November 5, 2010

Good News for Polar Bears: Goose Eggs on the Menu

Filed under: Adaptation, Animals, Arctic, Polar

Back in May, we reported on the Trumpeter Swan’s recovery from the edge of extinction that was being made a bit easier by a warming Arctic. Now comes word of another Arctic bird that is benefiting from the warming—and at the same time, helping the polar bear cope with climate change.

This time around it is the snow goose—a rather plentiful denizen of the far north.

Snow goose populations have been expanding as of late, and now are so large that some regions of the Arctic breeding grounds are getting a bit overpopulated and are facing degradation from the geese.

At the same time, polar bears are starting to have to come in off their preferred sea-ice hunting grounds sooner, as the ice is breaking up earlier and earlier in the season.

In the western Hudson Bay region, at least, this evolving situation is bringing the two species into ever-more contact. And the polar bears are finding snow geese eggs to be an excellent source of nutrition.

Such are the conclusions of a new research study performed by Robert Rockwell and Linda Gormezano just-published in the journal Polar Biology, titled “The early bear gets the goose: climate change, polar bears and lesser snow geese in western Hudson Bay.” The research was funded by the Hudson Bay Project and the American Museum of Natural History.

Rockwell and Gormezano have been studying the impacts of a warming climate on the biology of the Wapusk National Park located along the southwestern shores of Canada’s Hudson Bay. They have been paying particular attention to polar bears in the region as the bears there are thought to be particularly sensitive to “global warming” since their population lies near the southern limit of the current range of the species.

While the researchers were studying the bears, they noticed that the earlier arrival of polar bears returning to land as the sea ice broke up was starting to overlap with the nesting season of the snow geese. And some bears were observed foraging in the nests.

By tracking the trends in ice-break up with the trends in snow geese nesting season, Rockwell and Gormezano found that the period of overlap between the presence of the bears and the presence of nesting geese was expanding (Figure 1)—a sign that the polar bears were going to gain increasing access to a valuable (and largely untapped) nutritional resource. And if current trends continue, snow geese eggs could help replace a significant portion of the diet of the polar bears which may be lost to a declining seal hunting season out of the sea ice.


Figure 1. Trends in the dates of the profile of snow goose nesting and the first arrival of polar bears in the nesting area. The polar bears are arriving earlier faster than the snow geese nesting season is moving up, meaning that, if current trends continue, the bears will have increasing nutritional opportunities from snow geese eggs (figure from Rockwell and Gormezano, 2010).

Clearly, foraging for snow geese eggs would be an adaptive response by the polar bears to a changing climate and may even become a behavior of choice for a coming generation of bears, even if seal hunting remains productive, as the snow geese eggs are high in nutritional value. The authors ponder this possibility:

[S]ince eggs consumed earlier in the nesting period provide more energy, might individual polar bears be able to sense this and progressively come ashore earlier to exploit an even more valuable resource? Or is the consumption of goose eggs a simple opportunistic reaction to sea ice breakup that forces polar bears ashore?

The authors report that observations from polar bear populations in other portions of the Arctic indicate a preference for eggs even when the ice pack still supported seal hunting, and suggest that such a behavior may take hold in the western Hudson Bay population and “may be another example of the behavioral flexibility and adaptability of polar bears.”

As we, and many others have been saying ever since polar bears were elevated to climate change poster children, polar bears are not a species that is just going to roll over and perish as conditions change around them. This study provides a clear example of this.

In the press release from the American Museum of Natural History, the authors display a sense of optimism that is all-too-rare in today’s environment of scare tactics aimed to raise money, influence, or power. Instead of its-worse-than-we-thought, Rockwell and Gormezano seem to take the changes as part of the on-going cycle of making a living with what you’ve got—something the polar bears have been doing for the past several hundred thousand years, during ice ages and the warm periods between them.

“Polar bears went through the Eemian 125,000 years ago, when sea level was 4-6 meters higher than it is now and trees lived above the Arctic Circle. They’ve been through warming before,” says Rockwell. “I just read a piece in Natural History with a quote from Ilkoo Angutikjuak that sums this up: ‘If the changes continue…the animals will adapt. I’ve heard that because they depend on sea ice, polar bears will go extinct, but I don’t believe it…Polar bears might get skinnier and some might die, but I don’t think they will go extinct.’”

Certainly a refreshing and logical take on things and a rare exception to the general “bad for good, and good for bad” dogma of climate change reporting.

Oh, and just in case you were worried this change in bear behavior was going to cook the geese, Rockwell has this to say:

Although geese populations were in decline in the early 1900s, the population rebounded and expanded. There are now too many geese for the Arctic to support in the summer, mainly because their over-wintering habitat has increased to cover the northern plains, where they eat waste corn and forage in rice fields.

So there!

Reference:

Rockwell, R.F., and L.J. Gormezano, 2010. The early bear gets the goose: climate change, polar bears and lesser snow geese in western Hudson Bay. Polar Biology, 32, 539-547.




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