The need to account for Argos Doppler errors when estimating habitat use from Argos Doppler locations: evidence and solution

Abstract

Background. Due to the large errors in Argos Doppler location estimates, Argos-based satellite transmitter data are rarely used in studies of fine-scale habitat selection by animals. Novel state-space models (SSMs) for path reconstruction from animal movement data improve location estimates, delivering refined estimations of an animal’s most likely path and, also, re-estimating the uncertainties for each location. However, the SSM-refined uncertainties are still relatively large and the true locations of animals tracked with PTTs (Platform terminal transmitters) remain impossible to determine. We suggest an approach that uses the SSM-refined location uncertainties to quantify the probabilities of an animal’s occurrence in each habitat and infer which of the habitats it most likely visited.Methods. We test the performance of our approach against habitat use assays based on most likely locations from raw Argos Doppler estimates and Argos Doppler estimates refined with an SSM. For this, we combine a GPS tracking dataset (2214 location fixes) from one individual and an Argos-PTT tracking dataset (1708 location points) from 14 individual Continental Black-tailed Godwits (Limosa limosa limosa) breeding in agricultural grasslands in The Netherlands utilizing both simulations and empirical data to assess habitat use.Results. The approach that accounted for location uncertainties on top of a state-space model improved habitat assignments in the simulation study by 5% compared with only the SSM-refined Argos location points and by 23% compared with the raw Argos locations. We provide working code in R that can be reproduced for the analysis of habitat selection of animals followed with PTTs.Conclusions. Low-precision tracking data may be suitable to study habitat selection if location uncertainties are taken into account. The approach presented here has the potential to considerably improve the validity of such analyses, opening up new opportunities for the use of Argos Doppler data in analyses of habitat selection by animals. Since Argos Doppler location uncertainty parameters are required for the inference of the most likely used habitat, it is crucial that users acquire this information from Collecte Localisation Satellites (CLS) when initiating a new study.