As any hiker knows, valley soundscapes vary depending on physiography, echo potential, wind, and other factors that can be exacerbated by, for instance, long curves on a rail line. Studying curves has also uncovered another issue that’s only just beginning to be measured: magnetic anomaly. This potential factor was accidentally discovered in the vicinity of Five Mile Bridge — a place where several bears have been struck—when it was seen that magnetic bearings weren’t stable: a compass needle behaves strangely here, fluttering around and at certain points even flipping 180 degrees. It could be a natural geologic phenomenon or be related to material comprising the vast rock ballast required to support tracks on long curves. Bears might be capable of learning about these anomalies over time but be potentially confused in the short term. How confused?
“Well, to start, magnetic perturbations occur in lots of other places that aren’t strike sites, so it’s unlikely to be just that,” says Dr. Colleen Cassady St. Clair, scientific lead on the Parks Canada/Canadian Pacific Railway joint study. “But like so many other biological problems I’ve looked at, what seems to be emerging is that it’s probably a combination of things. For instance, if you’re a bear and can hear but not see a train and can’t tell which direction its coming from — maybe its dark, maybe its raining, maybe you’re already confused — you could even be moving away from the threat when your magnetic sense suddenly turns you around and into the danger. Engineers have indeed reported bears running away then inexplicably veering back into the train.”
Cassady St. Clair says some of this might mitigate itself when bears become more knowledgeable; in the meantime the role of magnetism is coming up again and again in animal research, and offers but one example of the confounding effects of studying animals that perceive their environment in a dimensionality that we don’t. Perhaps the most confounding issue of all, however, is this: the deaths are a relatively new phenomenon. The current spate of grizzly strikes really started on the railroad line in about 1999 and were rare before that. When trying to figure out the why, Cassady St. Clair thought right away of the highway mitigation, the loss of forage or grassy habitat it caused, but when they looked at the GPS information that didn’t seem to be part of it. But the mitigation also removed road kill they had foraged, and now they don’t have that either.
“The glass half-empty look is that this is getting complicated,” she notes, “but the glass half-full look is that it’s also getting more interesting.”