Acoustic surveys for Mexican spotted owls (Strix occidentalis lucida): An analysis Free

During acoustic surveys for Mexican spotted owls, the effective detection range is presumed to be 0.25 mi (433 m). However, variations within and between surveys are observed, leading to a variance in owl density estimates. While owl behavior may explain some variation, topography and ambient noise are also likely to be important. To determine the influence of these factors, data from acoustic surveys for Mexican spotted owls in the Gila National Forest (April–July, 2000–2001) were examined. Measurements of owl and human call levels were made with a Sony TCD‐10 Pro II DAT equipped with an ACO 7013 microphone. Ambient noise was collected using 40 Larson‐Davis 820 and 824 sound level meters in owl activity centers. Wyle Laboratories NMSIM software was used to model propagation of owl and human calls. Owls produced calls with estimated maximum source levels of 92–98‐dB SPL. Human callers produced maximum source levels of 88–95‐dB SPL. Detection was possible out to more than 2 km under ideal conditions, but topography and ambient noise had a large effect. Corrections for these factors would greatly improve estimates of area surveyed, and thus owl density estimates. [Work supported by the U.S. Air Force, Air Combat Command.]