Roseate tern decline perplexes researchers

[Donna]

CAPE COD —

Piping plovers get all the publicity but Cape Cod’s shoreline is even more important to the federally endangered roseate tern. Perhaps the terns need a new agent.

“Almost all the North American roseate tern population spends a couple of months on Cape Cod and the Islands at a handful of these important sites,� observed Becky Harris, director of Mass Audubon’s Coastal Waterbird Program at Long Pasture Wildlife Sanctuary in Barnstable.

Harris has been directing at three-year $70,000 project monitoring roseate terns through the summers on the Cape.

“Roseate terns are at the highest level of endangerment and there’s been about a 30 percent decline in population the last 10 years and people don’t know why,� she said. “If we can figure out what’s happening during this period of decline, that’s our ultimate goal.�

The population peaked at 4,310 pairs in North America in 2000 and fell to 3,320 by 2006. Harris employs a field staff of seven, scattered over the Cape and Islands, to monitor the terns.

The birds are feeding and hanging out (staging). Roseate terns breed primarily in Buzzards Bay on Bird Island (in Marion), Ram Island (Mattapoisett) and Penikese Island. It’s estimated 1,100 pairs breed on Bird Island and 450 plus on Ram’s, about half the total Northeastern population. Another 1,250 or so pairs nest on Great Gull Island off Long Island, N.Y. They generally nest alongside larger colonies of common terns and prefer islands to avoid predators such as coyotes, raccoons and skunks. Their summertime concentration around Cape Cod, however, makes them vulnerable to events such as Hurricane Bob.

Once the chicks can fly they depart the island, usually in late July, and like any other tourist, visit Cape Cod.

“They show up first in Falmouth, at Black Beach-Sippewissett Marsh, then spread out to Outer Cape sites through September,� Harris explained. “Plymouth Beach is a regular spot, Chapin Beach and off Crowes Pasture in Dennis (is another). The most heavily used area was Nauset Marsh, Coast Guard Beach and Hatches Harbor. There were up to 15,000 to 20,000 total terns, including common terns. Wood End (in Provincetown) was used spottily.�

They still can’t feed themselves so the adults forage and bring back fish, usually sand lances, for the chicks.

The task of the field researchers was to sift through massive tern flocks and count and identify the roseate terns via their leg bands. Needless to say, that required sharp vital eyes and a powerful scope.

“We had old scopes that weren’t up to the job,� Harris conceded. “We ended up getting really good Zeiss 80 power scopes. Zeiss helped out with the scopes.�

Identifying the birds isn’t easy. Researchers spend six to eight hours a day staring through the scope, waiting for the birds to flash a leg and give them a good view.

“Sometimes up to two-thirds of them in a flock are roseate terns, maybe 1,500 to 2,000 are banded. So you can get a lot of observations staring through a flock. It takes a lot of practice,� Harris said. “You can get exhausted by the end of the day but I certainly miss it.�

Chicks are banded after they hatch, adults at different migratory sites.

“There are six different colored bands on the adults and you can identify who the individual is,� Harris said. “They also identify as many fledglings as they can. They have only metal bands. If you can get close enough with the scope and have good focus, you can read their numbers.�

The numbers are like a zip code.

“If you can read the sequence, you can see a bird came from, say, Great Gull Island, N.Y.,� Harris explained. “We have identified a fledgling from every breeding colony in the Northeast where more than five chicks were banded. We’ve identified 15 to 20 percent of all the chicks banded this year. So we can pretty much confirm they are all coming here.�

Harris was especially impressed that birds from Connecticut and New York fly north to the Cape before flying south for the winter.

All told, 2,722 chicks were banded in 2009, and 413 were confirmed visiting the Cape, representing 11 colonies from Nova Scotia (in which case 13 of 14 banded birds showed up) to New York.

“We can’t identify every chick because the bands have to be read at a distance,� Harris conceded. “As far as the adults, the color banding has been going on for five years, and at the Buzzards Bay colony nearly 2,100 adults (75 percent) have been banded. That gives us a chance to learn about their movements.�

One thing noticed was that birds spent several days on a beach, disappeared for several more, then returned. A handful of roseate terns have been tagged with geo-locaters and those birds have flown as far as Bermuda, most likely foraging, before returning to Cape Cod.

“We’re thinking there may be more pelagic birds than we’re seeing,� Harris said. “It’s a hard thing to figure out where they are.�

The chicks also don’t return the next summer.

“Banding enabled people to tell that chicks raised here, took two to three years before returning to breed and the return rate was low. So something is happening between South America and here. They’re not coming back in high enough numbers to keep the population growing,� Harris said.

The terns winter in Brazil and Argentina and little research has been done there.

Another observation was that the males did most of the feeding, which could lead to greater mortality as they foraged.

“They are expending a lot more energy feeding the chicks,� Harris said.