SONGBIRD DISTRESS CALLS AS AN IMPROVED METHOD FOR DETECTING REDSHOULDERED HAWKS (Buteo lineatus)

摘要

We present an audio playback method that increases the probability of encountering, and consequently increases the efficiency of detecting, counting, and monitoring, Red-shouldered Hawks (Buteo lineatus). Our design involves a passive census period prior to and following a playback period with broadcast of one of two, five-minute pre-recorded playbacks: distress calls of Tufted Titmouse (Baeolophus bicolor),or perched calls of Eastern Screech-Owl (Megascops asio). We conducted fixed-radius point counts before, during, and after playback periods at 124 independent sites in north-central Florida from September 2012 to May 2013. We used generalized linear modeling to estimate the effects of habitat type, census period, and treatment (playback type) on the probability of the presence of Red-shouldered Hawks on surveys. We detected raptors (B. lineatus) on 10 (8%) surveys prior to playback of either treatment (distress, owl). Following playback of M. asio we detected raptors (Red-tailed Hawk, B. jamaicensis; Barred Owl, Strix varia) on two surveys (0.3%). Following playback of B. bicolor we detected raptors (Red-tailed hawk, Redshouldered Hawk, Barred owl) on 21 surveys (34%). A post-hoc multiple comparisons test of the fixed interaction effect among treatment and playback periods detected a significant effect of distress call playback on the probability of presence of Redshouldered Hawk both within, and across treatments. We conclude that songbird distress calls significantly enhance the detectability of Red-shouldered Hawk within the sound-exposed area, and thereby decreases the effort required to census for these, and possibly other, raptorial species.