Food habits of Japanese deer in an evergreen forest: Litter-feeding deer

Abstract

We observed the feeding behaviors of wild Japanese sika deer ( Cervus nippon yakushimae) in a warm temperate broad-leaved evergreen forest of the island of Yakushima using the focal animal sampling method from April 2002 to June 2006. Sika deer fed on species of at least 73 woody plants, 13 vines, 8 herbaceous plants, 8 ferns, 1 moss, and 3 fungi. We investigated time spent feeding on each food category in each season (spring: April–June; summer: July–September; autumn: October–December; winter: January–March). During each season, 45.6–59.8% of the deer diet consisted of fallen woody leaves. Half of the fallen leaves were those tinged with red and yellow colors. Fallen reproductive parts of plants constituted 8.7–23.7% of the seasonal deer diet. In contrast, living woody parts of plants and herbaceous plants, including ferns and moss, constituted 4.4–22.5% and 0.8–9.2% of the seasonal diet, respectively. Deer also fed on animal matters as minor food items, such as the feces of monkeys and raccoon dogs, bones of deer and monkeys, and bird carcasses. Animal matters constituted 0.3–1.6% of the seasonal diet. Sympatric monkeys supplied food to deer as a result of their daily activities. Monkey-supplied foods comprised 1.7–10.9% of the seasonal diet of sika deer. Monkeys tended to supply many fruits and seeds. Overall, 75.0% of the annual deer diet consisted of forest litter, even though deer had access to abundant living edible leaves in the study area. Therefore, sika deer in this forest ecosystem function ecologically as decomposers rather than primary consumers.