On thin ice

But the polar bears here have discovered a new menu option. They eat snow geese. Because the ice is melting earlier, the bears come on shore earlier, and the timing turns out to be fortunate for them. As a strange side-effect of climate change, polar bears here now often arrive in the midst of a large snow goose summer breeding ground. And with 75,000 pairs of snow geese on the Cape Churchill peninsula — the result of a continuing goose population explosion — there is an abundant new supply of food for the bears.

What’s good for the bears, however, has been devastating to the plants and the landscape, with the geese turning large swathes of tundra into barren mud. Nor does it mean the bears are going to be okay in the long run.

What is clear is that this long-popular fall destination for polar bear tourism has become a case study in how climate change collides with other environmental changes at the local level and plays out in a blend of domino effects, trade-offs and offsets. “The system is a lot more complicated than anybody thought,” said Robert H Rockwell, who runs the Hudson Bay Project, a decades-long effort to monitor the environment.

To fully appreciate how the chain reaction plays out in La Perouse Bay requires studying the individual links in the chain — the geese, the bears, and the plants and the land beneath them.

Rockwell, 68, has been counting geese in this area every summer since 1969. In the late 1970s, he started building his current camp — a few buildings surrounded by an electric bear fence. It is reachable only by helicopter from nearby Churchill. Rockwell and his team have witnessed the goose population swell to the point where they are harming their own nesting grounds. The number of geese that live and migrate in the continent’s central flyway exploded from 1.5 million in the ’60s to 15 million now.

The reason for the increase, Rockwell said, can be traced to Louisiana and Texas, in the coastal marshes, where the geese long spent their winters feeding on spartina, also known as salt hay. They then migrate north in spring to nest and raise goslings in the marsh and tundra of the bay shore.

The goose population, Rockwell said, was once limited in size by its sparse winter food supply in Southern states. “After many of the marshes were drained for various kinds of development, the snow geese just sort of said, ‘Wait a minute, what was that green stuff just north of here?’. And it turns out those are the rice prairies,” he said.

Some snow geese now winter in Nebraska and Iowa. But they keep coming to the sub-Arctic and the Arctic in the summer, following ancient habit.
By 2007, it was clear that the sea ice was melting earlier, on average, and the polar bears were often coming on shore in time to harvest the eggs from vast numbers of geese and other birds.

Rockwell, a researcher at the American Museum of Natural History, and Linda Gormezano, a graduate student he was supervising, decided to approach the bear diet question in a scientific way.

Gormezano, who this fall began post-doctoral research at the University of Montana, specialises in non-invasive methods for monitoring the behaviour of predators. In terms of diet, scientists can observe what goes in, or what goes out. With an animal like a polar bear, the second approach is more practical. They turned to polar bear faeces, or scat, as it is commonly called.

Gormezano trained a Dutch shepherd named Quinoa to find polar bear scat. She and Quinoa worked with Rockwell to collect and study samples for several years and found that the bears were eating lots of geese. They were also eating caribou and other animals, as well as berries.
Rockwell and Gormezano have published several papers on their findings.

Steven C Amstrup, chief scientist of Polar Bears International, says he does not doubt that bears eat geese but questions how important that fact is. He said he worried that these findings would be taken by the public to mean that polar bears were doing fine.

In the future, as sea ice declines, “There’s no evidence that anything like current polar bear populations can be supported.”