(Ondatra zibethicus). Patient Number 23-29.

Date of admission: February 14, 2023.
Reason for admission: Emaciated, dehydrated.

Patient History:

Muskrats can be found across Canada and the United States and as far south as northern Mexico. Muskrats are adapted to aquatic habitats and can be found in all wetlands and waterways except for the alpine region of Alberta. They are most active during the dawn and dusk hours. When swimming, it can be difficult to distinguish a muskrat from a beaver. Adult muskrats generally weigh 1.5 kilograms whereas adult beavers can weigh as much as 30 kilograms. A muskrat’s tail can also distinguish it from a beaver; muskrats have long, narrow tails as opposed to the large, flattened tails of beavers. Additionally, unlike the beaver, their larger hind feet are not webbed but rather have a fringe of specialized hairs along each side, giving the foot a paddle-like effect. They have small ears which are often hidden amongst their thick fur, and their four front teeth can grow to about 2 cm long. An interesting adaptation of the muskrat is their ability to chew on stems and roots underwater with their mouth closed. Their teeth actually protrude ahead of the cheeks, with their lips closing their mouth behind the teeth and allowing them to chew successfully underwater. Muskrats will thrive on bulrushes, horsetails, or pondweeds, along with willows. They are also known to be carnivores and will consume the occasional fish, frog, and clam when other food is scarce.

During the fall muskrats will build a lodge by heaping plant material and mud to form a mound. These act as burrows and also provide access to water throughout the winter. These will often appear as small mounds of dirt in the middle of a frozen pond but are in fact an indication of muskrat habitation. The mating season typically occurs after the first melt, and females often produce their first litter of 8-10 offspring a month after conception. The same female can have multiple litters a summer, often resulting in one a month, the last in August. The young are born blind, hairless, and almost completely helpless, but they grow at a rapid pace. They are fully furred after the first week, with their eyes opening by the second week. They are also weaned by three weeks old and are essentially independent at around six weeks.

This juvenile muskrat was rescued after being found alone, lethargic, and quite far from water. Upon arrival, our clinic team was able to assess that he was severely dehydrated as well as emaciated. He is currently improving daily but will remain at AIWC until spring when he can safely be re-introduced back into a suitable habitat.