Territorial Responses of Boreal Forest Birds to Habitat Gaps

Abstract

We used playback trials to determine whether birds will cross treeless gaps to respond to simulated territorial intruders. We evaluated the effect of gap width on responses by five forest bird species. We found that for forest specialists such as the Swainson's Thrush (Catharus ustulatus), Golden-crowned Kinglet (Regulus satrapa), and the Black-throated Green Warbler (Dendroica virens), the probability of crossing gaps decreased sharply with gaps 25-40 m wide. By contrast, control trials showed no significant decrease in their probability of response up to 100 m through continuous stands. Habitat generalists such as the White-throated Sparrow (Zonotrichia albicollis) and the Dark-eyed Junco (Junco hyemalis) were more prone to cross treeless gaps than forest specialists. Playback studies provide a new tool for understanding birds' responses to microscale habitat discontinuities.