Factors Affecting Rodents' Responses to Odours of Strangers Encountered in the Field: Experiments with Odour-Baited Traps

1. Live traps baited with deer mouse (Peromyscus maniculatus gambelii) odours were preferred over neutral traps by trap-naive deer mice in reproductive condition, whereas neutral traps were preferred by those not in reproductive condition (Fig. 1). Kangaroo rats (Dipodomys agilis and D. merriami) similarly preferred conspecific odours if in reproductive condition, and neutral traps otherwise (Fig. 2). This response pattern is interpreted as indicative of varying inclinations to risk or avoid social encounters. 2. A similar pattern of preferences as a function of the respondents' reproductive condition was apparent in pocket mouse (Perognathus fallax) responses to deer mouse odours, and in deer mouse responses to Merriam's kangaroo rat odours. Such interspecific responsivity may characterize competing species of similar body size. 3. Deer mouse odour-trapping trials were conducted in four evenly spaced periods from November to June. Deer mouse captures were maximal and reproductive activity was minimal in January, whereas the sex ratio increased monotonically from fall to spring in each of two years. Captured deer mice of both sexes changed from preferentially approaching female odours in winter to a spring preference for male odours.