ROCKLAND, Maine — An increase in emaciated and dying baby seabirds seems to indicate that something is different in the Gulf of Maine. The cause is difficult to pinpoint, but the U.S. Fish and Wildlife Service is concerned after numerous terns this summer accidentally starved their young.

In a typical year, about half the tern chicks born on Maine islands die. This year about two-thirds of the chicks died, many due to starvation, according to researchers.

In the summer, the U.S. Fish and Wildlife Service deploys interns to sit in tents on otherwise uninhabited islands to count seabirds, weigh their chicks and watch what food gets delivered to the babies, among other things. What was particularly strange this year was that instead of feeding their young a herring-rich diet, the terns gave their chicks a lot of butterfish and other large fish that they couldn’t eat. One problem with butterfish is that they are wide. Baby birds need long, thin fish to digest.

“You would see adults jamming food down their mouths, but they couldn’t eat it. The chicks’ mouths would be raw from all the jamming,” said Brian Benedict, the deputy refuge manager of the Maine Coastal Islands National Wildlife Refuge.

On Petit Manan for instance, the adult terns ate a diet of about 40 percent butterfish and 10 percent herring this year.

“It should be the reverse of that,” Benedict said. “This isn’t the first year we’ve seen this trend, but it is the most severe.”

As for the remaining 50 percent of the birds’ diets, the interns also found that the adults were trying to feed moths and other insects, as well other fish, to their babies. This isn’t a great idea because the insects don’t have the amount of protein and fat that the chicks need to become strong enough to make their southern migration in the fall, according to Stephanie Martin, the program coordinator for Friends of Maine Seabird Islands, a nonprofit that helps support the on-island internship program.

But the problem extends beyond the birds, Benedict said.

“The birds are a barometer of what’s going on in the Gulf [of Maine]. Something isn’t working,” he said.

What that something is is difficult to pinpoint. Benedict is hedging his bets on either climate change or overfishing of herring. Herring need a certain temperature water to live in, he said, and if they need to dive into deeper waters to get that chilly temperature, the shallow-diving terns would not be able to reach them. As for fishing, he said trawling ships can break up schools of herring, dispersing them, also making it more difficult for terns to hunt.

The research done this summer does seem to show that the herring are dispersed. The interns were allowed to follow some terns off Metinic Island by boat. They found that the birds flew up to 20 miles round-trip for their first fish of the day. The birds averaged a four-mile trip one way for their first fish.

“That is remarkable,” Benedict said. “That was just their first fish. It then has to find fish for its young — they had to go farther than that.”

The goal of following the birds was to find fishing hot spots — and they didn’t. The map Benedict has looks like a scribbled star-shape of the birds flying far away in all directions to find food.

While Benedict predicts climate and fishing are to blame, scientist Matt Cieri of the Department of Marine Resources isn’t as sure. His department tracks herring in New England and it seems like the fish population is remaining more or less stable in the area, he said. They might not be staying in Maine, or close to shore in Maine, but it’s hard to say why if that is the case, Cieri said.

“It’s very complicated, thinking like a fish,” Cieri joked. “It may not be that there are less herring, but those herring may have moved off-shore for some reasons. That could be because of temperature, salinity, those types of things. There is a multitude of factors.”

Without decades of data to draw on, it would be nearly impossible to say why this trend is popping up now, he said.

Benedict and his team plan to keep up the research on the uninhabited islands during the summers.

“This is the major focus of our research now. We have to figure out what’s happening to [the seabirds].”