The Estrous Cycle of Two Species of Kangaroo Rats (Dipodomys microps and D. merriami)

The estrous cycle of the kangaroo rats Dipodomys merriami and D. microps entails spontaneous ovulation and a spontaneous luteal phase. Corpora lutea are present throughout the cycle. The modal cycle length is 12 days in D. microps and 13 days in D. merriami, a significant difference. The duration of the cycle is unaffected by mating with a sterile male. Vulvar swelling and vaginal opening are conspicuous external indicants of estrus. The examination of vaginal cytology provides little information beyond that available from these overt signs. In both laboratory and field, the spontaneous activity of females in estrus is elevated severalfold compared to the anestrous state.