Are nests built for fun? Effects of alternative activities on nest-building by wild house mice

Abstract

Male and virgin female wild house mice, Mus musculus , aged 8 to 14 weeks, of the first generation bred in captivity, built nests of cotton wool in an ambient temperature of 23°C. Controls were each in a small cage (750 cm 2 ). Others had one of the following: (i) balsa wood to chew; (ii) a wheel in which to run; (iii) an additional small cage connected to the home cage; or (iv) a large cage (3600 cm 2 ) in which to explore. The cotton pulled in, and the quality of the nest built, were recorded on 2 successive days. No difference was observed between sexes or between days. The balsa wood had no effect. All other treatments led to a reduction in both cotton-pulling and nest-building. The large cage had the greatest effect. There was always a high positive correlation between amount of cotton pulled and nest quality. Nest-building resembles exploration in increasing the stimulation received and in being rewarding. The present experiments show exploration by mice in a warm environment to compete with nest-building and to have priority over it. Some nest-building may come in the general category of play.