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Polar bear taste for land food is growing this cause worries among scientists
Studies from 2 different sources suggest that polar bears are increasingly coming ashore in search of food.
The prospect of having to search for food on land would seem to be a recipe for disaster. But while that is increasingly the case for the species in parts of Norway and Canada, as a pair of recent papers suggests, the reason, and the impact, is less clear.

It has long been known that during summer months, polar bears will supplement their diet, primarily seal caught on sea ice, with food they can find on land, including berries, mushrooms, eggs and carrion. The two papers, released earlier this month, express concern that foraging appears to be making up a larger portion of the polar-bear diet, and that this may signal of an ecosystem that is out of balance.

In the first paper, published in Frontiers in Ecology and Evolution, scientists noted that over the course of the last decade, an increasing number of polar bears in the Norwegian Arctic were foraging for eggs in bird colonies. Over the course of the study, the bears also appeared to be arriving earlier each year, and were now showing up as many as 30 days prior to the original observations.

While this was not a direct sign that bears are in trouble, the study’s authors worry nevertheless that the trend correlates with the gradual retreat of the sea-ice margin.

Another concern was the number of eggs polar bears must consume in order to survive (as many as 20kg a day for an adult) and whether nesting colonies could survive the onslaught. The scientists, who were initially studying bird populations in the region but gave up in order to focus on the increasing amount of polar-bear foraging, report that in some years eggs are taken from as many as 90% of nests.

The authors suspect the increased foraging is linked to a receding annual ice extent, but suggest there may be other explanations, including an end to hunting in 1973 and what appears to be a population rebound.

A combination of all three factors – more bears, an end to hunting and worse maritime hunting conditions – is likely to be involved, but the paper notes that a similar increase in terrestrial activity had been noted in Greenland, even though polar bears continue to be hunted there.

The second paper, this one published in Frontiers in Ecology and the Environment, seems to support the evidence that polar bears are increasingly coming ashore to eat. Instead of looking at frequency, however, this report investigates whether polar bears could successfully transition to a land-based diet. Its conclusion is that this is unlikely.

Given that other species of bear, such as the brown and the grizzly, do survive on many of the types of foods polar bears have been observed eating on land, it had been suggested that a transition might be possible. The scientists, however, point out that these species are smaller and have an easier time converting plants into energy. For polar bears, which derive the energy they need from the blubber of seal and walrus, it would be all but impossible to consume enough plant-based food to keep them alive.

Another important difference is that polar bears do not hibernate, which would preculde the adoption of a terrestrial diet in winter.

Although neither of the papers differ significantly from previous findings or the historical observations, they did present a number of differences, including the location where foraging was happening and its increasing frequency.

Though still relatively rare (in both reports, the number of bears recorded coming ashore to eat was marginal, perhaps only 30 in each area, out of populations that may be as large as 3,000), the data suggest the trend is increasing.

But the rise may reflect polar bear’s opportunistic eating habits just as easily it does a lack of seal. "They will eat anything they can get their teeth on, trash even," says Andrew Derocher, a biologist with the University of Alberta. "They prefer to make their living eating seals, but when that’s not there they’ll look for something else."

He suggests that if there were nothing to forage on, the bears would likely search for seals elsewhere.

This, according Geoff York, of Polar Bear International, a conservation group, appears to be corroborated in the Canadian study.

"Individual bears in any given year or place will find ways to utilise novel or unpredictable food sources to their benefit," he says.

Even with their ability to find replacement sources of food, Dr York remains less than optimistic, particularly given the generally worse health and smaller size of polar bears that have spent longer periods in areas where there was adequate access to terrestrial foods.

"What the study says it that there is currently no evidence that these terrestrial sources will offset energetic losses from traditional sea ice prey," he says.

While the third study, this one produced by the Wildlife Management Advisory Council, which represents indigenous hunters, is careful to note that changes are occurring to polar-bear habitat, it takes a more cautious tack about the impact of global warming.

"There has always been significant annual variation in sea-ice conditions and hence in local abundance, distribution and condition of polar bears and their primary prey," the organistion writes.

Interviews with Inuvialuit hunters in northern Canada compiled for the study, 'A Polar Bear Traditional Knowledge Study', would seem to indicate that population and the health of individual bears are both stable. They also reveal that bears tend not to be as large or as fatty as those shot in the 1980s.

That might sound like good news for health-conscious humans, but for polar bears it may be an unnerving sign.

Original source :http://arcticjournal.com/culture/1485/growing-polar-bear-taste-land-food-worries-scientists Reply