Fix Success and Accuracy of Global Positioning System Collars in Old‐Growth Temperate Coniferous Forests

Abstract

Global Positioning System (GPS) telemetry is used extensively to study animal distribution and resource selection patterns but is susceptible to biases resulting from data omission and spatial inaccuracies. These data errors may cause misinterpretation of wildlife habitat selection or spatial use patterns. We used both stationary test collars and collared free‐ranging American black bears (Ursus americanus) to quantify systemic data loss and location error of GPS telemetry in mountainous, old‐growth temperate forests of Olympic National Park, Washington, USA. We developed predictive models of environmental factors that influence the probability of obtaining GPS locations and evaluated the ability of weighting factors derived from these models to mitigate data omission biases from collared bears. We also examined the effects of microhabitat on collar fix success rate and examined collar accuracy as related to elevation changes between successive fixes. The probability of collars successfully obtaining location fixes was positively associated with elevation and unobstructed satellite view and was negatively affected by the interaction of overstory canopy and satellite view. Test collars were 33% more successful at acquiring fixes than those on bears. Fix success rates of collared bears varied seasonally and diurnally. Application of weighting factors to individual collared bear fixes recouped only 6% of lost data and failed to reduce seasonal or diurnal variation in fix success, suggesting that variables not included in our model contributed to data loss. Test collars placed to mimic bear bedding sites received 16% fewer fixes than randomly placed collars, indicating that microhabitat selection may contribute to data loss for wildlife equipped with GPS collars. Horizontal collar errors of >800 m occurred when elevation changes between successive fixes were >400 m. We conclude that significant limitations remain in accounting for data loss and error inherent in using GPS telemetry in coniferous forest ecosystems and that, at present, resource selection patterns of large mammals derived from GPS telemetry should be interpreted cautiously.

GPS Bias Correction and Habitat Selection by Mountain Goats

“…The challenge remains however, to demonstrate correction of habitat coefficients from real-world data. When employing the stationary collar sampling design, the time interval should match those of collars deployed on wildlife [12] and the influence of animal behavior on P ACQ needs to be addressed for the specific species of interest [11,49]. The decision to pursue a bias correction model in future studies by other researchers shouldn't be ignored, but carefully consider in light of our results.…”

“…These two data sets enabled us to examine the relationship between GPS performance and site conditions at two spatial resolutions. We derived topographic predictor variables from a 10 m digital elevation model (DEM) masked to the spatial extent of the IVMP data and resampled to 25 m. We created slope, aspect, sky visibility [11,[23][24][25]] data layers.…”

“…Although GPS telemetry has increased the number of locations collected on an individual animal by orders of magnitude over traditional radio tracking, GPS receivers may fail to acquire a position under forest canopies or when topography blocks satellite signals [7]. Consequently, data from GPS-collared wildlife is biased toward areas of favorable GPS reception [8][9][10][11][12]. We expected the GPS bias problem to coincide with habitats typical of those used by mountain goats during the winter.…”

Tracking fish using ‘buoy-based’ GPS telemetry

“…The 'quality' of the fixes was also good, with values of HDOP and number of satellites per fix falling well within the ranges of values of GPDs used for tracking terrestrial animals (e.g. Hebblewhite et al 2007, Sager-Fradkin et al 2007, Hansen & Riggs 2008. Compared with acoustic tracking methods, the GPDs performed well, in terms of both the spatial accuracy and the number of fixes obtained within a given time (e.g.…”

Home range sizes and space use of African elephants (Loxodonta africana) in the Southern Kenya and Northern Tanzania borderland landscape

“…Dataset that had GPS errors like missing coordinates were removed from the dataset before analysis. The causes of GPS errors are: Temporal malfunction of the GPS collars (Gala, 2014), canopy cover (Jiang et al, 2008;Sager-Fradkin et al, 2007;Heard et al, 2008), topography (terrain and slope; Hebblewhite et al, 2007;Frair et al, 2004) and collar orientation (Sager-Fradkin et al, 2007;Heard et al, 2008;Moen et al, 1996;Frair et al, 2010). The data available for analysis after screening ranged between 58 and 92% (Table 2), which is within acceptable range to characterize wildlife movement patterns and make sound inference (Frair et al, 2010).…”