Beavers Helping Frogs And Toads Survive

Though considered a pest because of the culvert-clogging dams it builds on streams, the beaver is an ally in conserving valuable wetland habitat for declining amphibian populations, a University of Alberta study shows.

The study, conducted in the boreal forests of west-central Alberta, showed that frog and toad choruses are only present on streams where beaver dams are present. While surveying the calls of male frogs and toads engaged in acoustic displays for females, researchers recorded approximately 5,000 boreal chorus frogs, wood frogs and western toads at 54 beaver ponds over a two-year period. Pitfall traps on beaver ponds captured 5.7 times more newly metamorphosed wood frogs, 29 times more western toads and 24 times more boreal chorus frogs than on nearby free-flowing streams.

The study identifies beaver as a valuable 'surrogate species', said University of Alberta researchers Dr. Cam Stevens (lead author) and Dr. Cindy Paszkowski. The work is published in the January 2007 issue of Biological Conservation. Surrogate species can be indicators of changes to the environment caused directly or indirectly by human activities, population changes in other species, or they can act as 'umbrellas' protecting a large number of naturally co-occurring species.

"The concept of surrogate species in conservation planning offers simple, ecologically-based solutions to help conserve and manage ecosystems," said Paszkowski, a professor of biological sciences at the University of Alberta in Edmonton, Canada.

The beaver pond seems to provide suitable breeding habitats because of its warm, well-oxygenated water, which enhances development and growth rates of frog and toad larvae. As well, the ponds may be less hospitable to predatory fish because the dams are often located on small streams where winterkill conditions are common, the study suggests.

The findings could benefit amphibian conservation efforts for forestry and energy industries, by making room for beaver dams in their landscape-use plans, the researchers said.

"The challenge will be to promote modest levels of beaver activity even where conflicts with human interests might occur, such as areas designated for tree harvesting and landscapes with high road densities," Stevens noted.

Beaver may prove useful as a surrogate species in helping conserve frogs and toads in other remote parts of Canada's boreal forest and western North America.

The study was supported in part by the Natural Sciences and Engineering Research Council of Canada.