Unlocking Migration's Secrets

Unlocking Migration's Secrets

For centuries the study of bird migration has been riddled with mystery and unanswered questions: Where do birds go in winter? How far do they fly? Can they navigate a hurricane? Scientists are tapping new technologies to find the answers, and transforming everything we know--or think we know--about birds.

By Scott Weidensaul/Photography by Joel Sartore
Published: March-April 2012

And it's only through such all-encompassing approaches, Marra and others argue, that conservationists can hope to stem the declines and disappearances of migratory species, from songbirds to salmon and whales. That's why Smithsonian's Marra and Sue Haig from the U.S. Geological Survey, along with dozens of other scientists, and with support from Audubon, have created the Migratory Connectivity Project to encourage research into this poorly understood area.

The notion of connectivity has changed the way Marra looks at almost everything related to migratory birds. Whether as a cause or a consequence, Marra is now one of the leaders in the growing field of migratory connectivity research, which grew out of his decades of studying American redstarts on their wintering grounds in Jamaica. He found, to his surprise, that what happens in the Caribbean doesn't stay in the Caribbean.

Redstarts practice something called sexual habitat segregation--common in many birds--where adult males grab the best winter territories, and on down the dominance ladder to immature females, which get the worst. "Best" means wettest and buggiest, mangrove swamps being preferred in Jamaica. By testing stable chemical isotopes in redstart blood, muscle, and toenails in the breeding area, Marra and his colleagues have found that the birds that winter in the wetter habitats are able to head north on their spring migration earlier and arrive on the nesting grounds first.

What's more, the quality of their winter territory has what Marra calls "carryover effects" right into the breeding season. "When you track those birds and follow their reproductive success, you find that birds that are originating in wet habitat have significantly higher reproductive success than birds coming back from dry habitat," Marra says. "It doesn't matter what happens on the breeding grounds--most of the variation in the number of young fledged is controlled by winter habitat."

These findings, which made the ornithological world sit up and take notice, are of more than academic importance. Winters in Jamaica have been getting steadily drier for the past 16 years, and if--as climate models predict--that trend continues, it could mean that no matter how much management we do here in North America, birds like redstarts could be in trouble.

That makes the timing perfect for the Migratory Connectivity Project. The goal is to harness interest in connectivity with incredible advances in technology and analytical techniques like isotope studies. While satellite transmitters like the ones used on the whimbrels are still relatively bulky, restricting their use to larger species, new inventions are allowing scientists to track smaller birds with undreamed-of precision.

Take light-sensitive geolocators, for instance, which weigh less than a penny and record moment-to-moment changes in sunlight to calculate a rough latitude and longitude for two years or more. In 2007 a team of scientists including Iain Stenhouse affixed geolocators to Arctic terns nesting in Greenland and Iceland. They found that some of the terns were traveling more than 47,000 miles in a single year--nearly double the distance ornithologists thought they migrated.

"Had someone told me just 10 years ago that we would be able to track small seabirds like terns across whole oceans and entire years--never mind that I'd be involved in such a project--I would have been completely incredulous," says Stenhouse, who studies seabirds at the Biodiversity Research Institute in Maine.

Nor did they stop with terns. In 2007 he and two colleagues used geolocators to track Sabine's gulls from their Arctic breeding grounds to wintering sites off southern Africa--at almost 25,000 miles, the longest migration known for any gull. "Over the last decade or so we have seen an all-out revolution in the study of avian migration," Stenhouse says. "Seeing the actual tracks of individual birds traversing the face of a globe still gives me shivers."

Using these new techniques, scientists are redrawing the maps of migration, discovering how regional populations are often taking very different routes to disparate wintering grounds, or discovering new over-winter areas entirely. One of Marra's students has used geolocators to discover the previously unknown destination for eastern willets (they travel to southern Brazil, as it turns out), while other researchers have used the devices to track the ever-shifting movements of bobolinks after they leave the grasslands of North America.

"The bobolink stories are just amazing," Marra says. "These birds are in an almost constant circuit of movement, from their breeding areas in Vermont or Nebraska down to their wintering area in northern South America, then back up to what might be multiple breeding areas. It's just a fascinating story we're learning from these light-level geolocators."

Not all the techniques being marshaled to understand migratory connectivity involve high-tech gadgets. Bird bands, which scientists have used for more than a century, may seem unsophisticated, but they also provide a treasure trove of untapped data. Last year Marra and two colleagues combined banding data and information from geolocators to map the connections between different populations of gray catbirds, showing that those from the Midwest take a circum-Gulf route to winter in Central America, while those from the mid-Atlantic region flit down to Florida and the Caribbean each fall.

Building on that, the Migratory Connectivity Project is undertaking the first comprehensive analysis of millions of band-recovery records, with the aim of creating an atlas of migratory connectivity for hundreds of species.

 

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I have tears in my eyes as I

I have tears in my eyes as I type. What a story. Fly safely little Hope & let us all have hope that others will survive senseless hunters.

Whimbrel trek

Great article. Reminds me of how I feel about my ultra-trailrunning, likening it to a migration is a most excellent of analogies. Thanks for sharing this trek of the whimbrel.

Incredible research

What a great article! I love reading about wildlife research and keeping myself up to speed on the current conservation issues. I studied wildlife conservation at the university of Illinois at Champaign-Urbana and participated in a number of research projects through the Illinois Natural History Survey, including one study on the American Golden Plover. I tracked transmitted plovers using radio telemetry during one of their migration stop over spots in Arcola, Illinois. These awesome shorebirds fascinated me in their incredibly long migration and how each year they return to the same stop over spots on their journey, just like the whimbrels. The data I collected just gave us a small glimpse into one part of their migration. To read about this new tracking system with the whimbrels that gave the researchers constant real time locations is absolutely incredible. What an awesome data set and comprehensive look into these birds migration. Knowing this new information about their journey can really help us understand how to conserve this species.

How do I locate the sources

How do I locate the sources you use in your articles. I am interested in studying this topic further. Do you provide the references on your web page somewhere? I don't seem be able to find a link anywhere.

Beautifully written article.

Beautifully written article. Once again I am dropped to my knees in amazement and reverence for the birds-the fierce determination and drive to survive. We must become a global village where every culture understands we can not continue to do what we have always done-i.e. hunt relentlessly with ignorant abandon. It is not imposing our values on another culture, but teaching a higher consciousness of thinking and understanding how all things are related, the balance of life on this planet is so out of whack with too many people. What befalls the animals and nature, befalls us all. Perhaps it is more "manly" to protect and stand up for what is good and right, than to destroy and kill everything in sight.

Life on Earth

It won't make much difference if the tar sands oil mining is allowed to continues. Unless we stop this TransCanada debacle, life as we and all other creatures of this earth will change to a point that we will wish we were dead. The sooner the humans are gone from the planet, the better for all other species. Hopefully, by then, there will still be some clean air and water and food to sustain them.

Migration

As usual, Joel Sartore's photographs enrich the information immeasurably. Wow.

I am wondering what the

I am wondering what the migratory patterns of birds can tell us about the history of the planet, its changing temperatures and its life span!

Unlocking migrations secrets

Working for a wildlife shelter it will be huge bonus when the price of these transistors make them usable by everyone not just the few who can get the funds to support their use. I would love to be able to track our releases as opposed to release and HOPE!

Migration

Although generally familiar with the idea of birds migrating, it took Scott Weidensaul's delineating it as "a new frontier" to really drive home to me the incredible flying and navigational feats of so many of our common birds, as well as the need to provide way stations, and protect their winter homes (March-April 2012). I am inspired to learn of ornithologists who are advancing knowledge of "migratory connectivity." We must do more to support these scientists and find ways to protect migrating birds who provide us with delightful sound and beauty, asking little in return. Marie Barry, Beverly, MA

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