New Scientist, 10 August 2012
SALMON shortages on Canada’s west coast may leave grizzlies there more stressed than the average bear.
Heather Bryan at the University of Calgary in Alberta, Canada, working with the Raincoast Conservation Foundation in British Columbia, collected hair from grizzly and black bears across a 5000-square-kilometre area of British Columbia between 2009 and 2011. She looked for correlations between diet and hormone levels through DNA analysis, stable isotope analysis, and by quantifying hormone levels in the hair.
Male grizzly bears that depend on having salmon in their diet had higher levels of the stress hormone cortisol when they ate less fish. Studies in other mammals suggest that chronically high cortisol levels may suppress the immune system, leaving animals vulnerable to disease.
Coastal grizzlies also had higher levels of testosterone than their non-salmon-eating relatives in the interior. “That might be related to social interaction,” says Bryan. “Since there are more bears on the coast, they have a higher population density and potentially more competition over limited resources like salmon.”
Further monitoring should help predict how the coastal grizzlies will respond to environmental change, since many acquire 80 to 90 per cent of their dietary protein from salmon. Bryan presented her results at the Ecological Society of America meeting in Portland, Oregon, this week.
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