Ochrotomys nuttalli and Peromyscus leucopus are two small-mammal species that have similar life histories. This results in a relationship with a high degree of sociality between the two species, including extreme niche overlap. We investigated differences in diet preference and daily caloric intake under experimental field conditions in order to clarify this close relationship. Diets were based on reported food preferences in their natural environment. Five food resources were provided to 20 adult individuals (10 male, 10 female) of each species for three consecutive days. Individuals were contained in separate covered mesocosm tanks located in a riparian forest ecosystem. White-footed mice consumed more energy per day than golden mice (0.89 and 0.70 kcal • g live wt-1, respectively), which is considerably less (2.38 and 1.48 kcal • g live wt-1, respectively) than those reported by Gibbes and Barrett (1) when fed identical diets under controlled, laboratory conditions (22°C). This study also suggests that nest cavities and soundscape assist in mitigating environmental perturbations, such as food scarcity and predation, in their natural habitat.

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