Growth of Clethrionomys gapperi and Microtus pennsylvanicus in captivity.

Growth of Clethrionomys gapperi and Microtus pennsylvanicus from southern Manitoba was documented from birth to 30 days. Clethrionomys gapperi were smaller and grew more slowly (g/day) than M. pennsylvanicus, although both species were weaned at the same age. There were significant differences in growth rates between sexes in M. pennsylvanicus and among litter sizes in both species. Most of the variability in growth was due to differences among litters. The patterns of development was similar to those reported for other North American species of Clethrionomys and Microtus.