The Birds and the Beavers: Building Habitat Connections

Anna Morris

Director, Wildlife Ambassador Programs

Vermont Institute of Natural Science

Anyone who studies ecology for any amount of time is immediately awed by the way that everything in nature is connected, in some fashion, to everything else. We may ask ourselves what exactly a beaver does that is important to a Bald Eagle, or vice versa, and soon come up with dozens of connecting threads that weave together an ecosystem.

While beavers are regarded as keystone species, changing the character of an ecosystem simply by their presence or absence, birds are widely considered to be sentinel species. Sentinel species stand boldly out in front of other species to our human observations, and help us understand the less visible, underlying issues that an ecosystem may be facing. These issues can be everything from pollutants or toxins harming wildlife, to climate change wreaking havoc with the timing of nesting or migration.

Wetlands in general provide excellent habitat for many species of migratory birds, in the form of nutrient-rich “stopover” sites. Birds, such as Green Herons, traveling long distances during their migration need multiple reliable places to pause and refuel for their arduous journeys. The more wetlands, the safer the journey. Wetlands offer more abundant and diverse food to many types of birds, from insectivores like Marsh Wrens to Belted Kingfishers, to dabbling ducks, Common Loons, and many species of raptors.

But a study of beaver-engineered wetlands in California found that beaver dams doubled the probability of observing Willow Flycatchers, and doubled the density of Song Sparrows, compared to waterways without beavers. Another study in Wyoming found that beaver wetlands had 75% more waterfowl on them than their beaver-less counterparts. Many ecologists have observed a greater diversity and density of bird species near beavers than would be expected, demonstrating that there is some other element to how beavers manage their environment that is even more important to birds than the wetlands themselves.

One explanation comes from the dynamic nature of a beaver wetland. Beaver’s natural boom-and-bust population cycles mean that in some years, an area that was once flooded is left to dry, becoming a meadow or grassland. In future years, it will be flooded again. Without beavers periodically flooding flat areas, many of them would revert to forested land, which can support some bird species, but not others like Bobolinks. When beavers were hunted nearly to extinction in the northeast, grasslands were replaced by farmland, providing habitat for these grassland birds, so long as cutting and mowing practices did not disrupt their nesting cycle. In our modern age with more intensive farming and fewer beaver wetlands, Bobolinks are left with few places to go. Rather than creating a safe haven for Bobolinks with our farm fields, we have instead come to stand as an obstacle to a natural cycle of habitats that historically linked Bobolinks and beavers tightly together.

Managing land for wildlife doesn’t have to be a battle. When we understand that change is the only constant in nature, we can see the whole landscape for what it is: many threads connected to one another, constantly refreshing and forming new spaces over old ones. Like the beaver, we humans can choose to create habitat that supports a diversity of our wildlife neighbors.