Species of the Month

These species have been featured in our FYI newsletter as "species of the month."

• Brook Lampreys
• Snapping Turtle (Chelydra serpentina)
• Spotted Salamander (Ambystoma maculatum)
• Eastern Hog-nosed Snake (Heterodon platirhinos)
• Blue Ash (Fraxinus quadrangulata)
• Brook Trout (Salvelinus fontinalis fontinalis)
• Wood Frog (Rana sylvatica)
• Smooth Serviceberry (Amelanchier laevis)

Wood Frog (Rana sylvatica)

The wood frog (Rana sylvatica) ranges further north than any other amphibian in North America, persisting north of the Arctic Circle in parts of Nunavut, the Northwest and Yukon Territories, and Alaska. While reptiles and amphibians are not generally associated with ice and snow, this species is able to cope with northern life, having some unique adaptations to withstand extreme conditions, short seasons and varied habitats.

Adult wood frogs vary in colour from light to dark brown, bronze and orange.

Like all reptiles and amphibians, the wood frog must seek protection during the winter, by hiding in mostly frost-free places and entering a state of reduced metabolic function. However, the wood frog can withstand actual freezing for limited periods, using cryoprotectant chemicals that prevent its body from completely freezing. Wood frogs are commonly found seemingly frozen in snow or ice in early winter or during sudden freezes in early spring. When thawed, the frog slowly raises its heart rate and returns to normal activity, apparently unaffected by the potentially life-threatening ordeal. Excessively low temperatures or long durations of freezing can still harm this frog, but the anti-freeze-like chemicals it produces give it an advantage over many other species in northern latitudes.

In southern Ontario, wood frogs are most commonly associated with woodland habitats, where they are one of the earliest spring breeders along ephemeral pools and other wetlands.

The female wood frog lays egg masses under water, usually attached to branches or leaves. Tadpoles hatch and later transform into froglets within the same season.

Left: In transition - A wood frog “froglet” emerges from its watery nursery.

At a body length of 3.5-8 cm, the wood is a small to medium sized species. The frog’s dorsal (back) colour varies from dark brown, light brown, bronze to orange. A dark mask stretches from the tip of its nose, along either side of the head, through the eyes to its shoulders. The upper lip has a white line along it.

The prominent dorsolateral ridges (two ridges that run along its back) often appear darker or lighter than the surrounding skin. Varying amounts of dark mottling may be apparent along the back and sides. The belly may be solid white, or have grey mottling.

A similar species, the chorus frog, is smaller, has toe pads and does not have dorsolateral ridges.

Right: A wood frog's tummy.
Below right: The dorsolateral ridges run lengthwise along the body.

Depending on the quality of the habitat, wood frogs can be found in high densities, though many populations appear to have declined due to habitat loss, road mortality and pollution. In March and April, even while snow is still on the ground, its awkward, duck-like frog calls can be heard, letting locals know spring weather is right around the corner.

Wood frogs are an indicator of environmental health. To learn more about frog monitoring programs and what you can do to help, visit www.naturewatch.ca/english/frogwatch/on

Contact: , Species at Risk Biologist