Abstract
With the decline in their natural habitat, grassland bird species have become of conservation concern. When a grassland is completely destroyed, the impact on birds can be relatively easily estimated. However, when a grassland is altered qualitatively, the impact cannot be estimated without detailed research, and few studies have investigated this aspect. Here, we report the qualitative change of vegetation between 1998 and 2010 of a wet-grassland, Hotoke-numa, located in Aomori Prefecture, northern Japan, and its impact on the five grassland avian species. During the 12-year interval, the mean height of the reed Phragmites australis decreased by 20 cm, whereas the height and degree of grasses in the lower layer increased. The latter might be a consequence of the increase of light penetration to the lower layer as a result of the decrease in the height of the reed. The numbers of individuals of Locustella pryeri, Emberiza schoeniclus and E. yessoensis increased by 36%, 171% and 94%, respectively, whereas Acrocephalus orientalis decreased by 39% and A. bistrigiceps decreased by 43%. According to previous published studies, the three species which increased preferred the vegetation present after the change, while the two species that decreased preferred the vegetation present before the change. The change in vegetation clearly influenced the number of individuals of the five species. Since the study area has many endangered species, it is urgently necessary to identify precisely which factors are responsible for the change in vegetation.
