Using Dogs To Survey Simultaneously for Spotted and Barred Owls Without Relying on Vocalizations

One of the worst threats currently confronting the federally threatened northern spotted owl (Strix occidentalis caurina) is the ongoing range expansion of the closely related barred owl (Strix varia).  In addition to outcompeting spotted owls for territories, barred owls also attack spotted owls directly.  As a result, spotted owls call less frequently when in proximity to barred owls.  This poses a problem for managers who rely on vocalization surveys to establish spotted owl presence and ensure habitat protection.  We addressed this problem by training dogs to locate owl roosts, and by confirming species identity from owl pellets using Restriction Fragment Length Polymorphism analyses of mitochondrial DNA.  In 2010, we compared success of detection dog surveys to vocalization surveys using a slightly modified version of the U.S. Fish and Wildlife Service’s Draft 2010 Survey Protocol.  Dogs located pellets on all 20 study sites.  DNA analysis indicated that 14 sites contained northern spotted owl and seven contained barred owl; three sites contained both species.  DNA confirmed cumulative detection probabilities for dog teams were 40%, 80% and 90% after the first, second, and third sampling sessions, respectively.  Visually confirmed cumulative detection probabilities for vocalization surveys were 19% after session 1, increasing to 69% by session 6.  These results suggest that detection dog surveys can provide a valuable supplement to vocalization surveys for spotted and barred owls, particularly where barred owls are common or are just beginning to establish.