GLOUCESTER — Rob Bierregaard was in Gloucester and Essex recently, catching and tagging birds of prey on salt marshes owned by the Essex County Greenbelt Association.
A visiting research professor at the University of North Carolina Charlotte, Bierregaard is a leading expert on the osprey, sometimes referred to as a sea hawk or fish eagle.
Because of the raptor’s popular appeal and conspicuous presence — it has a 5-foot wingspan and often nests on man-made platforms in the center of open wetlands — Bierregaard calls it “the icon of the coastal marshes.”
He installed a solar-powered GPS transmitter on both of the two juvenile male birds he captured in Essex County, to track their southward migration that will begin next month.
One bird is named “Whit” (for the Whittemore Saltmarsh in Gloucester, where it lives), and the other is “Peirce” (for Jack Peirce, a Greenbelt founder). Bierregaard names the birds instead of assigning numbers to make it more interesting for the people who follow their journeys.
With traditional bird bands, he said, “you didn’t know what route they took to get from point A to point B.” The GPS-equipped transmitters will allow him to see their migration route and determine how long the journey lasts, information he shares on a website (www.bioweb.uncc.edu/bierregaard) that includes an interactive map tracing the migration of his banded birds between the Northeast and the Caribbean and parts of South America.
Whit and Peirce were the first birds he banded on the North Shore, said Bierregaard, who was on a mission that began in Hampton, N.H., and was working his way along the coast to Martha’s Vineyard, and then to Long Island, New York.
In total, he would fit six juvenile ospreys with the transmitters, which cost approximately $4,000 each.
“One of the interesting things we’ve found is that on the first trip south they have no idea what they’re doing, but when they come north they stay on land as much as they can,” he said. “The next time, when they go south, they know there’s a land route.”
The bird will refine its route each time it makes the trip, he said, and, “wind up in the same place.”
The Essex County banding was part of the Greenbelt’s osprey program, which has been expanded significantly this year, said Dave Rimmer, the nonprofit conservation organization’s director of land stewardship.
The program’s staff and volunteers build and maintain the sturdy platforms where ospreys nest; similar towers, which replicate the species’ preferred nesting habitats, have been built in marshes across coastal New England to encourage the population’s growth.
The Greenbelt program also monitors nesting pairs, which have made a comeback since what Bierregaard calls “the DDT days” of the 1960s and 1970s when the number of osprey declined; the nesting population in Essex County disappeared completely until the early 1980s, when the first returning pair was discovered.
This year, there are nearly 25 nesting pairs in the county, a jump of as many as 10 pairs from last year. “We’re growing now at a pretty good clip,” Rimmer said.
Bierregaard estimated that there are 400 to 500 nesting pairs in the state.
This year, the Greenbelt program expanded to include the banding of 13 osprey chicks (by Rimmer) last month; the transmitters attached to the two birds by Bierregaard; the use of volunteer citizen-scientists to monitor the nests; and a webcam focused on a nest at the Cox Reservation in Essex.
“We looked at the work we were doing and said, how can we expand this program in a meaningful way, to really contribute to what I call conservation biology, to get good information to help us understand what osprey are doing in Essex County, and to help improve conditions for the osprey population,” said Rimmer, who is also trying to engage and educate the public, and get more people involved with the association’s mission of conservation and protection.
“Individuals will eventually be able to go to our website and follow the migration of these two ospreys that we banded,” Rimmer said.
“These transmitters could last for years and years. As long as the bird is alive, we’ll be transmitting a signal up to a satellite that will tell us where this bird is.”
The Squam Lakes Natural Science Center in Holderness, N.H., has been running an osprey program since 1997, and calling on Bierregaard to tag birds with transmitters since 2011. While the center is in the Lakes Region of New Hampshire, its Project OspreyTrack hopes to put transmitters on 15 birds from all over the state within three years.
Bierregaard has put transmitters on seven birds through this project, though the mortality rate is high: three of the birds did not survive their migration.
The osprey tagged late last month at the Hampton Harbor salt marsh was the first from the New Hampshire seacoast. It was named “Weber” for Hampton resident Dave Weber, a volunteer who installed several of the platforms used for nesting in the area.
Greenbelt and Squam Lakes are part of Bierregaard’s larger research project, which has included the tagging of 61 birds, including 38 juveniles, since its start in 2000.
Since 2004, he has focused more on juveniles that are making their first, treacherous migration. Bierregaard estimated that the mortality rate for migrating adults is 10 percent, compared with 60 percent to 75 percent for inexperienced juveniles.
Bierregaard’s online entries and e-mails are written in conversational style, and he keeps an interactive focus intended to engage visitors to the site.
“The more people care about the natural world around them, the more they’ll work to protect it,” he said. “People forget we’re part of nature.”
Correction: An earlier version of this story misidentified the number of nesting pairs in the state.