Some water birds inhabit reservoirs, in which the water level fluctuates substantially throughout the year owing to agricultural demands. Such fluctuations of water level are expected to affect the colonisation of the reservoir habitat by birds. We monitored the numbers of grebes and other water birds at three reservoirs in Morita Village (present name: Tsugaru city), Aomori Prefecture, and here, report on the numbers of grebes in relation to varying reservoir water levels during the breeding seasons of 2002 and 2003.
