Of Grizzlies and Roads

Today, in an early release,  the Journal of Applied Ecology  gave us a preview of the results of recent study conducted by a team of biologists in western Alberta, Canada. For the first time,  they were able to record and document the response of grizzly bears to a wide range of traffic levels on roads that run through grizzly habitat, even causing some bears to become largely nocturnal to avoid the heaviest traffic times.   There findings were not unexpected, but finally the bears’ responses have been documented.  Roads and traffic are important elements as we plan for grizzly bear recovery in the North Cascades and Selkirk Ecosystems. The need for safe wildlife crossings is now underscored.  Although the Interagency Grizzly Bear Committee recognized that the highest threat that roads pose to grizzly bears is through direct mortality from collisions and increased access for hunting/poaching,  science has now pointed to another threat to grizzly bear survival:  the alteration of behavior in response to increases in traffic levels.

From the study abstract:

“We developed models of traffic volume for an entire road network in south-western Alberta, Canada, and documented for the first time the response of grizzly bears, Ursus arctos,  to a wide range of traffic levels. Roads were found to cause functional habitat loss, alter movement patterns and can become ecological traps for wildlife. Many of the negative effects of roads are likely to be a function of the human use of roads, not the road itself. However, few studies have examined the effect of temporally and spatially varying traffic patterns on large mammals, which could lead to misinterpretations about the impact of roads on wildlife.”

“Traffic patterns caused a clear behavioral shift in grizzly bears, with increased use of areas near roads and movement across roads during the night when traffic was low. Bears selected areas near roads travelled by fewer than 20 vehicles per day and were more likely to cross these roads. Bears avoided roads receiving moderate traffic (20–100 vehicles per day) and strongly avoided high-use roads (>100 vehicles per day) at all times.”

Synthesis and applications. Grizzly bear responses to traffic caused a departure from typical behavioral patterns, with bears in our study being largely nocturnal. In addition, bears selected private agricultural land, which had lower traffic levels, but higher road density, over multi-use public land. These results improve our understanding of bear responses to roads and can be used to refine management practices. Future management plans should employ a multi-pronged approach aimed at limiting both road density and traffic in core habitats. Access management will be critical in such plans and is an important tool for conserving threatened wildlife populations.
Edited By: EJ Milner-Gulland, Phil Hulme, Marc Cadotte, Mark Whittingham and Jos Barlow,  July 31, Journal of Applied Ecology