The Reproductive Cycles of the Vagrant Shrew (Sorex vagrans) and the Masked Shrew (Sorex cinereus) in Montana

The reproductive activities of Sorex vagrans and S. cinereus in western Montana were documented using histological methods. Testicular recrudescence in both species began in February with maximal development and spermatogenesis attained by late March to early April and testicular activity was maintained well into the autumn. Breeding began in late April and extended into August in S. vagrans, no conceptions were documented past June in S. cinereus. Average litter sizes in utero for both species were consistent with previously reported values for populations at similar latitudes. Both species exhibit similar breeding pattern in sympathy.