Sunday, December 11, 2011

Polar Bears Resort To Cannibalism

If a picture is worth a thousand words, for me this one is worth a thousand nightmares:
Photograph by Jenny Ross.
The photograph was captured by Jenny Ross, an environmental photojournalist working in Olgastretet, a part of the Svalbard archipelago, located in the Arctic north of Norway. Ross co-authored a paper with Dr. Ian Sterling a biologist with Environment Canada and a professor at the University of Alberta, about the photographs and observed instances of cannibalism among polar bears. 

For anyone who reads Science Decoded regularly, I don't have to tell you that polar bears are sort of my thing. I've written about them being Irish, mysteriously dying, having osteoarthritis, status as endangered, and their habitat needs. I make no bones about the fact that they are my favorite and I love them. I've loved them since I was a little kid, and have a large collection of polar bear themed...stuff. From earrings to ice cream scoops, I've got it all. My collection doesn't include nightmare inducing, zombie-evoking images of polar bears eating each other. The child in me is horrified by what I now know to be a normal occurrence.

Yes, that's right. While the above photograph might be some of the most jarring evidence to date about intraspecies polar bear predation, the behavior isn't abnormal. In fact, according to Dr. Stirling instances of infanticide (killing baby bears) and predation on older bears, in addition to cannibalism have been known to Inuit hunters in Canada and Greenland and reported in scientific literature. In these instances, the bear doing the killing is always an adult male, which would have the advantage over young bears, old bears, and even adult females.

In the paper with Ross, Stirling reports on three instances of what is most likely intraspecific killing and subsequent cannibalism by adult male polar bears. The instances were all observed on the sea ice in Svalbard in midsummer and early autumn. Each incident was photographed (see above). The victims in each case were killed by more than one bite to the head. This is an instantly lethal way to take down prey, and the way that polar bears would take down seals, their typical food source.

According to Stirling, the instances of cannibalism described in the paper, published in the journal Arctic, are different than the normal instances of intraspecies predation. The bears that did the killing appeared to be in good physical condition, not obviously thin which is typically the case in intraspecies killings. Stirling and Ross concluded that the behavioral and ecological factors present in the instances of killing they describe in their paper show that by late summer, when available ice and the number of seals to hunt are significantly reduced, young polar bears may become a source of prey for adult males to still hunt from the surface of the remaining sea ice. While this type of behavior may be relatively normal, Stirling says that as climate continues to warm and reduce sea ice the frequency of kills like this may increase.

I asked Stirling what we should take away from these photographs, and the instances of polar bear cannibalism, and this is what he said:
"Climate-driven concerns for polar bears are real. The bottom line is that polar bears need ice to hunt from and without that, most bears will not be able to survive. At present, it looks like the last ice will be in the area of the northern Canadian Arctic and in Greenland. Some relatively small, but unknown, number of bears may survive there for some time after they cannot continue in more southerly areas."
So basically, cannibalism is a natural behavior for polar bears. It happens. But due to climate change and the changes that are occurring to sea ice, it is likely that cannibalism is going to get worse. Which leads me to think, do we really want a unique and charismatic species that many people are working to protect to be eating itself? It seems somewhat backwards to invest in conservation and then just watch the bears duke it out amongst themselves. I wish there was a solution I could offer but climate change is its own beast entirely. I will say that intraspecies cannibalism wasn't something I had on my mind when thinking about conservation, but I'll definitely remember it next time.

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