Gap crossing decisions by forest songbirds during the post-fledging period

Gaps in forest cover, created by agriculture, forestry, and other anthropogenic activities, are assumed to impede the movements of many forest songbirds. Little is known, however, about the reluctance of different species of birds to cross habitat gaps. We studied this by inducing birds in the post-fledging period to cross gaps of varying widths and to choose between routes through woodland or across open areas by attracting them to a recording of mobbing calls by Chickadees (Parus atricapillus). In 278 experiments conducted in boreal forest and agricultural landscapes near Quebec city, 157 birds or flocks of birds of five species were attracted. Overall, birds were twice as likely to travel through 50 m of woodland than through 50 m in the open to reach the recording. When given a choice of traveling through woodland or across a gap, the majority of respondents preferred woodland routes, even when they were three times longer than shortcuts in the open. However, species differed greatly in their response to gaps. Our results show that woodland links significantly facilitate movements of birds across fragmented landscapes.