Connectivity of wintering and breeding Western Grebe (A. occidentalis) populations: An application of genetic markers

This Project is led by Diana Humple. This project is supported by the SeaDoc Society through the UC Extension.

Coastally wintering populations of Western Grebes (Aechmophorus occidentalis) in Washington and British Columbia are in evident decline. The majority of Western Grebes winter in nearshore marine waters from Baja California to British Columbia and breed inland at colonies on suitable lakes throughout much of western North America. Threats to their population occur on both breeding and wintering areas, and include high vulnerability to oil spills and heavy disturbance on many breeding colonies. Much concern has been raised about this species lately, and a Western Grebe working group was recently formed for precisely this reason. Increasing our understanding of metapopulation dynamics and source populations in this species is critical. Determining the linkages between wintering and breeding birds would be an important step in identifying the factors limiting their populations, and would result in appropriate management actions. In regions where population declines are observed, increased understanding of these linkages might aid in determining the causes of the declines and potentially lead to directed management actions that could curb or reverse these trends.

We will use genetic markers called microsatellites to differentiate breeding populations and determine the genetic associations among breeding and wintering sites. We previously received funding from the SeaDoc Society for the initial development of genetic markers for the species, a project currently underway and which will be completed shortly. The application of these genetic markers has the potential to produce information that is greatly needed to understand factors repsonsible for declines in Western and Clark’s Grebes. Additionally we have collected numerous samples, some directly at breeding colonies, and many through collaboration with other researchers, beached bird surveyors, museums, and rehabilitation centers.

The primary objective of our study is to examine patterns of genetic connectivity between coastally wintering Western Grebes and corresponding inland breeding populations. To this end, we propose to continue to collect genetic samples from wintering and especially breeding sites to complete geographic coverage of their range. Many of our samples, especially for wintering birds, will be collected through collaboration with researchers, beached bird surveyors, and rehabilitation centers. In addition, we would begin genetic analyses of population structure with a subset of the samples, which we have already acquired from ten regions. We will use standard population genetic measures of genetic distance, analysis of molecular variance, multi-variate analysis, assignment tests, and likelihood algorithms to evaluate the genetic structure among sample sites. As breeding populations are identified based on genetic differentiation, we will evaluate the genetic diversity for each breeding area and test for evidence of population declines using an M-ratio test. We will also conduct further analysis of banding recovery data already provided by the federal Bird Banding Lab in order to identify possible direct measures of movements between populations.