Creature Feature: Beaver (Castor canadensis)

Beaver feeding on plant materials - Photo Lindsey Krause
Beaver - Photo Tim Daniel

Beaver – Photo Tim Daniel

Imagine an Ohio awash in wetlands. Every stream with slow, willow-choked meanders, most rivers with meadows and pools, all without human intervention. This was how the state must have appeared during the early 1700s, when beavers were widespread. Most of Ohio’s watercourses would’ve looked more like those in Canada or the northern Rockies, where the terms beaver swamp, beaver pond, and beaver meadow have a meaning more than just historical. Such beaver-managed wetlands are tolerated there because all of their benefits outweigh the loss of some trees on mostly state- or federal-owned land. Beaver ponds are the original rain gardens, slowing and filtering rain- and floodwaters, as well as providing habitat for rare aquatic plants and animals (see this PBS information page). Most of Ohio’s land is private, however, and many owners are not impressed by felled trees or submerged fields. As a result, the re-population of our state by these industrious rodents has come with some controversy.

American beavers (Castor canadensis) are remarkable animals in many ways. These large (up to 10 pounds), long-lived (up to 20 years) aquatic rodents are one of the few animals besides man to form stable, long-term families that cooperate to manipulate their environment. Their favored habitat is slow-moving water. Clumsy on land, beavers are good swimmers, with webbed paws and a flat tail that can be used like a whale’s fluke. They also have a thick, water-repellent pelt that helps them with buoyancy and warmth while they are in the water.

To make their world safe and food-rich, beavers dam up streams. They use their huge front incisors to gnaw down trees, then drag the trees across a stream, forming a scaffold for a dam. The cracks between trunks are sealed with mud and grasses, backing up the stream flow to form a pool behind the dam (see this YouTube video). This pond is safer for them than the original stream, and the reeds and small trees that grow on its marshy edges are a tasty treat to beavers. Beavers still do much of their foraging and dam maintenance at night in order to avoid predators. This has forced them to evolve acute senses of smell and hearing, while vision has languished.

Beaver feeding on plant materials - Photo Lindsey Krause

Beaver feeding on plant materials – Photo Lindsey Krause

To further protect themselves against predators, beaver families build lodges. Usually these are mud and stick structures in the middle of beaver ponds, with hollowed-out chambers inside, but occasionally they will dig out an elaborate burrow system in a steep stream bank. The lodges usually have an ingenious underwater entrance that discourages most predators from entering. In the lodge, beavers raise their kits and socialize with older children and one-year olds (see this YouTube video). A Beaver pair is monogamous, but often has older children staying on to help maintain the pond and the lodge, especially when suitable habitat nearby is crowded. Food, in the form of cut water plants and small trees, is stored underwater near the lodge or in the nearby dam. These storage areas become especially dense during the fall, when the Beaver family “packs the larder” for the upcoming winter.

Extensive fur trapping effectively exterminated Beavers here by the 1830s. Beavers are nothing if not resilient, however. Small groups eluded capture in isolated areas of Pennsylvania, Michigan, and Wisconsin, and these started to recolonize the Midwest once beaver fur was replaced by synthetics. The first ones reached eastern Ohio in the late 1930s, and they’ve gradually spread back across the state. But it wasn’t the same state, with forests largely replaced by farms and suburbs. Unfazed, beavers have started to make homes in our parks, greenbelts, and watercourses.

Beaver evidence: a downed tree showing characteristic beaver tooth marks - Photo Rona Proudfoot

Beaver evidence: a downed tree showing characteristic beaver tooth marks – Photo Rona Proudfoot

Here in Columbus, they’ve penetrated even our most urban parks, but are still not yet common. The Metro Parks frown on Beavers because of their habitat manipulation, but water conservation areas like Hoover Reservoir and upper Alum Creek Reservoir and upper O’Shaughnessy Reservoir tolerate them. Delaware Reservoir has quite a few. To find Beavers, look for their characteristic triangular gnawings on the bases of trees, then return in the evening to attempt observing them. Your smell will give you away, but if you patiently sit, the Beavers will learn that you’re not a threat and will come out to work (though this may take several evenings). Nature author Hope Ryden famously insinuated herself into a Beaver family’s nightly routine this way. Perhaps you can learn something about how beavers are adapting to central Ohio.