Mysteries of osprey migration
Over the last month, ospreys have completed their long migration, returning from South America to Cape Cod and, for many, to previously established nests. It’s an annual sight many people look forward to, as these majestic birds soar above the shoreline and build their homes in the neighborhoods.
On Saturday, bird lovers had the chance to learn more about the bird of prey’s migration at a lecture sponsored by Mass Audubon, titled ‘Journeys: Ospreys, Technology and an Author’ And what they learned is troubling.
Large brown and white raptors get hit by cars and ships, shot by hunters, and blown off course during hurricane seasons. One even ended up on a ship that took it to Portugal. Drexel University research associate Rob Bierregaard spent 18 years tagging ospreys to better understand their movements.
“Most of the mortality is related to crossing the Caribbean during the hurricane season. That’s when most adults disappear,” Bierregaard said. “Many birds also die in the woods, where they spend the night during the migration and they often don't come out of the other end; sometimes we find in the forest a pile of feathers.”
Snowy, a young female osprey born in Martha’s Vineyard, was fitted with a solar-powered satellite tracking device. In 2014, she escaped the cold New England winter by flying 1,696 miles to northern Cuba, where, according to Bierregaard’s analysis, she found a rich fishing ground. As the spring arrived, Snow spent six days traveling back to Cape Cod.
Snowy is just one of the nearly 100 birds that Bierregaard equipped with trackers in the United States. The matchbox-sized devices use miniature GPS-enabled transmitters to show the birds' precise location, altitude, speed and time it takes for them to complete the trip south.
“Before I put a four-thousand radio on the back of a bird, I want to know that the bird can land,” Bierregaard said. “Flying is easy, but we have seen a number of ospreys who don’t survive the landing, often because they get stuck in vegetation and can’t get back up.”
The Brazilian rainforest is one of the ospreys' preferred winter havens, along with Mexico. The birds will rest in the Caribbean midway on their migratory path. During migration, it is vital for the birds to stay close to the land.
“Osprey cannot land on the water and rest like a duck would. If they get stuck in a hurricane in the open water, their lives are in huge danger,” said Bierregaard.
Years of studying ospreys inspired Bierregaard to publish "Belle's Journey," an illustrated book about the migration of an osprey from Martha's Vineyard who winters in Brazil.
The book has received one of two Honorable Mentions in the National Outdoor Book Awards' Children's Division, been placed on the National Science Teachers' Association list of outstanding trade books for 2019.