LB 5-35 - Weak genetic structure coupled with shared non-breeding areas and extensive movement in North American Black Terns

Background/Question/Methods:

Understanding the genetic structure and movements of avian populations is an important first step towards effective conservation, particularly for species that migrate over long distances, as this allows researchers to recognize how populations may face different risks throughout the annual cycle. In this study, we combined population genetic and individual tracking data (light-level geolocation) to quantify the genetic structure and full-cycle movement patterns of the declining North American Black Tern. A total of 147 genetic samples were collected from eight breeding colonies across the range (Maine, Ontario, Michigan, Iowa, Wisconsin, Nebraska, Saskatchewan, and Oregon), and a total of 17 geolocators were recovered with tracking data from individuals from three colonies (Ontario, Michigan, Saskatchewan).

Results/Conclusions:

Our results demonstrated weak genetic structure across the Black Tern breeding range, and tracking data demonstrated use of different migratory routes but shared use of non-breeding areas between central (Saskatchewan) and eastern (Ontario and Michigan) breeding populations. Our tracking data also provide novel evidence of long-distance breeding dispersal (~1400 km between breeding locations across years) based on an individual tracked across multiple years, as well as short distance dispersal (~2.5 km) based on new recovery locations of two tracked individuals. Our results are consistent with the hypothesis that the shared use of non-breeding areas can contribute to dispersal and gene flow among breeding populations of waterbirds. This study is the first to explore both population genetics and migration tracking for the North American Black Tern. The extensive movement of individuals may pose a challenge from a conservation perspective, and future studies should build on our work by examining carry-over effects to further investigate when in the annual cycle populations are most limited.