ORIGINAL PAPER What determines global positioning system fix success when monitoring free-ranging mouflon? Gilles Bourgoin & Mathieu Garel & Dominique Dubray & Daniel Maillard & Jean-Michel Gaillard Received: 25 October 2008 / Revised: 30 April 2009 / Accepted: 19 May 2009 / Published online: 5 June 2009 # Springer-Verlag 2009 Abstract We have assessed behavioural and environmen- tal factors influencing the success of global positioning system (GPS) fixes recorded from 15 collared free- ranging female Mediterranean mouflon (Ovis gmelini musimon x Ovis sp.). We have demonstrated that fix success was 8% lower in resting animals (0.81, 95% CI= 0.79–0.84) than in active animals (0.89, 95% CI=0.86– 0.91) at an average temperature (13.8°C), but was similar and relatively constant at lower temperatures. When temperatures increased above the average temperature, fix success strongly decreased in resting animals (0.44, 95% CI=0.36–0.52 at 30°C) as compared to active animals (0.76, 95% CI=0.65–0.85). These results probably in- volved behavioural changes in habitat use of mouflon, as temperature and activity strongly influence the use of cover in ungulates. We also found that the success of GPS fixes was influenced by habitat types, increasing from 0.76 to 0.93 (under average sky openness of 33%) along a continuum going from forested to open areas. After controlling for differences in vegetation, sky openness had a positive effect on fix success (from 0.76 to 0.97 in evergreen oak forest). Our approach based on free-ranging animals and using a robust interpolation procedure should provide biologists with a more reliable method to account for bias in GPS studies. Keywords Activity . Fix success . Global positioning system . Interpolation . Ovis gmelini musimon x Ovis sp. Introduction The use of global positioning system (GPS) collars has increasingly allowed biologists to collect a large quantity of accurate location data on animals over short time intervals and at large spatial scales. However, two main sources of error have been associated with GPS location data (D'Eon et al. 2002; Frair et al. 2004; Lewis et al. 2007): location inaccuracy and failure to locate. Location inaccuracy generally leads to ambiguous inference regarding habitat selection or to a misclassi- fication (Nams 1989; Visscher 2006; White and Garrott 1986). The magnitude of such biases depends on the degree of location error and on the scale of the landscape Eur J Wildl Res (2009) 55:603–613 DOI 10.1007/s10344-009-0284-1 Communicated by H. Kierdorf G. Bourgoin : M. Garel : J.-M. Gaillard Laboratoire de Biométrie et Biologie Evolutive, Université Lyon 1; CNRS, UMR5558, 43 boulevard du 11 novembre 1918, 69622 Villeurbanne, France G. Bourgoin Ecole Nationale Vétérinaire de Lyon, 1 av. Bourgelat, 69280 Marcy l’Etoile, France G. Bourgoin : M. Garel : D. Dubray : D. Maillard Office National de la Chasse et de la Faune Sauvage, Centre National d’Étude et de Recherche Appliquée sur la Faune de Montagne, 95 rue Pierre Flourens, BP 74267, 34098 Montpellier Cedex 05, France J.-M. Gaillard (*) Unité Mixte de Recherche no. 5558 “Laboratoire de Biométrie et Biologie Evolutive”, Bâtiment Grégoire Mendel, Université Claude Bernard Lyon 1, 43 Boulevard du 11 novembre 1918, 69622 Villeurbanne Cedex, France e-mail: gaillard@biomserv.univ-lyon1.fr