Demography of the Beach Vole (Microtus Breweri) and the Meadow Vole (Microtus Pennsylvanicus) in Southeastern Massachusetts

The beach vole, Microtus breweri (Baird), and the meadow vole, Microtus pennsylvanicus (Ord), were live trapped at monthly intervals from May 1972 to July 1975. The beach vole is endemic to Muskeget Island, Massachusetts, USA, a 2.6—km2 island off the coast of Cape Cod. The meadow vole was caught at Cape Cod and Plymouth, Massachusetts. Neither of the 2 populations of beach voles showed any sign of long—term cycles. One population had a flat density curve, and the other, in poorer habitat, cycled annually. Both of 2 meadow vole populations trapped underwent 3—yr or more cycles of density. One declined in the winter of 1973—1974. The other declined during the spring of 1975. Both species adjusted their reproductive effort to density. Microtus breweri showed changes in reproductive and mortality schedules that were also sensitive to season. Microtus pennsylvanicus showed changes in intensity of breeding, length of the breeding season, age at reproduction, and adult and juvenile mortality that agree with the generally recognized syndrome of events accompanying a vole cycle. During peak densities, meadow voles were larger in size. The beach vole is a large vole and shows many of the attributes of K—selected organisms (large size, larger age at maturity, sex ratio weighted towards @M @M, and lower reproductive output). Microtus breweri is the first naturally occurring vole population reported to show the complete absence of cycles.