Backpacking Ospreys: Following their migration

On a clear morning in early September 2008, a three-month-old female Osprey named Penelope pushed off from Martha’s Vineyard, Massachusetts, and flew, alone, 2,700 miles to French Guiana in 13 days.

She touched down in coastal Maryland and North Carolina for three days, lazed along the Bahamas for four, then blew through the Dominican Republic in 29 hours. At dusk she launched out over the Caribbean, flying all night and the next day to a tiny island off the coast of Venezuela. A week later she was exploring rainforest rivers in French Guiana, her home for the next 18 months.

Twenty years ago we couldn’t imagine the extraordinary trips that these fish-eating raptors—our summer neighbors on their big stick nests—take routinely. We occasionally glimpsed them at hawk watches, or very rarely recovered their leg bands when they died en route. Now researchers can strap a 0.75-ounce, solar-powered satellite transmitter onto the back of an Osprey and know the bird’s location, within a few hundred yards, for the next two to three years.

A few dozen Ospreys each year wear these tiny backpacks. With the help of Google Earth, we can see ecological details about the places Ospreys winter by visiting http://bit.ly/ospreytrack.

After 10 years and more than 150 tracked Ospreys, this project—the brainchild of Mark Martell at Minnesota Audubon and Rob Bierregaard at the University of North Carolina, Charlotte—is providing much-needed data revealing migrational differences among Ospreys and helping pin down where threats to Ospreys lie.

For example, like many adolescents, juvenile Ospreys wander, loiter, and even get lost, crossing open ocean when they don’t have to. Adults fly faster and more direct routes, more sure of where they’re headed.

Cuba and Hispaniola are key migration hubs for eastern Ospreys hopscotching across the Caribbean. In fall these migrants funnel down the Florida peninsula, hop to Cuba, then move east across Haiti and the Dominican Republic. From there they clear the rest of the Caribbean to wind up in South America. Western Ospreys don’t migrate as far, and spend less time crossing ocean. They winter in Central America.

Sadly, we’ve also learned that Ospreys are still shot during migration and on their wintering grounds. Fish ponds are often a lethal magnet: Ospreys find what must seem like a great food resource, and fish-farmers retaliate. Efforts are now under way to work with farmers to curb these losses.

Male Ospreys forage for their mates and young on the breeding grounds. By tagging males in the Massachusetts nesting colony I study, we are learning where they forage and what fish they target, information that helps protect fish and their spawning grounds.

Ospreys wear their satellite backpacks easily and the units are designed to drop off in 2–3 years. The burden is light, and the information gained helps focus conservation efforts where they are most needed. Tens of thousands of North American Ospreys migrate to the tropics each fall; we want to make sure that they return to continue their journeys in the years ahead.

Alan Poole is the editor of Birds of North America Online and author of Ospreys (1989, Cambridge University Press). [update 2/8/22: Birds of North America Online is now part of Birds of the World.]

Originally published in the Summer 2010 issue of BirdScope.