Kinkazan Island, northern Japan, is an example of a habitat of an overabundant sika deer population. It has been inhabited by the deer for over 300 years and the vegetation is heavily affected. Forest structure is deformed, and undergrowth is poor. A dwarf bamboo, is replaced by an unpalatable ericaceous shrub. The deer population density fluctuates 40-50 deer/km². According to overabundance, the deer are in a malnutritional condition. The body weight is smaller by 30-40% than the deer on the mainland. The pregnancy rate is around 50%, while it is over 80% on the mainland. The first pregnancy begins at around 5 years old while it usually begins at two years old on the mainland. The antlers are thinner and lighter than those of the mainland population. After 1980, at least two “die-offs” occurred, but the population did not “crash” but bottomed at around 20 deer/km². The forest regeneration is blocked because of lack of young trees. Ridges are deforested and invaded by grasses, which consequently attract deer as feeding grounds. They were firstly dominated by tall grasses, and were gradually replaced by a lawn grass. The deer fed on fallen leaves of deciduous broad-leaved trees during winter, which was observed even in the 1980s.