Amphibians

American Toad

NPS Photo/Paul Brown

Isle Royale's landscape supports many types of wetlands, from abundant wooded swamps and seasonally wet woodland ponds, to flooded meadows, peat bogs, and marshes. These wetlands, along with the numerous lakes scattered across the island, are where the few frog, toad, and salamander species breed during spring and summer months. Marshes and ponds (usually beaver ponds or associated terraces along streams) are by far the most productive breeding habitats for frogs and toads, although species appear to use almost all habitats available. Spring peepers are the most abundant frog on the island, and they sing in nearly deafening choruses beginning in the early summer. Wood frogs are the first species to begin singing in the spring, while green frogs and mink frogs are typically the last species singing in mid-summer. Salamanders and newts are present and probably common throughout the park, but they are rarely observed because they are typically hidden beneath objects on the forest floor or in water.

Little is known about the island's amphibian populations, although long-term research on boreal chorus frogs in the northeast part of the park has yielded interesting information. Boreal chorus frogs appear to be limited in their range to small pools along the rocky shorelines facing Lake Superior, dragonfly larvae can often eliminate tadpoles when both are present in the same pool, and competition for food is strong among tadpoles in pools without dragonfly larvae. Salamander larvae in these rock pools have also shown similar competitive dynamics.