Satellite transmitters reveal previously unknown migratory behavior and wintering locations of Yuma Ridgway’s Rails

Abstract

Preventing or reversing population declines of rare species often requires an understanding of their complete annual life cycle, but this information is lacking for many species. Such has been the case for Yuma Ridgway’s Rails ( Rallus obsoletus yumanensis ), a federally endangered marsh bird endemic to the Lower Colorado River Basin and Salton Sink in California, Arizona, Nevada, and Mexico. Yuma Ridgway’s Rails have been considered non-migratory, but incidental mortalities at solar facilities > 50 km from any rail habitat called this assumption into question. We attached transmitters to 89 Yuma Ridgway’s Rails during the summers of 2017 to 2019 and documented the migratory movements of 23 rails, including three adult male Yuma Ridgway’s Rails with breeding territories in the United States that wintered in Mexico and returned to the United States the following year. The rails flew > 900 km in the fall to mangrove wetlands along the coast of Sonora and Sinaloa, Mexico, and returned to their breeding areas in the United States the following breeding season. Of the rails in our study, 40.0% (20 of 50) of adults and 21.4% (3 of 14) of juveniles initiated fall migratory movements. Our results invalidate existing paradigms about Yuma Ridgway’s Rails by demonstrating that not all individuals remain in their breeding areas throughout the year. Instead, some migrate long distances over inhospitable terrain to reach wintering areas that, in some cases, are in wetland types different from those in their breeding territories. Our results provide actionable data to expand conservation strategies to better account for the annual life cycle of this endangered species and highlight the need for United States-Mexico cooperation, given the regular migration of this rare bird between the two countries.