Efficacy of Northern Goshawk Broadcast Surveys in Washington State PDF Format - [566KB] Acknowledgments: Support for this research was provided by the WDFW, the Cle Elum and Randal districts of the U.S. Forest Service, private timber companies including the Boise Cascade Corporation, Port Blakely Tree Farm, and ITT Rayonier allowed access to the northern goshawk nests. We thank M.E. McFadzen, M. Suzuki, and C. Fletcher who conducted the majority of field experiments. S.P. Finn and J. Wagenecht provided information on new nest locations and nest status. L.C. Bender, M.L. Nixon, T. Quinn, L.J. Salzer, P.F. Schempf, D.E. Varland, J.M. Williams, and members of the Yakima Management Resource Cooperative provided logistical assistance. We thank P. Garvey-Darda and the Cle Elum Ranger District of the U.S. Forest Service for providing housing to field personnel, and B.J. Behan and D.L. Mueller for cooperation and assistance on surveys in the Randal Ranger District. M.R. Fuller and K. Titus provided excellent comments that improved the manuscript.

Efficacy of Northern Goshawk Broadcast Surveys in Washington State James W. Watson, David W. Hays and D. John Pierce ABSTRACT: Statewide surveys conducted for northern goshawks (Accipiter gentilis) by the Washington Department of Fish and Wildlife (WDFW) in the early 1990s had relatively low detection rates throughout the state and different rates of detection between eastern (1bird/55 km) and western Washington (1 bird/174 km). To investigate the possibility that survey methods or regional habitat characteristics affected detection rates, we tested broadcast calls at 40 nest stands known to be occupied by nesting northern goshawks. During 439 station visits and 210 trials, we recorded 109 detections, 68% of which were vocalizations. Northern goshawks at 37 of the 40 (93%) occupied territories were detected at least once, including 4 occupied sites that failed. Detectability was greater at successful nests by 37% during the postfledging period and accounted for 87% of the responses. Logistic regression modeling identified distance of the surveyor to the nest as the only factor correlated with detection rates (P < 0.001). Probability of detecting northern goshawks at occupied stands increased as nest were approached from 400 m (0.20), 250 m (0.25), and 100 m (0.42). Binomial expansion of detection probabilities at a single nest visit found broadcasting to attain >=90% detections required 5 visits at 100 m, 5 at 250 m, and 10 at 400 m. Because analysis of detection rates by area did not show an effect of vegetation screening, slope, or topography, differences in the relative abundance of northern goshawks from earlier surveys reflect true variation in abundance, differences in nest success, or some combination of both. Results lend more justification for use of broadcast calling for northern goshawks in Pacific Northwest forests and provide a hypothetical model for estimating survey costs as a function of detection probability, trial frequency and station spacing. (Journal of Wildlife Management 63(1):98-106 )