Biology and Breeding Ecology of the East Asiatic Water Rail on Shunkunitai Island, Hokkaido, Japan

Abstract

Research on the Water Rail (Rallus aquaticus indicus) was conducted on Shunkunitai Island, Nemuro, Hokkaido, Japan in July 1998. A total of 23 Water Rail individuals or pairs responded to playbacks of Water Rail calls. All observed Water Rails inhabited wet hollows between long, low dune ridges. We recorded 11 different call types, captured 21 Water Rails, and banded 16 of them. Seven adults showed new feather growth; six showed brood patches. All captured adults had black-and-white barred under-tail coverts. The average number of black-and-white barred outer median and lesser wing-coverts on the left wing (dorsal surface) was 14. We found eight different types of vegetation in the 23 Water Rail territories and around seven nests. Vegetation height was 1.17 m on average (excepting Utricularietum intermediae and Alnetalia japonicae). Fresh water in the wet hollows was above the average sea level because of natural barriers and dense vegetation; the depth of water or (floating) root bed was 4-60 cm. The acidity (pH) of the surface water was 5-8. Phragmites australis was a dominant cover vegetation. We found three nests that contained egg clutches. The average water depth around nests was 10 cm; average nest height, 17 cm; average outside diameter of nests, 22 cm; average diameter of the nest bowl, 12 cm; average egg size, 38.2×26.4 mm; and average egg weight, 14 g. The median maximum nest bowl depth was 6 cm. Breeding occurred from May to July. Plant species used as nest materials were those found in the immediate vicinity of the nest. Wind-dried nest material from four nests weighed 95 g on average.