Investigating the Role of Mortality in Explaining the Negative Road Effect on Birds

Lower abundance of forest birds near high traffic roads has been attributed to traffic noise, but the potential role of traffic mortality has not been adequately tested. To test the hypothesis that traffic mortality is an important contributor, I predicted that where there is a higher risk of traffic collision, there would be a stronger decrease in the number of forest birds close to roads over the course of the breeding season. I compared relative abundance of forest birds, at four distances from high traffic roads, at ten sites where the birds were more likely to cross the road (forest on the other side) vs. at ten sites where they were less likely to cross the road (open field on the other side). The prediction was supported, suggesting that roads bisecting natural areas may create population sinks. This highlights the importance of mitigating traffic mortality in important bird habitats.