Cooper Island, a 4-mile slice of sand and gravel off the coast of the northern tip of Alaska, is home to the region’s biggest colony of Mandt’s black guillemots. The pigeon-sized seabird feeds on Arctic cod and breeds near sea ice off the island from June to September.

But the Cooper Island colony would probably not exist if not for George Divoky.

For nearly half a century, the American ornithologist and founder of the Friends of Cooper Island has spent his summers studying these Arctic seabirds. Now he’s documenting what could be the last days of this once-thriving colony.

Shedding light on more than just seabirds

Divoky first visited Cooper Island back in the summer of 1972 as part of a seabird survey. At that time, he discovered 10 Mandt’s black guillemot pairs nesting under scattered debris—such as ammo boxes, floorboards and wooden planks. It was the beginning of his love affair with the Arctic and the guillemot colony that make it their home every summer.

A unique ecosystem in decline

Decreasing sea ice means fewer birds

As Artic cod disappeared from the waters around Cooper Island, the seabirds were forced to find other fish species to feed their chicks. But these were neither as abundant nor as nourishing. This led to a dramatic decrease in chicks’ growth and survival. Parent birds were often able to raise only a single chick—and sometimes none at all.

The problem is being made worse by the recent lack of ice in the Bering Sea—the birds’ traditional wintering area. Divoky believes this is playing a role in the decrease in adult birds’ ability to survive the winter, and may be preventing many adults from incubating or laying eggs.

Less sea ice also means polar bears can regularly visit the Cooper Island colony during the summer, consuming large numbers of chicks. In 2011, in an effort to prevent further decline in numbers, Divoky and his team began providing bear-proof cases for the birds to nest in.