Abstract
Greater White-fronted Geese Anser albifrons have historically wintered in large numbers around Lake Izunuma-Uchinuma, northern Honshu, Japan. Since 1971, when goose hunting was prohibited, the number of geese has increased 7.6 fold from 14,647 in 1987/88 to 110,816 in 2006/07. Currently more than 80% of the Japanese A. albifrons population winters here. Agriculture in the surroundings of the lake system has also changed. The total average area of soybean fields increased 2.8 fold from 1,780 ha in 1996 to 4,940 ha in 2005. We investigated temporal and spatial changes in goose foraging strategies by comparing data on habitat selection between 1997/98–1998/99 and 2007/08. In 1997/98–1998/99, geese only foraged on rice fields, and shifted from rice fields near the lake to fields further away as these fields became depleted as winter progressed. In 2007/08, just after harvesting in late September, although waste rice grains on fields amounted to 65 kg/ha (N=6, range: 52–78), post harvest waste soybeans amounted to 355 kg/ha (N=9, range: 120–940) and the amount increased from mid November to mid January. Geese depleted waste rice grains by early December in areas within 10–12 km of the lake, and foraged on soybeans within 10 days of harvesting. In relation to these changes in relative food abundance, the geese now forage exclusively on rice fields in November, but switch to feeding primarily on soybeans in December and in January. With both the number of geese and the area of soybean fields increasing over the decade (1997/98 to 2007/08), geese now experience a shift in food resources from waste rice grains in early winter to soybeans in late winter.
