Department of Biology, Center for Conservation Biology, University of Washington, Seattle, Washington, USA.
PLoS One. 2012;7(8):e42892. doi: 10.1371/journal.pone.0042892. Epub 2012 Aug 15.
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.
州和联邦一级为保护北方斑点猫头鹰（Strix occidentalis caurina）栖息地而采取的行动主要是通过建立栖息地占有率来启动的。北方斑点猫头鹰的占有率通常是通过诱发它们对模拟同种叫声的反应来评估的。然而， barred owl（Strix varia）——北方斑点猫头鹰的一个重要威胁——可以抑制北方斑点猫头鹰对叫声调查的反应，从而降低它们的探测概率。我们开发了一种同时检测这两个物种的调查方法，该方法不需要叫声。探测犬（Canis familiaris）在使用栖息地关联图选择的搜索区域内，找到在栖息地点下积累的猫头鹰粪便。我们比较了探测犬调查和稍作修改的美国鱼类和野生动物管理局 2010 年调查草案中使用的叫声调查的成功率。在已知 1997 年以前有北方斑点猫头鹰筑巢的地区和 barred owl 密度较低的地区，17 个 2 公里×2 公里的多边形被多次调查。从犬类探测到的粪便中提取线粒体 DNA 以确认物种。与叫声调查相比，狗对斑点猫头鹰和 barred owl 的探测概率明显更高。对于斑点猫头鹰来说，这种差异随着访问次数的增加而增加。狗的调查在第 1 轮后北方斑点猫头鹰的累计探测概率为 29%，第 2 轮后为 62%，第 3 轮后为 87%，而叫声调查在第 1 轮后为 25%，到第 6 轮后增加到 59%。狗的调查中 barred owl 的平均探测概率为 20.1%，叫声调查为 7.3%。结果表明，探测犬调查可以通过提供一种可靠的方法来建立北方斑点猫头鹰和 barred owl 的占有率，而不需要猫头鹰的叫声，从而补充叫声调查。这有助于实现修订后的北方斑点猫头鹰恢复计划的恢复行动 24 和 25 的目标。
