From Genes to GPS: for Endangered Light-Footed Ridgway’s Rails, Modern Tools Provide Insight into Population Health
With the help of genetics and wildlife tracking, USGS scientists are monitoring an at-risk bird population and assessing outcomes of a captive breeding program.
The light-footed Ridgway’s rail is a handsome but secretive waterbird that lives on tidal marshland fragments in southern California from Santa Barbara County south to Baja California, Mexico. A subspecies of Ridgway’s rail, they forage in shallow water and mudflats, taking cover in nearby vegetation when the tide comes in. They nest near the water’s edge in dense stands of cordgrass.
This bird is exceedingly rare. In 1970, the light-footed Ridgway’s rail was listed as federally endangered due to population declines primarily driven by habitat loss, degradation, and fragmentation. They also face diseases, contaminants, predation, and other disturbances. Efforts to protect and restore rail populations in the U.S. portion of the range have included habitat restoration and management, predator abatement, the deployment of artificial nesting and high tide refuge platforms, and the establishment of a captive breeding program.
Earlier results from annual surveys indicate that these efforts may have been effective: the number of breeding pairs detected on surveys has more than tripled between the 1980s and 2010s. However, detections have declined again more recently.
But population size alone doesn’t tell the whole story. Small and fragmented populations can have low levels of genetic diversity, which makes it harder for a population or species to withstand disease and changing environmental conditions. A population where individual birds disperse widely and move between marsh habitats will have more genetic diversity than one where the birds are more isolated, even if the total population size is the same.
USGS scientists from the Western Ecological Research Center (WERC) and the Idaho Cooperative Fish & Wildlife Research Unit are collaborating to get a more robust picture of population health for light-footed Ridgway’s rails than numbers alone can provide. This effort rests on two key tools: genetic analysis and GPS-tracking, which together illustrate genetic diversity and movement behavior within the subspecies.
WERC’s Dr. Amy Vandergast is leading the genetics effort, gathering and analyzing DNA from blood samples throughout the subspecies’ range to document the light-footed Ridgway’s rail’s genetic health. They will use the data they collect to understand how genetic diversity has changed over time, identify genes that may influence survival, and map rail family trees. The USGS team has started by trapping and sampling birds from Point Mugu to Tijuana Estuary. This year, they will expand the study to Baja California in a binational collaborative project. Partners include Terra Peninsular, Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California (CICESE), Pro Esteros, Universidad Autónoma de Baja California (UABC), Fauna de Noroeste (Fauno), the University of Idaho, the California Department of Fish and Wildlife, Southern California Coastal Water Research Project (SCCWRP) and the San Diego Natural History Museum.
Meanwhile, Dr. Courtney Conway’s team at the Idaho Cooperative Fish & Wildlife Research Unit are documenting seasonal movements and estimating survival of the light-footed Ridgway’s rails using solar-powered satellite GPS transmitters attached to wild-caught and captive-bred rails. These data will allow federal agencies, zoos, and private partners to improve the captive breeding program and annual releases of captive-reared rails into the wild. When these movement data are combined with Dr. Vandergast’s genetic data, researchers and managers have a much more complete picture of how captive-bred birds and their descendants are doing and what the future looks like for the subspecies as a whole.
The light-footed Ridgway’s rail is just one of many wildlife species and subspecies that USGS biologists are monitoring through a combination of modern tools like genetic sampling and GPS-tracking alongside more classic, long-term population surveys. From desert tortoises to grizzly bears, USGS scientists are leveraging a wide variety of tools available to provide comprehensive species assessments for wildlife management agencies.
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