Muskrats at the FWG

At the FWG, we first observed a Muskrat in our man-made pond some years ago, then didn’t see another until 2005. The latter 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 water, particularly in cattail (Typha spp.) marshes, although it will inhabit almost any other wetland  provided the water is deep enough not to freeze to the bottom in winter, but not so deep that vegetation doesn’t grow. About 1-2 m is considered 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 muskrat lodges can benefit others. I’ve seen both Mallards (Anas platyrhynchos) and Canada Geese (Branta canadensis) nesting on top of these structures.

About the only time Muskrats travel any distance 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. The Muskrats at the 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, mainly because they are most active very early and very late in the day. Their habitat also 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 vocalization, nor have I been able to find any descriptions apart from a vague mention of squeals and grunts when they are 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, Red 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 American Mink (Mustela vison).

Territory

During most of the year, Muskrats inhabit a fairly small territory, and 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 6-10 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 spring 2008 when a pair appeared. 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 they were still around. 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.

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.

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), American Mink (Mustela vison), and American 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.

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.

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 24 March 2018
© Fletcher Wildlife Garden
Text: Christine Hanrahan
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