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Comparison of Detection Probability Associated with Burrowing Owl Survey Methods

Courtney J. Conway and John C. Simon
The Journal of Wildlife Management
Vol. 67, No. 3 (Jul., 2003), pp. 501-511
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3802708
Stable URL: http://www.jstor.org/stable/3802708
Page Count: 11
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Comparison of Detection Probability Associated with Burrowing Owl Survey Methods
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Abstract

Populations of western burrowing owls (Athene cunicularia hypugaea) appear to have declined in many portions of their range. A standardized survey and monitoring program is not available to quantify changes in abundance or distribution. Before a standardized survey method is selected for long-term, continent-wide burrowing owl monitoring, potential survey protocols should be rigorously tested. We evaluated 3 potential burrowing owl survey methods: line transect, roadside point-count, and driving surveys. We also examined the effectiveness of using call-broadcasts on point-count surveys to increase detection probability. We conducted 3 replicate burrowing owl surveys (either point-count or driving surveys) along 1,350 km of roads (114 survey routes) in eastern Wyoming, USA, between June and August 2000. Detection probability varied among observers for both point-count and driving surveys. Detection probability was higher on point-count surveys (x̄ = 64.3%) compared to driving surveys (x̄ = 37.5%), and point-count surveys sampled a larger effective area away from the road. Walking line-transect surveys proved ineffective and inefficient for monitoring burrowing owls at large (statewide) scales. Nest-site detection probability was 47% during driving detection trials and 79% during point-count detection trials. We detected over twice as many owls per unit distance on our point-count routes (0.038 owls/km) compared to our driving routes (0.016 owls/km), but detected more owls per unit time on our driving routes (0.339 owls/hr vs. 0.229 owls/hr on point-count routes). We detected 22% more owls using call-broadcast even though all of our detections on point-count surveys were visual rather than aural. Estimates of breeding density were fairly similar based on our driving and point-count surveys (0.110 and 0.074 nest sites/km2, respectively). Standardized point-counts using call-broadcast along roadsides offer the best approach for monitoring population trends of burrowing owls at large (statewide) spatial scales. Based on our results, we developed a standardized survey protocol for monitoring burrowing owls at large spatial scales. Implementation of these monitoring protocols would provide more precise estimates of population trends of burrowing owls in North America.

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