Weak genetic structure, shared nonbreeding areas, and extensive movement in a declining waterbird

Abstract

Understanding population mixing, movements, and connectivity of populations is an important first step towards effective conservation, particularly for long distance migrants that are suffering the greatest population declines, as this allows researchers to recognize how populations may face different risks throughout the annual cycle. We combined population genetic and individual tracking data to quantify the genetic structure and full-cycle movements of the declining North American Black Tern (Chlidonias niger surinamensis). A total of 147 genetic samples were collected from 9 breeding colonies across the range (Maine, Ontario, Michigan, Iowa, Wisconsin, Nebraska, Saskatchewan, and Oregon), and 19 light-level geolocators were recovered from 3 colonies (Ontario, Michigan, and Saskatchewan). Our results demonstrated weak genetic structure, and tracking data demonstrated the use of shared nonbreeding areas between central (Saskatchewan) and eastern (Ontario and Michigan) breeding populations. Our tracking data also provide novel evidence of long-distance breeding dispersal (~1,400 km between breeding locations across years) based on an individual tracked across multiple years, as well as short distance dispersal (~2.5–57 km) based on new recovery locations of 6 tracked individuals. Our results are consistent with the hypothesis that the shared use of nonbreeding areas influences physical condition, timing of departure, and subsequent reproductive timing in such a way as to facilitate dispersal across the breeding range and contribute to weak genetic structure among breeding populations. This study is the first to explore population genetics and migration of North American Black Terns. Extensive movement of individuals may pose a challenge from a conservation perspective as important areas and habitats throughout the annual cycle may be difficult to predict, and future studies should build on our work via extensive mark-resight effort using color bands, tracking individuals from more breeding sites, and examining carry-over effects to further investigate when in the annual cycle populations are most limited.

First‐ever satellite tracking of Black Terns (Chlidonias niger): Insights into home range and habitat selection

“…Capture methods are described in Shephard, Szczys, et al. (2023) and were part of a larger Black Tern banding effort throughout 2018–2022 (AEM, unpubl. data).…”

“…To ensure animal welfare guidelines were followed, we restricted tag deployments to individuals weighing more than 62 g. Note that at the time of this study, we were not aware of any satellite‐transmitting tags weighing <2 g, and we required tags to transmit their data (rather than collect and store data, i.e. archival tags such as light‐level geolocators or GPS loggers) due to the low site fidelity of the species (Heath et al., 2020; Shephard, Szczys, et al., 2023). Due to the high cost of tags and the limited availability of heavy‐enough individuals (only ~18% of individuals trapped at our study site weighed more than 62 g; AEM, unpubl.…”