Amami Woodcock
Scolopax mira is endemic to the islands of Amami-oshima (and its surrounding islands) and Tokunoshima, in the Nansei Shoto archipelago of southwestern Japan. The species is designated as vulnerable in the IUCN Red List and is under conservation management. Knowledge of behavioural sexual differences is essential to design an effective conservation plan for this species. However, because neither morphological sexual differences nor field criteria for sex determination are known for the Amami Woodcock, behavioural sexual differences remain mostly unknown. In the hope of revealing behavioural and morphological sexual differences, we banded and measured Amami Woodcock and determined the gender of banded birds using molecular sexing of sampled feathers. On Amami-oshima, adult females were found to be larger than adult males in six of nine external parameters (exposed culmen length, nalospi, bill width, bill height, total head length and weight), whereas males had longer tails than females. Using these data, a linear discriminant formula for sex determination was derived and it correctly designated approximately 86% of the birds banded on Amami-oshima. The formula was similarly valid for adults on Tokunoshima, but invalid for juveniles. During the mating period and in the early breeding season (March/April), adult males were more frequently captured than adult females. This difference in capture rate was considered to be associated with behavioural differences, in particular because males frequently display during this period, whereas females are incubating. This result suggests a likely male-biased risk of mortality on roads during March and April, the period when such mortality is most abundant. Among juveniles, a female bias in trapping was found during the late breeding season (May/June) and during the dispersal period of juvenile birds (November/December). The latter is likely to be associated with female-biased long-range dispersion, although the reason for the former is unknown.
View full abstract