Great Gray Owls (Strix nebulosa) in the Sierra Nevada were once believed to nest strictly within mid-elevation conifer forests in close proximity to montane meadows. However, recent observations of Great Gray Owls nesting at lower elevations suggest the lower-montane zone of the Sierra Nevada, where oak-dominated woodlands transition to conifer-dominated forests, may also provide habitat for this California-listed endangered species. We describe the reproductive success, apparent occupancy rate, and habitat associated with eight Great Gray Owl nests monitored between 2006–2014 on commercial timberlands in the lower-montane zone of the central Sierra Nevada, California. Reproductive success was high, with several breeding attempts producing three fledglings, and an average of 1.9 ± 0.9 young fledged during 21 breeding attempts. Apparent occupancy rates were also high (87.5% ± 20.9%) in the years following the discovery of a territory. Nests were in large-diameter (x¯ = 102.5 cm) trees, but smaller-diameter (25.4–50.7 cm) trees dominated the surrounding landscape, which was composed primarily of dense mixed conifer and hardwood forest interspersed with annual grasslands. Our results suggest that the lower-montane zone of the Sierra Nevada, though at the geographic limit of Great Gray Owl’s elevational range, can provide suitable nesting habitat. We used Maxent to identify potential Great Gray Owl nesting habitat throughout the lower-montane zone of the Sierra Nevada based on conditions around the nests we studied. Our model identified areas within 10 counties of the central and northern Sierra Nevada that we recommend be surveyed for Great Gray Owls. Identifying such locations could focus survey efforts to determine if this cryptic species is nesting in the identified areas, perhaps in numbers that may be a significant component of the very small statewide population.
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Vol. 50 • No. 2