DOI: 10.5061/dryad.79cnp5hvj
title: Recording fine-scale movement of ground beetles by two methods: Potentials and methodological pitfalls

description: Movement trajectories are usually recorded as a sequence of discrete
 movement events described by two parameters: step length (distance) and
 turning angle (bearing). One of the most widespread methods to record the
 geocoordinates of each step is by a GPS device. Such devices have limited
 suitability for recording fine movements of species with low dispersal
 ability including flightless carabid beetles at small spatio-temporal
 scales. As an alternative, the distance-bearing approach can avoid the
 measurement error of GPS units since it uses directly measured distances
 and compass azimuths. As no quantification of measurement error between
 distance-bearing and GPS approaches exists so far, we generated artificial
 fine-scale trajectories and in addition radio-tracked living carabids in a
 temperate forest and recorded each movement step by both methods.
 Trajectories obtained from distance-bearing were compared to those
 obtained by a GPS device in terms of movement parameters. Consequently,
 both types of trajectories were segmented by state-switching modeling into
 two distinct movement stages typical for carabids: random walk and
 directed movement. We found that the measurement error of GPS compared to
 distance-bearing was 1.878 m (SEM = 0.181 m) for distances and 31.330°
 (SEM = 2.066°) for bearings. Moreover, these errors increased under dense
 forest canopy and rainy weather. Distance error did not change with
 increasing distance recorded by distance-bearing but bearings were
 significantly more sensitive to error at short distances. State-switching
 models showed only slight, not significant, differences in movement states
 between the two methods in favor of the random walk in the
 distance-bearing approach. However, the shape of the GPS-measured
 trajectories considerably differed from those recorded by distance-bearing
 caused especially by bearing error at short distances. Our study showed
 that distance-bearing could be more appropriate for recording movement
 steps not only of ground-dwelling beetles but also other small animals at
 fine spatio-temporal scales.
description: Datasets contain fine-scale trajectories and movement
 parameters collected by two different methods - distance-bearing and GPS
 device - in two different experiments. In the first experiment, we
 artificially generated trajectories mimicking the movement of ground
 beetles. In the second experiment, we radio-tracked six individuals of
 large ground beetle <em>Carabus coriaceus </em>in a managed
 temperate forest. For each experiment, we provide three
 csv files containing (1) dataset for linear mixed modeling (long/lat
 coordinates, distances, turning angles, and consequent measurement errors
 between recording methods), (2) trajectory dataset for Hidden Markov
 models (long/lat coordinates, track ID and time) and (3) dataset with
 decoded movement states by Viterbi algorithm and total length of a
 particular trajectory. Finally, an R script is also included where we
 describe in detail all used datasets and functions to get results provided
 in the final publication