Daily and seasonal movements of a shrubland-obligate breeder in relation to mature forest edge habitat

• We tested four hypotheses that could produce a pattern of apparent edge avoidance.
• Yellow-breasted Chats did not actively avoid habitat edges.
• Our results support the passive displacement hypothesis.
• There was some support for the conspecific interactions hypothesis.
• Edge habitat may still provide quality habitat for shrubland birds in our system.

The effects of edge habitat on wildlife populations have been studied extensively in recent decades, but most studies have focused on describing patterns of edge effects rather than identifying the mechanisms driving these effects. Based on evidence of lower densities of shrubland birds in edge versus interior habitat, we tested four hypotheses that could produce a pattern of apparent edge avoidance: (1) active avoidance of edges due to high risk of predation in edge habitat, (2) conspecific interactions that promote greater use of interior habitat due to territorial defense, (3) passive displacement of avian home ranges, such that sampling in the interior is more likely to intersect multiple home ranges compared to sampling at edges, and (4) home range expansion along edges. To test these hypotheses, we radio-marked 39 male Yellow-breasted Chats (Icteria virens) during the breeding seasons of 2005 and 2006 and relocated each bird 4–5 days/week. Our results did not support the hypothesis that Yellow-breasted Chats avoided habitat edges in either home range placement or habitat usage within their home ranges though there was some support for greater usage of interior habitat during the peak of the breeding season. Size of home ranges did not vary with distance from edge. These results support the passive displacement hypothesis and, to a lesser extent, the conspecific interactions hypothesis. The passive displacement hypothesis predicts lower abundances in the edges compared to the center of a habitat patch because areas in the patch center receive individuals from all directions whereas areas near the edges do not. Thus, edge habitat may still provide quality habitat for shrubland birds in our system.