Alaska Fish & Wildlife News
November 2007
ASK A WILDLIFE BIOLOGIST
How are Muskrat Push-ups Made?
Do all bears hibernate? How do wood frogs freeze solid? How far can caribou migrate? If you’ve you ever wondered anything about Alaska’s wildlife, here is your chance to ask. Email your questions to wildlife educator Elizabeth Manning (elizabeth.manning@alaska.gov) and she will try to find an answer from Fish and Game or other wildlife agency biologists. Each month, we will highlight one of the inquiries in Alaska Wildlife News. Here is this month’s question, and answer:
Annette Iverson, Interpretative sign writer, Alaska State Parks
QUESTION: How exactly are muskrat push-ups made? In some places I have read that the muskrats build them by pushing vegetation up through a hole. Other sources say the vegetation is deposited on a hole. Which is correct? Are the houses and feeding huts conical or dome-shaped, or both?
Howard Golden, research biologist specializing in furbearers, Alaska Department of Fish and Game
ANSWER: Muskrats build push-ups, a small, cave-like structure where they can rest and sometimes eat, by opening a 10-15-cm hole through thin ice and pushing up a 30-45-cm pile of fine roots, submerged vegetation, and other debris. As the pile grows it forms an enclosed cavity that sits on top of the ice and serves as a breathing station where muskrats can rest away from their den while still being concealed from predators.
Pushups are sometimes used as a feeding station during severe weather, but food storage is not their primary purpose. They are temporary structures associated with frozen marshes and collapse as snow melts in the spring. Push-up holes also sometimes freeze solid in winter, which can cause large over-winter die-offs. The Alaska blackfish relies on the muskrats’ push-up holes to obtain surface oxygen, and in turn, the blackfish aid the muskrats by helping to keep their breathing holes open.
To complicate things, muskrats make two other types of houses: primary houses or lodges and feeding huts. Both of these structures are conical or dome-shaped in shape and can be hard to distinguish from push-ups, though they are both generally larger in size than push-ups. Houses are the largest of these structures (up to 2.5 m in diameter and 0.5-2 m high) and are multi-chambered nest sites with plunge holes into the water. A feeding hut is a place where muskrats bring food to eat. Muskrats feed mainly on aquatic plants but may occasionally eat small fish, mussels, shrimp or other small aquatic animals. These feeding huts are generally smaller than lodges but, like push-ups, also provide a resting platform and protection from weather and predators.
All three types of structures, i.e. primary houses, feeding huts, and push-ups, are typically conical in shape but I believe lots end up with a dome-shaped appearance.
One good place to find muskrat push-ups around Anchorage is at Potter Marsh. Look for small vegetation piles out in the middle of the ice.
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