Ministry of Environment
Boreal Chorus Frog
|Common Name:||Boreal Chorus Frog|
|Scientific Name:||Pseudacris maculata|
Boreal Chorus Frogs are the smallest frogs in B.C. Adults have a body length of less than 4 centimetres. Chorus Frogs have a long body and comparatively short legs; their long straight toes have small, indistinct toe pads, and the webbing is only along the base of the toe. These frogs may be almost any colour, including grey, tan, brown, red, olive, or green. A well-defined dark stripe runs along the side, from the tip of the nose through the eye to the groin. Three dark-coloured, irregular stripes, often broken or blotched, usually run along the back. The skin on the underside is granular and pale, sometimes marked with a few dark spots on the throat and chest.
Males can be distinguished by the swollen thumb pad they develop in the breeding season, and by their greenish-yellow to dark olive throat and vocal sac. Adult males are generally smaller than females.
Tadpoles are dark with gold flecks above, and light with a metallic shine below. They have an arched tail fin marked with small dark spots, and grow to 30mm in total length.
Boreal Chorus Frogs may be confused with Pacific Chorus Frogs (Pseudacris regilla), which are similar in appearance. Pacific Chorus Frogs, however, have large toe pads at the tips of their toes, and their mask stops at the shoulder rather than extending the length of the body. The distributions of these species do not overlap; Pacific Chorus Frog occurs in southern B.C.
Boreal Chorus Frogs make their home in terrestrial habitats for much of the year, particularly in damp grassy or wooded areas surrounding wetlands. They can be found in and around almost any body of water, as well as in wet meadows, moist brush, grasslands, forests, and some residential and agricultural areas. They breed almost anywhere there is shallow standing water, including seasonal pools, roadside ditches, flooded meadows, and the quiet backwaters of streams. Breeding sites usually have some vegetation present, particularly in shallow water areas 0.5 m deep or less. Tadpoles live in the warmest, most shallow part of wetlands, where some vegetation is present along the shore.
Boreal Chorus Frogs emerge from hibernation in early spring, arriving at breeding ponds or lakes even before all the ice has melted. Congregations of singing males sound a distinctive chorus of high- pitched, rising trills. Each call sounds rather like a fingernail running along the teeth of a plastic pocket comb. At the height of the breeding season these choruses can be heard day and night. The choruses are courtship displays, alerting females to the presence of the males. Breeding pairs join together to fertilize and deposit the eggs. Each female produces 150 to 1500 eggs, usually attached to vegetation in clusters of jelly containing 30 to 75 eggs.
Once breeding activities are complete, adult Boreal Chorus Frogs disperse to more terrestrial habitats. They may spend much of the summer under leaves at the base of willows or brush, or hidden underground. They hibernate over winter in relatively dry sites. Like the Wood Frog, Chorus Frogs can endure temperatures to a few degrees below zero. Increased blood sugar in the tissues resists freezing, while water outside the cells turns to ice. In the spring, the frog thaws and hops away.
These frogs breed in the year following their metamorphosis, and may not live more than one or two years in the wild.
Adult Boreal Chorus Frogs feed primarily on ground-dwelling insects and invertebrates, which they catch with a sit-and-wait strategy. They are particularly fond of ants and spiders, but also consume flies, beetles, aphids, and snails. They will even eat millipedes and caterpillars, which often have nasty-smelling defensive secretions, or mites and springtails, which are very small. The tadpoles are herbivores, feeding on algae
In B.C., Boreal Chorus Frogs occur only in the northeastern corner of the province. Their range extends west from Alberta into the lowland and montane areas of the Peace River region around Fort St John and Fort Nelson. They may be present at elevations of up to 2000 metres.
Breeding may occur from early May through June depending upon local weather, elevation, and latitude. Though egg laying may occur over two or three weeks at a site, in wet weather years breeding may continue until early summer. Eggs take 10 to 14 days to hatch, and the tadpoles reach metamorphosis in about 2 months. Juveniles and adults may hibernate from November through April.
While not in immediate jeopardy, B.C. populations are at the western edge of the Boreal Chorus Frog’s range in Canada and as such may be more vulnerable than populations in other parts of its range. At present, habitat loss due to development is the greatest threat to this species. Boreal Chorus Frogs are on the provincial Yellow List of species considered of conservation concern.
How We’re Helping
Very little is known of the biology of B.C.’s Boreal Chorus Frogs. We’re aiming to learn more about this species’ distribution, ecology, and life history.
Boreal Chorus Frogs are protected under the British Columbia Wildlife Act.
Learn about these fascinating critters and share your knowledge with others. Contribute to B.C. Frogwatch by monitoring when and where Boreal Chorus Frogs are breeding.
- These secretive and largely terrestrial frogs are often heard, but seldom seen. Their tiny size makes them difficult to find, even when the males are calling. Their calls are relatively loud, but deceiving, often sounding as if they’re calling from someplace else!
- Despite their tiny size, these frogs call so loudly that if you stand at the edge of a large chorus, your ears will ring.
- Boreal Chorus Frogs are like the groundhogs of spring. One of the earliest amphibians to emerge from hibernation, this frog comes out before the snow and the ice have even melted!
Photo © Wally Edwards. No reproduction or distribution without permission.