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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Rocky Mountain Tailed Frog
Ascaphus montanus
Family: Ascaphidae
COSEWIC status:- Threatened
- Threatened
- Least Concern
Description
The Rocky Mountain Tailed Frog is a small frog that is generally under 5 cm in body length, with males being smaller than females. Individuals are tan, reddish brown, brown, olive green or black with fine black speckling and sometimes light and dark blotching on the back. There is often a dark-edged light bar between the eyes and some individuals have a dark stripe on the face. The belly is light grey, yellowish-white or pinkish. Rocky Mountain tailed Frogs have granular, bumpy skin, flattened hind toes with prominent webbing, and they lack tympani (outer eardrums) and dorsolateral folds (folds of skin running down each side of the back). The “tail”, after which the species is named, is only present in males and is an extension of the cloaca that is used for copulation. Larvae (tadpoles) have a laterally compressed tail with a straight fin, a flattened body, a large, sucker-like mouth, and lack front legs (newly hatched tadpoles are legless). They are dark gray, black or reddish-brown with tan mottling and there is often a white spot at the end of the tail. Larvae can grow up to 6 cm in total length before metamorphosis. This species does not have a mating call.
Similar Species
The Rocky Mountain Tailed Frog may be confused with the Coastal Tailed Frog. However, the distributions of these two species do not overlap. Coastal Tailed Frogs also lack the fine black speckling on the body, while the larvae are relatively uniform in colour and lack light mottling. Rocky Mountain Tailed Frogs can be differentiated from all other Canadian Frogs based on the absence of the tympanum and the presence of the “tail” in the males.
Distribution
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This species’ Canadian distribution is limited to a small area in extreme southeastern British Columbia. The Rocky Mountain Tailed Frog also has a small distribution in the United States and occurs in western Montana, northern Idaho, northeastern Oregon and southeastern Washington.
Habitat
Rocky Mountain tailed Frogs inhabit and breed in clear, cool headwater streams in old growth coniferous forests. This species requires streams with clear, fast-flowing water, rocky bottoms, little aquatic vegetation, a dense forest canopy and summer water temperatures below 16° C. Rocky Mountain Tailed Frogs are highly aquatic and adults are typically found in streams or in the surrounding forest understory. Rocky Mountain Tailed Frogs hibernate under rocks in unfrozen, snow-covered streams or underground in nearby terrestrial areas.
Biology
In Canada, Rocky Mountain Tailed Frogs hibernate during the winter and are active from April or early May until October. The breeding season generally occurs from late August to early October. This species has internal fertilization and the male uses it’s “tail” to transfer sperm directly into the female’s cloaca. Female lays the eggs the following summer. The female lays 400–1,300 eggs in clutches contain 40–85 eggs, which are attached to the underside of rocks in flowing water. The eggs are creamy white to yellowish, are surrounded by two clear jelly envelopes, and are enclosed in two gelatinous strings. The eggs develop slowly and hatch after 4–6 weeks, and the larvae do not undergo metamorphosis until they are 3–5 years of age. Rocky Mountain Tailed Frogs reach maturity at 7–8 years of age (3–4 years after metamorphosis) and can live up to 14 years. Females only reproduce every other year. Adults and juveniles forage in aquatic and terrestrial habitats, though most terrestrial activity occurs at night. They eat a variety of small invertebrates, particularly spiders. Rocky Mountain Tailed Frogs have small home ranges and typically do not move far from the streams that they inhabit.
Threats
Pollution, particularly sedimentation from forestry operations, cattle grazing or roads, is the most significant threat to this species in Canada and is causing ongoing declines. Logging damages terrestrial and aquatic habitats by removing forest cover and it can also alter hydrological regimes, all of which can cause local decline and extirpation. Road mortality is not a major issue for this species, but it can occur in areas where roads bisect the species’ habitat. Pathogens, such as chytrid fungus and Ranavirus, can cause mass mortality of frog and toad populations; however, chytrid fungus does not appear to be present in Rocky Mountain Tailed Frog populations. Climate change also poses a threat to this species, particularly by increasing the frequency and severity of droughts and flood events.