Reproduction, productivity and food habits of muskrats on Prince Edward Island

Muskrat populations were studied on Prince Edward Island from 1968 to 1970. Eutrophic conditions and stable water levels result in high quality habitat in the Province. The breeding season extended from late March to late August but most litters were produced in May, June and July. Litter sizes of 7.9 and 7.5 derived from placental scars and embryos were significantly higher than the average of 6.6 found from litters handled in the field. The mean litter size found for seven precocial females was.4.4. The average annual reproductive rate was 17.0. Adult females had from 1 to 4 litters per year and averaged 2.1. First litters were significantly larger than second and subsequent litters. Kits at birth and immatures in the fall population had a preponderance of males but the adult sex ratio approached 1.31 or slightly favored females. Immatures comprised 79.9% of the fall population in 1968 and 79.7% in 1969. Survival of immatures from birth to the trapping season varied from 48.7% in 1968 to 44.6% in 1969. Recoveries of marked animals suggested that early born litters had a higher survival rate than those born later. Scirpus acutus, Typha latifolia, Sparganium eurycarpum and Carex spp. were the four major plants eaten by muskrats in summer. The fresh water clam (Anodonta sp) was the only animal food eaten. Evidence of mink predation on muskrats was found. Four common endoparasites of the muskrat were recovered.