Comparative Permeability of Roads, Rivers, and Meadows to Songbirds in Banff National Park

Roads exert a variety of negative effects on wildlife and one of the most severe may be that they form barriers to animal movement. However, the role of roads as barriers has seldom been compared to that of natural barriers. I examined the permeability of roads, rivers, and meadows to songbirds in Banff National Park, Alberta, Canada, where a four‐lane highway dissects a wide montane valley. An audio recording of a chickadee ( Poecile atricapillus ) mobbing call was played to lure birds to travel either parallel or perpendicular to the three barrier types over a range of distances. Relative to parallel trials, forest‐dependent birds were reluctant to cross rivers but not roads or meadows, and they crossed barriers less often when the barriers were noisy. Across all gap and barrier combinations, responses declined as trial distance increased, and kinglets were less likely to respond than other families, which included chickadees, nuthatches, warblers, and corvids. The responses of sparrows and thrushes—both forest generalists—showed a weak interaction between barrier type and family, indicating that robins were slightly less likely to respond to trials associated with meadows, and sparrows were less likely to respond in association with rivers. These associations occurred irrespective of gap configuration. Together, these results suggest that the response to barriers by montane birds is strongly dependent on their degree of forest dependence. The surprising result that forest birds were less likely to cross rivers than either roads or meadows may stem from evolutionary history and suggests that birds do not perceive the risk of mortality posed by road traffic.