WDFW LogoWashington Department of Fish & Wildlife
  HELP | EMPLOYMENT | NEWS | CONTACT  
WDFW LogoPublications

You will need Adobe Reader to view and print publications.

Get Adobe Reader
Get Adobe® Reader

Archived Publications
contain dated information
that do not reflect current
WDFW regulations or policy.
These documents are provided
for archival purposes only.


 

    Advanced Search
  Search Tips

 
Download PDF Download Document

Get Adobe® Reader

Efficacy of Northern Goshawk Broadcast Surveys in Washington State

Category: Wildlife Research and Management - Wildlife Research

Date Published:  1999

Number of Pages: 9

Author(s): 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.