Return to Conservation Biology Research on Birds

Mosher, J.A. 1987. Woodland hawk census project. Final report submitted to the Minnesota Department of Natural Resources. 40 pp.


It is essential to the effective management and conservation of wildlife populations to be able to reliably assess their status over space and time. Such quantitative data for woodland raptors have been difficult and often prohibitively expensive to acquire. Public and private concern for these species has led to requirements for determining their status within political boundaries by both State and Federal agencies.

Forested habitat places severe restrictions on our ability to detect and observe raptors. Detectability is further reduced by the secretive behavior of several of these species. This project, final results of which are reported here, was initiated in 1979 to develop methods for monitoring raptor populations in forested habitat. We asked these questions among others: 1) do woodland raptors respond to broadcast of tape-recorded conspecific and/or Great-horned Owl vocalizations? they do; 2) does the use of these broadcast vocalizations increase the detectability of raptor species over surveys without broadcast? it does; 3) which is most effective at eliciting responses from woodland hawks, conspecific or Great-horned Owl broadcasts? of the species tested, the Great-horned Owl broadcasts produced higher contact rates for Red-shouldered Hawks and rates at least as high as the conspecific broadcasts for other species; 4) is there a correlation between survey contact rates and the actual number of hawks resident on the area surveyed? yes.

This report presents the results of the final development and testing of the broadcast technique for censusing/indexing woodland hawk populations. The best regression models for individual species and species groups are presented along with their statistical characteristics. Recommendations for the application of this technique to monitoring woodland hawk populations are provided.

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