Muskrat Reproduction in Areas of Controlled and Uncontrolled Water-Level Units

Basic aspects of muskrat (Ondatra zibethicus) productivity in the Lake Erie marshes were investigated to determine if differences in reproduction could be detected between animals living in areas of controlled (managed) and uncontrolled (unmanaged) water-level habitats. From the regular trapping seasons of 1954-55 through 1957-58, and in the summer of 1955, 9,091 muskrats were exam- ined. The results suggest that diked units will increase population densities through a reduction of mor- tality, but these enclosures apparently have little influence on reproductive physiology. Pregnant musk- rats were captured from February through August. Corpora lutea were present in ovaries from January through August. Thus the breeding period would be long enough for one female to produce at least three litters if gestation is approximately 30 days. Further data suggest that during the latter part of the breeding cycle (April-August) sexual activity is reduced. The anestrous period apparently extends from September through December.