Linking aquatic and terrestrial environments: can beaver canals serve as movement corridors for pond-breeding amphibians?

Beavers Castor canadensis are well known as ecosystem engineers for creating ponds by damming streams. However, in wetlands with soft substrates and shallow banks, beavers often dig networks of foraging canals, the ecological effects of which have received little study. We examined how canals are used by pond-breeding amphibians during dispersal and migration between aquatic and terrestrial habitat, focusing on the wood frog Lithobates sylvaticus, in Miquelon Lake Provincial Park, Alberta, Canada. In late summer, the number of emigrating young-of-the-year (YOY) wood frogs encountered at drift fences in riparian zones was highest at beaver canals and declined with distance from canal edges. On visual encounter surveys along the pond perimeter, YOY and adult wood frogs were up to nine times more abundant on beaver canals than along shorelines not modified by beavers. Beaver canals provided habitat for adult wood frogs and also functioned as movement corridors for emigrating YOY frogs, with possible implications for survival to maturity, meta-population dynamics and nutrient transfer between aquatic and terrestrial environments.