Effects of geolocators on hatching success, return rates, breeding movements, and change in body mass in 16 species of Arctic-breeding shorebirds (original) (raw)
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Ornis Fennica
Small light-level geolocators have revolutionized research on avian migration and breeding ecology. However, proper evaluations of their impact on the life history of individuals compared to control individuals that experience the same conditions are still rare. Geolocator effects may be species specific and depend on the type of mounting, sex and size of individuals. While geolocators have been used extensively and without negative effects on large shorebirds, relatively little is known about their effects on small shore-birds, especially of those attached on leg-flags. We mounted 30 leg-flagged geolocators (15 on each sex) on Southern Dunlins (Calidris alpina schinzii) – a small, long distance migratory shorebird (40–52 grams) – and examined the effects of geolocators on return rates and reproduction through comparisons to a control group. The whole attachment weighed 1.5–2% of an individual's body mass. We found no evidence of lowered return rates. Out of 30 birds, 22 (73%) r...
Effects of geolocators on reproductive performance and annual return rates of a migratory songbird
Journal of Ornithology, 2013
Our understanding of the annual life-cycle movements of small migratory birds has advanced rapidly with the advent of light-weight geographical positioning devices (i.e., geolocators), yet the effects of geolocators on reproduction and survival have not been adequately quantified. We tested for impacts of attaching a 1-g geolocator (using a harness around the legs and back, anterior to the tail) to adult Tree Swallows (Tachycineta bicolor) on parental feeding behavior, nestling growth and size, fledging success, and return rates between 2011 and 2012. At one breeding site, we compared feeding visits, nestling growth, and nestling size between paired nest boxes where one parent was marked at the ‘geolocator’ box with a ‘control’ nest box where neither parent was marked. We detected no differences between geolocator and control nests in either the frequency of feeding visits to nestlings or the amount of time spent at nests. Birds marked with geolocators fed nestlings as frequently as their unmarked mates. Likewise, nestlings raised at geolocator nests grew at similar rates to those at control nests, and had similar structural size and body mass at fledging. At three widely-separated sites across the Tree Swallow breeding range in Canada, we also found that fledging success was similar for geolocator and control nests. Although we found no evidence for short-term negative impacts of geolocators, the return rates of geolocator-marked Tree Swallows tended to be significantly lower than those of unmarked control birds. Thus, we found little evidence for short-term impacts of geolocators on reproduction but our study does suggest that long-term impacts of geolocators could be manifested in terms of lower survival, higher emigration rates, or lower breeding propensity.
Data from location logging tags have revolutionised our understanding of migration ecology, but methods of tagging that do not compromise survival need to be identified. We compared resighting rates for 156 geolocator-tagged and 316 colour ringed-only whinchats on their African wintering grounds after migration to and from eastern Europe in two separate years. We experimentally varied both light stalk length (0, 5 and 10 mm) and harness material (elastic or non-elastic nylon braid tied on, leg-loop 'Rappole' harnesses) in the second year using a reasonably balanced design (all tags in the first year used an elastic harness and 10 mm light stalk). Tags weighed 0.63 g (0.01 SE), representing 4.1% of average body mass. There was no overall significant reduction in between-year resighting rate (our proxy for survival) comparing tagged and untagged birds in either year. When comparing within tagged birds, however, using a tied harness significantly reduced resighting rate by 53% on average compared to using an elastic harness (in all models), but stalk length effects were not statistically significant in any model considered. There was no strong evidence that the fit (relative tightness) or added tag mass affected survival, although tied tags were fitted more tightly later in the study, and birds fitted with tied tags later may have had lower survival. Overall, on a precautionary principle, deploying tags with non-elastic tied harnesses should be avoided because the necessary fit, so as not to reduce survival, is time-consuming to achieve and does not necessarily improve with experience. Geolocator tags of the recommended percentage of body mass fitted with elastic leg-loop harnesses and with short light stalks can be used without survival effects in small long-distance migrant birds.