How much can we trust GPS wildlife tracking? An assessment in semi-free-ranging Crested Ibis Nipponia nippon

Abstract

GPS tracking has been increasingly used for wildlife studies in recent decades, but its performance has not been fully assessed, especially for newly developed lightweight transmitters. We assessed the performance of eight GPS transmitters developed in China by attaching them to Crested Ibises Nipponia nippon confined to two acclimation cages mimicking real habitats. We calculated the distance between GPS locations and the centroid of the cages as the positioning error, and used the 95% (95th percentile) positioning errors to define the accuracy. The positioning success averaged 92.0%, which is much higher than that of previous studies. Locations were not evenly distributed by Location Class (LC), with the LC A and B locations accounting for 88.7%. The observed 95% positioning error in the locations of LC A (9–39 m) and B (11–41 m) was quite accurate, while up to 6.9–8.8% of poor-quality locations were detected in LC C and D with >100 m or even >1, 000 m positioning error. Positioning success and accuracy were different between the test sites, probably due to the difference in vegetation structure. Thus, we argue that the tested transmitters could provide a large proportion of high-quality data for fine-scale studies, and a number of poor-quality locations that need attention. We suggest that the HPOD (horizontal dilution of precision) or PDOP (positional dilution of precision) be reported instead of the LC as a measurement of location accuracy for each location to ensure identification and filtering of implausible locations.

Gps Telemetry and Home Range of the White-Backed Woodpecker Dendrocopos leucotos: Results of the First Experience

“…Recent technological advances have made possible the development of lightweight GPS-tagging devices for small-size birds (see review in Liu et al 2018). Our results demonstrate that miniaturized GPS-tags of 3.4 g are suitable for tracking adults of the forest specialist Lilford Woodpecker.…”

“…The filtering criterion adopted (HDOP < 5) further reduced the effective number of fixes used for home range estimation, but not as much as expected under a dense canopy forest (Recio et al 2011). The proportion of accurate fixes (76%) was indeed as high as observed by Liu et al (2018) under experimental conditions, which suggests that the filtering criterion adopted was not too restrictive.…”

“…Next, we estimated the location error of fixes on the basis of HDOP (horizontal dilution of precision) recorded by the GPS. HDOP is a measure of the satellite geometry constellation that is widely used in wildlife tracking studies for filtering implausible fixes (Recio et al 2011, Silva et al 2017, Liu et al 2018. The greater the value of HDOP, the lower the constellation geometry, and hence the lower possible accuracy of a given location (Liu et al 2018).…”

“…HDOP is a measure of the satellite geometry constellation that is widely used in wildlife tracking studies for filtering implausible fixes (Recio et al 2011, Silva et al 2017, Liu et al 2018. The greater the value of HDOP, the lower the constellation geometry, and hence the lower possible accuracy of a given location (Liu et al 2018). We filtered out fixes with a HDOP value > 5, which according to the manufacturer's information and field tests carried out by ourselves with three emitters prior to deployment is equivalent to a location error lower than 20 m.…”

Animal Movement Prediction Based on Predictive Recurrent Neural Network

“…Despite the high quality of tracking data, GPS location accuracy and positioning success (ratio between the observed and expected number of locations) are negatively influenced by a number of factors, including the terrestrial atmosphere, satellite constellation, environment of the transmitters (habitat, topography, and weather), and behavior pattern and movement intensity of the tagged animal [29]. When analyzing animal trajectories, lack of observation or erroneous geo records lead to inaccurate results.…”