Ecology

Beavers

Anne Gageby
Strawberry Hill Nature Preserve

(3/2023) There are few animals that agitate the well of emotions quite like the beaver. On one hand, farmers and landowners regularly lament the immense damage done by this instinct-driven animal. On the other hand, ecologists praise the positive ripple effect brought about by the animals’ efforts. The undeniable reality is both are correct and justified in their opinions. Beavers are simple animals that produce complicated outcomes. They are, in effect, a true keystone species.

Keystone species are either predators, mutualists, or ecosystem engineers. Beavers fall into the latter category. River ecosystems depend on beavers to take down and remove old and dead trees. In doing so, healthier trees have more resources and opportunities to flourish. Furthermore, beaver dams affect a wide variety of species. Once a dam is built, the area surrounding the dam becomes a pond and marsh. As water covers the bases of trees, it cuts off oxygen for trees’ root systems, killing the trees within a relatively short time frame. Snags, dead trees that haven’t fallen, provide homes and perches for a wide variety of birds and animals, from owls and hawks to bats. These new marshes provide a healthy habitat for ducks, geese, fish, reptiles, and amphibians. Otters, raccoons, herons, ospreys, and other predators are drawn to the marsh’s abundant prey. The new wetland quickly becomes a thriving ecosystem with incalculable benefits to local flora and fauna.

It's easy to wax poetic about beavers’ ecological impact but the reality isn’t entirely positive. Innumerable farmers have faced crop loss and devastation because of beavers damming creeks and ponds. The resulting floods can and have decimated a year’s worth of crops, costing farmers income and lost time. Repairing damaged fields and streams further digs into landowners’ pockets. To many, beavers are a frustrating and damaging animal to have around. Trapping and hunting are seen as vital to controlling population numbers and saving landowners from potential financial ruin.

The back-and-forth between valuable asset and troublesome nuisance isn’t new. This strange-looking rodent has a storied yet complicated history going back thousands of years and spans the globe. Beavers have been featured on some of the oldest animal effigies in the world. The oldest known monumental wood carving (10,000-12,000 years ago), the Shigir Idol, was partially carved with tools made of the lower jawbone of a beaver. In ancient Persia, beavers were considered sacred and protected by law. A medieval bestiary held within Oxford’s Bodleian Library contains depictions of beavers with silvery coats and long, wolf-like bodies. Beavers were considered so important to the city of Oxford that heralds included the rodent on the city’s coat of arms alongside an elephant. We still see evidence of this importance in modern-day America. Oregon, which was founded in 1859, adopted the beaver as the official state animal.

During America’s early days, beavers were an especially valuable resource. Their pelts are thick and were used to trim clothing. In the early 1800s a single raw beaver pelt could earn a trapper roughly $4, or about $80 in today’s money. Castoreum, produced from castor sacs, located near the anus of a beaver, has been used for centuries in medicines, perfumes, and even food additives. The oil can be processed with alcohol to create a surprisingly vanilla-like aroma.

Within a few generations, however, this valuable resource was nearly wiped out by unregulated trapping and hunting. By the end of the nineteenth century, beavers had been eliminated from most of the East coast and Pennsylvania. The tide turned for beavers after the state legislature passed a law protecting this keystone species in 1903. The Pennsylvania Game Commission released a pair of beavers from Wisconsin in the northern part of our state in 1917, setting off a string of planned releases between 1918 and 1925. The Game Commission imported Canadian beavers to be released within designated refuges throughout the state. The effect was nearly immediate. By 1934, the beaver population was large enough and healthy enough to allow trapping. There are now an estimated two million beaver thriving across North America.

Beavers once roamed North America in numbers estimated to be hundreds of millions. During the Pleistocene, beavers fell into the megafauna category alongside saber-toothed tigers and giant sloths. Prehistoric beavers were at one point the size of grizzlies. As the last ice age melted into history and glaciers became swirling rivers and lakes, beavers settled in for the ride. They chewed through the prehistoric forests and built dams, eventually redirecting the flow of massive waterways. Over the years, these waterways encouraged rich sediments to swell from within. Eventually, the water receded, through beaver colony dispersion, dam failure, or something else, leaving behind a slurry of nutrients vital to a budding ecosystem. After all, rich soil begets rich forests. The forests of North America would, in time, become something breathtaking.

Though considerably smaller than their ancestors, beavers haven’t changed much over the ages. They are herbivores, preferring branches, twigs, and buds from trees such as poplar, willow, aspen, cottonwood, maple, birch, and black cherry trees. Pine, on the other hand, is usually too sticky for the average beaver, though there are exceptions to this rule. They also feast on water lilies, ferns, mushrooms, duckweed, algae, and water plants such as cattails. Beavers gather sticks to build their feed piles and anchor them to the bottom of the creek or pond. From there, they gather sticks and branches to create a pile of brush beneath the water. From this pile of brush comes their feed pile which provides food throughout the winter.

Despite appearances, beavers don’t actually eat the wood of a tree, just the bark. They prefer trees that are about three to four inches in diameter though they will fall trees several times if necessary. Ironically, beavers don’t produce cellulase, the all-important enzyme needed for digesting cellulose. Instead, microorganisms called caecal microbes convert cellulose into nutrients on behalf of the host. Beavers, similar to ruminant animals such as sheep, goats, deer, and cows, digest their food twice.

On a larger scale, keystone species such as Yellowstone’s wolves garner more attention and more debate than beavers. It’s not likely beavers will ever be splashed about on television with experts chiming in on news segments or writing major articles for or against their existence. No, the North American beaver is less sensational than other keystone species. And yet, if you ask locals for their opinion, you’ll likely get a heated opinion, one way or another.

Anne Gageby is the Environmental Education Manager of the Strawberry Hill Foundation. Strawberry Hill inspires stewardship of our natural world by
connecting the community with educational opportunities.
 Learn more by visiting StrawberryHill.org.