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05/11/2022 07:00 AM

Why Do Birds Migrate?

(Left) Scott Yanco holding an ICARUS tag. ICARUS stands for International Cooperation for Animal Research Using Space, is a space-based wildlife tracking project that is tracking species across central Asia, Japan, Papua New Guinea, and other far-flung spots. Photo courtesy of Scott Yanco

From mid-April to mid-May, hundreds of people descend upon Mount Auburn Cemetery in Cambridge to watch the birds, hoping to catch a glimpse of species as varied as the commonly sighted red-tailed hawk to the somewhat more rare appearance of a white ibis, like the one that recently stopped by the cemetery’s Halcyon Lake, about a 1,000 miles north of its typical habitat, much to the delight of those birders.

Scott Yanco used to be one of those birders when he was a kid. He frequently attended events sponsored by Massachusetts Aubudon and is now an enthusiastic supporter of the Connecticut Aububon, which is hosting a Migration Madness event that will start at midnight, Friday, May 13 and run through midnight, Sunday, May 15. The event, open to all, is a fun, friendly competition to encourage bird lovers to see as many species as possible over the weekend. Find out more at

When he was a bird-watching kid, Yanco was content fulfilling his curiosity about which birds he was seeing, how many he was seeing, and when. But then he found his curiosity straying to a new question, why? Why, when there are so many ways for animals to adapt to New England winters, did some birds in the fall opt instead to fly thousands of miles in a complex, highly perilous journey, and then fly back again this time of year?

These days, with his morning coffee, Yanco often takes a few minutes to enjoy the birds singing as they stake out their territory and search for food in his North Haven backyard before he heads off to work. As a postdoctoral associate in the Max Planck Yale Center for Biodiversity Movement and Global Change, he is currently working with a network of scientists around the world to help solve the puzzle of why birds migrate.

Understanding that might help us understand what shifts in migration can tell us about global patterns of diversity. It might help inform us about the increased risk of spillover events from animals to humans that can spark deadly pandemics. Yanco and his colleagues also are trying to puzzle out how information gleaned from the movement the smallest of creatures, from birds to bumblebees, might help create a more sustainable future for humans.

It’s Not Obvious

“Basically, what I’m interested in is why migrate, right? So there is a lot of research about how animals do it, where they are going. But to me, it’s not so obvious why it’s a good solution. So if you think about it, the problem is winter, the seasons. And there are a lot of ways that animals and organisms handle seasons. Bears hibernate. Some species change their coats. They eat different foods. There are all sorts of ways evolution has come up with just to deal with seasons,” he says. “So, to me, it’s a little bit mind boggling that some of these solutions include flying thousands of miles and the incredible adaptations that make that possible.”

He wants to know why some species do and some species don’t, and what those differences mean. Part of his research is examining how migration strategies fit into that puzzle. Luckily for Yanco, and for the rest of us who will benefit from this research, we are living in the golden age of animal tracking.

In addition to looking for birds with binoculars, like Yanco did when he was a kid, animal migration and movement now can be monitored with the help of tiny transistors attached to bears and birds and bees, tracked by satellites deep in space, and beamed back down to earth to databases where Yanco and his colleagues sort through it to make sense of it all.

“The rate of technological development and inbound data is literally exponential,” he says.

When he first became interested in doing this kind of work, birds were tracked with little aluminum bands that were put around their legs. Someone would have to catch them, band them, and then, maybe, someone would catch them again “and we’d get a second or maybe a third data point,” Yanco says.

Then the technology advanced to using little light level-reading geolocators, which were attached to the backs of birds. Using the same kind of math that mariners used hundreds of years ago, scientists could figure out, roughly, where these birds were located on the planet.

A Careful Cost-Benefit Approach

And then GPS technology was added into the mix. First, due to the size of the equipment, they could only be used on elephants, then bear, then deer.

“For birds, it was a no-go for a long time,” he says.

Then, since 2010, there has been a rapid increase in the miniaturization of GPS tags.

“So we are down to a gram now,” he says. “So you can put them on birds that are a little bit smaller than a robin, say, which still excludes about half of all birds.”

Adapting the technology to increasingly smaller creatures is advancing only as fast as is safe, he says. For some birds, whether due to their size or the way they are built or the way they nest, attaching the tracker can affect their ability to travel and it sometimes appear to have a negative effect on their mortality rate.

Yanco says it’s important to take all of that information into account, and evaluate it along with taking a cost-benefit approach to attaching items to animals. It is not enough to show that you can, and that you can safely, you also have to show that there is a benefit to doing so.

A War Gets In The Way

There are other issues to resolve as well. A project, optimistically dubbed International Cooperation for Animal Research Using Space, or ICARUS, is a space-based wildlife tracking project that was having great success tracking 15 species across central Asia, Japan, Papua New Guinea, and other far-flung spots. The data was beamed up to the International Space Station and then down through a ground station in Russia. And then Putin happened. Following Russia’s invasion of Ukraine, the data stream stopped.

Scientists decided to hold off on placing more tags on birds until they come up with a solution, and are now trying to figure out other options.

While that has paused some of the work, Yanco is optimistic a solution will be developed. He’s looking forward to solving other challenges as well. One such challenge is figuring out how best to handle, sort through, and use the tsunami of data being generated.

One early finding is that migration is a whole lot more complex than a bird flying down to its winter home and then flying back, like human snowbirds.

It’s Complicated

“There is this growing appreciation that it’s all a lot more complicated,” says Yanco. “We used to have this picture that birds have their breeding territories. They fly south in the winter, they find their wintering territories, and then they all pick up and come back. It’s a lot messier than that.”

The data is showing that there is a lot more diversity when it comes to individual birds, and across individuals within a species. Take that white ibis that made all those birders happy recently at Halcyon Lake. Why did it pick up and head to Massachusetts when many of its brethren prefer to fly from Florida to somewhere in Virginia or maybe Texas?

“Some of them migrate. Some of them don’t. They might shift their location a couple of times. Some of them are going way further than we thought,” he says.

As more data is collected, patterns will start to emerge that will help explain some of these complexities and, potentially, provide information that could help both animals and people improve survival rates as climate change changes the planet.

For example, a recent article in Trends in Ecology & Evolution says the combination of space-based tracking technology and low-cost tags might make it possible at some point in the near future to track thousands of animals from hundreds of species every half hour. The current tagging technology can be used with about 40 percent of birds and more than 50 percent of mammals, or about 7,000 different species, along with hundreds of species of crocodiles, turtles, and lizards.

Early Warnings About Epidemics, Pandemics

Because animals are signalers and sentinels of environmental conditions, tracking their movements could provide us with early information about issues relating to conservation, environmental change, and human health.

For example, climate change is producing all sorts of new, and potentially dangerous, opportunities for viral sharing among wildlife species that in the past have been geographically isolated. If viral surveillance is combined with efforts to track species’ range shifts, it could provide scientists with valuable information to help protect both animals and people from epidemics and pandemics that originate in wildlife.

Yanco provides another example.

“So birds provide a massive ecosystem service in terms of reducing insect populations,” he says. “In order to make good predictions, you need to understand how these organisms relate to their environment…The central challenge for us is now taking advantage of these massive data streams to better understand this stuff and make predictions at a completely different scale.”

What the Rest of Us Can Do

While Yanco and his colleagues develop new tools and overcome the challenges, there is much the rest of us can do to help birds and bugs survive as the climate changes. We can plant native plants that will help sustain them, plants that provide food across a range of seasons. We can put off lawn mowing and leaf raking in the spring until insects and bees no longer need that refuge. We can work with organizations that help preserve wide swaths of habitat, both in Connecticut and other parts of the world where our Connecticut birds visit as part of their migrations.

At the policy level, people should support funding that allows for research that affects conservation efforts.

“And then, finally, I would just say, you know, that one of the best ways that people can engage is by getting outside and seeing these individual birds and appreciate what they are seeing,” he says, including participating in the Migration Madness event hosted by Connecticut Audubon this coming weekend.

“I mean, it’s amazing to see the sheer numbers of birds, the colors, all the activity in the spring,” he says. “If people understand even a tiny glimmer of understanding as to where that bird started, where it’s going, and that they are witnessing one tiny part of a massive global scale process, I think that will help turn all of us into stewards of that, once we understand the interconnectedness of it and the importance of advocating for it.

To find out more about ICARUS and the recent halt due to the war, search for War Halts Project Tracking Wildlife from Space in To find out more about projects being run at Yale, visit,, and

An owl carrying a GPS tag. While attaching tags to birds and other animals can help scientists glean important data that can help shed light on some of humanity’s most vexing problems, like climate change, it is done in a way that evaluates the effect on the animals, as a sort of cost-benefit analysis. Photo courtesy of Scott Yanco
(Above) The ICARUS antenna on the International Space Station. ICARUS stands for International Cooperation for Animal Research Using Space. That cooperation was interrupted recently when Russia, a party to the project, invaded Ukraine. Scientists are now seeking workarounds to that problem. Photo courtesy of Scott Yanco
A map of migrations of several species of cranes for the 1,000 Cranes Project Graphic courtesy of Scott Yanco
Bluebirds usually winter in the southeastern United States or Mexico and then, after migrating thousands of miles, arrive in Connecticut. Unlocking the mystery of why birds like these migrate is one of the goals of work being done by Scott Yanko and his colleagues. Photo by Bill Canosa courtesy of Connecticut Audubon
Northern cardinals generally do not migrate, opting instead to make places like Connecticut their year-round home. Why some birds migrate, and others don’t, along with changing patterns of migration, are questions and puzzles being explored with projects like ICARUS. Photo courtesy of Connecticut Audubon