Wing marker woes: a case study and meta-analysis of the impacts of wing and patagial tags

Abstract

The marking of individual birds has a long history in ornithology. This inexpensive and simple practice has been used to shed light on migration, behavior, and age-specific survival and recruitment. However, problems associated with markers and tags have often been overlooked. Wing tags have been used for over 40 years on frigatebirds, but their effects on this family of highly aerial seabirds have not been examined. Following higher than expected nest failure of treatment birds in the previous breeding season, we designed a study to test the impact of wing tagging and other standard capture and sampling methods on the nest success of Magnificent Frigatebirds (Fregata magnificens). Twelve nests were assigned to each of various band, measure, bleed, wing tag, and control treatments in the 2010/2011 breeding season on Barbuda, West Indies. We modeled nest fates using generalized linear models. Wing tags had a substantial negative effect on pre-fledging nest success, which was 42 % (10/24) for control nests, 39 % (14/36) for all non wing-tagged treatments, and 15 % (7/48) for wing-tagged treatments. We also conducted two meta-analyses, with different effect size calculations, to explore the general impact of wing and patagial tags on all birds. Our log odds ratio model showed a significant effect on survival and hatch and nest success, while our standardized mean difference model dealing largely with outcomes of behavioral, condition, and reproductive parameters (e.g., number of chicks and hatch date) showed no difference between marked and control birds. We consider possible mechanisms by which wing tags might contribute to lower nest success in frigatebirds, and propose that alternative markers be considered carefully before being applied to any species.