islands off the coasts of Peru and Chile, studying blue footed and Peruvian boobies. When I traveled south to Peru in 2007, it was the first time I'd ever visited South America.

The journey from Toronto to Lima was among the longest flights I'd ever taken at that point in my life. About eight hours. The ocean off the coast of Peru is one of the most productive on the planet.

It teems with life, a food web anchored by the cold, nutrient rich upwelling of the Humboldt Current that feeds millions of sardines and anchovies that subsequently get eaten by everything from whales and dolphins to sea lions and millions of seabirds. The seabird colonies there are among the densest in the world.

Hundreds of thousands of boobies, cormorants, pelicans, and even penguins call the islands I was visiting home. And though I was always struck by the resident birds, I was there to study the migrant birds there shocked me.

As we approached one of the first islands we visited, I could see rafts and rafts of gulls. Honestly, as far as you could see on the ocean, it was gulls in their winter plumage.

I didn't recognize them, so I asked my colleague Carlos what we were looking at. And the answer was Franklin's gulls. Now, although I grew up in Ontario and spent a lot of time birding there, we did sometimes see Franklin skulls.

They breed in the central and western parts of North America in Alberta, Saskatchewan and Manitoba. And nearly the entire population winters off the coast of Peru in the Humboldt Current, an annual round trip migration of around 10,000 miles.

Seeing that endless raft of Franklin's gulls on the ocean has really stuck with me. It was among the first times that I saw any bird species at the other end of its annual migration.

Imagine if you ran a marathon every day for days, without gps, without snacks, without sneakers. That's basically what some birds do every single year. Migration is one of nature's most outrageous endurance tests. And birds absolutely ace it.

Take the Arctic turn this pint sized overachiever flies from the Arctic to Antarctica and back again each year. Every year. That's about 25,000 miles round trip for a bird that weighs less than a lemon.

Why, why not just stick around, find a nice Airbnb in the tropics and ride out the winter? It turns out migration isn't just a luxury, it's a strategy.

Birds follow food, daylight, temperature, and ancient cues we still don't fully understand. And they do it with a level of precision that would make even the best airline jealous.

Today we'll explore the how, the why, and the whoa of avian migration. From high altitude flights to nocturnal journeys. And even birds fly for seven days without stopping.

We're diving into the science of the great flyways. Stay with us. Welcome back, everyone. I'm really excited that we have Dr. Nate center with us today to talk about bird migration.

Dr. Nate Senner
Thanks so much for having me, Scott. Really happy to be here, for sure.

Dr. Scott Taylor
Yeah. And I thought we could start off with just the why of it all.

Why would birds migrate, in the case of the Arctic tern, from the Arctic to Antarctica and back every year?

Dr. Nate Senner
Yeah. You know what it really comes down to, and this may be a little disappointing, is resources.

So those resources could be like food, they could be shelter. And it is either the fact that the place that they were has a really declining set of resources.

So you could imagine an Arctic tern is up in the Arctic and at the end of the summer, there's not a whole lot left. For an arctic tern, Antarctica is really that much better. So they're either running away from someplace or they're running to someplace. And.

And I should say, instead of running, they're flying. Right. We're talking about birds here.

Dr. Scott Taylor
Yeah. Flying crazy distances. As someone who studies migration, what is like the most memorable migration that you've tracked?

Dr. Nate Senner
Oh, man, I've been waiting years for someone to ask me this, Scott. I mean, come on. Sony and Godwitz. This is the bird right, right here over my, my shoulders. So let's see. They're about a foot and foot and a half tall.

In the breeding season, the males are brick red. But I think the feature that everybody notices right away is actually how long and slightly upturned their bill is.

So in Spanish and Portuguese, their name means the shorebird with the upturned bill. They fly from the southern tip of South America all the way back up eventually to their breeding grounds in either Alaska or Canada.

And along the way they have a five to seven day non stop flight out over the middle of the Pacific Ocean. And you know, we just talked about Arctic terns and arctic terns are pretty cool.

But here's the thing about terns is they can forage and feed on the ocean, but Godwitz cannot. So they are flapping continuously for that entire time. And they're not eating, they're not drinking, so far as we know, they're not sleeping.

And that to me, like, I've thought about Godwitz probably every day for the past 25 years, and I still find that really flipping cool.

Dr. Scott Taylor
That's amazing.

So if they're flying for five to seven days continuously, and godwits for our listeners are shorebirds, so they need to be at the shoreline feeding on invertebrates and other things, and mud flats mostly, I guess. Although Nate can speak more to that.

Dr. Nate Senner
Exactly right.

Dr. Scott Taylor
What happens to them? How much body mass do they lose if they. I can't imagine being awake and doing something for five. Well, I think I would just die.

I think any human would die if you tried that. But what happens to these Godwits? How much do they have to put on? How much weight do they lose and those sorts of things.

Dr. Nate Senner
Yeah, they're at least doubling their body weight from what they are normally, and most of that is fat. And this is one of the key things about bird migration, is that unlike humans, birds are burning fat as their main fuel.

If you watch the Chicago Marathon, the people at the front of that race did not look really fat at the beginning and then really skinny at the end.

But that is exactly what birds like Godwits are doing because they're able to burn that fat, whereas humans are burning carbohydrates as their main fuel source while they're exercising. So Godwits are doubling their body weight, putting on a whole bunch of fat.

And initially they're also building up their, their muscles, like their pectoralis muscles, their main muscle that allows them to flap.

And then while they're gorging on food, they've got huge digestive organs so that they can assimilate all of the nutrients from all the food that they're eating.

But then right before they take off, they shrink all of those digestive organs, because while they're flying, they're not eating, they're not drinking, so they have no use for those organs. So they've completely sort of reorganized their body plan in order to maximize their ability to go these incredible distances.

Dr. Scott Taylor
That's amazing. Well, I guess my next question then is how do you know that that's what they do?

So you say they leave from the tip of South America, they show up in Alaska. But how do you know that? What do you do to track migration?

Dr. Nate Senner
Yeah man, computers can be really tiny. So quite a long time ago, the very first sort of tracking devices looked like Cadillacs that you put on the back of a bird.

So we understandably, we're putting them on only very big birds like penguins or condors. But we've gotten down to the point where we can, we have tracking devices that are about 0.3 grams.

And I usually say that a gram is about a paperclip. So we're talking a third of the weight of a paperclip that we can put on a bird.

Dr. Scott Taylor
It took me a long time to learn the route to drive to my grandparents house. And we did that, you know, twice a year my whole childhood.

And I think I could probably do it now, but it took me like learning landmarks and, and basically my parents guiding me along the way right while I was watching whatever Sesame street in the backseat they were driving. But for birds, do they have to learn a migration? Is it something that they're born knowing or what's the latest on that from a science perspective?

Dr. Nate Senner
How did they learn it? Well, it really depends on the species.

So for some species there is an innate mechanism that tells them probably something like the general direction they should head and how long they should spend flying in that direction. But other longer lived species like cranes and geese, this is a culturally learned thing.

So they're learning it from their parents or other birds that may have been in the area when they took off on their migration. So there's really this wide array of how it is that birds come across, the knowledge that allows them to migrate.

On the spectrum between learning migration from your parents or grandparents to maybe doing something that seems innate. To me, the most mind boggling example of innate migration is what sharp tailed sandpipers do.

So an adult sharp tailed sandpiper, they breed in Siberia, in Russia and they go down to Australia and they do the thing that you would expect them to do, which is they more or less go down the Asian coast. But what all of the young sharp tailed sandpipers in the world do is something completely different. They fly east until they hit Alaska.

They spend a while in Alaska and then they fly across the Pacific south, going towards the southern coast of China and then further on towards Australia and the Malaysian Peninsula.

So they've got this whole dogleg to their migration that their parents don't do, meaning that the second year that they make their migration, they don't do it again. It's just this one time that the young birds do this crazy thing.

And so, yeah, the ways in which migration sort of develops in birds varies dramatically across species. In some ways, it doesn't always make a whole lot of sense.

Dr. Scott Taylor
Does anyone know why that would have evolved?

Dr. Nate Senner
Well, where the juveniles go and spend time in Alaska is the Yukon Kuskokwim Delta. So if you're thinking about Alaska, maybe you can picture where Nome is. It's sort of like up in the northwest corner.

So this is south of there and is one of the most productive delta river deltas in the world. So the amount of food in the mudflats there is just incredible. And so, coming back to our theme, I think it's all about the resources.

And so they're just going to this place that is super abundant, super predictable resources.

Dr. Scott Taylor
It's interesting when a bird messes up, right, and you have a Townsend Solitaire, you know, appear in Ontario, what happens? Like, how do birds get thrown off course? Why do we see these vagrancies or birds that shouldn't be in a place show up during.

Particularly during the migration, migration period?

Dr. Nate Senner
Yeah, well, a lot of them are young birds. So that process of gaining the knowledge about where to migrate can go wrong for a number of reasons. And so it might.

The mechanisms sort of leading to vagrancy could very well differ between different species. I mean, a lot of the time it is weather related.

So young birds just may not have the ability to sort of deal with, say, crosswinds or headwinds in the way that a more experienced bird might. But for some of these birds that migrate using sort of some innate mechanism, it could be actually that their genes got it wrong.

And so their innate mechanism is telling them to head in the wrong direction. And, you know, over time, if actually that new route works, that could be a way that a new migratory pattern evolves.

But in the short term, most of what we see is a bird that looks pretty lost and unfortunately may not ever make it to what we think of as its, you know, most optimal destination.

Dr. Scott Taylor
Yeah, I guess a lot of vagrants, they tend not to make it as.

Dr. Nate Senner
A birder it's so much fun when you get this phone call or a text message these days, where they're like, oh, man, that bird from Europe is just a county over or whatever. And you're like, wait, a bird from Europe is here in the middle of the country? And then you're like, oh, right, vagrancy. This just happens.

Birds get off course and then for us humans, it's a gold mine to just be like, let's go and see this thing we'd never otherwise see.

Dr. Scott Taylor
I think one of the more famous vagrants in North America right now is this stellar sea eagle that showed up a few years ago.

Dr. Nate Senner
Oh, man, I. Oh, you didn't see it? I didn't see it. I'm kicking myself. I live like four hours from where it was and I didn't go see it. I just thought it was going to stick around.

And then. Yeah.

Dr. Scott Taylor
Is there evidence that climate change is leading to vagrancy or at least affecting migration?

Dr. Nate Senner
Well, climate change is definitely affecting migration at totally global scales. Is it driving vagrancy? Well, one of the things that can lead to vagrancy is increasingly strong storms.

This is something that has been linked to climate change. Our hurricanes are getting both more frequent and stronger. They're happening at later points in the season.

We know that bird migration routes have evolved to try to avoid hurricanes. You know, we can imagine hurricanes are a pretty bad thing for a bird.

And so the fact that they're, you know, those hurricanes are appearing in sort of unexpected times and with unexpected force could absolutely lead to increasing vagrancy for birds that otherwise would have avoided those storms.

Dr. Scott Taylor
But what about your birds? So you've been studying Godwitz for a very long time, as you alluded to.

And how have you noticed climate change impacting their migration, whether timing or their breeding success?

Dr. Nate Senner
Yeah, this has been, you know, a lot of what we try to focus on, and it's been something of a roller coaster, actually.

So when I first started doing this work about, yeah, 20 years ago or so, what we found is that Godwits were making their northward migration earlier and earlier each year. And that actually was lined up with how the climate was changing when spring was happening on their breeding grounds in Alaska.

And so I sort of thought Godwits were doing all right. And then at some point in, say, like, 2015, 2016, we started to notice that they weren't timing their breeding as well as they had been.

They were a little too late relative to when spring was starting. And then all of a sudden, in about 2020, we started to notice that they were actually arriving later than they had the previous year.

We've seen this trend over the course of 35, 40 years where they're getting earlier actually now over the past decade, they have completely erased that trend. And they're now arriving basically as late as they were in the early 1980s.

So they did this like, and then back up the other way in terms of their arrival timing.

And this is really our focus right now, is trying to figure out what is going on climatically that would have caused them to come there earlier and now is telling them to come there later because it's not optimal for the birds. They're breeding too late, their chicks are starving. And yeah, it's just, it's a big mystery for us and, and it's happened so fast.

Dr. Scott Taylor
It's interesting too. It seems like they were like there was some cues they were trying to track or whatever that either changed or were not successful.

So the strategy's going the other direction. How do you figure that piece of it out? Like, are you looking at climate variables, food availability, all of the above stopover sites?

Like, how do you kind of try to solve that puzzle?

Dr. Nate Senner
So got collaborators in Chile who are trying to investigate like, what may or may not be changing down in the spots where godwits are spending the winter.

Then we're definitely trying to look at food resources in the mid continent of the us so in the Dakotas, that's like the one sort of place that God would stop on their way from Chile back to Alaska and then investigate what might be changing in Alaska too.

And then on top of that, I've got a new person in my lab who is an expert in how to use genetics to understand shifts in the traits that birds exhibit.

And so she's now looking into the genomics of what might have changed in the population that we have in Alaska, if anything, because it could be, as you said, that it's just cues and so birds are just perceiving their environment some way differently than they used to. Or it could be that there's been this evolutionary change for some reason.

Dr. Scott Taylor
Yeah, it's cool to take that kind of multi pronged approach to try and understand a really complicated puzzle.

And I think again, we tend to think about birds when they're here with us and not the fact that many birds in North America spend more time elsewhere, you know.

Dr. Nate Senner
Yeah, totally.

Dr. Scott Taylor
Which is important to remember when, you know, when you refer to what's changing on that island in Chile or deforestation in Central America or like you said most of these godwits go to one island. And, you know, many birds have very specific kind of small areas where they spend the winter.

And if that small area is impacted, it can have such a big impact on the whole breeding population, which is kind of scary.

Dr. Nate Senner
Yeah, absolutely. We estimate that There are about 30,000 or so GodWits that breed in Alaska. So you think about.

Yeah, that whole state of Alaska down to an island that's. Yeah. About New Jersey. So it's definitely a very different, you know, spatial scale that they're. They're condensing into.

Dr. Scott Taylor
I always think about golden winged warblers in this context where you have the population breeding in the Appalachians that's precipitously declining, and then the population in the Great Lakes region, which is declining, but not as fast. Nowhere near as fast.

And it wasn't until recently that people realized, well, that one population all goes to this one part of South America that's experiencing rapid deforestation and the other population doesn't. And so that kind of. Even if they had equal success on the breeding grounds, they don't have this overwintering habitat left.

Dr. Nate Senner
Storks in Europe are one of the, like, harbingers of spring.

It's one of the reasons why storks are one of those things we associate with humans having babies is because they tend to come back during the spring, and that's often when humans were giving birth as well. And.

And, well, yeah, lo and behold, one year, I think it was 1861 or 62, one showed up in Germany with a spear that they somehow associated with having come from Sub Saharan Africa.

And so this stork had been hit by a hunter that was trying to kill it, and it evaded that hunter and made it at least a good long ways before it met the end that it might have otherwise met in Africa.

Dr. Scott Taylor
Yeah. And I mean, in that case, birds fly across the Sahara Desert, which is a. It's such a huge obstacle.

And then the reality for a lot of birds breeding in Europe is that they. They do that every year, which is just incredible. And there's some really recent. I don't know.

Well, I don't know if it was recent research, but looking at the stomach contents of, like, sharks somewhere.

Dr. Nate Senner
Yeah.

Dr. Scott Taylor
And they were finding that during the migration period, the sharks were eating a lot of forest birds that were. Yeah. Not making it.

Dr. Nate Senner
I think that was over the Caribbean. Yeah, well, the sharks are not over the Caribbean. The sharks are in the water. But the birds were trying to go.

Dr. Scott Taylor
Over the Caribbean and Not making it.

Dr. Nate Senner
And not making it.

Dr. Scott Taylor
That's an interesting way how migration connects to terrestrial ecosystems with the ocean, when migration doesn't work out so well for the birds.

So a little while ago I talked about the Arctic tern, which is maybe not the, the bird with the longest nonstop flight like the birds that Nate studies, but it is, you know, within the lifetime of Arctic ter, they're flying from the Arctic to Antarctica every year. And so if you add it all up across their lifetime, they're basically flying to and from the moon three times. Kind of mind blowing.

But why go all the way from the Arctic to Antarctica? Why not stop somewhere in between and hang out there? What is it about these places that's so important for this species in particular?

Dr. Nate Senner
That's a great question, because I think this is really on the sort of the boundary of what we know about both migration and what drives migration.

But, but my hypothesis is that if you're going to go all the way to the Arctic, you need to have resources that will fuel you being in the Arctic while you're there. And that can only come from other places that have really super abundant resources.

So if you're going to go that far in one direction, then you need to go somewhere else in the other direction that will be there every year and be really good every year. And so Antarctica is actually super predictably good because it's going to have 24 hours of daylight during the Antarctic summer.

And that daylight brings this huge burst of resources, whether you're over the ocean or on land. And at the same time, there are also some reasons to not stop in between. A lot more diseases in the tropics.

Heat is actually not always a good thing either. You might want to avoid the cold, but you might also want to really avoid those high temperatures.

And then there may be a whole lot of other species that spend time year round in those places in between that could out compete you for the resources that you might want to make use of when you come there after your migration. But I like to think that they're going to that really good place, that great restaurant at the other end of.

Dr. Scott Taylor
The globe often, and even when I was younger, I guess, when I thought about places with lots of biodiversity or resources, I thought about the tropics. And that's true from like a coral reefs perspective.

But the tropical oceans are actually quite nutrient poor, which means there isn't really a lot of food there for birds like Arctic terns or godwits. And so we think about the Arctic and Antarctica as these Frozen wastelands.

But during their summers, they're actually among the most resource rich, productive places on the planet. And so that's important to remember when we're puzzling over why a little bird would fly to and from.

But, yeah, I like thinking about it as the restaurants, the really good restaurants on the ends of the world.

So we've reached the part of the show that we call that's BS or bird stuff, where a guest gets to debunk a myth about birds that they think you should all know. Nate, what do you want to call BS on?

Dr. Nate Senner
So, we've been talking a lot about how hard migration is for birds, but what I actually want to tell you is that migration is not necessarily dangerous for birds.

Dr. Scott Taylor
Can you elaborate a bit on that?

Dr. Nate Senner
I mean, we talked about how. I'm dropping the mic right there. It is not dangerous for birds.

Dr. Scott Taylor
Not just not dangerous. We did just talk about the fact that some birds get eaten by sharks, though. So could you maybe elaborate on what you mean?

Dr. Nate Senner
Well, I mean, okay, so for us, right, this migration just seems like this incomprehensible feat because we can't do it. And so by virtue, then, we think it has to be incredibly hard for the birds as well.

And therefore, it is probably dangerous, and it is dangerous sometimes.

But migration also would not have evolved in the first place if it weren't actually beneficial for the birds doing it relative to other birds who aren't migrating. And so within Godwitz, if we look at wind during the year, they actually are most likely to die. It's not necessarily during migration.

In some species, it's during the breeding season.

Because actually sitting on a nest and hoping that nobody else notices you while you're sitting on your nest is way more dangerous than flying across continents. So it definitely differs among species, but migration is not necessarily that thing that is most dangerous for birds to do.

Dr. Scott Taylor
That's a great point. Not inherently dangerous.

Humans have made it more dangerous, as we alluded to, with some cities and artificial light at night and a lack of food resources because we've modified habitats, but in a natural setting. Of course, it wouldn't have evolved if it wasn't beneficial, but we've definitely made it more challenging, which is maybe the thing to focus on.

Awesome.

Well, I've really appreciated hearing about your research and your thoughts on migration, and I just want to say thanks so much for joining us on the podcast today.

Dr. Nate Senner
Well, thanks so much for having me. And yeah, it was a lot of fun.

Dr. Scott Taylor
Okay, so birds are dinosaurs, and around here we like our snacks so we end each of our episodes with a dinosaur nugget. Today's dinosaur nugget is that migration is all about resources. Why would an Arctic tern fly from the Arctic to Antarctica and back every year?

Well, polar summers are resource rich.

There's tons of food for an arctic tern in the Arctic during the Arctic summer and in Antarctica during the Antarctic summer, which is our winter here in North America.

It's important to remember that tropical oceans, although they have coral reefs, don't have a lot of nutrients in the water, and so wouldn't be a good place for an Arctic tern to spend the winter. It's also important to remember that migration isn't inherently risky. Birds have evolved for millions of years to complete these amazing migrations.

But humans are introducing a lot of risks. We're building cities, we're having lights on at night. We're destroying habitats.

And climate change is shifting when resources are available, all of these things are challenging migratory birds more than resident birds. And so we see declines in migratory bird populations because of the changes humans are making to our planet. That's a wrap on this week's episode.

Okay, but why fly from the Arctic to Antarctica and back every year? If you liked this episode, leave a comment like and subscribe and we'll catch you next time. Byeee.

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.