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four litters and 45 young a year, but Nebraska muskrats normally have two to three litters of five to seven young each. Additionally, first-litter females will sometimes have a litter late in the same year they were born. In the spring, dispersal and mating are the two most noticeable activities of muskrats. Dispersal is associated with ice break-up and is primarily the result of increased aggression between animals. Dispersal movements can be long, cross-country treks or shorter, less dramatic movements within a marsh. Dispersing muskrats experience extremely high mortality from predators, exposure, starvation and accidents, but the movements play a vital role in repopulating vacant habitat.
In Nebraska, the breeding season begins in March and runs through summer. After pair bonds are established, muskrats establish territories and defend them fiercely against neighbors. Peaks in litter production occur in April, May and June, and there is another small peak during August-September. Litters are born blind and helpless, four weeks after mating occurs. The young go on short excursions within two weeks and are weaned at about three weeks. Adult females breed soon after the birth of a litter and prepare their dens for the new arrivals soon after the litter is weaned.
Mortality:
While muskrats are prolific, they are short-lived. Most muskrats live less than one year, and two- to three-year-olds are extremely rare. Muskrats are prey for a wide range of predators, including hawks, owls, mink and northern pike. Many muskrats are killed or seriously wounded in territorial battles throughout spring and summer, and few spring dispersers make it safely to a new home. Muskrat populations can fluctuate wildly from year to year, based on vegetation and water conditions, and populations can actually be too successful for their own good.
Sometimes a marsh produces so many muskrats during the summer that there is insufficient vegetation left in the fall for food and lodge construction. This is called an "eat out'-the muskrats eat themselves out of house and home. When muskrat numbers get too high in late summer and fall, the population becomes stressed. Fighting and cannibalism increase, reproduction decreases and mal- nutrition increases. Two contagious diseases, Tyzzer's disease and tularemia, can have devastating effects on local muskrat populations under these conditions. Muskrat numbers can be reduced to a fraction of the original population in just a few weeks by these diseases. Unfortunately, these diseases will persist in a marsh and continue to depress muskrat populations for a number of years. Regulated trapping can reduce the impacts of disease, starvation and fighting on muskrat populations, by removing surplus animals when numbers are high and populations are under stress.
Importance:
Muskrats have both positive and negative economic values to the people of Nebraska. Positive values center on the income generated by the harvest of muskrats by trappers for their meat and fur, as well as the recreational value derived from their pursuit. From 1942-89, an estimated 6.1 million muskrats were taken by fur trappers in Nebraska. Harvest totals from 1980-89 indicate an average annual harvest of 95,900 muskrats valued at over $283,000 . Muskrat is highly desirable for the manufacture of women's coats because the fur is very durable and the skin is tough and makes excellent leather which takes and holds dye well. People who eat muskrat say its flesh has a moderate gamy flavor that is in no way unpleasant. Musk dried from the animal's glands is used to make perfumes and a scent used for trapping other animals.
Management:
Muskrats are also important in the management of wetlands. Muskrat lodge construction provides openings in vegetation-choked wetlands, which greatly increase the wetland's value to waterfowl and shorebirds. The negative economic impacts of muskrats center on burrowing activities that can cause shoreline erosion and structural damage to farm ponds, stock dams and dikes. This damage can be controlled, however, with proper population regulation. Nature made the muskrat prolific, but most of each year's production dies before the next year's breeding season begins.
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