Several weeks ago Naturespeak examined the wintering habits of a common local water mammal, the beaver ( Castor canadensis ). But there exists another common mammal in our local waterways with a much higher population density than the beaver. Study estimates of Common Muskrat (Ondatra zibethicus) populations in North America, indicate up to seven mammals per hectare (ha) in open ponds and up to 85 per ha. in cattail marshes.
Like the beaver the Muskrat belongs to the orderRodentia but it is much more closely related to the voles, lemmings and mice. In fact, the muskrat is not a rat at all but is actually a large field mouse adapted to live in and around the water. Like the field mouse it has a long, scaly tail that is nearly naked; unlike it the muskrat’s tail is laterally flattened with ventral and dorsal keels that aid in movement and steering in water. Muskrats are much smaller mammals than beavers, weighing only 0.8-1.8 kg and measuring between 25 and 60 cm. Muskrats do not have webbed feet like beavers but their hind legs have thick hairs that act much like webs to propel them through the water.
The high numbers of muskrats in local bodies of freshwater is due to their incredibly high reproduction rate. Muskrats derive their name from the ‘musk’ scent they secret from glands in their perineal (anal) region to mark their territory during mating season. Mated pairs are monogamous and in their 2-3 year lifespan together, will produce 2 to 3 litters of 4-7 young, per year during the breeding season, which lasts from late March to September. The males live separate from their spouses in extended "add-on chambers" attached to the main dwelling, only while the female is suckling the young. The young muskrats can fully care for themselves one month after birth and occasionally young born in the first litter of a year will themselves, mate and reproduce in late summer.
Muskrats are very social animals, living in close quarters. Late summer litters will often remain with their parents through the winter and siblings from litters born earlier in the summer will often build and live in dwellings only metres away from their parents. Muskrats may dwell in lodges, similar to beaver lodges, built from cattails, bulrushes and other cut up aquatic vegetation plastered with mud in the middle of a stable body of water, or they may live in ponds, rivers or ditches where they have dug a burrow into the bank.
Muskrats are considered plant eaters or herbivores. They eat the roots and stems of cattail, pondweeds, water lilies, rushes, sedges, and irises. Because of their "vegetarian" diet muskrats benefit wetland communities by regulating marshland succession and keeping algae growth levels in check. In agricultural areas muskrats will often leave the water to feed on clover, grasses and even corn.
But, the story of the muskrat as a communal, social, family oriented, vegetarian changes if the muskrat is unable to secure adequate amounts of plant material. If unable to maintain their energy levels through a plant-based diet muskrats will resort to feeding on carrion and animals such as fish, snails, frogs and even other muskrats! A bad winter, a drought, a flood can all result in food acquirement problems.
At other times muskrat populations can be too successful; over a summer too many kits may be produced resulting in insufficient vegetation left in the fall for food and construction of winter dwellings. This situation is called an "eat out". The result of any of these situations is aggressive infighting among individual muskrats living within that area, even amongst members of a family. Muskrat yearlings or weaker individuals may be forced to leave the area, thus traveling several miles overland at the serious risk of predation, to seek a new place to live. Sometimes muskrats in these situations will even resort to acts of cannibalism, eating their young!
All of these are natural acts, controls that balance muskrat populations with their food supplies.
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Written by: Sorcha Masterson
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