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

Abstract

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.

Effect of light‐level geolocators on apparent survival of two highly aerial swift species

“…This conclusion is supported by results obtained on two species of swallows by Fairhurst et al (2015), who observed that, despite the clear negative effect of geolocators on return rate, returning individuals had similar stress levels (as measured by corticosterone levels in feathers) compared to control ones. Similar observations come from other studies on species where surviving geolocator birds seemed not to differ in migration or breeding performance compared to control birds (Rodriguez et al 2009, Peterson et al 2015, Matyjasiak et al 2016, van Wick et al 2016, Bell et al 2017, although geolocator birds suffered higher inter-annual mortality (Raybuck et al 2017). In a meta-analysis of the effect of geolocators on shorebirds, the simple presence of the device was the most significant factor affecting return rates and hatching success (Weiser et al 2016).…”

“…Similarly, northern weathears Oenanthe oenanthe equipped with geolocators had reduced survival, delayed migration and lower breeding success than control birds (Arlt et al 2013). However, barn swallows equipped with geolocators seemed to have the same flight performance as control individuals (Matyjasiak et al 2016). Small passerines equipped with geolocators may also perform similar to controls during breeding, but suffer increased inter-annual mortality (Raybuck et al 2017).…”

“…Since these devices can be miniaturized, they are currently widely used to track the annual migrations of even small-sized birds, including highly aerial species, like swifts (Stuchbury et al 2009, Åkesson et al 2012, 2016, Bairlein et al 2012, Bridge et al 2013, Kristensen et al 2013, Wellbrock et al 2017), but their impact on survival and flight performance remains to be fully explored (cf. Costantini and Møller 2013, Fairhurst et al 2015, Matyjasiak et al 2016, Raybuck et al 2017. Indeed, deployment of tracking devices such as geolocators on birds may entail negative effects, including, for instance, increased drag when the device is attached on the back of the bird, which may result in higher cost of transportation (Bowlin et al 2010, Pennycuick et al 2012.…”

“…Small passerines equipped with geolocators may also perform similar to controls during breeding, but suffer increased inter-annual mortality (Raybuck et al 2017). Overall, it seems established that smaller species and aerial foragers suffer the most from carrying geolocators (Fairhurst et al 2015; but see Matyjasiak et al 2016 for lack of short-term effects on flight performance). On the other hand, evidence exists that several small-sized, highly migratory species did not suffer detectable effects of carrying a geolocator (Pakanen et al 2015, Peterson et al 2015, Blackburn et al 2016, van Wijk et al 2016, Bell et al 2017).…”

Carrying a logger reduces escape flight speed in a passerine bird, but relative logger mass may be a misleading measure of this flight performance detriment

“…Because aerodynamic drag scales with the flight speed squared, the relative effect of weight and aerodynamic drag on flight efficiency varies with bird size, flight speed and streamlining of the tag (Bowlin et al., ; Pennycuick et al., ). Flight simulations for a range of small‐sized to medium‐sized birds showed that during migratory flights, where flight speeds are relatively high, aerodynamic drag has a larger detrimental effect on flight range than tag weight (Bowling et al, , but also see Mathjasiak, Rubolini, Romano, & Saino, ).…”