Effects of geolocators on migratory birds: a meta-analysis

J. KOLECEK; D. BECKER; M. BURGESS; V. BRLÍK; N. COOPER; S.V. BARISIC; BRAVO, S.P.; B. CHUTNY; T. EMMENEGGER; PROCHÁZKA, P.; D. ARLT; E.J. BELDA; D. CIKOVIC; CUETO, V.R.

Congreso; XI Congress of the European Ornithologists Union; 2017

The use of tracking devices is currently one ofthe most rapidly developing approaches to study bird migration. The recentadvent of miniature light-level geolocators has led to a massive increase inthe number of studies employing these devices, especially in small species, whosedirect tracking was virtually impossible in the past. Although severalmeta-analytical and single-species primary studies have already examined theinfluence of geolocators on birds, their results are equivocal. Therefore, theevaluation of the effect of geolocators on birds clearly deserves moreattention. Here, we test for the effect of geolocators on passerine and near-passerinebirds by comparing return rates, body condition, phenology and breedingperformance between around 7000 geolocator-tagged and 9000 control birds frommore than 100 published studies. In addition, we include numerous unpublisheddata to evaluate a likely publication bias resulting from a lower probabilityof publishing studies where only few or no geolocators were retrieved. In the presentation,we will specifically examine the effects driven by species traits (such as bodysize and migration distance) and geolocator design. Our preliminary resultsshowed a slight negative effect of geolocators on thereturn rate. Moreover, the effect tended to be stronger in unpublished comparedwith published studies.We also revealed that theinformation essential for rigorous testing for geolocator effects is often missing.We thus strongly recommend establishing procedural control groups in future geolocatorstudies.