Optimal sampling for radiotelemetry studies of spotted owl habitat and home range.

Abstract

Carey, Andrew B.; Horton, Scott P.; Reid, Janlce A. 1989 SummaryRadiotelemetry is the only feasible method for determining spotted owl ranges and habitat use. Although there is no guidance in the literature on what constitutes an adequate sample of telemetric relocations for an individual owl, it is apparent that data used for estimating home range sizes and habitat selection must be independent, unbiased, and sufficient in number. And a sufficient number of owls must be studied to describe the population.We examined time series of relocations and the size, shape, and composition of ranges of nine adult spotted owls in the Oregon Coast Range. We approached the question of independence of relocations in two ways. Our statistical approach tested relocations for senal correlation. Our biological approach examined movement patterns of the owls relative to the average size of patches in their ranges. Statistically independent relocations were separated by 3 days in the breeding season and 5 days outside the breeding season; biological independence occurred after 3 and 2 days, respectively. The disparity of the two results is due to the large size of nonbreeding season ranges compared with the small size of patches within those ranges. Because we seek guidance for sampling plans and do not wish to undersample, we use the estimates of times to independence provided by the biological approach.We can increase our opportunities for following more owls by attempting to relocate individuals no more often than every other night and by rotating 2 and 3 nights a week for individuals. Under this schedule, we could obtain 130 relocations per owl annually, 115 of which could be independent. These data will be adequate, in terms of sample size and independence, for estimating home range size and habitat use by spotted owls in the Oregon Coast Range.

Northern Spotted Owls: Influence of Prey Base and Landscape Character

“…Methods are described by Forsman (1983). We followed telemetry procedures developed during a pilot study in 1986 (Carey et al 1989(Carey et al , 1990. We followed telemetry procedures developed during a pilot study in 1986 (Carey et al 1989(Carey et al , 1990.…”

“…Owls were classified as adults (~3 yr) or subadults (1-2 yr) based on plumage (Forsman et al 1984). Daytime telemetry procedures were identical to nighttime telemetry procedures; the owls generally roosted in the same stands they foraged in the night before (Carey et al 1989). Procedures included periods offamiliarization for each new telemetry technician and study area.…”

“…This sampling schedule was designed to maximize the number of independent foraging locations (Carey et al 1989). In addition, we attempted to get one daytime (roost) location every 2 wk.…”

“…We defined these events as interactions between owls because these owls were generally in the same stand (average stand width was 451 m) and spotted owls generally stay in the same stand while foraging, but move an average of 516 m within a night (Carey et al 1989). Owls were observed at night near roads and during the day in the forest during attempts to capture resident owls, assess reproductive status, describe roosts, and check the accuracy of telemetric locations.…”

Forest Structure Within Barred Owl (Strix varia) Home Ranges in the Eastern Cascade Range, Washington

“…Their study assumed that all night locations were foraging locations, which would exclude other typical activities. However, Carey et al (1989) concluded roosting and foraging sites were often synonymous (also see . Underestimates of availability of prey could affect estimates of selection, as could underestimates of abundance.…”