bats at halloween

What is the largest rodent in Iowa? Castor canadensis – the American Beaver – of course. It tips the scales at up to 60 pounds and grows to about 4 feet long. Their hairless, paddle-like tail can be anywhere from 9 – 18 inches long. They also have large, webbed back feet to help with swimming.

One cool thing about beavers is the valves in their nose and ears that can be closed while swimming. That means they don’t have to worry about getting water in their ears or sucking water up their noses like we humans do. Their lips also come together behind their front teeth (incisors), and they can use their tongue to help keep water out of their mouth and lungs while gnawing on branches under water.

We all know beavers live in streams, ponds, and lakes; but some may even live in drainage ditches and river backwaters. In this water environment, they eat bark, twigs and leaves of trees and other woody growth. They may also eat aquatic plants like duckweed, grass, and water lilies.

Beavers living in streams and rivers will build dams of branches, rocks, and leaves, and the spaces will be filled with mud from the stream’s bottom. These can grow to 7 or more feet across, and they will be added to as the water level rises. The entrances will be hidden under the water. Those beavers living in ponds or lakes do not usually build dams, but they will burrow into the bank of the water body. You will still see piles of braches, but this will not be their home.

You may ask why they would build a dam in moving water. The dam will increase the depth and surface area of the water. This makes it easier to drag branches because they will not have to drag it on land as far, and may provide greater access to food. The extra depth also adds protection from predators and keeps the underwater entrances from freezing during the winter.

They do not hibernate during the winter months, but they are rarely seen above water during this time. In the fall, they spend much time cutting braches and sticks into smaller pieces and securing them to the bottom of the stream or pond for a winter food source. When they need to eat, they will swim from the lodge to the food source and return to the lodge with their meal. Mating will take place between January and February with young born in May or June. Six weeks later, the 3 or 4 young will be weaned, but they will remain with the family group for 1 or 2 years before they are forced to make it on their own.

Beavers do not have many predators. Mink may sometimes take young, and larger predators may be able to take an adult. You will have no trouble finding where these large rodents live. Just look for the tell-tale sign of their chews on trees near water. If you hear a slap of the tail and a splash, you probably got too close and scared them into their underwater oasis.

The accompanying photos are from Gray Eagle Wildlife Area, where the beavers burrow into the bank and do not build dams.