Geolocator deployment reduces return rate, alters selection, and impacts demography in a small songbird.

Conor C Taff,Gunnar R Kramer,Henry M Streby,Corey R Freeman-Gallant,Sébastien Descamps

doi:10.1371/journal.pone.0207783

Conor C Taff, Gunnar R Kramer + Show 3 more

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https://doi.org/10.1371/journal.pone.0207783

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Journal: PloS one	Publication Date: Dec 12, 2018
Citations: 5	License type: CC BY 4.0

Affiliation: University of Toledo, Cornell University, Skidmore College

Abstract

In the past few years, miniature light-level geolocators have been developed for tracking wild bird species that were previously too small to track during their full annual cycle. Geolocators offer an exciting opportunity to study the full annual cycle for many species. However, the potential detrimental effects of carrying geolocators are still poorly understood, especially for small-bodied birds. Here, we deployed light-level geolocators on common yellowthroat warblers (Geothlypis trichas). Over two years, we monitored return rates and neighborhood demography for 40 warblers carrying a geolocator and 20 reference birds that did not carry a geolocator. We compared the two groups with long-term data from 108 unmanipulated birds breeding at the same location in previous and subsequent years. Overall, we found that individuals carrying a geolocator were less likely to return to the study site in the following year (21% to 33% returned, depending on inclusion criteria) than either contemporaneous controls (55%) or long-term controls (55%). Among birds marked with geolocators, we also detected viability selection for greater wing length, whereas this pattern was not present in control birds. Finally, in each year after geolocator deployment, inexperienced breeders colonized vacant territories and this demographic effect persisted for two years after deployment. Sexual selection and ornamentation are strongly age-dependent in this system, and behavioral data collected after geolocator deployment is likely to differ systematically from natural conditions. Clearly geolocators will continue to be useful tools, but we suggest that future studies should carefully consider the potential for biased returns and the ecological validity of behavioral data collected from geolocator marked populations.

Highlights

Light-level geolocators and other miniaturized tracking devices offer an exciting opportunity to gain insight into aspects of the biology of small birds that have been difficult or impossible to study in the past [1]
Geolocators have been deployed on wild birds for ten years [2, 6], but within the last five years, the devices have become small enough to allow deployment on species weighing as little as 9 grams
We found that after attaching geolocators to common yellowthroats males were 60–78% less likely to return to our sites the following year

Summary

Introduction

Light-level geolocators and other miniaturized tracking devices offer an exciting opportunity to gain insight into aspects of the biology of small birds that have been difficult or impossible to study in the past [1]. Geolocators have been deployed on wild birds for ten years [2, 6], but within the last five years, the devices have become small enough to allow deployment on species weighing as little as 9 grams. These advances in tag design have led to studies on several species that had previously been studied primarily on the breeding grounds [5, 7,8,9,10]. Several studies have examined the effects of geolocators on return rates for larger birds [11,12,13,14], relatively few have looked at effects on return rates in the smallest birds that can currently be tracked with these devices (but see [7, 9, 15])

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Results

Conclusion