Rana sylvatica
Wood Frog

The earliest spring breeders in the Chicago Region are found in beech-maple or maple-basswood forests around the shores of Lake Michigan. Wood Frogs are small, ranging from 1 3/8 to 2 3/4 inches long (3.5 to 7 cm). The basic body color can be highly variable, from pink through tan to brown, but they can always be distinguished by a mask-like dark mark behind each eye. Wood Frogs have dorsolateral folds and a white line along the upper lip.

The mating call of male Wood Frogs is "quack-quack" like a duck, but is much quieter than that of the fowl. One cold moonless night in late March-early April, I watched as a female approached a male that had been quietly croaking. As soon as he was aware of her presence, the call tempo speeded up. At last, a "plop" and a splash indicated he had left his calling perch and joined the female in the vernal pond. Texts say that paired Wood Frogs swim while clasped together to deeper water. Up to 3,000 eggs can be laid by each female. Egg masses are usually attached to submerged vegetation and most of the egg masses in any pond are laid together. In just a few days, all breeding is over, and the adults disperse to the surrounding woods to forage. About three weeks after the eggs were laid, tadpoles emerge and by three months later, juvenile Wood Frogs transform and leave the pond.

Chicago region breeding records are available from the first week of March through the first week of April. Usually there are only a few nights of intense breeding activity in any year. tadpoles are believed to leave the ponds in early July, but there have been only a few observations in the region. Summer observations are rare, but where wood frogs are common juveniles are frequently observed from late September through the end of October.


Wood frogs reach peak abundance in the beech-maple dominated mesic forests of Indiana. Breeding usually occurs in red maple swamps, buttonbush swamps, or vernal ponds. In the fall individuals are encountered among the leaf litter of the forest floor or under decaying logs. At one LaPorte County site, we observed several juveniles among low herbaceous vegetation in a seepage fed wetland opening within the forest.

In northeastern Illinois, most reports have been from localities which include both northern flatwoods and mesic woodland communities.

Distribution and Status

The wood frog is abundant in the more heavily forested portions of northern Porter and LaPorte Counties. In some areas, large congregations of calling frogs can be heard from the road on early spring evenings. In the fall it is not unusual to encounter half a dozen juveniles in a short span of time.

In northeastern Illinois, where suitable habitat is less extensive, this species is now very rare and was probably never abundant. However, as recently as the late 1940s, it was apparently possible to collect several individuals on a spring night in parts of Lake County. The causes of the apparent decline are uncertain but are believed to include unpredictable pond hydrology related to drainage, ground water drawdown, increased and more rapid runoff of precipitation, and increased evapotranspiration from an increase in the density of exotic and weedy shrubs.

Historical Illinois records are available from southeastern Lake County, where despite extensive collecting there have been no verified reports since we photographed several individuals in the mid 1980s; from parts of extreme northern and southern Cook County; and from eastern Will County, where there have been a few valid reports in the late 1990s.

Field Notes

March 19, 1986. Lake Co., IL northern flatwoods site. One Rana sylvatica in the (drift fence) cans this morning. It's been in the 50s and raining for the past couple of days, and the soil is finally thawed but barely above freezing in some places. Colder today.... The Rana sylvatica was inactive and did not move until handled. Haven't heard any frogs calling yet.

April 3, 1986. Lake Co., IL northern flatwoods site. Light rain this morning and again this evening. One Rana sylvatica calling around 10:00 pm, and found another, a female, in one of the (drift fence) cans. Also a few Pseudacris calling.

March 8, 1987. Lake Co., IL northern flatwoods site. Mid-morning soil temperature 37 degrees F, air at ground level 63 degrees. One male Rana sylvatica (in drift fence). Pond mostly free of ice. [Note: This is the most recent documented Lake County observation].

March 27, 1997. LaPorte Co., IN, large shrub swamp in second-growth beech-maple forest. Lots of Rana sylvatica calling at 4:30 pm, also some Pseudacris crucifer. Seined, got only two adult male Rana sylvatica and several Rana clamitans tadpoles. Frog calls louder after dark, same two species.

March 27, 1998. LaPorte Co., IN. Warm (70s) and humid, with rain moving in late. At same location as last year, an incredibly loud chorus of Pseudacris crucifer and Rana sylvatica calling from the shrub swamp. Rana sylvatica also calling near Pinhook Bog and a few other nearby spots. Then to Smith, same two species calling there, at least three different wetlands.

October 28, 1999. LaPorte Co., IN. Seepage wetland along drainageway, 50 percent canopy cover of small trees, dense herbaceous layer, small open rivulets, beech-maple on both sides. Saw two juvenile Rana sylvatica, two Rana clamitans, and one Pseudacris crucifer. Photos of one each. More Pseudacris crucifer calling. A couple of Plethodon cinereus in the woods.

April 7, 2000. Indiana Dunes National Lakeshore, Porter Co., IN. Around 80 degrees F., becoming cloudy, brief light rain. Arrived around 4:00 pm, walked a little east, then back west to second pond. Saw (numerous amphibians of six species including) two Rana sylvatica. Out 8:15 pm after photographing numerous animals. by Ken Mierzwa and Ellin Beltz, February 25, 2002

Species of Frogs and Toads of the Chicago Region

Northern Cricket Frogs
Acris crepitans blanchardi
American Toads
Bufo americanus
Fowler's Toads
Bufo woodhousii fowleri
Tree Frogs
Hyla versicolor complex
Spring Peepers
Pseudacris crucifer
Western Chorus Frogs
Pseudacris triseriata
Rana catesbeiana
Green Frogs
Rana clamitans
Pickeral Frogs
Rana palustris
Northern Leopard Frogs
Rana pipiens
Wood Frogs
Rana sylvatica
Plains Leopard Frogs
Rana blairi
Amphibian links . My homepage

Ellin Beltz ebeltz@ebeltz.net
October 26, 2008

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