Abstract
Modern studies of animal movement use the Global Positioning System (GPS) to estimate animals’ distance traveled. The temporal resolution of GPS fixes recorded should match those of the behavior of interest; otherwise estimates are likely to be inappropriate. Here, we investigate how different GPS sampling intervals affect estimated daily travel distances for wild chacma baboons (Papio ursinus). By subsampling GPS data collected at one fix per second for 143 daily travel distances (12 baboons over 11–12 days), we found that less frequent GPS fixes result in smaller estimated travel distances. Moving from a GPS frequency of one fix every second to one fix every 30 s resulted in a 33% reduction in estimated daily travel distance, while using hourly GPS fixes resulted in a 66% reduction. We then use the relationship we find between estimated travel distance and GPS sampling interval to recalculate published baboon daily travel distances and find that accounting for the predicted effect of sampling interval does not affect conclusions of previous comparative analyses. However, if short-interval or continuous GPS data—which are becoming more common in studies of primate movement ecology—are compared with historical (longer interval) GPS data in future work, controlling for sampling interval is necessary.
Highlights
Understanding how animals interact with and move through their environment enables researchers to better understand animal behavior, physiology, and ecology (Getz and Saltz 2008; Nathan et al 2008)
The estimated daily travel distance becomes progressively shorter with less frequent Global Positioning System (GPS) sampling because fewer GPS fixes do not properly capture the animal’s movement path (Fig. 1; ESM Video S1)
Less frequent GPS fixes result in a significant reduction in calculated daily travel distances (Fig. 2a; ESM Table S1; Video S1), and this reduction changes with GPS sampling interval according to a logarithmic function (proportion distance captured = 0.081ln(sampling interval) + 0.9682; r2 = 0.99; Fig. 2b and c)
Summary
Understanding how animals interact with and move through their environment enables researchers to better understand animal behavior, physiology, and ecology (Getz and Saltz 2008; Nathan et al 2008). Recording of GPS at intervals in time (rather than continuously) is common because it saves battery life and allows researchers to increase the time over which data are collected (Mitchell et al 2019; Ryan et al 2004; Sahraei et al 2017). This practice underestimates travel distance (McGavin et al 2018; Sennhenn-Reulen et al 2017). Extensive theoretical and empirical work has shown that the temporal resolution of GPS fixes needs to match those of the behavior of interest; otherwise estimates are likely to be inappropriate (Borger et al 2006; de Weerd et al 2015; Ganskopp and Johnson 2007; Johnson and Ganskopp 2008; McGavin et al 2018; Mills et al 2006; Mitchell et al 2019; Noonan et al 2019; Postlethwaite and Dennis 2013; Rowcliffe et al 2012; Sennhenn-Reulen et al 2017; Swain et al 2008; Tanferna et al 2012)
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