Pass It On: Sheep and Moose Teach Knowledge Of Migration Routes

IRA FLATOW: This is Science Friday. I’m Ira Flatow. The end of the summer, it’s back to school. But for wild animals, it’s time for migration.

How do animals know where to go? And do big and small animals use the same sense of direction? For bigger animals, like deer, sheep, and moose, there’s a theory that the route is something that needs to be learned. These hooved animals need to develop a mental migratory map, kind of like your parents showing you their favorite fishing hole.

Well, a team of scientists tested this idea out by following herds of sheep and moose, all equipped with GPS collars. Their results were published this week in the journal Science. Let me introduce them to you.

Matthew Kauffman is a USGS researcher, associate professor at the University of Wyoming in Laramie. Welcome to Science Friday. Matthew, are you there?

MATTHEW KAUFFMAN: Yep.

IRA FLATOW: Ah, welcome to the show.

[LAUGHTER]

MATTHEW KAUFFMAN: Thank you.

IRA FLATOW: You’re welcome. Brett Jesmer is an ecology researcher, also at the University of Wyoming. And they’re both authors on this recent study. Welcome, Brett.

BRETT JESMER: Thank you, Ira.

IRA FLATOW: Let me start out with you. I heard that this study was part of your PhD dissertation that you defended yesterday. How did that go?

BRETT JESMER: It was fantastic.

IRA FLATOW: Well, I’m glad.

BRETT JESMER: Absolutely. I’m feeling wonderful today.

IRA FLATOW: That’s great to hear. Matt, in your study, you looked at bighorn sheep and moose. Can you give us a sort of thumbnail overview of the summer and winter migration these animals– what do they do in Wyoming? What is their general pattern?

MATTHEW KAUFFMAN: Yeah. So Wyoming is– a lot of people that drive through Wyoming think it’s a pretty flat state. But in fact, this is where Yellowstone National Park is, where Grand Teton National Park is. This is a landscape of mountains and plains.

And so what most of the hooved animals, the ungulates, in Wyoming– including bighorn sheep and moose– do in this state is they winter at low elevation, these valleys or sagebrush basins. And then, in the spring, they migrate up to the mountains for better forage. And in the fall, they do a return journey back down to the low-elevation valleys. And so that’s what we call seasonal migration.

IRA FLATOW: Mhm. And, Brett, for this study, you introduced animals who are not from the area into a new location, and they did not immediately start to migrate. What did you find about this?

BRETT JESMER: We found that when you took migratory sheep, bighorn sheep, and you put them into landscapes where they had no prior experience and no knowledge of that landscape, they simply did not migrate, even though they were migratory in their previous landscape. And part of migration is following, as Matt said, these waves of forage across the landscape. And they also showed very little knowledge of how to do that on their new landscape.

IRA FLATOW: So does that say to you that someone has to teach them– their parents, their other siblings, so to speak– how to migrate?

BRETT JESMER: Yes, that’s what it does indicate. And so we think that what happens is that, over time, animals are learning about their landscapes and when and where to migrate. And with large herbivores, like bighorn sheep and moose, young individuals are literally following in the footsteps of their parents during their first year of life. And they follow them on these seasonal migrations. And we think that’s when they learn how to migrate and how to track this food across the landscape.

IRA FLATOW: So an animal that doesn’t know how to migrate– and you had GPS collars on them to learn this. What are they doing instead? Are they just hanging out?

[LAUGHTER]

What’s happening?

BRETT JESMER: Yeah, they’re just hanging out. They move around, not quite at random, but more or less like you would if you were just wandering aimlessly on the landscape when they first arrive.

MATTHEW KAUFFMAN: Yeah, and that’s one of the aspects of this research. Brett did this simulation where you basically– he created these random sheep which had no information about the landscape. And they were just sort of moving around like automatons on this simulated landscape. And then he compared those to what the actual sheep did. And some of the sheep that were just newly translocated on completely new landscapes were no better than those simulated random movers.

IRA FLATOW: So does that mean, if a sheep has no mental image, no mental map of where to go– or any of these animals– they’re going to starve to death?

BRETT JESMER: Well, they might not starve to death, because they also are able to perceive their local environment. They can see and smell food. And they still forage and gain energy from their environment. But relative to the amount of energy and nutrients they would be gaining from their food if they were in a landscape where they had a lot of knowledge about when and where to go to find the best food, they typically do poorer than the animals who have lots of knowledge about their landscape.

IRA FLATOW: So what happens to a new herd of animals that just happens to be– let’s say your old migration route is wiped out. How do you learn a new one?

BRETT JESMER: Right. And in many cases, when migration routes are wiped out, it might be impossible for these animals to learn new migration routes because there might not be places for them to migrate to. But what happens nowadays, we’re trying to restore a lot of these migration routes and get these connections on the landscape between their winter and summer range put back together. And what we think is going to happen is that it’s going to take these animals decades to relearn how to use the landscape and migrate from their winter to their summer range.

IRA FLATOW: Decades.

MATTHEW KAUFFMAN: Yeah, and that’s actually something that we showed in the study. Not all the animals– some of these animals were translocated 30, 40, 50, even 70 years ago. And so we could go back in, capture these animals, put GPS collars on them, and then ask how well they migrated and how well they track the greenup. And so we could look at time since translocation and then watch as the propensity to migrate increases in these herds.

And what you see is that bighorn sheep take anywhere from 40 or 50 years to become partially migratory. And moose might take up to a century before they become fully migratory. So it takes decades and decades and generations to learn how to do that.

IRA FLATOW: That’s amazing, because we hear about the birds and the bees using magnetic particles or the sun or stuff like that. And these animals just basically have to learn it over decades of where to go.

BRETT JESMER: Yes, absolutely.

IRA FLATOW: Wow. And, Matt, this information is passed on. And you called it “culture.” This is a culture.

MATTHEW KAUFFMAN: Yeah. So as opposed to– with some migratory taxa, like birds and fish and some insects, they actually know how to migrate. It’s hardwired into their genes.

But this we refer to as cultural evolution, because essentially, you have a new individual on the landscape. They learn how to do it. Then they pass that information on to their young.

The next generation does it a little bit better, explores and finds new places, new patches on the landscape, makes a better migration. They pass that on to their young. And over time, each subsequent migration has more knowledge about the landscape, until ultimately, you have a herd of individuals who all have sufficient knowledge to fully exploit with a migration from the mountains to the plains and make a great living on these landscapes.

IRA FLATOW: So, to me, that says that if we lose an animal, we’re wiping away a migratory map.

BRETT JESMER: Yeah, in fact, we are. So if you lose one or two animals, you might decrease the amount of knowledge that these populations have about their landscape. But if you lose an entire population due to disease or some other reason, or if you just cut their migration route off, after a few generations, that knowledge will be lost because animals won’t be continuing to migrate and passing that information on to their young. So the loss of these populations is not only a loss of individuals, but it’s a loss of knowledge and a loss of their culture.

IRA FLATOW: Matt, you have a project called Wyoming Migration Initiative. What’s going on there?

MATTHEW KAUFFMAN: Yeah, that’s right. So we do a lot of migration research in our group in Wyoming, where we still have these sort of vast landscapes and very few people. Mule deer, elk, moose, bighorn sheep, pronghorn, all these species migrate across the state. And we were doing a lot of research, but recognizing that that research wasn’t getting into the hands of conservation groups and agency managers who want to work to keep these migrations connected and on the landscape. And so the Migration Initiative is a research initiative at the University of Wyoming where we focus on developing conservation tools– basically, better migration maps– and also public outreach to help people understand about these migrations.

IRA FLATOW: Well, Brett, now that you know and you’ve confirmed this idea about the maps, how should we think about conservation plans for these animals?

BRETT JESMER: Well, simply, if we can conserve the landscapes that these animals use to connect their winter ranges to their summer ranges, then we’re conserving their knowledge. So by conserving what we have on the landscape today, I think that’s a much better way to go about conservation than trying to restore a lost migration, which again, is going to take decades of time. And during these decades that it takes them to learn, their populations are going to suffer because they’re using these migrations to access this high-quality forage that really underpins their reproduction and survival.

IRA FLATOW: And, Matt, but these landscapes are changing all the time. Is climate change also involved in this, changing what the landscape is?

MATTHEW KAUFFMAN: Well, that’s kind of a difficult question. So one of the things with climate change– what we’ve seen is that these animals– so partly, they do have this memory. They have this mental map of where they’re going. But that’s not all they use.

They also are sampling the environment. They’re feeding on this fresh green grass and using that as a cue. And so as climate change advances spring, these animals can detect that and then move accordingly.

So they use the mental map to move along that migration corridor. But they use the information about greenup and snowmelt and all those types of things, which climate change is influencing, to trigger the timing of their movement. So they’re actually fairly adaptable to the effects of climate change. And this is precisely because they don’t have a genetic code, such as day length or something like that, that hard-wires when they are to migrate.

IRA FLATOW: Do they use any sort of pheromones to follow each other? Or it’s just pure memory of the map and being guided by where the vegetation is?

MATTHEW KAUFFMAN: I’ll let Brett answer that one. Or I should say, Dr. Jesmer answer that one.

IRA FLATOW: Congratulations, doctor.

BRETT JESMER: Thank you. That’s actually an active area of research. We don’t know what other types of potentially chemical cues– like you said, pheromones– might be involved.

But in some of these migrations, there are– these are large groups of animals. We’re talking groups in the size of hundreds and over. These groups, we’re talking about thousands of animals moving on the landscape every year.

And these animals, they’re only together, sometimes, during this actual act of migration. And other parts of the year, they’re off in their own space. And so it’s possible that, as they come together, they could be following these pheromones or chemical cues that you’re talking about. And that might add to their knowledge about where to migrate.

IRA FLATOW: I want to thank you both, Dr. Matthew Kauffman, associate professor at University of Wyoming in Laramie, Dr. Brett Jesmer, ecology researcher, University of Wyoming. And you can see the Wyoming Migration Initiative maps up on our website at sciencefriday.com/migration. Thank you both for taking time to be with us today.

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