Declining sea ice pushes sea birds to the brink

It’s not just polar bears. Yes, climate change’s spirit animal really is threatened by rising temperatures and disappearing sea ice in the Arctic, but the frozen wastes of the north are home to a lot more than the largest bear on the planet. And other animals may be even more susceptible to the ravages of climate change in the Arctic.

Take the ivory gull (Pagophila eburnea): this little bird lives year-round in polar regions that are supposed to be covered by ice much of the year. Depending on whom you ask, the gull is either endangered (Species at Risk Act, the Canada-specific species protection law) or “near threatened” (Red List, which includes the birds’ habitats elsewhere in the Arctic where it appears to be doing a bit better). The reason it is endangered specifically in Canadian terms has a lot to do with sea ice decline.

The bird’s population specifically in Canada has plummeted in recent years, by as much as 70 to 80 percent. According to study authors writing in the journal PLoS One, the gulls are most often found over pack ice of 70 to 90 percent concentration; they are almost never observed more than 5 kilometers from sea ice. The researchers used satellite trackers attached to 12 birds to see just how important ice is to their survival; they had a full four years of data on the birds, all of which were tagged on Seymour Island in the Nunavut region of northern Canada.

The data, the authors wrote, “markedly changed” what we know about ivory gull migration; more specifically, they appear to rely on sea ice formation and recession heavily, and the Davis Strait and Labrador Sea areas may be important even for international, non-Canadian populations of these birds. This isn’t just a matter of how much ice is available—it’s the timing of the ice that also matters, the dates and lengths of time that sea ice recedes, reforms, and recedes again. And obviously, climate change has messed with that timeline in dramatic fashion.

The point here is that this is a real, extensive, and important habitat; sea ice supports a huge variety of life, and its continued disappearance is going to cause problems for all of them. The problems will differ in scope and in kind—the ivory gull is one of only two birds, along with the black guillermot, that remains north of the 70th parallel all year round—but they will turn up for virtually every species you can think of. In the case of the ivory gull, the researchers suggested that their unwillingness to fly over land could be a strategy to avoid land-based predators.

“Arctic seabirds, like the ivory gull, live in a dynamic and harsh environment that is experiencing dramatic changes due to global warming,” the authors wrote. “Like the predictions for polar bears, recent declines in ivory gull populations may be a harbinger of the future for ice-associated species in the Arctic.” – Dave Levitan | January 6 2015

Source: Spencer NC, Gilchrist HG, Mallory ML (2014). Annual movement patterns of endangered ivory gulls: the importance of sea ice, PLoS One, 9 (12) e115231. DOI: 10.1371/journal.pone.0115231

Image: Shutterstuck, BMJ

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