No short-term effects of geolocators on flight performance of an aerial insectivorous bird, the Barn Swallow (Hirundo rustica)

J Ornithol No short-term effects of geolocators on flight performance of an aerial insectivorous bird, the Barn Swallow (Hirundo rustica) Piotr Matyjasiak 0 1 2 Diego Rubolini 0 1 2 Maria Romano 0 1 2 Nicola Saino 0 1 2 0 Department of Biology and Environmental Sciences, Cardinal Stefan Wyszyn ́ski University in Warsaw , Wo ́ycickiego 1/3, PL-01-938, Warsaw , Poland 1 Communicated by A. Hedenstro ̈m 2 Department of Biosciences, University of Milan , Via Celoria 26, 20133 Milan , Italy Miniaturized light-level geolocators are becoming increasingly popular devices for the study of avian migration. However, the effects of these devices on birds' flight behaviour, and hence fitness components, are poorly known. We investigated the effect of miniaturized geolocators on flight performance of the Barn Swallow (Hirundo rustica), which may be especially susceptible to geolocator deployment as it is a small (*20 g), aerially insectivorous, long-distance migratory species. We tested whether miniaturized geolocators (*3.5 % of body mass) affected short-term flight performance traits of breeding males by comparing flight manoeuvrability, velocity and acceleration of geolocator-equipped versus control (handled only) birds in flight tunnels. We used a robust experimental design wherein the within-individual change in flight performance was compared between geolocatorequipped birds (after allowing for a period of acclimation) and control birds (that were also tested twice). We found no statistically significant evidence that short-term flight performance traits were affected by geolocator deployment. Here we discuss the implications of our findings for the deployment of geolocators in studies of migratory behaviour of small birds. Barn Swallow; Bird flight; External transmitter; Flight performance geolocator; Locomotion; Datalogger; Light-level - Geolokatoren haben keine kurzfristigen Auswirkungen auf die Flugleistung der in der Luft nach Insekten jagenden Rauchschwalbe Hirundo rustica Miniaturisierte Helldunkelgeolokatoren werden zunehmend f u¨r Untersuchungen des Vogelzugs eingesetzt. Die Auswirkungen dieser Gera¨te auf das Flugverhalten und somit auf gewisse Fitnesskomponenten der Vo¨ gel sind jedoch nur schlecht verstanden. Wir haben den Einfluss von miniaturisierten Geolokatoren auf die Flugleistung der Rauchschwalbe (Hirundo rustica) untersucht, die als kleiner (20 g), in der Luft nach Insekten jagender Langstreckenzieher besonders empfindlich auf den Einsatz von Geolokatoren reagieren ko¨nnte. Wir haben getestet, ob miniaturisierte Geolokatoren (3.5 % der K o¨rpermasse) die Flugleistung bru¨tender Ma¨nnchen kurzfristig beeinflussen. Hierfu¨r haben wir in Windtunneln die Mano¨vrierfa¨higkeit, Geschwindigkeit und Beschleunigung von mit Geolokatoren ausgestatteten V o¨geln und Kontrollvo¨geln, die lediglich gehandhabt wurden, verglichen. Wir haben ein robustes experimentelles Design verwendet, bei dem die individuelle A¨ nderung der Flugleistung von mit Geolokatoren ausge statteten V o¨geln (d.h. vor Anbringung des Gera¨ts und nachdem sich das Tier an das Gera¨t gew o¨hnt hatte) und Kontrollvo¨geln (die ebenfalls zweimal getestet wurden) verglichen wurde. Wir fanden keine statistisch signifikanten Hinweise darauf, dass die Flugleistung kurzfristig durch den Geolokatoreneinsatz beeintra¨chtigt wurde. Wir diskutieren die Folgen unserer Befunde fu¨r den Geolokatoreneinsatz in Studien des Zugverhaltens von Kleinvo¨geln. The development of miniaturized tracking devices has revolutionized the study of bird migration ecology, life-history strategies and conservation biology, as it has given researchers previously unattainable possibilities for investigating bird movements across broad spatial and temporal scales (Robinson et al. 2009; Bridge et al. 2011; Guilford et al. 2011). Increasingly popular and relatively cheap devices to track migrating birds on a continental scale are small (0.5–2 g) light-level dataloggers, or geolocators (Bridge et al. 2011, 2013; McKinnon et al. 2013). Geolocators record light levels over time, thereby allowing researchers to estimate the global position of the bird with an accuracy on the order of 102–103 km. Thanks to their small size and weight, geolocators have already been used to identify migration routes (including staging areas) and wintering areas of a number of small birds (up to 50 g) that are too small to carry satellite- or GPS/GSM-assisted tags (Stutchbury et al. 2009; A˚ kesson et al. 2012; Fraser et al. 2012; Schmaljohann et al. 2012a, b; Stach et al. 2012; Salewski et al. 2013; Hobson et al. 2015; Liechti et al. 2015). There has been increasing concern, however, that external tracking devices might be harmful in terms of viability or other life-history traits, that they might negatively affect bird flight performance, and that observed migratory behaviour may not reflect natural behaviour in the absence of geolocators (Barron et al. 2010; Costantini and Møller 2013), ther (...truncated)