Nancy Heerens-Knudson: La Crosse River marsh remains active in winter

As winter settles in (and spring seems far off) the La Crosse River Marsh seems frozen and dead. Although a few birds are around (the eagles, woodpeckers, cardinals, chickadees and the tufted titmouse among others) most have ﬂed to warmer climates and will return in the spring. What has happened to the other kinds of animals? Where have the dragonﬂies, frogs and turtles gone? Did they migrate too?

Amazingly, some kinds of dragonﬂies do migrate to lay eggs elsewhere but many of them lay eggs in water which hatch into nymphs or larva. In this form they feed on mosquito larvae, other aquatic insects and sometimes tadpoles and small ﬁsh. They can survive under ice and can emerge in the spring to transform into the dragonﬂies we see in the summer.

Aquatic turtles survive the winter cold by burrowing into the mud in the bottom of the marsh and rivers.They are coldblooded and can slow their metabolism and regulate their requirement of oxygen. They ﬁnd enough oxygen in the mud that can sustain them through the winter cold.

Frogs are cold-blooded, too, but they require more oxygen than turtles so they need to hang out on top of the mud to get oxygen from the water under the ice. They also can really slow their energy needs way down to survive the winter.

Many mammals, which are warm-blooded, hibernate to get through the winter: bats, ground squirrels, many rodents, and bears, to name a few. Two important mammals we can see in the winter in the marsh don’t hibernate, the beaver and the muskrat. There are some similarities and sometimes it is hard to tell them apart. They are both semi aquatic rodents and both live along rivers and marshes. They both have tails that help them move in water, but the beaver tail is wide and ﬂat and where winter fat is stored, and the muskrat tail is long, ﬂat and thin.

Muskrats are smaller than beavers and make “push ups” or lodges in the marsh with underwater entrances that they close with aquatic plants. Muskrats don’t stockpile food but they can eat their entrance plants if they need to. Ninety ﬁve percent of their diets are plants, especially cattails and waterlilies and pondweed. Unlike beavers who just eat plants, muskrats

can eat snail, mussels, salamanders and small ﬁsh. Muskrats can have several litters of kits in a year.

Beavers are the second largest rodent in the world, and have a very thick layer of fat under their fur. They stock up on trees that they cut down in the fall and carry to the underwater area around their lodges to eat in the winter and for lodge material. Their favorite food is quaking aspen, cottonwood, willow, alder, birch and maple trees. Beavers mate for life and reproduce just once a year and have one to six kits.

Both beavers and muskrats are nocturnal, so the best time to see them is early morning or at dusk. It can be challenging to spot them now because they both can swim under the ice for 12 to 15 minutes at a time without needing to surface. Beavers are considered an index species because they increase the diversity of wetlands by creating dams that provide habitat for birds, ﬁsh, insects and other animals.

Appearances deceive. Life still abounds in the marsh under the ice.

Life abounds even in the frozen marsh.