When Habitats Collide

Cooper Island, Alaska, July 27, 2009 — In the late 1970s during the first field seasons on Cooper Island, my colleagues and I were preoccupied with the possibility of encountering polar bears since we were sleeping in a tent 20 yards from the Arctic pack ice, the primary habitat of polar bears. We assumed we would see bears with some regularity. But it turns out we didn’t see any bears in the first five summers on the island. The lack of sightings was due to being “adjacent” to polar bear habitat, but not “in” polar bear habitat. As is clear from their coloration — (or lack of it) — anatomy, and preferred prey of seals, polar bears are adapted to living on sea ice. A sand and gravel island like Cooper offers little to interest or sustain polar bears.

Cooper Island’s unattractiveness to polar bears is demonstrated by my seeing only one bear on the island between 1975 and 2002. That bear was a young male that in 1980 was sleeping in back of one of the larger guillemot nest boxes. I got too close to it before realizing it was there which scared both of us. It caused me to run back to camp and the bear to swim to the pack ice, visible just north of the island. For the next twenty-one years I did not see a polar bear on Cooper Island. I did rarely see tracks and other signs that bears had visited the island but the encounter in 1980 was the sole observation I made over a 27-year period.

The almost complete lack of polar bear observations over a quarter-century makes my recent experiences on Cooper Island all the more unsettling. I have seen polar bears annually for the past seven years, and in two of those years had to terminate the field season early because of the frequency and nature of bear encounters. Not only are bears now a regular and predictable part of being here on Cooper Island in late July and August, individual bears are spending more time on the island both looking for food and sleeping after or before having to swim in the ice-free Arctic Ocean. Last summer polar bears regularly visited the cabin during my last week on the island.

Given their regular occurrence in recent years it was not surprising when I looked out the window of my cabin last Tuesday (July 21) and saw a bear making its way through the colony turning over nest boxes and debris. It walked through much of the colony and headed to the cabin but, as frequently happens, moved away from the cabin when it saw me and picked up the scent of a human. The bear did not flee but simply returned to turning over guillemot nest sites, eventually disturbing 28 of the 138 nests in the colony. While the bear ate eggs and nestlings at the first few nests it encountered, at other sites, the bear only broke eggs and killed young, but did not consume them. Guillemot nests have little to offer a polar bear at this stage of nesting. Newly hatched nestlings and late-stage embryos have little fat or mass to offer a carnivore weighing many hundreds of pounds.

On Saturday, July 25 the bear returned to the colony, apparently having spent the intervening days on islands to the east. It flipped over six more nest sites before finding a low spot in the sand and sleeping for three hours. It then walked to the north beach and swam north from the island. This strategy would, in the recent past, take it to the nearby pack ice a few miles north. This year, however, the main pack is currently more than 50 miles to the north.

The presence of a polar bear on the island elicits a range of emotions. The first is for my own safety and if I am working in the colony I return to camp where the shelter of a sturdy cabin provides a strong feeling of security. The danger to me is more hypothetical than real. While polar bears have a reputation for being dangerous to humans, in Alaska there has been only one recorded human fatality from a polar bear attack. They are a real threat to my study species, however. It is disturbing to see parent guillemots, many that I have known as individuals for at least a decade, rapidly flying around the bear as it destroys their nest sites, where I have recently seen downy nestlings hatch. But the overriding feeling when I see a bear on the island is that I am observing a species that is only here because its primary habitat, the Arctic pack ice, is rapidly disappearing. Now, unlike during my first 27 years on the island, these amazing creatures are reduced to walking the beach, looking for whatever food they can find while they wait for the sea ice to reform in the fall.

While Cooper Island used to be adjacent to polar bear habitat, now with the loss of pack ice, it has become polar bear habitat. Recent changes in the numbers and activities of bears on the island are a clear sign of the altered state of the Arctic sea ice. When the summer sea ice is gone from the Arctic Basin, as is predicted to happen this century, Cooper Island, and similar locations around the Arctic Basin will be the only habitat for polar bears to occupy until the ocean freezes again in the fall.

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