Sexual dimorphism in morphology and plumage of endangered Yuma Ridgway’s Rails: A model for documenting sex

Journal of Fish and Wildlife Management
By: , and 

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Abstract

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 intersexual 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 classified correctly ≥ 95.6% 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 intersexual 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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Publication type Article
Publication Subtype Journal Article
Title Sexual dimorphism in morphology and plumage of endangered Yuma Ridgway’s Rails: A model for documenting sex
Series title Journal of Fish and Wildlife Management
DOI 10.3996/JFWM-20-095
Volume 12
Issue 2
Year Published 2021
Language English
Publisher U.S. Fish and Wildlife Service
Contributing office(s) Coop Res Unit Seattle
Description 11 p.
First page 464
Last page 474
Country United States
State Arizona, California, Nevada
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