A new study reports the negative effects of human food on wild black bears

Published: March 8, 2019

a-black-bear-eating-on-a-log-on-grass Photo by Andrea Izzotti/Shutterstock

“Don’t feed the bears” is pretty much a given, but bears have a way of feeding themselves with human foodstuff, especially trash. A bear sighting at a cottage-country dump is a common occurrence, and every cottager knows (or should know) that if you leave food or any kind of garbage around, a bear will find it.

Now, a new study on wild black bears in Colorado suggests that plugging holes in their menu with human “food subsidies” could be shortening their lifespans. If the findings can be extended to other black bear populations, we may have one more reason to try to keep them on a natural diet of things like berries and grubs. The findings are also a reminder of the negative impact that human encroachment can have on natural spaces.

The study, “The Cascading Effects of Human Food on Hibernation and Cellular Aging in Free-Ranging Black Bears,” appears in the journal Scientific Reports. Its lead author, Rebecca Kirby, of the department of forest and wildlife ecology at the University of Wisconsin—Madison, is conducting her Ph.D. research on how humans and their food influence black bear foraging ecology, as well as biological aging, in Wisconsin and Colorado.

This new research looks at the relationship between human “food subsidies,” hibernation, and cellular aging in the American black bear (Ursus americanus), which is your basic black bear in North America. The authors point out that these bears often supplement their diet with human stuff, especially when there are natural food shortages.

They also note that bears that hang around human development tend to have decreased hibernation periods, maybe because they’re eating more human food subsidies. Because hibernation may be a factor in slowing cellular aging—which means a bear can live longer—the researchers wanted to know if there was a cascading effect that begins with bears eating human food, hibernating less effectively, and not living as long as they might otherwise. A key indicator was the length of telomeres—repetitive DNA sequences on the ends of chromosomes—as they are the markers that scientists use to quantify cellular aging.

The researchers tracked and sampled a group of female black bears through several summer and winter seasons as part of a larger study in Durango, Col. “We found that bears that foraged more on human foods hibernated for shorter periods of time,” the authors state. “Furthermore, bears that hibernated for shorter periods of time experienced accelerated telomere attrition.

Together these results suggest that although hibernation may ameliorate cellular aging, foraging on human food subsidies could counteract this process by shortening hibernation. Our findings highlight how human food subsidies can indirectly influence changes in aging at the molecular level.” The upshot is that bears who eat human food may not live as long as those who have a more natural diet.

So, do the study’s conclusions have any bearing (sorry) on black bear aging elsewhere? Ontario’s Ministry of Natural Resources and Forestry isn’t persuaded yet. Asked to comment, the MNRF replied: “The study’s sample size is low and the results are speculative so it is difficult for the Ministry of Natural Resources and Forestry to provide comment on the applicability of the study to bears in Ontario. We recommend additional research is necessary to support the study’s findings.”

Jennifer Vonk, a professor of psychology at Oakland University in Rochester, Mich., who has studied bear cognitive abilities, is intrigued by the findings. “This adds to the growing body of work implicating the huge, and sometimes unanticipated effects of humans encroaching on the natural territories of other organisms,” she writes in an email. “The effects may be magnified to the extent that bear cubs learn from their mothers where and how to forage to some degree, so any harmful effects of adopting this foraging strategy are likely passed down.

The fact that bears are generalists makes them quickly adapt to new opportunities to access food, but this particular strategy also places them at a higher risk to be directly harmed by humans. Time will tell if there are also negative impacts on their natural abilities to exploit multiple natural sources. This points to yet another possible negative consequence of human population growth in Ontario on black bear populations in particular.”

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