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Avian research may require investigators to capture birds for many reasons, including to collect measurements and attach leg bands or transmitters. The effectiveness and efficiency of capture techniques varies by species, habitat, and time of year. Rails are particularly challenging to capture because of their secretive behavior and the dense vegetation they inhabit. As such, basic natural history questions for many rail species remain unanswered. We paired audio lures with modified noose carpets to capture and study 69 Yuma Ridgway's rails (Rallus obsoletus yumanensis) in the southwestern United States during 2016–2018. We compared results with other more commonly used capture methods, and our results show that noose carpets paired with audio lures can be an effective tool to capture rails, thereby facilitating studies of their ecology and life history. Noose carpets are easy to use, cheap to build and maintain, and effective over a wide range of conditions. This method could be used to capture rails other than the Yuma Ridgway's rail by adjusting the noose size, noose line weight, and audio lures to match the target species. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

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.

Many applications in wildlife management require knowledge of the sex of individual animals. The Yuma Ridgway’s Rail Rallus obsoletus yumanensis is an endangered marsh bird with monomorphic plumage and secretive behaviors, thereby complicating sex determination in field studies. We collected morphometric measurements from 270 adult Yuma Ridgway’s Rails and quantified the plumage and mandible color of 91 of those individuals throughout their geographic range to evaluate inter-sexual differences in morphology and coloration. We genetically sexed a subset of adult Yuma Ridgway’s Rails ( N =101) and used these individuals to determine the optimal combination of measurements (based on discriminant function analyses) to distinguish between sexes. Males averaged significantly larger than females in all measurements and the optimal discriminant function contained whole-leg, culmen, and tail measurements and classified correctly 97.8% (95% CI: 92.5-100.0%) of genetically sexed individuals. We used two additional functions that correctly classified ≥95.5% of genetically sexed Yuma Ridgway’s Rails to assign sex to individuals with missing measurements. These simple models provide managers and researchers with a practical tool to determine the sex of Yuma Ridgway’s Rails based on morphometric measurements. Although color measurements were not in the most accurate discriminant functions, we quantified subtle inter-sexual differences in the color of mandibles and greater coverts of Yuma Ridgway’s Rails. These results document sex-specific patterns in coloration that allow future researchers to test hypotheses to determine the mechanisms underlying sex-based differences in plumage coloration.

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