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

Abstract

Tracking devices are used in a broad range of species for a broad range of questions, but their potential effects on study species are debated. Outcomes of earlier studies on effects are equivocal: some studies find negative effects on behaviour and life history traits, while others do not. Contrasting results might be due to low sample sizes, temporal scale (no repetition of the study over multiple years) and a limited range of response variables considered. We investigated effects of geolocators on a range of response variables: body condition, physiological states, reproductive performance and, ultimately, annual apparent survival for a medium-sized Palaearctic-African long-distance migrant, the Eurasian Hoopoe Upupa epops, for the combined study period (2009)(2010)(2011)(2012)(2013)(2014) and for individual years. We investigated response variables 1 year after deployment of the geolocator and found no differences in body condition, physiological states and several components of reproductive performance between individuals with and without geolocators when data were combined. Also, apparent annual survival did not differ between geolocator and control birds. We did, however, find effects in some years possibly related to environmental stochasticity or chance events due to lower sample sizes. We argue that results of studies on the effects of tracking devices should be interpreted and generalized with great caution and suggest that future studies on the effects of tracking devices are conducted over multiple years. Future studies should also apply capture-recapture models to estimate survival, rather than focus solely on return rates.

Context‐dependent effects of radio transmitter attachment on a small passerine

“…In addition to our study, there is evidence that light devices (< 3% body weight) and even flipper‐bands on penguins can have significant effects in some years but not others (Bro et al , Saraux et al , Wilson et al , van Wijk et al ). We cannot infer from our study the maximum transmitter weight that great tits or other similar songbird parents can carry without an increase in desertion rates, only that it is below 7.3% body weight under poor conditions, but at least 7.3% under good conditions.…”

Cold spell en route delays spring arrival and decreases apparent survival in a long-distance migratory songbird

“…However the recent evidence is ambiguous, with a number of studies showing no apparent effect on return rates of the tagged birds [e.g. 31, 32], while some report negative influence [33] including delayed breeding site arrival time and decreased breeding success in the year following the geolocator deployment [34]. Furthermore, the differences in return rates between tagged and control birds seem to vary among sites within the same species [24, 35].…”

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

“…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). These contrasting findings suggest that species-specific traits and features of the devices can determine large variation in the size of the detrimental effects of tracking devices.…”

“…because of longer manipulation or because they suffered more stress by carrying a device, so this parameter should be estimated separately for either group of birds. In such cases, mark-recapture models (White and Burnham 1999), which have been designed specifically to estimate both survival and recapture probabilities simultaneously (van Wijk et al 2016), may be applied. However, markrecapture models have been seldom used in these studies, probably because they require data from at least three consecutive recapture occasions (i.e.…”