Impact of miniaturized geolocators on barn swallowHirundo rusticafitness traits

Abstract

Miniaturized light‐level geolocators may revolutionise the study of avian migration. However, there are increasing concerns that they might negatively affect fitness. We investigated the impact of two miniaturized geolocator models (SOI‐GDL2.10, deployed in 2010, and SOI‐GDL2.11, deployed in 2011) on fitness traits of the barn swallow Hirundo rustica, one of the smallest migratory species to which geolocators have been applied to date. The 2011 model was lighter (by 0.09 g) and had a shorter light stalk compared to the 2010 model. Using data from 640 geolocator and 399 control individuals from three geographical populations, we found that geolocators reduced annual survival probabilities (control birds: 0.19–0.63; geolocator birds: 0.08–0.40, depending on year, sex, and how birds that lost the device were considered), with more markedly negative effects on females equipped with the 2010 model. In addition, among birds equipped with the 2010 model, onset of reproduction in the subsequent year was delayed (by 12 d) and females laid smaller first clutches (by 1.5 eggs, i.e. a 30% reduction) compared to controls. Equipping parents with geolocators while they were attending their brood did not affect nestling body mass or fledging success. A reduction of geolocator weight and drag by shortening the light stalk slightly enhanced the survival of females but not that of males, and mitigated the negative carry‐over effects on subsequent reproduction. Our study shows that geolocators can have a negative impact on survival and reproduction, and that even minor differences in weight and drag can make the difference. We suggest that studies aiming at deploying geolocators or other year‐round tagging devices should be preceded by pilot experiments to test for fitness effects.

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

“…Impairment of manoeuvrability from the effect of geolocators could be reflected in reduced aerial foraging efficiency, and hence reduced chick-feeding ability. Scandolara et al (2014) recently reported that applying geolocators (a model similar to the one we deployed in this study) to Barn Swallow parents showed no negative impacts on their subsequent reproductive performance, estimated as nestlings' body mass or fledging success. In a similar study, Gómez et al (2014) showed that equipping Tree Swallows (Tachycineta bicolor) with geolocators while they were attending their broods had no significant negative impact on their nestling feeding rate, nestling's growth rate or fledging success.…”

“…This is believed to result in a reduced flight range and increased energetic costs of sustained flight, which could hamper fitness (Bowlin et al 2010). Scandolara et al (2014) reported a significantly lower return rate of geolocator birds compared to controls after migration, an effect which was mostly evident among females. Moreover, geolocator birds showed delayed reproduction and smaller clutch sizes (Scandolara et al 2014).…”

“…We decided to apply geolocators on males only in order to reduce the negative effect of geolocators on the survival of sample study birds, as geolocators have proven to be more harmful to female than male Barn Swallows in terms of survival (Scandolara et al 2014). We applied miniaturized Swiss Ornithological Institute (Sempach, Switzerland) geolocators with a mean weight of 0.64 g, including harness (0.02 SD; see also Scandolara et al 2014). The weight of geolocators constituted 3.2-4.1 % of body mass of a male Barn Swallow upon capture (mean = 3.5 %), and their light-sensing stalks protruded ca.…”

“…We fitted these tags using a leg-loop harness (Rappole and Tipton 1991) made of an elastic silicone rubber mixture (MVQ 60 shore A). We used leg-loop harnesses with a diameter of 28 mm and a thickness of 1.25 mm (Scandolara et al 2014). This caudal position of geolocators was conducive to minimizing the aerodynamic drag they may cause (Bowlin et al 2010).…”

“…Because of the ethical, conservation and scientific implications, the deployment of such devices should therefore be associated to the assessment of their impact on birds (e.g. Arlt et al 2013;Scandolara et al 2014;Peterson et al 2015).…”