Like the swallows returning to Capistrano, the puffins are winging their way back to their nesting grounds around the Atlantic – including two islands off the coast of Maine that play host to the largest colonies of the birds in the U.S.

This year’s nesting season looks to be a more joyful occasion than last summer, when many puffin chicks starved to death. A shortage of herring meant that puffin parents could only offer their young fish foods like butterfish, which were much too big for the little birds to swallow. Thankfully, this season more bite-sized food is plentiful, according to Steve Kress, a Cornell University professor who's also the director of the National Audubon Society’s seabird restoration program.

“This summer, the chicks are getting plenty of hake and herring,” Kress told the Associated Press.

The puffin looks a bit like a penguin decked out for Carnival – though its body is tuxedo-like, it sports a brightly colored beak with strips of reddish orange and spots of yellow. It spends most of its life at sea, swimming, hunting, and bobbing atop the waves. Though only about 10 inches long, these birds have impressive stats: they can dive up to 200 feet below the surface; in flight, they can reach speeds of up to 55 miles an hour. Atlantic puffins nest all across the North Atlantic, from Maine up to Canada, Greenland and Iceland, and across the ocean on the shores of England and Scandinavia.

The two Maine islands with the largest U.S. puffin colonies are the 22-acre Matinicus Rock and the 65-acre Seal Island. Both islands are managed by the U.S. Fish and Wildlife Service and the Audubon Society. Seal Island is closed year-round because of unexploded ordnance scattered about the refuge, thanks to its former life providing bombing target practice for the U.S. Navy. Matinicus Rock is closed to the public during the puffin breeding season, from April to August.

This year there are a lot of vacancies at the burrows on Seal Island and Matinicus Rock – occupancy is down by at least one-third, Kress told the AP. Some birds probably died during the winter; others couldn’t muster the strength to have offspring this season.

Many researchers worry that the puffin is already suffering ill effects from climate change. Puffin burrows on Seal Island are being washed away by unusually extreme storms at sea. The warming waters of the Gulf of Maine might be contributing to a boom in the butterfish population, crowding out the herring that puffins need to feed their young. Adult and baby puffins on Machias Seal Island (a different place than Maine’s Seal Island, located a bit further north on the Maine-Canada border) have been thinner and thinner in recent years. Puffin populations in the North Sea have seen massive die-offs – just this last winter, 2,500 dead puffins washed up on the coast of Scotland, many of them showing signs of starvation.

Exactly what's contributing to puffin declines and deaths isn’t certain. But scientists think that what’s bad for the puffin is bad for other birds and sea life as well.

“It’s our marine canary in a coal mine, if you will,” Rebecca Holberton, a puffin researcher at the University of Maine, told the AP in June.