Text and Photos by Linda Hagan, Maryland Master Naturalist
I had the opportunity to go to a program about beavers sponsored by the Natural History Society of Maryland. The program was held at Boordys Vineyards where they had been having problems with flooding of a roadway caused by beavers. Rather than have them trapped and removed, they wanted to find a way to co-exist with the beavers, so they contacted a local conservation company which specializes in beaver restoration projects. The presentation covered management practices which could be used to save the beavers and allow them to do what beavers do best, make and restore wetlands.
Beavers are considered a “keystone” species. The dictionary definition: a species upon which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. One great example of a keystone species was when wolves were reintroduced to Yellowstone National Park. There has been much written about the remarkable change wolves made in a very positive way to the habitat. So much so that other creatures who were no longer there came back. If you can, I would advise everyone who cares about ecosystems and the diverse animals that exist in them to read about the wolves of Yellowstone. Today, however, I am going to write about a creature who lives in Frederick and surrounding counties. This keystone species is the American Beaver.
Beavers are the largest rodent in North America and second largest in the world. They can weigh from 30-60 lbs and can be 40” in length which includes their tail. Beavers were almost hunted to extinction in the mid-1800’s for their valuable thick fur which was used to make top hats. I’m happy to say that beavers have been aided by wildlife management practices and, with their prolific breeding have made a comeback and are hopefully now here to stay. The importance they plan in wetland creation can not be understated.
Beavers can live near humans, but because they are shy they prefer more isolated locations which are unfortunately getting harder to find. Beavers live near streams, creeks, ponds, marshes and small lakes where there is constant water sources; they prefer them to be narrow enough for easy damming. They build dams made of tree cuttings which they pack together with mud and rocks. Beavers cut down trees within 200 feet of the water’s edge so they don’t have to drag the wood very far. Staying close to where their dam and lodges are also helps them avoid predators. Beavers sometimes dig canals from the pond to land so they can float the logs back to the dam. One beaver can cut down between 216 and 300 trees with diameters of 3” or less in a year. On average one acre of aspen trees can support a 5-6 member colony of beavers for 1 to 2.5 years. Beavers are monogamous and have one mate usually for life. They have a single litter of between two to five kits which are born between May and early July. They weigh 1 pound and are a foot long. Kits are fully furred, and their eyes and ears are open. They can swim within hours of being born, but are too buoyant to submerge themselves for several days and the fur is not yet water repellent. At 3-4 weeks old the anal glands used to oil the fur are functioning and they can waterproof their fur. Beavers are also social animals and their colony consist of a breeding pair and two generations of offspring which stay with their parents until 2 yrs of age at which time they are driven off to find their own territory.
They build dams to backup water around the domed shaped lodge they live in so they are protected from predators. These lodges are made of sticks and logs which is plastered together with mud. The lodge can be up to 5’ high and consist of a feeding den, a resting den, and a small air hole at the top for fresh air. When the mud of these lodges freezes it is almost impossible for a predator to break through, but if they succeed the beaver has two underwater entrances they can use to escape. The entrance to the lodge is always below water level. The beaver dams can hold back a great deal of water, but it also allows the water to continue to flow through it. Beavers are constantly maintaining the dams and can heighten the water level by making the damn higher. They need a water height of 2’-3’ to feel safe.
Beavers are herbivores. During the spring and summer they eat aquatic plants such as tubers from cattails and water lilies and shoots from young plants. Beavers cut down trees to get the newer, more succulent growth. During the winter they eat woody vegetation like bark and twigs from birch, ash, willows, poplar, aspen, cottonwoods, pines and other species of trees.
During the fall months beaver have three important jobs they must perform before winter. They refurbish their lodge, they repair and strengthen the dam and they must cut and store food for the winter months. They cut branches, twigs and small logs which they anchor in the mud at the bottom of the pond. This allows them to have a food supply when the pond freezes over. If the ice is thin the beavers can break it from underneath by bumping it with their heads which creates a crack. The beaver then pokes its head through the hole, lifts its front feet up onto the edge of the ice and lunges forward breaking a path with its body and continues to do this until it gets to its destination. If the water level of the dam is too high the beavers will raise the floor of their lodge and the roof of the sleeping chamber.
Beavers must continue to cut wood because, like other rodents, their teeth never stop growing. The eyesight of beavers is weak, but they have a good sense of smell and hearing. They can stay underwater for up to 15 minutes and have a membrane that seals the ears and nose while underwater. They also have transparent eyelids that help them see underwater. The tail which is trowel shaped, has scaly, leathery covering and is 8”-12” long and about 6” wide. The beaver uses its tail as a propeller and rudder. It will also smack its tail on the water as a warning of danger to other beavers. They have long claws on heir feet for digging and the hind feet are webbed to help them propel through the water.
Beavers have a thick winter coat, a water proofing oil and thick layer of fat. At 32 degrees a beaver’s resistance to heat loss in water is about 1/8 of that in air at the same temperature. The fur is compressed in the water which allows the insulating air between the hairs to escape. Beavers also retain heat through their tails and hind legs which serve as heat exchangers. The beaver will only loose 2 percent of its body heat through its tail in winter, but 25 percent of it in the summer. They must constantly groom their fur to keep it clean and oiled to keep it waterproof. Without the oil the fur would become water soaked.
Both sexes have a musk sac that makes an oily substance called “castoreum.” Beavers use a mixture of urine and castoreum to mark their territory on “scent mounds”. They do this by piling up mud and leaves from the pond into a mound. They than deposit the castoreum by straddling the mound and everting the castor sacs and dragging them across the mound. These mounds can vary in size from a few inches to three feet. This scent mound conveys information about the beavers age and sex. The purpose is to communicate to other male beavers to continue on their way. Castoreum is used for communication and oil from the anal glands is used for water proofing their fur. Castoreum has also been used commercially in perfumes and medicines.
As a keystone species, beavers play a very important role in creating wetland habitat. They build a dam in a wooded portion of an area and as the water covers the tree bases, the trees will eventually die. These dead trees called “snags” will become homes for cavity-nesting birds such as woodpeckers, owls, ducks and others. These “snags” are vital nesting sites. It also creates habitat for shorebirds, ducks, fish, reptiles and amphibians. This rich diversity of life will than attract predators like otters, minks, raccoon, hawks, owls and others to the area. When after many years the wood supply they need is gone the beaver will move on to find a new territory. Once they have left and they are no longer there to maintain the dam, it will eventually break and the water will run off creating an open area where grass, shrubs and berry bushes will grow that attract insects and rodents. This new habitat will now attract insect eating birds such as songbirds, plus deer, bear, turkeys and herons. The flow of the natural world continues as a different habitat emerges and has been created. All of this is due to the American beaver.
Beavers were once hunted and trapped to the point of extinction and thought of as only rodents who caused trouble with their dams because they flood roads, pastures and crops. However we now know we can manage their dams with devices such as the flow devices like one installed at Boordys. Humans can actually benefit by letting beavers help us with wetland restoration projects. They can reduce costs because the beavers do the work for free. People are now coming from around the world to attend Beaver Conferences where they learn how beaver can be used to restore wetlands and river restorations. Using funding from NOAA, salmon habitat is being restored in Bridge Creek Oregon. Beavers are industrious creatures whose dams trap sediments, increase flood plains and create wetlands for wildlife. We have learned so much by studying them. No more are they considered just a nuisance to be trapped. They play a role. An important role that would be vacant if not for them.
I hope we can continue to call the return of the American Beaver a success story and witness more success stories for other creatures we share our planet with in the future. All creatures play a role…either predator or prey. Keystone creatures play a vital role for all other creatures by creating and protecting habitats. You remove the keystone and the whole ecosystem changes drastically.