Species Differences in Activity Patterns During Oestrus

The onset of oestrus in females has been associated with an increase in locomotor activity; however, we predicted that there would be species in which the females would not increase their activity during oestrus. We tested this in the laboratory, using running wheels, with white-footed mice ( Peromyscus leucopus ) and California mice ( Peromyscus californicus ), which were predicted to increase activity, and hispid cotton rats ( Sigmodon hispidus ), which were predicted to show no change in activity level. The results supported our predictions, as cotton rats showed no change, while both Peromyscus species increased activity during oestrus. Based upon laboratory activity patterns we conducted a field study to examine the relative levels of activity of two species, white-footed mice and prairie voles ( Microtus ochrogaster ). We predicted that significantly more white-footed mice than prairie voles would be caught during oestrus. Before trapping we generated a model to predict the probability of capturing oestrous females. Live-trapping results supported our prediction, as significantly more oestrous female white-footed mice were captured than prairie voles (48.8 vs. 7.5%), and capture of oestrous white-footed mice deviated significantly from the model's prediction. The capture of oestrous prairie voles fit within the lower limits of the model's predictions. The results are discussed in terms of mating strategies, how oestrus is achieved, and predation risk.