An experimental evaluation of the effects of geolocator design and attachment method on between‐year survival on whinchats Saxicola rubetra

Abstract

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.

A minimum‐impact, flexible tool to study vocal communication of small animals with precise individual‐level resolution

“…In small animals, particularly in birds, devices need to be light weight and ergonomic to prevent constraints on locomotion and other behaviours (Hooge 1991;Barron, Brawn & Weatherhead 2010;Vandenabeele et al 2012Vandenabeele et al , 2014Blackburn et al 2016). So far, the effects on vocal behaviour in addition to locomotor activity were reported only once (Anisimov et al 2014), and, compared to in our study, ceased after a longer period of time.…”

“…, ; Blackburn et al . ). So far, the effects on vocal behaviour in addition to locomotor activity were reported only once (Anisimov et al .…”

Miniaturization of biologgers is not alleviating the 5% rule

“…(). The earliest deployments began in 1968 (Johnson & Berner, ) and the latest began in 2013 (Blackburn et al., ; Chivers, Hatch, & Elliott, ). Species names were checked against the taxonomic reference associated with the online tree of life (Hinchliff et al., ) using the rotl package (Michonneau, Brown, & Winter, ) of r (R Core Team ).…”

Cyprus wheatears Oenanthe cypriaca likely reach sub‐Saharan African wintering grounds in a single migratory flight

“…Tags were fitted using the harness design and methodology in Blackburn et al (). In summary: we deployed 24 geolocators of model ML6740 developed by the British Antarctic Survey (BAS), 13 with a 10 mm (0.64, 0.02 SE g) and 11 with 5 mm (0.57, 0.01 SE g) light‐stalk positioned at a fixed angle of 45°.…”

“…Here we present the migration tracks and wintering locations of the first six adult Cyprus wheatears to be tracked with geolocators. We first established that the tagging methodology itself did not affect survival (Blackburn et al ) and so that we could be confident that our results came from a representative sample of returning birds. We then predicted that: 1) there would be no or very short stop‐overs during migration; 2) individuals would have a single wintering site; 3) spread of individuals on the non‐breeding ground will be at the large scale (> 1000 km).…”