Beaver colonies: A wonderful home for wildlife

Immersing yourself in a beaver colony is something all outdoorsy people should experience. There are few habitats in Montana that more resemble a jungle than a good beaver colony. Explore one and you will find yourself in a maze of side channels and backwaters choked with thick vegetation and interspersed with open meadows, broad ponds and a seemingly endless variety of wildlife species. The abundance and diversity of wildlife is no coincidence; it results from the work of a "keystone species" the beaver.

A keystone species is one whose presence allows certain plants and animals to exist in an area where they may not otherwise occur. Beaver activity, especially building dams, causes dramatic changes to streams and riparian areas, including creating a diversity of habitat niches that other species can fill. Before we explore some of the species that can benefit from beaver activity, here are some key impacts beavers can have on a stream and riparian area:

1. Beaver dams create ponds and push water into alternate flow pathways through the floodplain.

2. Beaver ponds collect sediment that falls out of the water column when the current is slowed. The combination of a high water table and sediment build-up can expand the riparian area adjacent to the stream.

3. Beavers cut and redistribute vegetation throughout their colony. This increases the diversity of vegetation types by killing some and encouraging growth of others.

So how do these activities benefit such a multitude of species? Let's look at some examples:

Deer, elk, moose, and bears: Most large mammals like cool, secluded places to hang out during the hot, dry parts of the year. The area surrounding a beaver colony may be especially attractive because the expanded riparian area provides more green forage, shade and resting areas for large mammals. Riparian areas are also valuable travel routes for many species, so a broader riparian area provides greater security as they try to move through an increasingly humanized world.

Amphibians: Frogs, toads and salamanders require a variety of different habitat types for mating, egg-laying, growth and overwintering. Amphibians can struggle to maintain strong, well-connected populations when these different habitat types are rare or separated by great distances. Beaver colonies provide many of the habitats amphibians need in close proximity: stagnant pools, pools that are fed through groundwater, backwaters and side channels and both terrestrial and aquatic habitats that are rich with invertebrates.

Ducks: Like amphibians, to successfully breed, ducks need a few different habitat types. Many duck species nest in grassland or shrub habitats, then lead their ducklings on a dangerous journey to water. Beavers push water closer to duck nesting habitat so ducks can quickly move their young to secluded ponds full of aquatic vegetation and invertebrates. In some areas the presence of beaver ponds is the only thing that allows ducks to exist and breed in the stream drainage. Beaver ponds are also important migration stopover habitats as the ponds may be the only open water for many miles.

Otters and Muskrats: Otters are frequent visitors to beaver ponds where they find open water, lots of fish and plenty of channels and backwaters where they can corner those fish. All otters observed in over 150 miles of beaver surveys over three years in southwest Montana were observed in beaver ponds. Muskrats need pooled water and aquatic vegetation to survive which the beavers can provide. They will often build their huts in the same pond as the main beaver lodge, even attached to the lodge!

Songbirds: The diversity of songbirds in an area is often directly tied to the diversity of vegetation types and vegetation structure that is available. By cutting and flooding vegetation, beavers can turn an even-aged stand of riparian vegetation into a mosaic of different vegetation growth forms. This allows a greater variety of songbird species to thrive, while the expansion of the riparian area provides for greater numbers of songbirds overall.

Bats: Many bat species need slow, open water to get a good drink. Stand at a glassy beaver pond at twilight you will often see big groups of bats swooping down over the water to drink before their nightly foraging. Beaver ponds also tend to produce a lot of flying insects and an open place for the bats to hunt them down.

Fish: Beaver impacts to fish are more complicated. Beaver ponds can sometimes warm the water in a stream by reducing shade and creating slow-moving pools. Beaver dams may block movement of spawning fish and the accumulation of silt can also ruin spawning gravels. In some areas, ponded habitat may favor nonnative fish species.

Despite these potential negatives, beaver ponds can also provide overwinter habitat for fish that need deep waters and easy swimming to survive long winters. Beaver activity can also provide critical water resources in late summer and during drought by slowing and storing water both behind the dams and in the floodplain. There is evidence beaver activity along a stream can modulate water temperatures and keep those temperatures from reaching high and low extremes.

Of course, the potential impacts to the wildlife species outlined above will change depending on environmental factors that are specific to each stream. However, we see many of these benefits to plants and animals in most stream systems where beavers successfully create long-term colonies. It is not surprising that there has been a ground-swell of interest in restoring beavers to areas of their historic range or mimicking their dam-building activities throughout North America and Europe. We are starting to learn that beaver activity is an essential component of many stream systems and can result in landscape-scale benefits to water storage and wildlife habitat.