Teenaged male bear handling a screen used by researchers to measure grain spilled from passing train cars. Photo credit: Niels de Nijs
Spilled grain, rail-killed ungulates, and the effects on other species of increased light and warmth may all attract grizzly bears to forage along railways in Canada's mountain parks, but this attraction is highly variable, conclude Maureen Murray and Colleen Cassady St. Clair from the University of Alberta.
Trains are known to kill wildlife along railways worldwide, but little is known about what attracts animals to the rail area to guide mitigation. Potential attractants include agricultural products that leak from train cars, vegetation that benefits from light and disturbance, and scavenging opportunities from rail-killed animals. To assess these effects, collaborators in Canada's Banff and Yoho National Parks fitted 21 bears with GPS collars.
Biologist St. Clair and her team then measured stable isotopes and analyzed 230 grizzly bear scats collected over three years, some of which could be attributed to individual GPS-collared bears.
The study shows that just four of the 21 collared bears used the rail area as often as 20% of the days they were monitored. The same four animals produced all the retrieved bear scats that contained spilled grain and could also be attributed to a known individual. Scats found within 150 m of the rail were six times more likely to contain nutrient-rich grains, including wheat, barley, canola seeds, and lentils. Scats near the rail also contained more ant parts and ungulate hair, while scats containing grain also contained a greater diversity of both plants and animals.
St. Clair was surprised by the large variation among bears in rail use and the apparent diversity of their foraging targets. "Rail use was high for three skinny teenagers plus the biggest, most dominant male bear and they might have been targeting different things."
To reduce the risk of trains killing the bears, the researchers recommend that managers continue to remove grain and ungulate carcasses from the railway, reduce grain spills from trains, and target mitigation on the specific bears and locations that generate high rates of rail-based foraging.
The findings were published in the open-access journal PLOS ONE on May 24, 2017.