Feeding strategies of Japanese monkeys against deterioration of habitat quality

Field observations of the feeding behaviour of Japanese monkeys were carried out from autumn to winter on Kinkazan Island which is covered with cool temperate forest. As a result, the following two points became clear: (1) the available food items were fixed for a long time; and (2) the habitat quality deteriorated monotonously because the monkeys themselves or their competitors, such as wild mice, utilized the food resources. Against the decrease in food intake caused by this deterioration of the habitat quality, the monkeys controlled the decrease in food intake by employing the following strategies: (1) they recovered their feeding speed by exploiting new food patches (patch-increase strategy); (2) they extended the time spent on feeding (time-extension strategy); and (3) they changed their food (food-change strategy). The former two strategies operated earlier than the third one.