Conspecific aggression in the laboratory rat.

Attacks by dominant colony males of a domesticated rat strain on conspecific strangers introduced into the colony include both a full range of threat displays and actual biting attack. These dominant males attack and bite both anesthetized and unanesthetized strangers, but threat displays and bites to anesthetized rats are limited. Lesions resulting from these bites are nonrandomly distributed, with most damage to the head and upper back and very few bites to ventral surfaces. When introduced strangers were left in the colonies for several days, 66% were killed, indicating that domesticated rats are capable of lethal attacks on conspecifics without external provocation.