Boreal Chorus Frog
Boreal Chorus Frog
Other names: Boreal Tree Frog
The Boreal Chorus Frog is the smallest frog found in British Columbia, growing to a maximum body length of 4 cm. Its legs are relatively short for its body, and it has indistinct toe pads to help it climb, with webbing only at the base of the toes. Boreal Chorus Frogs can be found in a variety of colours including tan, brown, grey, orange, green, or olive and are characterized by a pattern of three stripes running down the back that may often be broken into blotches or spots. They have a dark brown or black mask that runs through the eyes and along the side to the groin, a white stripe on the upper lip, and usually dark blotches on the hind legs. The belly is usually white or cream-coloured and may display some mottling. Males may be differentiated during the breeding season by the presence of a swollen ‘thumb’. The tadpoles are dark olive, brown, or grey with long, multi-coloured tail and a large fin. Tadpoles sometimes gain bronze-metallic speckling on the head and tail fin as they age. Tadpoles will grow to 3-4 cm before undergoing metamorphosis.
Boreal Chorus Frog Call
The call of the Boreal Chorus Frog is a series of high-pitched, rising trills. It has been said to resemble the sound made by running a finger along the teeth of a comb. The breeding call is similar to the Western Chorus Frog, but is longer and pulses more slowly. During the breeding season, many frogs will begin to call together, creating a loud ‘chorus’.
The Boreal Chorus Frog may be confused with the Pacific Treefrog. However, ranges of these species do not overlap in B.C., so they are best distinguished by their location. The Boreal Chorus Frog has three stripes down the back (may be broken into blotches). The Pacific Treefrog has a black mask that also runs horizontally through the eye, but does not extend past the shoulder, and it has larger, more distinct toepads. Also, adult Treefrogs are much larger than Boreal Chorus Frogs.
Credit: Andrew Dubois
Boreal Chorus Frog
Credit: Dave Huth
The Boreal Chorus Frog is only found in a small section of northeastern British Columbia from western Alberta into the lowland montane areas of the Peace River region. However, within the rest of Canada, the Boreal Chorus Frog is widely distributed from James Bay in Quebec through northwestern Ontario, Manitoba, Saskatchewan, Alberta, and through the Northwest Territories along the Mackenzie Valley. It is also found in the central United States where it overlaps with the Western Chorus Frog for part of its range. Boreal Chorus Frogs can be found at elevations up to 2000 m.
Boreal Chorus Frogs prefer forest openings around woodland ponds although in the far north it is found on the tundra. They will breed in almost any fishless body of water with at least 10 cm of water, including splash pools, roadside ditches, flooded fields, beaver ponds, marshes, swamps, or shallow lakes. Breeding sites typically have at least some type of vegetation present, particularly in shallow ponds. Tadpoles live in the warmest, shallowest parts of the wetlands where they occur. After the breeding season, adult Boreal Chorus Frogs move to terrestrial habitats and spend much of their time under leaf litter and debris at the base of trees or bushes, or hidden underground. They hibernate through the winter in relatively dry sites, and endure temperatures below zero by raising the glucose level in their cells to act as a natural antifreeze.
Boreal Chorus Frogs breed very early in the spring and are often present at ponds before the ice has completely melted. Breeding occurs from early May to June, depending on local weather, elevation, and latitude. Males will congregate and call during the day and night to attract females. Fertilization occurs externally via. Females deposit between 150-1,500 eggs in clusters of 30-75 attached to vegetation. Eggs hatch within a 10 – 14 days and tadpoles reach metamorphosis by early to mid-summer. Boreal Chorus Frogs will begin reproducing after one or two years and rarely live beyond three years.
Boreal Chorus Frogs use a sit-and-wait hunting strategy to feed on ground-dwelling insects and invertebrates. Their favourite foods are ants and spiders, but they also eat flies, beetles, aphids, and snails. Some Boreal Chorus Frogs will even eat millipedes and caterpillars which are notorious for having defensive secretions or toxins. The tadpoles are mostly herbivorous and feed on algae.
Boreal Chorus Frogs do not appear to be in immediate danger, however, the populations within British Columbia represent the extreme western edge of the species range, thus, they may be more vulnerable than populations in other areas. The greatest threat to the species at present is habitat loss due to development. Very little is known about the ecology and biology of B.C.’s Boreal Chorus Frogs. Recent studies suggest Boreal Chorus Frogs may be declining in eastern Canada due to a loss of wetland habitat. As more knowledge on the species is acquired, we will gain a better understanding of their conservation status.
Did You Know?
Boreal Chorus Frogs can be thought of as the groundhogs of spring. While these little frogs probably don’t cast much of a shadow, they are one of the earliest amphibians to emerge from hibernation, and they will often come out before the snow and ice have even melted.
The call of the Boreal Chorus frog is very loud, and if you stand near the edge of a pond where many males are chorusing together, your ears will ring!