Beaver, Architects To The Birds

"Beaver are very successful today in Pennsylvania and contribute to all types of wetlands -- forested, scrub, emergent and open water -- except marine wetlands," says Diann Prosser, graduate student in wildlife ecology. "One of the questions we had was what is the relationship between beaver pond succession and waterfowl productivity."

The Pennsylvania Game Commission, which is interested in understanding beaver for possible future management purposes, funded this research along with the Penn State Cooperative Wetlands Center. Prosser and Dr. Robert P. Brooks, professor of wildlife and wetlands, investigated beaver pond succession -- the stages a pond goes through during its life span -- and the birds, both waterfowl and others, that enjoy the habitat created by beaver.

"The Game Commission was particularly interested in waterfowl and broods -- mothers and their chicks," says Prosser. "They were interested in the types or stages of beaver ponds that are most valuable for waterfowl and their broods. We found that beaver pond succession creates a variety of good habitat for waterfowl and their broods as well as other birds," she told attendees at the annual meeting of the Ecological Society of America today (Aug 5) in Baltimore.

That beaver play a major part in Pennsylvania forest ecology today is amazing considering that the last native beaver in the state was trapped in 1912. Reintroduced in 1917, today there are an estimated 32,000 beaver in the state according to the Pennsylvania Game Commission estimates. Prosser estimates about 6,500 beaver ponds in Pennsylvania.

Beaver ponds are typically active for 30 years from initial damming of a stream to abandonment. The three main stages of a beaver pond include new active, old active and abandoned. In the first stage, a stream is dammed and a pond forms, providing a combination of wooded cover and surface water.

In the old active stage the dam is wider and the pond enlarged. Tree trunks, but little overhead cover remain. The pond is somewhat channelized with open water mixed with shrubs and herbaceous ground cover. In the abandonment stage, the dam, no longer maintained, breaks and the water level decreases. Herbaceous and shrubby cover characterize this stage.

All six of the Commonwealth's common breading waterfowl were found on beaver ponds in Pennsylvania -Canada goose, wood duck, green winged teal, American black duck, hooded merganser and mallard. Overall, waterfowl used all stages of beaver ponds, but were more common on new active ponds and old active ponds. These areas produced the most broods. Wood duck, mallard and hooded merganser were the most common species seen. Geese prefer the more open older and abandoned ponds, while wood duck, hooded merganser and black duck used areas with more cover.

Beaver ponds also create habitats for marsh and song birds. The American Bittern and Virginia Rail, both secretive marsh birds, were found in older ponds. Among the wetland-dependent song birds, the Louisiana waterthrush and Acadian flycatcher were only found at active ponds, the alder flycatcher and red-winged blackbird prefer older ponds and the swamp sparrow, common yellowthroat and veery were found in all beaver pond habitats.

"A beaver pair's goal in building a dam is to create a pond where they can build a lodge, hide from predators in the water, raise offspring and store food for the winter," says Prosser. "In the process, they are creating a variety of wetland habitat for waterfowl and other wetland-dependent birds."