External determination of age and sex of the common moorhen

The United States Fish and Wildlife Service uses the Parts Collection Survey (PCS) to monitor migratory bird populations through examination of parts collected by hunters. An important new addition to the PCS is the inclusion of migratory shorebirds and upland game birds (MSUGB) in the survey. However, age and sex keys have been developed for only 2 MSUGB species. For the survey to be effective, keys for all MSUGB need to be developed. To that end, we examined collected specimens and museum mounts to develop an age and sex key for common moorhens (Gallinula chloropus) based on various quantitative and qualitative morphological characteristics. Culmen-shield width proved to be the best qualitative characteristic for aging moorhens. Ninety-three percent of adults had culmen-shield widths >10.4 mm while only 4% of juveniles had shield widths >10.4 mm. Bill length was also a good predictor of age. Wing-covert color and degree of point on tertial tips were the best qualitative characteristics for aging common moorhens. juveniles tended to have olive-brown dorsal wing coverts and highly pointed tertials while adults usually had slate gray-black coverts and rounded tertials. Only one characteristic, wing chord, showed promise for sexing common moorhens. Males of both age classes tended to have longer wing-chord lengths than females of both age classes. Managers can use culmen-shield width to accurately age harvested common moorhens. However, damage to soft parts during shipping may render culmen shields less useful. Color of dorsal coverts and degree of point on tertial tips may be more practical for aging moorhens and, when used in combination, are highly accurate. Managers can use wing chord as a reliable indicator of sex; however, we recommend that specimens first be aged to increase the reliability.