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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Boreal Chorus Frog
Pseudacris maculata
Family: Hylidae
The population of Boreal Chorus Frog in eastern Ontario and Quebec was previously believed to be Western Chorus Frog, and that population is listed as Threatened (as the Western Chorus Frog) under the federal Species at Risk Act (SARA).
COSEWIC status:- Not Assessed
- No Status
- Least Concern
Description
The Boreal Chorus Frog is a small frog that only grows to 4 cm in body length. Individuals range in colour from brown, tan, grey, orange, green, or olive with a pattern of three stripes running down the back, which are often broken into blotches or spots. There is a white stripe along the upper lip, dark stripes or blotches on the hind legs, and a dark stripe that extends from the snout, through the eye and part way down the side to the groin. The belly is white or cream-coloured, sometimes with grey mottling. The skin is granular in texture and individuals have small toe pads and generally lack webbing on the feet. Larvae (tadpoles) have long tails with a large fin and lack front legs (newly hatched tadpoles are legless). Young larvae are dark olive, brown or grey with a bi-coloured tail and a clear tail fin, but they gain bronze mottling on the head and small blotches on the tail fins as they age. The larvae typically grow to 3–4 cm in total length before metamorphosis. The call of this species is a series of short trills that resembles the sound made by running a finger along the teeth of a comb.
Similar Species
The Boreal Chorus Frog can be easily confused with the Western Chorus Frog, Spring Peeper and Pacific Treefrog. The Western Chorus Frog has slightly longer hind limbs but is difficult to tell apart from the Boreal Chorus Frog. The Chorus frogs are best differentiated by their call; the call of the Boreal Chorus Frog is shorter and faster than that of the Western Chorus Frog. The Spring Peeper has an X-shaped blotch on the back, whereas the Boreal Chorus Frog has three stripes (sometimes broken into blotches). The Pacific Treefrog has a black mask that does not extend past the shoulder and it has large, distinct toe pads.
Distribution
Click for larger image
The Boreal Chorus Frogs has a huge range in Canada that extends from the southeastern Yukon and the Northwest Territories south into Northern British Columbia and across most of Alberta, Manitoba and northwestern Ontario, with an isolated populations in central and eastern Ontario and western Quebec. It was previously believed that the eastern extent of this species’ distribution in Canada was in northwestern Ontario; however, populations in eastern Ontario and Quebec that were previously thought to be Western Chorus Frogs are now known to be Boreal Chorus Frog. This species can be found across a large portion of central and western United States from Idaho south to Arizona and east to Indiana, with a disjunct population in northern New York.
Habitat
This species breeds in small, shallow, open-canopy, fish-free wetlands with short, grassy vegetation, such as wet meadows, swamps and flooded fields. Individuals inhabit a range of moist terrestrial habitats near the breeding sites, including forest, prairie, field, forested foothills and tundra (in the north). They will also use flooded agricultural fields and small ponds or ditches in urban areas as breeding sites, as long as there is sufficient natural habitat surrounding them. Whenever possible, individuals hibernate below the frost line in mammal burrows, ant mounts and other underground cavities.
Biology
In Canada, Boreal Chorus Frogs hibernate during the winter and are active from April or early May until September or October, depending on latitude. Males call to attract females during the breeding season, which occurs in the early spring from April to June, depending on latitude. During breeding, the male grasps the female (amplexus) and fertilization occurs externally in aquatic habitats as the female lays eggs. The female lays 150–1500 eggs in small clusters of 15–190 eggs, which are attached to submerged vegetation. The egg masses are 10–20 cm wide by 30–40 cm long and the eggs are tan to black and are surrounded by a clear jelly envelope. The eggs develop rapidly and hatch in 1–4 weeks, depending on water temperature. The tadpoles transform into frogs after about 2 months and individuals reach sexual maturity in 1–2 years. Boreal Chorus Frogs can live up to 6 years, but most individuals only live for about 3 years. Like several other species of frogs that extend into northern Canada, Boreal Chorus Frogs are able to survive sub-freezing temperatures during hibernation by increasing the levels of glucose in their blood, which acts as a “cryoprotectant” (prevents water from freezing inside the cells). Individuals forage for a wide variety of insects, as well as other invertebrates such as spiders and centipedes.
Threats
Boreal Chorus Frogs occur throughout large expanses of Canada that are relatively undeveloped, and threats to this species are minimal throughout most of its range. However, the disjunct eastern Ontario and Quebec populations occur in a highly developed region where most of the species’ habitat has already been converted to agricultural and urban uses. Pollution, such as herbicides, agricultural effluent and road salt, can be detrimental to frog populations by causing direct mortality as well as developmental deformities. Road mortality can be a significant threat when roads bisect the species’ habitat. Pathogens such as chytrid fungus and Ranavirus can cause mass mortality of frog populations. Climate change may also pose future threats to Canada’s frog populations. Although the species is widespread and abundant throughout most of its Canadian range, populations in eastern Ontario and Quebec have experienced significant declines and local extirpations.