Factors affecting rice grain density unconsumed by white-fronted geese in relation to wheat damage

Lake Miyajimanuma, in central Hokkaido, is an important stopover site for white-fronted geese (Anser albifrons) wintering in Japan. In this area, increasing numbers of the geese are causing damage to wheat crops. The effects of several factors on the unconsumed density of food resources in rice fields, their main foraging site, were investigated with a view to propose a method for reducing damage. It is shown that unconsumed rice grain density increased with decreasing distance from houses, roads and windbreaks, which seemed to act as disturbance factors. Unconsumed rice density was also affected by the type of harvester used, probably because of the difference in net intake rate between the sites where different types of harvester operated. It is recommended that rice fields be harvested using the current machinery, and located further from houses, roads and windbreaks, wheat fields being located nearer to houses, roads and windbreaks.