Comparison of detection probability associated with burrowing owl survey methods

Call Number:

URL:

Keywords:

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. The authors evaluated 3 potential burrowing owl survey methods: line transect, roadside point-count, and driving surveys. They also examined the effectiveness of using call-broadcasts on point-count surveys to increase detection probability. Three replicate burrowing owl surveys (either point-count or driving surveys) were conducted along 1,350 km of roads (114 survey routes) in eastern Wyoming 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 (x– [“x–“ should be the symbol in which the “–“ is atop the “x”]= 64.3%) compared to driving surveys (x– = 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. The authors detected over twice as many owls per unit distance on the point-count routes (0.038 owls/km) compared to the driving routes (0.016 owls/km), but detected more owls per unit time on driving routes (0.339 owls/hr vs. 0.229owls/hr on point-count routes). They detected 22% more owls using call-broadcast even though all of the detections on point-count surveys were visual rather than aural. Estimates of breeding density were fairly similar based on the 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 these results, the authors 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.

Notes:

ELECTRONIC FILE - Zoology