Habitat preference of Japanese Marsh Warbler in the lower Iwaki River

Abstract

Reedbeds along the lower Iwaki River, Aomori Prefecture are among the main breeding areas of the Japanese Marsh Warbler (Locustella pryeri), after Hotokenuma marsh, Aomori Prefecture and the lower Tone River, Ibaraki and Chiba Prefecture. For the past 30 years, the lower Iwaki River has been known as a breeding area of this endangerd species. People in this region utilize reeds and manage the reedbeds by cutting the stems in winter and burning some parts of the reedbed in spring. These human activities appear to create suitable habitat for the Japanese Marsh Warbler. Our investigation examined the relationship between reedbed management and breeding of the Japanese Marsh Warbler in 2002 and 2003. In spring, Japanese Marsh Warblers arrived at the breeding ground and settled in non-burnt areas where patches of dead reeds remained and some types of sedge had grown. These types of vegetation are necessary for breeding. In summer, the late breeding season, they dispersed gradually to burnt areas where new reeds had grown. The non-burnt areas were continuously used by large numbers of birds until the end of the breeding season. The burning of the reedbed was carried out in different areas in each year of the study, with the result that the territories of the Japanese Marsh Warbler shifted. This study clearly indicated the importance of non-burnt areas for breeding and suggested that reedbed management activities, such as burning of the reedbed to prevent vegetational succession, also contributed to the maintenance of breeding area of the Japanese Marsh Warbler.