There is a trade-off between the frequency of telemetry locations (fix interval) and battery life when using Global Positioning System (GPS) collars. In general, decreasing the fix interval lowers the effective battery life of the collar. However, the strong relationship between fix interval and movement metrics is often underappreciated. Mean movement rates, maximum movement rates, total distance estimates, and some screening algorithms change dramatically with different fix intervals, particularly for highly mobile animals such as caribou (Rangifer tarandus), and must be interpreted in relation to the fix interval used to collect the data. We used a multi-year, high-resolution data set from GPS collars with 2-hr fix intervals deployed on female caribou of the Teshekpuk Caribou Herd, Alaska, USA, 2006–2011, to examine the effect of fix interval on estimates of movement metrics. By calculating straight-line distances between locations taken at different fix intervals, we examined the rate of change in various metrics of caribou movement as a function of fix interval. We also calculated correction factors for different fix intervals, and examined how they changed seasonally. We fit an equation to the maximum rate of movement of caribou as a function of fix interval and used this equation in a modification of one screening algorithm to assess how it is affected by fix interval. We demonstrate how the maximum speed equation could potentially be used to derive a modified filter for telemetry data from highly mobile animals. Our results highlight the importance of incorporating fix-interval information into comparisons of movement metrics from different herds and time periods.
Prichard, A. K., D. A. Yokel, C. L. Rea, B. T. Person, and L. S. Parrett. 2014. The effect of frequency of telemetry locations on movement-rate calculations in arctic Caribou. Wildlife Society Bulletin 38:78–88. <DOI:10.1002/wsb.357>