GPS collars have greatly increased the number of locations obtained for individual animals during telemetry studies, but missed location attempts (missed fixes) may create bias in habitat analyses unless appropriately modeled. We placed GPS collars on captive grizzly bears (Ursus arctos) and observed their behavior while the collars attempted to obtain locations. Bear behavior influenced indices of GPS signal attenuation, the angle of the GPS antenna to the horizon, and collar height above the ground, but because bears sometimes rotate their collars, antenna angle varied within a behavior, particularly when collars fit snugly. We used a model selection approach to evaluate the influence of the angle of the GPS antenna to the horizon, collar height above the ground, and bear behavior on fix success. The model with both antenna angle and collar height was most parsimonious. We recommend fitting GPS collars such that the GPS antenna is opposite the battery pack (i.e., oriented up) for greatest fix success. Because collars sometimes rotate, sensors recording the antenna's angle to the horizon and bear height would help researchers model missed fixes related to signal attenuation caused by behavior. Although captive bear behavior may differ from wild bears, we provide a first look at the relative influences of antenna angle, antenna height, and bear behavior. When antenna angle and height information is not available, using activity sensors and bear movement rates to identify resting behavior should be considered to reduce bias in habitat analyses of GPS collar data.
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Vol. 24 • No. 2