Effects of Antenna Orientation and Vegetation on Global Positioning System Telemetry Collar Performance

Use of global positioning system (GPS) collars to improve our understanding of bear movements and habitat use has increased markedly in the last 10 years. Habitat use has been better defined using this technology, but variation in acquisition rates across covertypes and with varying antenna orientation could bias results. I assessed the effects of vegetative habitat characteristics and antenna orientation on percent of successful fixes and 3-dimensional (3D) fixes for GPS collars designed for Ursus americanus (American Black Bear) in Michigan during April-July, 2001-2002. I placed collars in 5 habitats with varying tree density, diameter, and canopy cover and also in an unobstructed area with antennas oriented 0-90 degrees from horizontal. Basal area was the only habitat parameter measured that influenced fix success; the correlation was negative. Percent of successful locations obtained in the open area decreased as antenna orientation increased away from the vertical position. Habitat characteristics and antenna orientation appeared to influence the percent of total fixes and 3 D fixes obtained, which could have adverse effects on accuracy. Thus, bear or other wildlife use of certain covertypes and behavior (e.g., sleeping) can reduce GPS collar acquisition rates. Variation in acquisition rates among covertypes and antenna orientation warrants consideration for development of correction factors based on habitats encountered and animal behavior.