Influence of individual biological traits on GPS fix-loss errors in wild bird tracking

Ruth García-Jiménez,Antoni Margalida,Juan M Pérez-García

doi:10.1038/s41598-020-76455-x

Abstract

In recent decades, global positioning system (GPS) location data and satellite telemetry systems for data transmission have become fundamental in the study of basic ecological traits in wildlife biology. Evaluating GPS location errors is essential in assessing detailed information about the behaviour of an animal species such as migration, habitat selection, species distribution or foraging strategy. While many studies of the influence of environmental and technical factors on the fix errors of solar-powered GPS transmitters have been published, few studies have focussed on the performance of GPS systems in relation to a species’ biological traits. Here, we evaluate the possible effects of the biological traits of a large raptor on the frequency of lost fixes—the fix-loss rate (FLR). We analysed 95,686 records obtained from 20 Bearded Vultures Gypaetus barbatus tracked with 17 solar-powered satellite transmitters in the Pyrenees (Spain, France and Andorra), between 2006 and 2019 to evaluate the influence of biological, technical, and environmental factors on the fix-loss rate of transmitters. We show that combined effects of technical factors and the biological traits of birds explained 23% of the deviance observed. As expected, the transmitter usage time significantly increased errors in the fix-loss rate, although the flight activity of birds revealed an unexpected trade-off: the greater the proportion of fixes recorded from perched birds, the lower the FLR. This finding seems related with the fact that territorial and breeding birds spend significantly more time flying than non-territorial individuals. The fix success rate is apparently due to the interactions between a complex of factors. Non-territorial adults and subadults, males, and breeding individuals showed a significantly lower FLR than juveniles-immatures females, territorial birds or non-breeding individuals. Animal telemetry tracking studies should include error analyses before reaching any ecological conclusions or hypotheses about spatial distribution.

Highlights

In recent decades, global positioning system (GPS) location data and satellite telemetry systems for data transmission have become fundamental in the study of basic ecological traits in wildlife biology
The endangered Bearded Vulture Gypaetus barbatus represents a good case study for assessing GPS fix-loss errors—measured in this study though the monthly fix-loss rate, FLR. This species inhabits rugged mountain landscapes that allows the evaluation of the influence of abrupt topography on GPS fix-loss
Five PTTs showed an FLR less than a 30%, seven showed FLRs of between 30 and 40%, one had an FLR of 48.2%, and the remaining five registered an FLR equal to or higher than 50% (Table 1)

Summary

Introduction

Global positioning system (GPS) location data and satellite telemetry systems for data transmission have become fundamental in the study of basic ecological traits in wildlife biology. Very little is known about how, or to what extent, individual biological traits such as sex, age, size, territorial or breeding status, and their associated behaviour and ecology may affect satellite connection, fix-loss and location a ccuracy[10,11,12,13] This kind of information is essential to properly interpret geolocation data and to draw useful conclusions regarding animal movement patterns or species behaviour. The raw data registered through GPS-Argos telemetry still suffer from errors and biases (e.g. fix rate bias, fix-loss errors and spatial location errors) that must be considered to avoid drawing incorrect conclusions and making the wrong management r ecommendations[13,15,18] These tracking problems are especially relevant for threatened species where reliable information is important for reintroduction projects and conservation plans. The species is being reintroduced in several European countries, and GPS transmitter monitoring is one of the main tools used by managers and conservationists to assess its habitat use and reintroduction success[22]

Methods

Results

Conclusion