Pushup

Muskrats (Ondatra zibethica) construct and utilize several different types of homes, feeding places and safe zones. The most visible are lodges built from vegetation on the ground or on a substrate of anchored aquatic herbage. These structures can rise five or more feet and contain several rooms and a nest chamber.

Muskrats dig two types of burrows along banks – one is a complicated maze of passages, rooms and nest chambers while the other is a simple cavity used for escape, rest or insulation.

Muskrats also construct exposed feeding platforms or use logs, rocks or other naturally occurring features as places to eat vegetation, which comprises over 95% of the muskrat’s diet.

Although active throughout the year, muskrats spend much time in their dens over the winter. They do not store food, so must continue to find vegetation even under the ice. Muskrats create channels in the mud under the ice to reach their food. In autumn and winter, this rodent makes another structure, called a “pushup” or a “breather”, used in foraging under the ice.

In autumn as the water begins to freeze, muskrats find a crack in the ice or chew a hole in thin ice (often near an air bubble or methane escape). They then push masses of vegetation from underwater through the hole, creating a dome on the surface of the ice. This dome forms an enclosed cavity big enough for one muskrat. Often these pushups are built about twelve feet apart along a channel used for gathering food. The pushup is a resting place where the muskrat can eat in safety without returning to its permanent den or burrow and is also a breathing hole. The insulating effect of the vegetation keeps the entrance hole in the ice open and provides the muskrat temporary  warmth from the frigid water.  If food becomes scarce the muskrat can even eat the herbage lining the pushup.

These pictures were taken at Baum Lake (Shasta County CA), before the heavy snows arrived this winter.

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