Squirrel stockpiles may expose grizzlies to train danger

Could red squirrels be putting grizzly bears in the crosshairs of locomotives?

Sounds a bit nonsensical on the surface of it, but new research out of the Canadian Rockies suggests otherwise. A team from the University of Alberta has discovered that squirrel stashes of grain dribbled from railcars might be drawing grizzlies to the vicinity of railroad tracks in Banff and Yoho national parks, thus possibly exposing the bears to a greater risk of train collision.

A grizzly bear digs into a squirrel midden. Video credit: Julia Put

The study, published last month in Nature Conservation, focused on the 134-kilometre corridor of the Canadian Pacific Railway that passes through Yoho and Banff, two of the most celebrated "mountain parks" in western Canada.

A locomotive hitting a grizzly bear isn't quite the freak, once-in-a-blue-moon occurrence it might sound like. In the past decade, trains have been the culprit in ten known grizzly deaths in the Banff-Yoho area – from sows with cubs to adult males. (It's a fate that's also befallen black bears in the area.) One roughly 300-kilogram (660-pound) Banff boar, Bear 122 ("The Boss") – famously seen chowing down on a black bear in 2013 – apparently survived a run-in with a train several years ago and nonetheless continues to travel along railways.

Some of those collisions come when bears are simply crossing railroad tracks, but it's long been known that grain leaked or outright spilled from so-called hopper cars also attracts hungry grizzlies:

Such seed spillage also lures in red squirrels, and the University of Alberta study suggests the middens these industrious rodents stockpile as larders may play a role in encouraging high-risk grizzly foraging along railways.

The researchers found heavy squirrel presence along Yoho and Banff's railway corridor, which also included all but one of the surveyed squirrel middens that contained grain (mostly canola and wheat). The only middens that showed signs of being dug into by grizzlies were close to the tracks, and nearly all of those harboured seeds.

"The fact that we observed digging by grizzly bears in middens only near the railway and almost exclusively where we also detected agricultural seeds suggests that bears smell the seeds and target seed-containing middens," the researchers wrote.

If grizzlies become conditioned to targeting railway squirrel caches for their concentrated stockpiles of grain, the researchers speculate, the bears might also generally search for spilled seeds along the tracks – a potentially hazardous strategy, to say the least. Check out this close call between a Banff grizzly and a train:

The impetus for the University of Alberta research was a GPS-collared grizzly pilfering a squirrel midden with agricultural seed in 2013. Previously, the only morsels grizzlies were known to seek out in squirrel pantries were pine nuts. In drier portions of the American Rockies such as Montana's Rocky Mountain Front and especially the Greater Yellowstone Ecosystem, the protein-rich seeds of the subalpine whitebark pine provide a major summer and autumn food source in the high country for grizzly bears – and exclusively via squirrel middens.

While pine nuts, overall, don't appear to be as significant a grizzly menu item in the Canadian Rockies, recent fieldwork reveals grizzlies in Banff do eat the squirrel-harvested seeds of both whitebark and limber pines. According to the new study, that tradition could possibly predispose grizzlies in the area to key into the lower-elevation rodent stashes along railways.

In presenting their findings, the researchers note there's still much to learn about the potential relationship between squirrels, grizzlies and railroads. For one thing, most of their data comes from 2014, a year that saw a poor crop of one of local grizzlies' favoured foods, buffaloberry – that means more bears may have been seeking out middens as alternative food sources. (Grizzlies have an impressive appetite for buffaloberries, to put it mildly: they can inhale more than 200,000 of them per day.)

It's also possible that grizzlies were at least partly excavating middens in search of the squirrels themselves, or perhaps other rodents raiding the caches. (The team recorded plenty of evidence of grizzlies digging after burrowed Columbian ground squirrels around the railroad.)

Besides the possibility of more grizzlies getting killed by trains, the University of Alberta team highlights another potential side effect of railroad squirrel middens: squirrels, bears and other grain-nibblers could spread the non-native cultivated plants in Banff and Yoho through their droppings.

"Our study exemplifies the complexity of both food conditioning and vulnerability to train strikes associated with spilled agricultural products on railways," the authors conclude. "The only feasible mitigation for these effects is likely to reduce spillage from hopper cars via careful attention to loading and gate maintenance."

Some of the funding for the University of Alberta study came from a partnership between Parks Canada and Canadian Pacific, which recently wrapped up a five-year assessment of the risk posed to grizzly bears by railways and potential measures to reduce train-caused bear mortality.