Blog Post

Great Migrations: Tracing Birds, Bats, Butterflies, Bumblebees

Martin Wikelski uses tiny sensors and radio transmitters to trace the secret journeys of even the most elusive birds, bats, butterflies, and bees--some of them astonishingly small. Great Migrations continues tonight in the U.S. on the National Geographic Channel.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop

By Ford Cochran

The largest programming event in the ten-year history of the National Geographic Channel, Great Migrations continues tonight in the U.S. at 8 p.m. EST/PST tonight, with related coverage in National Geographic magazine and an official companion book.

Who says you can't LoJack a bumblebee? Not Max Planck Institute for Ornithology Director and National Geographic Emerging Explorer Martin Wikelski, who has created a suite of tiny radio transmitters and biomonitors to track the doings of some 50 different species on the move. He has received multiple National Geographic Committee for Research and Exploration grants to support his team's work on projects that literally span the globe. His compact and inventive tracking tools helped reveal several of the astonishing animal stories told in Great Migrations.

Wikelski called me from the West African country of Ghana, where (he noted) he was observing thousands of migratory bats leaving a cave as we spoke.

Your lab has created a multitude of small devices for tracking animals' travels in detail, which is of course essential to understanding their migrations. What other sorts of things can your instruments reveal?

Many things. Sometimes you hear an animal's wing beats, you hear what they do, what they talk about, what they say to other individuals of their species. Then you begin to understand how they orient in the landscape.

For example, you could follow a Mexican freetail bat, which might be just one of a million leaving a cave. I flew in my small plane with one for seven hours the other night, maybe 1,500 feet above it all the time. I was listening to every wingbeat it was making. That's when you start to understand what they're doing.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop

So beyond just where they go, you monitor how animals get there--their wingbeats, their heartbeats, their metabolism, and other sorts of factors that indicate what they're up to and how it's sustained, how they gather and expend?

Exactly. We're learning more and more that if you see an animal, and you see the environment around it, and you see what it decides to do, it's like asking the animal, Hey, what do you think about your environment? Tell us. And it tells us by walking or flying or swimming here or there. So we get a glimpse into the animal's mind as well. Often, we're getting that glimpse for the very first time.

Take what I'm doing here with bats in Ghana: There are millions and millions of these major seed dispersers that fly through Africa every year, really large distances, transport seeds--and nobody knows what they're doing. They also transmit diseases. So they're good and bad. And we have no clue, I mean, it's just unbelievable. I stand here on a hill, and there are tens of thousands of bats flying by. People from our institute were the first to track them a year or so ago with new devices. And now we're waiting for a bunch of those bats to come back after their annual migrations.

We knew nothing beforehand, and then just like that we'll know what they do in Africa, where they go, with details that tell us which tree they were foraging on on which night and how many wingbeats it took them to fly there. That's really, really exciting!

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop

I gather that some of the most fundamental questions about familiar creatures such as songbirds still remain to be answered: What's causing their decline, what the best steps might be to protect them. There are still a lot of mysteries about animal behavior, correct?

Absolutely. We still don't know why some animals die. We don't know how they disperse. There was a major publication about a whale that was seen off South America and then off Madagascar--one individual seen in both places. Just seen, so we don't even know how it got there, but it did get there.

And then you think, well, is that the level of our ignorance, that we don't even know where whales are? They're the biggest creature on this planet and we don't know what they're doing. Are we that ignorant? Unbelievable!

When you came to our headquarters for the Geographic's Explorers Symposium, you discussed creating a database, MoveBank, where scientists could share migration data and insights. Have you made progress?

Yes. MoveBank's up and running now, and there are already about 180 studies in there even without us really promoting it yet. Now we can use it to share data. We can link every point on an animal's measured migratory path in space and time with weather, wind, and other species around it. For the first time, we're building a global database, a global museum of what's happening to this planet because of animal movement.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop

Are the bumblebees, orchid bees, and monarch butterflies the smallest creatures you've successfully attached transmitters to so far?

Yes. Of those, I think the most exciting were the butterflies, because we tried it once before, but the technology wasn't there yet. We gave up for two years and then came back with better tags, smaller tags, newer technology, tried again and it worked out beautifully.

We first tried it in a greenhouse, and were totally astonished that the butterflies had an easy time flying. Then we went out to Kansas with National Geographic and tried in the field. And it worked.

The effort's been stimulated by the Geographic--people asking on faith, "Can you do this? It should be possible, shouldn't it?" And then we said, you know, I guess you're right. We should try it, we should do it. And it turns out it truly is possible, it's doable, and the kinds of information we can get now are incredible.

In the case of monarch butterflies, your tiny transmitters weigh in at a third to half of the animal's body weight, correct? It's remarkable that the butterflies' flight appears relatively unimpeded, and that you've actually tracked them over long distances.

We were surprised, but it looks really good. I'm sure we are impeding them somehow. I can't imagine it doesn't have an affect. There's an ethical component to this work. It's a difficult decision sometimes to say yes, we want to do attach a transmitter.

Every time we place a tag, we're considering that we are loading the animal with a weight it wouldn't ordinarily have, and obviously we want to avoid that. It's a hard decision to take, but it's worth doing it, I believe, because the information we get is so important to understanding the bigger picture of how we may be affecting these animals and their ability to survive.

I'm guessing a few birds have gotten a crunchier lunch than they expected. Have you been able to follow the movements of any predators after they've eaten the animals you're tracking?

Not quite, but we had one dragonfly with a transmitter get eaten by a kestrel. It took the wings off first, then took the tag off, put it on the ground, and ate the body. It knew exactly what it was doing.

We've seen the same with ocelots. When they eat small rodents called agoutis, they usually put our tag aside. We had none of the agoutis we were following live for more than a year in the forest in Panama, but that's normal. There, the tags don't really hurt them. It's just that the ocelots are good hunters. They cut the head off, the collar falls off, and then they eat the agouti.

Nice. Is there anything else you'd like to share?

Nothing except to thank National Geographic. Twelve years ago, nobody believed that what we're doing today would ever be possible, that we could make it work. The only funding we got was from the Geographic. Your colleagues said "We've funded crazy ideas before. Just do it." And that made it all happen.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop

  • Watch more of Great Migrations on the National Geographic Channel at 8 p.m. EST/PST tonight in the U.S. (Check local listings for air dates and times outside the U.S.)
  • Purchase the official companion book to the series.
  • Read about "Great Migrations" in National Geographic magazine.
  • Help conserve the landscapes of migratory species with National Geographic's Global Action Atlas.

Photos by Christian Ziegler; book cover courtesy National Geographic Books

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop

Ford Cochran directs Mission Programs online for National Geographic. He has written for National Geographic magazine and NG Books, and edits BlogWild--a digest of Society exploration, research, and events--and the Ocean Now blog. Ford studied English literature at the College of William and Mary and biogeochemistry at Harvard and Yale, with a focus on volcanoes, forests, and long-term controls on atmospheric CO2. He was an assistant professor of geology and environmental science at the University of Kentucky before joining the National Geographic staff.

More posts by Ford Cochran

Join Nat Geo News Watch community

Readers are encouraged to comment on this and other posts--and to share similar stories, photos and links--on the Nat Geo News Watch Facebook page. You must sign up to be a member of Facebook and a fan of the blog page to do this.

Leave a comment on this page

You may also email David Braun ( if you have a comment that you would like to be considered for adding to this page. You are welcome to comment anonymously under a pseudonym

Back to Top
About National Geographic Society

The National Geographic Society is a global nonprofit organization that uses the power of science, exploration, education and storytelling to illuminate and protect the wonder of our world. Since 1888, National Geographic has pushed the boundaries of exploration, investing in bold people and transformative ideas, providing more than 15,000 grants for work across all seven continents, reaching 3 million students each year through education offerings, and engaging audiences around the globe through signature experiences, stories and content. To learn more, visit or follow us on Instagram, LinkedIn, and Facebook.