Where Do Wood Frogs Live? The Frog of the Far North

The wood frog’s range at a glance

The wood frog has one of the largest ranges of any North American amphibian. In the east it reaches south along the Appalachian Mountains to northern Georgia, with isolated colonies in Alabama. From there it spreads north through the northeastern United States and the Great Lakes region, then right across Canada’s forests from the Atlantic provinces and Labrador to British Columbia, the Yukon and Alaska.

There are also isolated populations far from the main range, including in the Medicine Bow area of Wyoming and Colorado, in lowland eastern North Carolina and in parts of Missouri. Such isolated populations are often thought to be relics of the ice ages, when cool forests extended farther south.

The northernmost frog in North America

No other North American amphibian or reptile lives as far north as the wood frog. It is the only North American frog found north of the Arctic Circle and the most widespread frog in Alaska, where it lives in boreal forest, muskeg bogs and the edges of the tundra.

Its secret is freeze tolerance. In the far north, winters are long and the ground freezes deeply, so a frog that cannot survive being frozen has nowhere to hide. Wood frogs simply freeze in the leaf litter and thaw in spring. In interior Alaska, they have been recorded spending more than six months frozen and surviving temperatures of about −18 °C (0 °F). The full story is in How do wood frogs survive freezing?

Northern summers are short, so wood frogs breed as soon as the snow melts and their tadpoles develop quickly, changing into froglets about two to four months after hatching.

Woodland homes

As its name suggests, the wood frog is a forest animal. It lives in moist deciduous, mixed and coniferous woodland, from the hardwood forests of New England and the Appalachians to the spruce of the boreal forest. It also uses forested swamps, bogs, cool damp ravines, thickets and wet meadows.

Wood frogs do not climb. They spend their time on the forest floor among dead leaves, where their brown, tan or rusty color and dark eye mask make them very hard to see. Unlike many frogs, they are mostly active by day. They need shade and moisture, and in most of their range they are rarely found far from woodland.

Vernal pools: where wood frogs breed

For a few weeks each spring, wood frogs gather to breed in water. Their favorite breeding sites are vernal pools: temporary woodland ponds that fill with snowmelt and spring rain and usually dry out by late summer or autumn. They also use other shallow waters without fish, such as semi-permanent ponds and bog pools.

Choosing a pool that dries up has a big advantage: no fish can live there, so the eggs and tadpoles escape a major group of predators. The risk is that a pool dries too early in a dry year, killing the tadpoles before they can change into frogs. Breeding very early in spring gives the tadpoles as much time as possible.

This preference sets wood frogs apart from large pond frogs such as the American bullfrog, which needs permanent, warm water and whose tadpoles in the north often take a year or more to develop.

Moving between habitats through the year

Wood frogs use different parts of the forest in different seasons. In early spring adults travel to their breeding pool, and studies have found that they are extremely faithful to the pool where they first bred. After breeding they move into moist woodland, swamps and ravines for the summer. In autumn many move to slightly higher ground to spend the winter in the leaf litter, usually within about 65 m (210 ft) of a breeding pool.

Over a year an individual frog may range over hundreds of meters, and populations around one pool are connected to others more than 1 km (0.6 mi) away. Most young frogs return to the pool where they hatched, but fewer than one in five move to a new pool, which keeps neighboring populations linked.

Do wood frogs live in Europe?

No. Wild wood frogs are found only in North America. Europe has its own brown woodland frogs, however. The common frog looks rather similar, has a dark patch behind the eye, breeds early in spring and also reaches north of the Arctic Circle in Scandinavia and northern Russia. Unlike the wood frog, it cannot survive freezing solid, so it spends the winter in frost-free shelters or at the bottom of ponds.

Threats to wood frog habitat

Wood frogs are still common, and the IUCN lists them as Least Concern. But because they need both forest and nearby breeding pools, they are sensitive to changes in the landscape. Studies have shown that wood frogs disappear from areas once forest cover falls below certain levels or road density becomes too high.

Many frogs are killed on roads during spring migrations, and road salt washing into breeding pools can harm tadpoles. In the United States, small, isolated wetlands such as vernal pools have little federal protection, so their conservation depends largely on individual states. Protecting wood frogs therefore means protecting whole landscapes: the pools, the forest around them and the paths between them.