MITIGATING SPATIAL DIFFERENCES IN OBSERVATION RATE OF AUTOMATED TELEMETRY SYSTEMS

Wildlife ecologists are increasingly interested in determining spatial distributions and habitat use of ungulates from locations estimated f rom both conventional and automated telemetry systems (ATS). If the pe rformance of an ATS causes spatial versus random variation in probabil ity of obtaining an acceptable location (observation rate), analysis o f habitat selection is potentially biased. We define observation rate as the percentage of acceptable locations (i.e., those that meet signa l strength, signal-to-noise ratios, geometric dilution of precision cr iteria) of the rural locations attempted. An ATS at the Starkey Experi mental Forest and Range (Starkey) in Oregon tracks movements of elk (C ervus elaphus), mule deer (Odocoileus hemionus), and cattle. We detect ed localized variation in observation rate of stationary radiocollars in 1993. Subsequently, we devised a method to estimate observation rat e at various spatial scales using animal location data over 4 years (1 992-95; n = 907,156 location attempts) to determine if the variation w as spatial or random. We formulated 5 variants of a general linear mod el to obtain estimates of spatial variation in observation rate. All 5 models assumed spatially correlated error terms estimated from isotro pic semivariograms. Three models included environmental variables as c ovariates correlated with observation rate. Models then were compared based on mean error, coefficient of determination, and residual plots. Random variation accounted for 47-53%, and spatial variation accounte d for 38-45% of the variation in observation rate. One model was selec ted to demonstrate application of the correction to mitigate spatial b ias in observation rate. Our results demonstrate the utility of semiva riograms to detect and quantify spatial variation in observation rate of animal locations determined from an ATS.