Wood Frog

Wood Frog is the common name given to Rana sylvatica. The Wood Frog has a broad North American distribution, extending from the Southern Appalachians to Boreal forests. As for other northern frogs hibernating close to the surface in soil and/or leaf litter, wood frogs are resistant to freezing. Liver glycogen is converted in large quantities to glucose, in response to ice formation in their tissues. Glucose acts as an antifreeze, inhibiting ice formation in and rupture of cells. If ice formation is confined to extracellular fluids, they can survive the winter.

Wood frogs are forest-dwelling organisms that breed primarily in ephemeral, freshwater wetlands: 'woodland vernal pools'. Long-distance migration plays an important role in their life history. Individual Wood Frogs range widely (hundreds of meters) among their breeding pools and neighboring freshwater swamps, cool-moist ravines, and/or upland habitats. Genetic neighborhoods of individual pool breeding populations extend more than a kilometer away from the breeding site. Thus, conservation of this species requires a landscape (multiple habitats at appropriate spatial scales) perspective. Although the wood frog is not a particularly rare species (unless on the edges of its range), its habitat is rapidly disappearing due to conversion to housing, road building, and wetland loss and degradation.

Physical description

Wood Frogs range from 51 to 70 millimeters (roughly 2.5 to 3.0 inches) in length. The females are much larger than males. They are usually brown, tan, and rust colored. The underparts of the frogs are yellowish and sometimes greenish-white.

DietWood Frog adults eat a variety of small, forest-floor invertebrates. The tadpoles primarily consume algae growing on leaves and other surfaces in breeding ponds. However, "trophic reversal" has been documented for wood frog tadpoles and salamander larvae.

Habitat

Wood Frogs are found from northern Georgia and in isolated colonies in the central highlands in the eastern to central parts of Alabama, up through the northeastern United States, and all the way across Canada into Alaska. It is the most widely distributed frog in Alaska. They can be found from southeastern Alaska to north of the Brooks Range.

Wood Frogs primarily breed in ephemeral pools rather than permanent water bodies such as ponds or lakes. This is believed to give Wood Frogs, and other ephemeral-pool breeding amphibians, a selective advantage in avoiding predation by fish and other predators typical of permanent water bodies. Adults emerge from hibernation in early spring and migrate to nearby pools. There, males chorus (duck-like quacking sounds). Females deposit eggs in floating masses, often aggregated with those of other females in rafts. Some selective advantage is conferred by being first to breed, as masses closer to the center of the raft absorb heat and develop faster than those on the periphery. If pools dry before larvae have completed metamophosis, larvae are stranded and reproductive effort is wasted. Thus, pool hydroperiod (length of time pools holds water) is of utmost importance for individual reproductive success of Wood Frogs. Following successful metamorphosis, a small percentage (generally less than 20%) of juveniles will disperse and breed in other pools. The majority are philopatric, returning to natal pools to breed.

Adult Wood Frogs spend summer months in moist woodlands, forested swamps, ravines, and/or bogs where they maintain body moisture as surrounding evironments dry out. By late fall, they typically leave moist summer habitat and migrate to neighboring uplands to overwinter. Some may remain in moist areas to overwinter. Hibernacula tend to be in the upper organic layers of the soil, under leaf litter. By overwintering in uplands adjancent to breeding pools, adult wood frogs insure a short migration to thawed pools in early spring. By breeding early, adult wood frogs maximize the probability that their offspring will reach metamorphosis before pools dry.

Wood Frogs have complex life cycles, requiring multiple habitats throughout their life history stages. Thus, their habitat conservation is complex, requiring landscape-scale connectivity. In this, they are no different than most ranids; habitat destruction including road building, wetland loss and degradation are primary causes for amphibian declines globally.

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