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doi: 10.1371/journal.pone.0042892. Epub 2012 Aug 15.

Using detection dogs to conduct simultaneous surveys of northern spotted (Strix occidentalis caurina) and barred owls (Strix varia)

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Using detection dogs to conduct simultaneous surveys of northern spotted (Strix occidentalis caurina) and barred owls (Strix varia)

Samuel K Wasser et al. PLoS One.2012.

Abstract

State and federal actions to conserve northern spotted owl (Strix occidentalis caurina) habitat are largely initiated by establishing habitat occupancy. Northern spotted owl occupancy is typically assessed by eliciting their response to simulated conspecific vocalizations. However, proximity of barred owls (Strix varia)-a significant threat to northern spotted owls-can suppress northern spotted owl responsiveness to vocalization surveys and hence their probability of detection. We developed a survey method to simultaneously detect both species that does not require vocalization. Detection dogs (Canis familiaris) located owl pellets accumulated under roost sites, within search areas selected using habitat association maps. We compared success of detection dog surveys to vocalization surveys slightly modified from the U.S. Fish and Wildlife Service's Draft 2010 Survey Protocol. Seventeen 2 km × 2 km polygons were each surveyed multiple times in an area where northern spotted owls were known to nest prior to 1997 and barred owl density was thought to be low. Mitochondrial DNA was used to confirm species from pellets detected by dogs. Spotted owl and barred owl detection probabilities were significantly higher for dog than vocalization surveys. For spotted owls, this difference increased with number of site visits. Cumulative detection probabilities of northern spotted owls were 29% after session 1, 62% after session 2, and 87% after session 3 for dog surveys, compared to 25% after session 1, increasing to 59% by session 6 for vocalization surveys. Mean detection probability for barred owls was 20.1% for dog surveys and 7.3% for vocal surveys. Results suggest that detection dog surveys can complement vocalization surveys by providing a reliable method for establishing occupancy of both northern spotted and barred owl without requiring owl vocalization. This helps meet objectives of Recovery Actions 24 and 25 of the Revised Recovery Plan for the Northern Spotted Owl.

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Conflict of interest statement

Competing Interests:The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Northern spotted owl and barred owl detections during dog and vocalization surveys per polygon.
Red squares correspond to northern spotted owls and yellow squares correspond to barred owls. An owl inside the square indicates a dog detection, a sound wave illustration inside the square indicates a vocalization survey detection. A ? inside the square indicates a one-time DNA amplification from a pellet, which thus did not meet the criterion of two successive DNA amplifications to confirm a species. Blue circles represent pellets located by dogs that failed to amplify for mtDNA. Each polygon number is indicated in white inside the black square outlining the polygon. The thin black lines indicate dog survey routes. Habitat quality ranges from high (green) to intermediate (yellow) to low (brown) and were generated from the Zabel et al. and Carroll and Johnson habitat models. The two models are merged by making the coarse model transparent and overlaying it on the more fine-grained model . This collectively increases and decreases color contrast on the map when the two models concur or differ, respectively.
Figure 2
Figure 2. Northern spotted owl detection probabilities by dog versus vocalization surveys (A) per session and (B) cumulatively across sessions.
These probabilities are derived from occupancy models using data for all polygons sampled, after controlling for occupancy . Error bars in Fig. 2A represent one standard error.
Figure 3
Figure 3. Barred owl detection probabilities by dog versus vocalization surveys.
As per Figure 2a, detection probabilities were derived from from occupancy models using data for all polygons sampled, after controlling for occupancy . These probabilities also incorporate the mean CJ-habitat quality values from the sites (see text). The lines represent 1 SE.
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References

    1. MacKenzie DI, Nichols JD, Lachman GB, Droege S, Royle JA, et al. (2002) Estimating site occupancy rates when detection probabilities are less than one. Ecology 83: 2248–2255.
    1. Forsman ED (1983) Methods and materials for locating and studying northern spotted owls. Gen. Tech. Rep. PNW-162. U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 8.
    1. Olson GS, Anthony RG, Forsman ED, Ackers SH, Loschl PJ, et al. (2005) Modeling of site occupancy dynamics for northern spotted owls, with emphasis on the effects of barred owls. J Wildlife Manage 69: 918–932.
    1. Crozier ML, Seamans ME, Gutierrez RJ, Loschl PJ, Horn RB, et al. (2006) Does the presence of Barred Owls suppress the calling behavior of Spotted Owls? Condor 108: 760–769.
    1. Wiens JD, Anthony RG, E. D. Forsman ED (2011) Barred owl occupancy surveys within the range of the northern spotted owl. J Wildlife Manage 75: 531–538.

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This research was funded by a grant from the USF&WS grant # 10100-0-J001MOD4, Seattle Audubon (http://www.seattleaudubon.org/sas/), the Washington Forest Law Center (http://wflc.org/), and the Wilburforce Foundation (http://www.wilburforce.org/). The Assistant Project Leader, Endangered Species and Habitat Conservation, Red Bluff Fish and Wildlife Office provided partial funding and participated in the design and implementation of this study. However, as indicated by the disclaimer in the manuscript, The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service. No other funders had a role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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