Animal movement has profound implications for organisms’ survival, population dynamics, and conservation. Increasingly, movement behavior studies track animals using GPS technology, which has additional capabilities compared to traditional methods using radiotelemetry-based technologies. However, GPS tracking technology rarely is tested to see if its capabilities (e.g., higher sampling frequency and customizable sampling schedules) yield ecologically meaningful differences in results. To test this, we used GPS animal movement data to ask: How do sampling frequency and timing affect space use inferences for fox squirrels (Sciurus niger)? To investigate effects of sampling frequency, we sampled our GPS dataset (n = 35 squirrels) to emulate datasets with lower sampling frequencies of fixes. To investigate effects of sampling timing, for a given sampling frequency (e.g., 3 fixes per 24-hr period clustered around mid-day as a baseline), we created datasets with the timing of fixes shifted earlier or later in the day and that varied the proportion of the 24-hour period covered by fixes (e.g., an 8-hour vs. a 16-hour period). For all datasets, we calculated utilization distributions with Brownian bridge kernels to estimate 95% and 50% home range areas. For the sampling frequency datasets, we also calculated 95% and 50% home-range overlap between animals.
Results/Conclusions
With lower sampling frequency, home range areas generally increased. However, sampling frequency had a greater effect on 50% home range areas, which were approximately 3 times larger when calculated from the lowest sampling frequency compared to the highest sampling frequency dataset. Home-range overlap between animals generally increased with lower sampling frequency, although this pattern was not consistent. As the timing of fixes shifted away from mid-day (either earlier or later), we often, but not consistently, found 95% home range areas increased and 50% home range areas decreased. This pattern also occurred as the proportion of the day covered by fixes increased. Sampling frequency and timing can substantially alter estimates of home range areas, and lower sampling frequency tended to provide larger estimates of home range area and home-range overlap. However, sampling effects on animal space use inferences may vary among individuals and populations. Customizable sampling schedules may provide unique information about spatial overlap among individuals, strengthening the ability to accurately detect and measure potential conspecific interactions. We encourage scientists to critically consider goals when deciding if and how these potential differences in space use inferences due to sampling frequency and timing may affect understanding of ecological patterns and processes.