Effects of Breeding in Captivity on Conflict among Wild Rats

Abstract

Ten male wild rats (Rattus norvegicus) trapped as adults were kept singly and exposed daily for 15 minutes to a strange adult male of the same species. Seven adult males of the sixth through ninth generations reared in the laboratory were similarly exposed. In contrast with the trapped rats, the laboratory-bred males attacked and “threatened” the strangers little and their propensity to attack was not increased by the presence of females. Certain other activities were rare among trapped residents but common among residents bred in captivity: these were resident grooming interloper, resident crawling under and huddling with interloper, and resident mounting interloper as though the interloper were a female. Interlopers ran from, and squealed at, trapped residents more than they did in response to laboratory-bred residents.