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Muskrats at the FWG

by Christine Hanrahan

The first time I saw a muskrat (Ondatra zibethicus), many years ago, I thought it was a young beaver (Castor canadensis). Even today a second look is sometimes required, for these two semi-aquatic species bear more than a passing resemblance to each other if seen when they are swimming, despite the significant size difference. Muskrats are very common right across Canada and can be found in almost any wetland, particularly cattail marshes.

At the FWG, a muskrat was first observed in our man-made pond some years ago. We didn't see another until 2005. This one was very active for the first few months, and could be seen sitting on mats of dried cattails, or heard rustling around in the shoreline vegetation. No doubt the muskrats found in subsequent years at FWG, were each seeking new territory and thought they had found a good place to call home.

Habits

The muskrat spends most of its life in or near the water, particularly in cattail (Typha spp.) marshes, although it will inhabit almost any other wetland habitat provided the water is deep enough not to freeze to the bottom in winter, but not so deep that vegetation doesn't grow. It is generally accepted that about 1 to 2 m is a good depth.

Muskrats frequently make channels through the cattails, and in fact are quite adept at clearing large swathes of vegetation which in turn creates good habitat for other wildlife, such as waterfowl and various water birds. Even the muskrat lodges can benefit others. I've seen both mallards (Anas platyrhynchos) and Canada geese (Branta canadensis) nesting on top of these structures.

The muskrat is really a large, semi-aquatic vole, not related to the beaver as is sometimes supposed. It weighs an average of 1.5 kg and measures up to about 62 cm including the tail. Despite its name it is not a rat, but it is a rodent, and together with the musky discharge emitted from its anal glands, it is easy to see where the common name comes from.

Like the beaver, muskrats have a rich chestnut brown waterproof coat and small ears close to the head. Also in common with beavers, they are well able to chew food underwater, because, as Banfield (1974) explains, they can close their lips behind their incisors which prevents water from getting into their mouth. You will often find beavers and muskrats sharing the same wetland or pond.

About the only time muskrats travel any distance away from water is in the spring when they are seeking new territory, in the fall if their habitat dries out, or anytime their wetland is drained. Our muskrats at FWG are probably a result of spring or fall dispersal as those are the seasons when they are most visible at the garden.

Although very common, muskrats can be surprisingly difficult to see. This is largely because they are most active early and late in the day. It is also a reflection of their habitat which doesn't make for easy observation. However, if you are patient (or lucky) you should be able to observe them swimming and feeding, moving across mats of aquatic vegetation, or even trundling across dry land.

Apart from a sort of "chittering" sound when they have been distressed by my presence, I have never heard any muskrat vocalizations, nor have I been able to find any descriptions apart from a vague mention of squeals and grunts when agitated or cornered.

Their biggest enemy is probably us. Not only do we kill countless numbers on the road, but we trap millions every year for their pelts. They also fall prey to a number of other species, although at the FWG their most serious predator would be dogs, foxes (Vulpes vulpes), and possibly some of the large raptors that sometimes occur there. I have heard that weasels (Mustelidae) and raccoons (Procyon lotor) will also take muskrats and both these species occur at FWG, although in small numbers. Of course, in other areas of Ottawa coyotes (Canis latrans) can be added to the list of predators, along with mink (Mustela vison).

Territory

During most of the year, muskrats inhabit a fairly small territory, roughly 0.06km. Population density varies considerably. Banfield (1974) gives anywhere from 3 animals per 0.5 ha to 3 per 14 ha of wetland As with so many rodents, populations are cyclical. Muskrats seem to reach their peak every 6 to 10 years after which, numbers crash. No particular reason is given but Forsyth (1985) probably correctly, assumes the cycle is related to food supply and water fluctuation. He also comments that the greater (10 year) cycle which typically occurs in the northern part of their range, is likely related to a shorter breeding season and slower growth rates, meaning it takes longer for northern animals to recover to their previous numbers.

At the FWG, we had never seen more than one muskrat at a time in our pond, until the spring of 2008 when a pair was found. They were very active for a couple of days, but after that we had only sporadic sightings of a single animal, and by mid-summer it was unclear whether the pond still had a resident muskrat or two, or none. As to whether they actually bred, or moved on to better prospects, I don't know for sure, but if they'd had young, our pond is small enough that we'd have eventually noticed them, and we didn't. Furthermore, as you will see below, the pond doesn't provide particularly good natal sites.

Feeding habits

Muskrats are especially partial to cattails which form a large part of their diet. They also consume a variety of other aquatic vegetation including but not limited to, sedges (Carex spp), arrowhead (Sagittaria spp.), and bur-reed (Sparganium spp.) all of which grow in and around the FWG pond.

At FWG, I've watched a muskrat busily feeding on the roots of the invasive flowering rush (Butomus umbellatus). For a short time I entertained hope that we'd found a way of ridding the pond of this fast-spreading plant while feeding local wildlife. However, the muskrat seemed to return to the more palatable cattails. Nonetheless, for some time after this first observation, I continued to see bits of Butomus floating on the pond surface which could have been the result of muskrat feeding. We also noticed pieces of cattails and other vegetation floating on the pond, as if the tasty parts had been eaten and the rest left to float away. Since this kind of thing is typical of muskrats, it probably was done by "our" muskrat.

For a few years we'd watched cattails dying off in one section of the pond. Once we discovered the muskrat in residence we wondered if it had anything to do with this. We still don't know, but the area of cattail die-back was not far from the lodge.

Although primarily herbivores, it is reported that muskrats will eat animal matter. Opinion as to the importance of this type of food in its diet varies considerably. Most agree, however, that they will eat fresh-water mussels, frogs and other aquatic creatures when the opportunity arises.

If you've watched muskrats for any length of time around the region, you've probably noticed their "feeding mats" or platforms. These look like large flat bundles of vegetation, and are very strong, allowing the muskrat room to feed in comfort. Most of the ones I've seen have been close to vegetation, but I've seen a few floating around like tiny islands. I am quite certain that a good sized feeding mat was constructed near the west end of the pond, at least it certainly looked like those I've seen elsewhere. I occasionally saw the muskrat on it and it was also well used by both midland painted turtle (Chrysemys picta) and Blanding's turtle (Emydoidea blandingi) for sunning. Muskrats also make use of the previous year's cattails which are often beaten down by winter snow to form a relatively strong "platform."

Reproduction

Muskrats give birth somewhere around mid-May to late June (Banfield 1974) and may have several litters per year, each with about 5-9 young. As with most wildlife species, many of the young die within a few weeks of birth, often falling prey to a wide range of predators.

Muskrats generally prefer to give birth in dens built into the bank and with underwater entrances. However, in places where this is not possible, they will use their winter lodge which they refurbish. I have seen muskrats gathering grass on the shores of wetlands in spring and then swimming off with long grassy tendrils hanging from their mouth, presumably destined for lining the den or the lodge, but possibly also being used as food.

Many people are surprised to discover that muskrats will use bank burrows but that is only because, being underwater they are largely invisible, and therefore not the familiar sight that lodges are. Sometimes, when water levels drop, you can see these bank burrows quite clearly. Of course, other creatures such as river otter (Lutra canadensis), mink (Mustela vison) and beaver also use bank burrows, so don't automatically assume they are the domain of muskrats, particularly if they are found in locations providing suitable habitat for any or all of these species.

There are a couple of burrows on the slope of the FWG pond, now mostly filled in. Whether they were used by muskrats is unclear, but I doubt it as they are well above the water line, and would always have been so.

Winter

Muskrats are active throughout the winter, but unlike many rodents they don't appear to stockpile food. Instead, they rely on being able to find enough to eat under the ice, where they search for submerged aquatic vegetation (Banfield 1974, Forsyth 1985). In the coldest weather they remain beneath the ice, using their ‘push-ups' as feeding areas. On mild winter days you may see these animals out and about. The balmy start to winter in December 2006 encouraged a muskrat in the Dunrobin area to wander about and feed on submerged grass. The water was open and flowing, and the animal was so busy eating that I was able to stand nearby and watch for 10 minutes without it being aware of my presence. A few days prior to that, in another area, I watched a muskrat walk along a water-filled ditch beside a dirt road, stopping every so often to investigate the cattails and grasses growing there.

A particular feature of muskrats in winter, is their creation of what is usually called a "push-up." This consists of an area of water cleared of ice at first freeze-up, covered with submerged vegetation to create a dome, which when frozen and snow covered, provides perfect insulation from the cold. Several times I thought I'd found one at FWG, but was never able to satisfactorily convince myself that is what it was. Some of these ‘push-ups' are big enough to rival lodges in size.

At the FWG, there was a good sized, but well-hidden, muskrat lodge in the middle of the pond during 2005-2006. Typical of all muskrat lodges that I've seen, this one was built of cattails and mud, heaped up to form a substantial mound. Elbroch (2003) describes the interior of a muskrat lodge. He says that they "usually have one entrance-exit, although larger lodges may have several. The entrance leads up to a small chamber created above the water level, where the muskrats congregate and huddle to stay warm. These lodges can be quite small, standing less than two feet (0.6 m) above the water level, or they can be quite large, holding several muskrats and standing 4 feet (1.2 m) above the water, with an ever wider base."

We are not entirely sure that the lodge at FWG was used throughout that winter. I did see a muskrat up until the weather got cold, and then again in early summer of the following year, 2006. But whether this was the same animal, I can't say. It certainly appeared as if the animal intended to remain all winter, hence the lodge. The water would be just about deep enough for this in winter despite the fluctuation in levels in late fall. By winter, the water level has usually risen again giving a depth of about 60-70 cm. Cattail growth is abundant and there would be no shortage of food. But, as far as I know, muskrats were not seen during that winter of 2005-2006. Over the next couple of years there were occasional muskrat sightings, including the two mentioned above, in spring of 2008.

During 2009, a muskrat family was seen in the pond, no doubt the offspring of the pair found in 2008. For about one week in July, two youngsters and an adult could be found during daylight, busily cutting and eating cattails. After that, sightings were sporadic. However, in December, I noticed a muskrat examining the food raft made by our newest resident, a young beaver.

We'd be happy to hear about any muskrat sightings at the FWG. Please contact us at fletcher@ofnc.ca. If you would like more information or have any questions about muskrats, please contact me at fletcher@ofnc.ca.

References

  • Banfield, AWF. 1974. The mammals of Canada. University of Toronto Press, 438 pp.
  • Elbroch, Mark. 2003. Mammal tracks and signs: a guide to North American species. Stackpole Books, 779 pp.
  • Forsyth, Adrian. 1985. Mammals of the Canadian wild. Camden House, 351 pp.

More information

  • Hinterland Who's Who: Muskrat from Environment Canada and the Canadian Wildlife Federation
  • Canada's aquatic environments: Muskrat, Ondatra zibethicus from the University of Guelph
  • Newell, T. 2000. Ondatra zibethicus on the Animal Diversity Web, University of Michigan.

This page was revised 26 January 2015
© Fletcher Wildlife Garden
Text and photos (except where indicated): Christine Hanrahan
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