Endangered Birds Were Dying Where They Shouldn’t. Now Scientists Know Why.

A new study reveals the surprising cross-border migration to Mexico of the rare and elusive Yuma Ridgway’s Rail.

Like many mysteries, it started with a death. In 2013 and 2014, employees of the California Department of Fish and Wildlife recovered corpses of Yuma Ridgway’s Rails, a federally endangered subspecies native to specific marsh areas in the southwestern United States and northern Mexico, from solar farms. This wouldn’t have been too unusual—birds sometimes die from the heat when they mistake reflective solar panels for bodies of water—except for one thing: The rails shouldn’t have been there in the first place. Yuma Ridgway’s Rails are known to be sedentary, non-migratory birds, but the carcasses had been found more than 30 miles from their nearest habitat. 

Many questions surrounded this event, but one puzzled researchers the most: What were these birds doing there? 

When this news reached Courtney Conway, director of the Idaho Cooperative Fish and Wildlife Research Unit and a wildlife biologist who has studied these rails for more than 30 years, he knew he needed to find the answer. This spurred him, along with regional conservation group Sonoran Joint Venture, into an investigation that has now supplied a reason. The notoriously secretive bird sometimes migrates, they concluded, but no one had recorded it before. The finding, Conway says, recasts what scientists know about these endangered birds and how they can be protected.

“I feel like we’ve learned more about rails in the last few years than in the last 10 or 15,” says Adam Hannuksela, a science coordinator with Sonoran Joint Venture.

The research, published last month by Conway and biologist Eamon Harrity in the Journal of Field Ornithology, involved tracking the movements of 89 birds—close to 10 percent of the bird’s estimated population in the United States—using solar-powered satellite transmitters. Of the 89 individuals tracked during the past three falls, 23 juvenile and adult rails began fall migration leaving from freshwater marshes in California and Arizona and headed to wetlands along the coast of Sonora and Sinaloa in Mexico. Three adult males were tracked completing a full migration to and from the habitats in Mexico.

With this conclusion, however, more questions arose. The birds were tracked to mangrove wetlands along the coast of Mexico, a forested, brackish habitat different from the freshwater cattail marshes where the bird lives in the southwestern United States, leaving researchers interested in how these birds survive in an environment they’d never been known to visit. “There has always been some thought that they might move, but no one knew where,” Conway says. “It really was not a consideration that this bird might migrate down to saltwater, brackish water marshes for part of its life cycle, so that’s the other part that makes it exciting.”

Tice Supplee, director of bird conservation with Audubon Southwest, also found the study results surprising. “The fact that some of them went that far, all the way down the Gulf of California, is interesting,” she says. “We’re now intrigued to see if we can better understand this tendency to migrate.”

The rarity and secretive nature of the Yuma Ridgway’s Rail offer some explanation for why these findings are just now coming to light. They only number around 1,000 in the United States, with more than 75 percent of the subspecies living in freshwater marsh areas of northwest Mexico. Additionally, they hide from predators in thick, muddy, and nearly impenetrable marshland, keeping them safe but making them a tough study subject. “You virtually never see them, even though you're working on them full time, every day,” Conway says. “And to study an organism that you never see is just really limiting on what kind of data you can collect.”  

Uncovering their movements and habitat preferences could improve more than just the biological understanding of these birds. As the subspecies faces serious habitat loss from water instabilities in the Lower Colorado and Gila Rivers and the Salton Sea, as well as other ecosystem threats, new data could offer more options for protecting them. For example, their movements might be considered in land use permits for solar facilities, as well as in setting federal and state water priorities in both the United States and Mexico.

Supplee and others involved with Yuma Ridgway’s Rail conservation point to cross-border, binational cooperation as the key to continuing research of the bird’s migratory behaviors and protecting this at-risk subspecies. The researchers plan to expand on their findings in hopes they can one day help remove the bird from the Endangered Species List, where it’s been since 1967.

“At a simply natural history level, it’s eye opening and almost awe inspiring,” Harrity says. “And from a conservationist's perspective, it just broadens our scope and allows us to plan for conservation throughout the annual life cycle.”