Home ranges and habitat selection of red-shouldered hawks in Central Maryland: evaluating telemetry triangulation errors

Abstract

Telemetry triangulation provides an estimate of a radio-tagged animal’s location that is influenced by various time and site-specific factors that can cause errors. If these errors are not considered when using location data, the conclusions drawn about animal behavior such as habitat use might be misleading. I determined home range and habitat use and selection characteristics of red-shouldered hawks (Buteo lineatus) in central Maryland. The effects of telemetry triangulation errors on these characteristics were examined. Red-shouldered hawk location estimates were obtained by triangulation to radio-tagged birds. Point estimates were determined by using ≥3 azimuths. A confidence ellipse was calculated around each point estimate which represented the error area associated with that point estimate. From the distribution of possible points within the error area of each point estimate, sampled points (simulated points) were generated for use in additional analyses to assess telemetry error. Home range sizes, based on point estimates and simulated point estimates were delineated using the convex polygon and harmonic mean models. Habitat occurrence was described from a digitized cover type map.

Average home range sizes based on point estimates and simulated point estimates for 3 male hawks were larger than average home range areas for 2 female hawks. There were differences detected between pooled point estimate home range sizes and the pooled simulated point estimate home range sizes. There were fewer differences in home range sizes based on the harmonic mean model than the convex polygon. No significant seasonal differences were found for point estimate or simulated point estimate home range Sizes.

Seasonal habitat use did not vary based on pooled data from all hawks on PWRC. Bottomland forest was the most frequently used habitat type; however, water habitats (ponds and river) were the most frequently selected. Bottomland forests, river swamps, terrace/bluff forests, residential/structural areas, seepage swamps, pine forests, and pine/oak forests were selected occasionally by most hawks. The two most infrequently selected habitats were powerlines and upland oak forests.