Effects of geolocators on reproductive performance and annual return rates of a migratory songbird

Abstract

Our understanding of the annual life-cycle movements of small migratory birds has 1 advanced rapidly with the advent of light-weight geographical positioning devices (i.e., 2 geolocators), yet the effects of geolocators on reproduction and survival have not been 3 adequately quantified. We tested for impacts of attaching a 1g geolocator (using a harness 4 around the legs and back, anterior to the tail) to adult Tree Swallows (Tachycineta bicolor) on 5 parental feeding behaviour, nestling growth and size, fledging success, and return rates 6 between 2011-2012. At one breeding site, we compared feeding visits, nestling growth, and 7 nestling size between paired nest boxes where one parent was marked at the 'geolocator' box 8 with a 'control' nest box where neither parent was marked. We detected no differences 9 between geolocator and control nests in either the frequency of feeding visits to nestlings or 10 the amount of time spent at nests. Birds marked with geolocators fed nestlings as frequently 11 as their unmarked mates. Likewise, nestlings raised at geolocator nests grew at similar rates 12 to those at control nests, and had similar structural size and body mass at fledging. At three 13 widely-separated sites across the Tree Swallow breeding range in Canada, we also found that 14 fledging success was similar for geolocator and control nests. Although we found no 15 evidence for short-term negative impacts of geolocators, the return rates of geolocator-16 marked swallows tended to be significantly lower than those of unmarked control birds. 17Thus, we found little evidence for short-term impacts of geolocators on reproduction but our 18 study does suggest that long-term impacts of geolocators could be manifested in terms of 19 lower survival, higher emigration rates, or lower breeding propensity.

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

“…Significantly lower return rates of Tree Swallows equipped with geolocators compared to control birds were shown also by Gómez et al (2014). The lack of statistically significant negative effects of geolocators on short-term flight performance and chick-rearing ability suggests that the negative fitness effects of geolocator deployment reported by Gómez et al (2014) and Scandolara et al (2014) are related to processes acting largely outside the breeding season. These may be associated with increased drag during sustained flight (Bowlin et al 2010) and/or impaired pre-migratory fattening from wearing a leg-loop harness.…”

“…Moreover, geolocator birds showed delayed reproduction and smaller clutch sizes (Scandolara et al 2014). Significantly lower return rates of Tree Swallows equipped with geolocators compared to control birds were shown also by Gómez et al (2014). The lack of statistically significant negative effects of geolocators on short-term flight performance and chick-rearing ability suggests that the negative fitness effects of geolocator deployment reported by Gómez et al (2014) and Scandolara et al (2014) are related to processes acting largely outside the breeding season.…”

“…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. Our finding of no statistically significant negative impact of geolocators on the short-term flight performance of male Barn Swallows corroborates these findings.…”

Migratory connectivity of Golden-crowned Sparrows from two wintering regions in California

“…To date, a number of geolocator studies have reported no statistical difference in return rates between tagged and control birds [12,24,39,40], but see [39,41,42]. Negative effects to breeding have been found in some studies, including greater fledgling mortality the year after tagging [43], later egg laying and lower nest success [41], although this was not the case for all species [42]. We recommend continued evaluation of tag effects as studies increase their sample sizes, and as more species with different life histories are fitted with geolocators.…”

No detectable effects of lightweight geolocators on a Palaearctic-African long-distance migrant

“…Even though it is commonly acknowledged that effects can occur, evidence is equivocal for many investigated traits such as body condition (Adams et al 2009; Barron et al 2010), physiological state (Barron et al 2010;Quillfeldt et al 2012), components of reproductive performance like onset of breeding (Arlt et al 2013;Quillfeldt et al 2012) or fledgling mass (Ackerman et al 2004;Quillfeldt et al 2012), and also survival, usually investigated in the form of return rates (Arlt et al 2013; Barron et al 2010;Costantini and Møller 2013;Gómez et al 2014;Phillips et al 2003;Rodríguez et al 2009;Scandolara et al 2014;Townsend et al 2012). Because these traits may be differently affected by the tracking device, it is difficult to draw general conclusions on device effects when only one or a few traits are studied.…”