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Western Chorus Frog

Pseudacris triseriata

Family: Hylidae

COSEWIC status:
  • Not at Risk (Carolinian population)
  • Threatened (Great Lakes / St. Lawrence - Canadian Shield population)
SARA status:
  • No Status (Carolinian population)
  • Threatened (Great Lakes / St. Lawrence - Canadian Shield population)
IUCN status:
  • Least Concern

Description

The Western 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 is a series of short trills that resembles the sound made by running a finger along the teeth of a comb.

Similar Species

The Western Chorus Frog can be easily confused with the Boreal Chorus Frog and Spring Peeper. The Boreal Chorus Frog has slightly shorter hind limbs but is difficult to tell apart from the Western 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 Western Chorus Frog has three stripes (sometimes broken into blotches).

Distribution

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In Canada, the Western Chorus Frog is limited to southwestern Ontario. Until very recently, it was believed that this species also occurred in eastern Ontario and western Quebec, but those populations have now been identified as Boreal Chorus Frog. This species has a relatively limited distribution in the U.S., occurring from Michigan east to western New York and south to northern Tennessee.

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, Western Chorus Frogs hibernate during the winter and are typically active from late march or April until late September or October. Males call to attract females during the breeding season, which occurs in the early spring from March to May, 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 400–1500 eggs, usually in small clusters of 20–100 eggs, which are attached to submerged vegetation. The eggs are dark brown to black on top and white underneath and are surrounded by a clear jelly envelope. The eggs develop rapidly and hatch in one to four weeks, depending on water temperature. The tadpoles transform into frogs after about 2 months and most individuals reach sexual maturity in the first year after metamorphosis. Most Western Chorus Frogs likely only live for 3–4 years. Western 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, centipedes and slugs.

Threats

Western Chorus Frogs occur in the most heavily developed region in Canada where habitat loss is a significant and ongoing threat. 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. This species has undergone localized declines, but it does not appear to be at risk in Canada.

Additional Information About This Species In Canada