Bioacoustic techniques to monitor great gray owls (Strix nebulosa) in the Sierra Nevada

• Main Author: Rognan, Cameron B.
• Other Authors: Szewczak, Joseph M.
• Format: Master Thesis
• Language: English
• Published: California State Polytechnic University, Humboldt 2007
• Subjects: ARU; Meadow; Bioacoustics; Sierra Nevada; Vocal individuality; Great gray owl; Humboldt State University > Theses > Biology; Survey; Monitor; Strix nebulosa
• Online Access: http://hdl.handle.net/2148/227

The Great Gray Owl (Strix nebulosa) is listed as a State of California endangered species due to their low population of approximately 100 individuals. Annual surveys and long-term monitoring efforts are frequently conducted to determine the status of this species within its very limited range in the Sierra Nevada. Great Gray Owls are difficult to study because they are rare, nocturnal, and secretive. I investigated two bioacoustic techniques that may be useful to incorporate into current survey protocols and monitoring efforts of Great Gray Owls: (1) vocal individuality, and (2) the use of autonomous recording units (ARUs). To investigate the potential of individually distinct vocalizations for population monitoring, I recorded the territorial calls of 14 male and 11 female Great Gray Owls between March and July 2006 and 2007. Nineteen of these owls were recorded on multiple occasions within a season, and eight owls were recorded on separate occasions between seasons. Seventeen frequency and 15 temporal variables of the calls were analyzed from 312 sonograms. A stepwise discriminant analysis selected the nine best discriminator variables and correctly classified 92.8% of the calls to the correct individual within a season. Between seasons, 71.4% of the calls were classified to the correct individual. My results indicate that territorial calls could be used to monitor individual Great Gray Owls for both short and long-term studies. To investigate the use of autonomous recording units (ARUs), I installed ARUs in 15 potential Great Gray Owl territories from March to July 2006 and 2007. Each unit recorded 12 hours per night (from 1800 to 0600). Great Gray Owl vocalizations were successfully recorded at 10 of the 15 territories. In locations where owls were detected, audible calls were recorded during 49.5% of the nights sampled. Recorded chick calls late in the breeding season were the loudest and may be the most useful indicator for owl presence and nest success. Adult territorial calls recorded by ARUs could also ...