The estrous cycle in female wood mice (Apodemus sylvaticus) and the influence of the male

Based on studies of vaginal smears from wild-caught Swedish wood mice, females with three types of estrous cycles were identified: females with a continuous estrus; females with an estrous cycle between 6 and 11 days in length; and females that only rarely showed signs of estrus. We tested the pregnancy rates and how stable the estrus patterns were among the females. Ninety-one percent of the females with a continuous estrus pattern became pregnant, 50% of the females showing a cyclic estrus pattern, and 60% of the females showing an infrequent estrus. However, pregnancy occurred about 2 weeks later in females with an infrequent estrus pattern. Some females changed their estrus pattern after pregnancy, indicating that estrus patterns are not fixed.