Changes in environmental habitat or un-seasonal weather conditions affecting the availability of local food sources can force wild animals into situations of contact with humans where their behaviour becomes aggressive.
In February 1998 villagers in the town of Ito in southern Japan found their community invaded by foraging monkeys who were believed to have been driven down from their normal mountain habitat by the exceptionally hard winter. Over 30 people, mostly middle aged to older women in their homes were attacked and bitten by the 1 metre high monkeys who had learned to open doors and enter houses. This was the first recorded instance in living memory of the normally placid animals attacking humans.