Many bats use a reproductive strategy called delayed fertilization. Mating occurs in the late fall, but the female's egg is not fertilized until early spring. Parturition takes place from early June to mid-July. The gestation period varies widely in response to environmental conditions. A cold, rainy spring may result in a later parturition date, while a warm, dry spring may result in an earlier one.
Pups grow rapidly.
By approximately 3 weeks of age, they are able to fly, and by approximately 5-6 weeks, they are weaned. Of the species you have studied in lab, Eptesicus fuscus and Myotis lucifugus, are known to overwinter in hibernacula in Montana. Lasiurus cinereus, Lasionycterus noctivagans, Antrozous pallidus, and Euderma maculatum migrate south during winter. Corynorhinus townsendii has been observed hibernating in the state, but no large aggregations have been observed, suggesting that many members of this species may also migrate outside the state during winter.