Assessing Distribution Habitat Suitability And Site Occupancy Of Great Gray Owls Strix Nebulosa In California

Author : Joseph Robert Rowley Medley
Publisher :
ISBN 13 : 9781303154102
Total Pages : pages
Book Rating : 4.1/5 (541 download)

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Download or read book Non-invasive Bioacoustic Techniques for Detecting and Monitoring the Sierra Nevada Great Gray Owl (Strix Nebulosa) written by Joseph Robert Rowley Medley and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: California great gray owls are rare, nocturnal, secretive, and have a limited geographic distribution in the Central Sierra Nevada, rendering them a difficult species to study. Current survey methods are time and cost intensive, and require the use of nocturnal broadcast surveys to elicit territorial responses. Using autonomous recording units (ARUs) and acoustic editing software, we investigated the utility of bioacoustic technology as an alternative survey methodology for great gray owls. We conducted ARU sampling at a total of 50 meadow sites divided evenly between Yosemite National Park and Stanislaus National Forest. Half of these sites within each category consisted of sites historically occupied by great gray owls, while the other half consisted of randomly selected but suitable habitat during the spring and summer of 2009. Specifically, our goals were to estimate probabilities of detection for great gray owls using ARUs and compare those estimates with those afforded by the broadcast survey methodology. Additionally, we aimed to quantify sampling design tradeoffs of ARU spacing and recording duration, describe great gray owl vocalization behaviors, and conduct a comparative cost estimation between survey methods. We used a maximum likelihood-based modeling approach to estimate probabilities of detection and occupancy. Estimates of single visit probability of detection for ARUs (0.708) were similar or favorable to those afforded by the broadcast method, with the exception of Stanislaus National Forest random sites, where estimates of probability of detection for ARUs were slightly lower than those from the broadcast method. Under our ARU sampling strategy, and multiple reduced sampling strategies that we analyzed, very high overall probabilities of detection >0.90 could be achieved after two to five nights of sampling. We detected a total of 63,612 great gray owl vocalization events across 24 sample sites. 88% of all vocalization events were detected during the twelve-hour period between 1900 and 0700 hours. Our comparative cost estimate suggests that ARU surveys are more cost effective than broadcast protocol strategies when the number of annual sampling sites exceeds 20, especially in multi-year studies, as the annual cost for ARU sampling decreases significantly once the units have been acquired. Our results indicate that ARUs provide a non-invasive, cost-effective alternative method with comparable estimates of probability of detection to broadcast survey techniques for monitoring the rare and elusive California great gray owl. Additionally, our methods have broader management implications, as they can be applied to monitoring multiple species of birds or other terrestrial vertebrates. We suggest that land managers tasked with monitoring great gray owls and other rare species consider ARUs as a non-invasive monitoring alternative or supplement to methodologies currently in use.