"We don't know how the puffin will adapt to these changes — or if they'll adapt to these conditions," Kress said.
The Gulf of Maine's largest puffin colony — with more than 10,000 birds — is found on Machias Seal Island on the Maine-Canada border 10 miles off the eastern Maine coast. There, the average body weight of both adult and baby puffins has been on the decline, most likely because of a shortage of food, said Tony Diamond, a University of New Brunswick professor who studies puffins on Machias Seal. The amount of herring in the puffin's diet has been falling by about 5 percent a year, he said.
What's more, puffins on Machias Seal are breeding later this year than any time on record, another sign of stress, Diamond said.
Another big concern is the unprecedented puffin die-offs this past winter. More than 2,500 dead puffins were found washed ashore in Scotland, and about 40 of the birds (along with hundreds of razorbills) were found on the Massachusetts shore. More dead puffins were found in Bermuda.
For every bird found dead, there are probably tens or hundreds more that died and didn't wash ashore, scientists agree.
"That's a large number of birds for the Gulf of Maine," Kress said. "We don't have that many birds to spare."
Necropsies on the Cape Cod birds indicated they starved, said Julie Ellis, project director for The Seabird Ecological Assessment Network at Tufts University.
Diamond has seen other seabird colonies virtually vanish overnight. Machias Seal Island used to have more than 3,000 terns, the largest such colony in the Gulf of Maine. But since 2007, only small numbers have come back each summer, and those that have returned haven't been able to breed, Diamond said.
Nobody knows what the future holds for puffins, but anything's possible, he said.
"In the Gulf of Maine, we're on the southern end of the bird's range. It looks like the range might be set to contract northward," Diamond said.
Kress is hopeful the Gulf population will sustain itself. But he's concerned about what he's seeing.
"You never know what climate change will bring," he said. "Historic fish could move out and more southerly fish could move in, and puffins may adapt to the new fish. Only they will know how the story will unfold."