A polar bear paper just out in Science concludes the experts were wrong, polar bears are not “walking hibernators” – in summer, they slow down and live off their accumulated fat just like other mammals. Take home message: experts are not infallible and spring fat is critical for polar bear survival over the summer.
This paper presents no compelling evidence that Southern Beaufort polar bears, or those in any other region, lack the ability to survive predicted summer sea ice declines in future decades – although they claim it does. See what you think.
This update on polar bear biology in relation to sea ice comes from graduate student John Whiteman, supervisors Merav Ben-David and Henry Harlow (University of Wyoming), Alaskan polar bear experts Eric Regehr and Steven Amstrup, and a few others (Whiteman et al. 2015). The study examined the body temperature and activity levels during the summer for a sample of Southern Beaufort Sea polar bears, including bears that spent the summer onshore as well as those that stayed on the retreating sea ice (see also “Ice Story: The Bears of Summer”, photo below).
The primary scientific conclusion made by Whiteman and colleagues is that polar bear experts were wrong to have described polar bears as “walking hibernators.” The authors claim to have overturned previous studies (Nelson et al. 1983; see also Atkinson and Ramsay 1995; Derocher et al. 1990) that concluded polar bears have a unique ability to reduce their metabolism during summer and winter. Whiteman and colleagues found instead that in summer, polar bears simply move less and live off accumulated fat, just like other mammals do when food is scarce.
The authors boldly state that “sea-ice loss increasingly limits spring and summer hunting opportunities in parts of their range.”
However, the two papers they cite (Stirling and Derocher 2012; Meier et al. 2014) discuss summer ice losses only. Studies that include spring ice predictions show minimal losses are expected in future decades, contradicting their claim.
Significantly, the authors admit that bears eat little during the summer whether they are on the sea ice or onshore (as I have pointed out previously, see Crockford 2015: “The Arctic Fallacy”), and have not demonstrated that future summer ice declines are expected to impinge on either spring or fall seal hunting opportunities.
If polar bears normally eat little in summer, how can predicted summer sea ice declines in the future have a meaningfully negative impact on future health or survival?
Remarkably, by working in 2008 and 2009 only, the authors managed to avoid including in their study the low summer ice years of 2007 and 2012, when Southern Beaufort bears experienced the two longest open-water seasons since 1979.