Population sizes of four small mammals, Peromyscus leucopus, Microtus pennsylvanicus, Blarina brevicauda, and Sorex cinereus, were monitored for over twenty years at the UWM Field Station. P. leucopus had moderate fluctuations in size, but showed no evidence of cyclic or regular fluctuations. M. pennsylvanicus exhibited dramatic fluctuations with cycles of 3-5 years. Neither shrew species appeared to have cyclic fluctuations. The population sizes of the two shrew species were positively correlated with each other. No other significant correlations were found between species. Population sizes were probably influenced by a number of factors including predation, competition and weather.
Popp, J.W., P.E. Matthiae, C.M. Weise and J.A. Reinartz. 1988. Long-term population fluctuations of small mammals at the UWM Field Station. Field Station Bulletin 21(1): 10-18