Wood Frog
Encyclopedia
The Wood Frog has a broad distribution over North America
, extending from the southern Appalachians to the boreal forest with several notable disjunct populations including lowland eastern North Carolina. The wood frog has garnered attention by biologists over the last century because of its freeze tolerance, relatively great degree of terrestrialism (for a Ranid), interesting habitat
associations (peat bogs, vernal pools, uplands), and relatively long-range movements. The ecology
and conservation of the wood frog has attracted a great deal of research attention in recent years. This may be because they are often considered "obligate" breeders in ephemeral wetlands (sometimes called "vernal pools") that are themselves more imperiled than the species that breed in them (see below). The Wood frog is the state amphibian of New York
Similar to other northern frogs that hibernate
close to the surface in soil and/or leaf litter, wood frogs can tolerate the freezing of their blood and other tissues. Urea
is accumulated in tissues in preparation for overwintering, and liver glycogen
is converted in large quantities to glucose in response to internal ice formation. Both urea
and glucose
act as "cryoprotectants" to limit the amount of ice that forms and to reduce osmotic shrinkage of cells. Frogs can survive many freeze/thaw events during winter if not more than about 65% of the total body water freezes.
If you see a small brown frog with a dark eye mask in the woods, it is likely to be a wood frog. There are no other species with a similar appearance to the wood frog in North America. The first evasive leap is fast and long. Close observation will often glimpse a second short dive under the leaf litter, making the frog appear to disappear.
s feed on plant detritus, algae
and also attack and eat eggs
and larva
e of amphibians, including those of wood frogs.
The feeding pattern of the wood frog, basically similar to that of other ranids, is triggered by prey movement and consists of a bodily lunge that terminates with the mouth opening and an extension of the tongue onto the prey. Note that the ranid tongue is attached to the floor of the mouth near the tip of the jaw, and when the mouth is closed the tongue lies flat, extended posteriorly from its point of attachment. In the feeding strike, the tongue is swung forward as though on a hinge, so that some portion of the normally dorsal and posterior tongue surface makes contact with the prey. And it is at this point in the feeding strike that the wood frog differs markedly from more aquatic Rana species, such as the green frog, leopard frog, and bullfrog. The wood frog makes contact with the prey with just the very tip of its tongue, much like a toad. A more extensive amount of tongue surface is applied in the feeding strikes of the other 3 frog species, with the result that usually the prey is engulfed by the fleshy tongue and considerable tongue surface contacts the surrounding substrate.
is from northern Georgia and northeastern Canada in the east to Alaska
and southern British Columbia in the west. It is the most widely distributed frog in Alaska.
It is also located in the Medicine Bow National Forest.
, freshwater wetlands: woodland vernal pool
s. 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
Rana sylvatica primarily breeds in ephemeral pools rather than permanent water bodies such as ponds or lakes. This is believed to provide some protection of the adult frogs and their offspring (eggs and tadpoles) from predation by fish and other predators of permanent water bodies. Adult wood frogs emerge from hibernation in early spring and migrate to nearby pools. There, males chorus, emitting duck-like quacking sounds. Females deposit eggs attached to submerged substrate, typically vegetation or downed branches. Most commonly, females will deposit eggs adjacent to other egg masses, creating large aggregations of masses. Some advantage is conferred to pairs first to breed, as clutches closer to the center of the raft absorb heat and develop faster than those on the periphery. If pools dry before tadpoles metamorphose into froglets, they die. This constitutes the risk counterbalancing the anti-predator protection of ephemeral pools. By breeding in early spring, however, wood frogs increase their offspring's chances of metamorphosing before pools dry. Following metamorphosis, a small percentage (less than 20%) of juveniles will disperse, permanently leaving the vicinity of their natal pool. The majority of offspring are philopatric, returning to their natal pool to breed.
Adult wood frogs spend summer months in moist woodlands, forested swamps, ravines, or bogs. During the fall, they leave summer habitats 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 adjacent to breeding pools, adult Rana sylvatica ensure a short migration to thawed pools in early spring. Wood frog are mostly diurnal and are rarely seen at night, except maybe in breeding choruses. They are one of the first amphibians to emerge for breeding right when the snow melts, along with Spring Peeper
s.
The wood frog has a complex life cycle that depends on multiple habitats, damp lowlands, adjacent woodlands. Wood frog habitat conservation
is, therefore, complex, requiring integrated, landscape-scale preservation.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, extending from the southern Appalachians to the boreal forest with several notable disjunct populations including lowland eastern North Carolina. The wood frog has garnered attention by biologists over the last century because of its freeze tolerance, relatively great degree of terrestrialism (for a Ranid), interesting habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
associations (peat bogs, vernal pools, uplands), and relatively long-range movements. The ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and conservation of the wood frog has attracted a great deal of research attention in recent years. This may be because they are often considered "obligate" breeders in ephemeral wetlands (sometimes called "vernal pools") that are themselves more imperiled than the species that breed in them (see below). The Wood frog is the state amphibian of New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
Similar to other northern frogs that hibernate
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...
close to the surface in soil and/or leaf litter, wood frogs can tolerate the freezing of their blood and other tissues. Urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
is accumulated in tissues in preparation for overwintering, and liver glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
is converted in large quantities to glucose in response to internal ice formation. Both urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
and glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
act as "cryoprotectants" to limit the amount of ice that forms and to reduce osmotic shrinkage of cells. Frogs can survive many freeze/thaw events during winter if not more than about 65% of the total body water freezes.
Physical description
Wood frogs range from 51 millimetres (2 in) to 70 millimetres (2.8 in) in length. Females are larger than males. Adult wood frogs are usually brown, tan, or rust colored, and usually have a dark eye mask. Individual frogs are capable of varying their color; Conant (1958) depicts one individual when light brown and dark brown at different times. The underparts of wood frogs are pale with a yellow or green cast.If you see a small brown frog with a dark eye mask in the woods, it is likely to be a wood frog. There are no other species with a similar appearance to the wood frog in North America. The first evasive leap is fast and long. Close observation will often glimpse a second short dive under the leaf litter, making the frog appear to disappear.
Feeding
Wood frogs eat a variety of small, forest-floor invertebrates. Omnivorous, wood frog tadpoleTadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
s feed on plant detritus, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and also attack and eat eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of amphibians, including those of wood frogs.
The feeding pattern of the wood frog, basically similar to that of other ranids, is triggered by prey movement and consists of a bodily lunge that terminates with the mouth opening and an extension of the tongue onto the prey. Note that the ranid tongue is attached to the floor of the mouth near the tip of the jaw, and when the mouth is closed the tongue lies flat, extended posteriorly from its point of attachment. In the feeding strike, the tongue is swung forward as though on a hinge, so that some portion of the normally dorsal and posterior tongue surface makes contact with the prey. And it is at this point in the feeding strike that the wood frog differs markedly from more aquatic Rana species, such as the green frog, leopard frog, and bullfrog. The wood frog makes contact with the prey with just the very tip of its tongue, much like a toad. A more extensive amount of tongue surface is applied in the feeding strikes of the other 3 frog species, with the result that usually the prey is engulfed by the fleshy tongue and considerable tongue surface contacts the surrounding substrate.
Geographic Range
The contiguous wood frog rangeRange (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
is from northern Georgia and northeastern Canada in the east to Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and southern British Columbia in the west. It is the most widely distributed frog in Alaska.
It is also located in the Medicine Bow National Forest.
Habitat
Wood frogs are forest-dwelling organisms that breed primarily in ephemeralEphemeral
Ephemeral things are transitory, existing only briefly. Typically the term is used to describe objects found in nature, although it can describe a wide range of things....
, freshwater wetlands: woodland vernal pool
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
s. 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
Rana sylvatica primarily breeds in ephemeral pools rather than permanent water bodies such as ponds or lakes. This is believed to provide some protection of the adult frogs and their offspring (eggs and tadpoles) from predation by fish and other predators of permanent water bodies. Adult wood frogs emerge from hibernation in early spring and migrate to nearby pools. There, males chorus, emitting duck-like quacking sounds. Females deposit eggs attached to submerged substrate, typically vegetation or downed branches. Most commonly, females will deposit eggs adjacent to other egg masses, creating large aggregations of masses. Some advantage is conferred to pairs first to breed, as clutches closer to the center of the raft absorb heat and develop faster than those on the periphery. If pools dry before tadpoles metamorphose into froglets, they die. This constitutes the risk counterbalancing the anti-predator protection of ephemeral pools. By breeding in early spring, however, wood frogs increase their offspring's chances of metamorphosing before pools dry. Following metamorphosis, a small percentage (less than 20%) of juveniles will disperse, permanently leaving the vicinity of their natal pool. The majority of offspring are philopatric, returning to their natal pool to breed.
Adult wood frogs spend summer months in moist woodlands, forested swamps, ravines, or bogs. During the fall, they leave summer habitats 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 adjacent to breeding pools, adult Rana sylvatica ensure a short migration to thawed pools in early spring. Wood frog are mostly diurnal and are rarely seen at night, except maybe in breeding choruses. They are one of the first amphibians to emerge for breeding right when the snow melts, along with Spring Peeper
Spring Peeper
The Spring Peeper is a small chorus frog widespread throughout the eastern USA and Canada.-Subspecies:There are two subspecies of the Spring Peeper, the Northern and the Southern Spring Peeper . The Northern is similar to the Southern except for a strong dark marking on the Southern frog's belly...
s.
Conservation status
The wood frog is not endangered or threatened. In many parts of its range urbanization is fragmenting wood frog populations. Several studies have shown that under certain thresholds of forest cover loss or over certain thresholds of road density, wood frogs and other common amphibians begin to "drop out" of formerly occupied habitats. Another conservation concern is that wood frogs are primarily dependent on smaller, "geographically isolated" wetlands for breeding. At least in the United States, these wetlands are largely unprotected by federal law, leaving it up to individual states to tackle the problem of conserving pool-breeding amphibians.The wood frog has a complex life cycle that depends on multiple habitats, damp lowlands, adjacent woodlands. Wood frog habitat conservation
Habitat conservation
Habitat conservation is a land management practice that seeks to conserve, protect and restore, habitat areas for wild plants and animals, especially conservation reliant species, and prevent their extinction, fragmentation or reduction in range...
is, therefore, complex, requiring integrated, landscape-scale preservation.
External links
- Animal Diversity Web - University of Michigan Museum of Zoology
- Alaska Department of Fish and Game - Wildlife Notebook
- USGS Northern Prairie Wildlife Research Center
- Photographs, video and audio recording of breeding Wood Frogs
- Laboratory for Ecophysiological Cryobiology
- Medicine Bow National Forest (A Habitat of the Wood Frog)-Biodiversity Conservation Alliance
- Wood Frog, Natural Resources Canada