Effects of water level on habitat selection by foraging Whooper Swans

Abstract

Use of foraging habitat by the Whooper Swan Cygnus cygnus was observed to determine habitat selection in relation to water level of Lake Izunuma-Uchinuma, a shallow lake in northern Japan. During the wintering season of 2008/2009, the abundance of swans was recorded at a variety of suitable foraging habitats in the vicinity of the lake. During 21 counts, the mean abundance of swans was 645 birds (range 186 to 1,239). As the water level in the lake increased, the percentage of swans foraging in the areas of lotus and wild rice significantly decreased, while swans increased in rice fields. As the aquatic plants became unavailable due to deepening of the lake, it appears that swans shifted their feeding habitats to those that remained shallow or exposed.