TERRITORIAL RESPONSES OF BOREAL FOREST BIRDS TO HABITAT GAPS

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 u stulatus), Golden-crowned Kinglet (Regulus satrapa), and the Black-thr oated Green Warbler (Dendroica virens), the probability of crossing ga ps decreased sharply with gaps 25-40 m wide. By contrast, control tria ls showed no significant decrease in their probability of response up to 100 m through continuous stands. Habitat generalists such as the Wh ite-throated Sparrow (Zonotrichia albicollis) and the Dark-eyed Junco (Junco hyemalis) were more prone to cross treeless gaps than forest sp ecialists. Playback studies provide a new tool for understanding birds ' responses to microscale habitat discontinuities.