B.C. Reptiles & Amphibians

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Credit: Dave Huth

Coastal Tailed Frog

Ascaphus truei

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Description

Other names: Pacific Tailed Frog, Western Tailed Frog

Coastal Tailed Frogs are very unusual looking frogs. They do not have an external eardrum (tympanum) and males have an external copulatory organ that looks like a tail. Coastal Tailed Frogs are small, growing to 4-5 cm in body length, and, like most other frogs, males are generally smaller than females. They can also be recognized by their vertical pupil, bumpy skin, flattened and webbed hind toes, and lack of dorsolateral folds. Coastal Tailed Frogs are generally dark coloured and range from olive, grey, tan, brown, or black. They will sometimes have a dark-edged light bar or triangle between the eyes and some will have a dark stripe on the face. The belly is cream coloured. Both tadpoles and adults are well adapted to living in fast-flowing streams. Tadpoles have a sucker-like mouth that they use to cling to rocks and debris in fast-flowing water. The tadpole body is dorso-ventrally flattened with a low tail fin. They are dark grey or dark brown and get lighter in colour as they age. Tadpoles grow up to 6 cm in body length before metamorphosis. Coastal Tailed Frogs are the longest living frogs in North America, reaching up to 20 years of age.

Listen to the Indigenous words for “frog” here!

Coastal Tailed Frog Call

This species lacks a tympanum and, therefore, does not have a breeding call. This may be an adaptation to living with the constant noise of mountain streams.

Coastal Tailed Frog Call

This species lacks a tympanum and, therefore, does not have a breeding call. This may be an adaptation to living with the constant noise of mountain streams.

Similar Species

The Coastal Tailed Frog is very similar to the Rocky Mountain Tailed Frog, and the two were considered a single species until recently. The distributions of the two species do not overlap. The Rocky Mountain Tailed Frog has black speckling on the body, and tadpoles have distinct light mottling; both of these features are absent in Coastal Tailed Frogs. The Coastal Tailed Frog can be recognized from all other Canadian frogs by the absence of the tympanum and the presence of the ‘tail’ in males.

Coastal Tailed Frog

Rocky Mountain Tailed Frog

Distribution

Coastal Tailed Frogs are limited in Canada to the coastal mountains of British Columbia, from the Lower Mainland to the Nass River on the North Coast, and within the associated windward and leeward drainages. Within the United States, Coastal Tailed Frogs can be found along the West Coast to Northern California and along the Alaska Panhandle. They have small home ranges and typically will not move very far from the streams they inhabit.
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Habitat

In Canada, Coastal Tailed Frogs hibernate throughout the winter and are active from April to October. They will hibernate under rocks in unfrozen, snow-covered streams or underground in nearby terrestrial habitats. Coastal Tailed Frogs are highly aquatic and will usually be found in streams, or very close to them. Adults are mainly active at night, but can sometimes be found during the day, especially in damp, cool habitats. Coastal Tailed Frogs prefer non-fish bearing streams that are permanent, cold, and fast-flowing with coarse rocky substrates. Headwater streams are very important for this species, which makes them particularly vulnerable to logging. The ideal home for a Coastal Tailed Frog is within a stream with step-pools and cobbled stretches and minimal amounts of detritus and fine sediments that flows through old-growth or older-stage second growth forests with dense understory. Conversely, tadpoles may be abundant in streams flowing through clear-cuts. However, high densities of tadpoles in clear-cuts may be a short-term reaction to an abundance of food caused by algal growth from increased sun exposure after logging and does not necessarily reflect a healthy ecosystem. If ideal habitats do not exist post-metamorphosis, the population will not survive. Therefore, the abundance of reproductive adults is a better indicator of habitat quality and population health.

Reproduction

The breeding season for Coastal Tailed Frogs occurs from August to October. Coastal Tailed Frogs lay eggs later than the inland species, have smaller clutch sizes, shorter incubation periods, and smaller hatching sizes than the Rocky Mountain Tailed Frog. As they lack a tympanum and do not produce breeding calls; it is unknown how mates find each other. Tailed Frogs are the only frog species in North America that use internal fertilization. Mating occurs in streams after a successful courtship ritual. The male will use its ‘tail’ to transfer sperm directly into the female’s cloaca. The female will not lay eggs until the following summer. At that time, she will lay up to 1300 eggs in clusters of 30-80 by attaching them to the underside of rocks in flowing water. The eggs are creamy or yellowish in colour and are surrounded by jelly envelopes and enclosed in two strings. Eggs hatch after 4-6 weeks, but tadpoles do not undergo metamorphosis for 3-5 years in Canada. Coastal Tailed Frogs do not reach sexual maturity until 4 years after metamorphosis (or 7-9 years after hatching) and will live up to 20 years. Females will only breed every second year.

Diet

Coastal Tailed Frog tadpoles survive mostly on diatoms within their stream habitats. Adult tailed frogs are generalists and feed on most insects and invertebrates they encounter, although one of their favourite foods are spiders. They will forage in both aquatic and terrestrial habitats, mostly at night, using a sit-and-wait hunting strategy. Coastal Tailed Frogs do not grab prey with a sticky tongue like other frogs, as the tongue is attached too closely to the floor of its mouth. Instead, Tailed Frogs pounce on their prey and grab them with their mouth.

Conservation Status

Global: G4 (2016)

COSEWIC: SC

SARA:1-SC (2003)

Provincial: S4

BC List: Yellow

Learn more about conservation status rankings here

Threats

Coastal Tailed Frogs are heavily reliant on specific stream habitat characteristics, thus, any activities that alter or degrade these types of streams are detrimental to Coastal Tailed Frogs. Pollution, especially from sedimentation after forestry, cattle grazing, or roads is the most significant threat to Coastal Tailed Frogs in Canada. Logging degrades terrestrial and aquatic habitat by removing forest cover and shade and alters hydrological processes. Both of these factors can cause local declines or extirpations for Tailed Frogs. Road mortality is not a major concern for Tailed Frogs as they do not travel far from their stream habitats, but it can be an issue where roads bisect the species’ habitat. Chytrid fungus and Ranavirus can impact frog populations, and may be major causes for concern if spread to Tailed Frogs. Climate change may pose a risk to Coastal Tailed Frogs by increasing the frequency and severity of drought and flood events.
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Did You Know?

Fact #1

Tailed Frogs are the only members of the Family Ascaphidae. They are considered to be ‘primitive’ frogs as their bodies resemble older groups of frogs that have since gone extinct. They have 9 presacral vertebrae, where most other frogs have 8, and they possess ribs which have been lost in most other groups of frogs.

Fact #2

The closest living relative of Tailed Frogs in B.C. is a species found only in New Zealand.

Fact #3

Coastal Tailed Frogs have no eardrums, but they may be able to sense vibration in the water.

Species Account Author: Marcus Atkins

References
B.C. Conservation Data Centre. 2021. BC Species and Ecosystems Explorer. B.C. Minist. of Environ. Victoria, B.C.
Available:https://a100.gov.bc.ca/pub/eswp/ (accessed May 19, 2021).
Bury, R.B., and M.J. Adams. 1999. Variation in age at metamorphosis across a latitudinal gradient for the tailed frog, Ascaphus truei. Herpetologica 55: 283-91.
COSEWIC. 2011. COSEWIC assessment and status report on the Coastal Tailed Frog Ascaphus truei in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xii + 53 pp. (www.registrelep-sararegistry.gc.ca/default_e.cfm).
Matsuda, B.M. 2001. The effects of clear-cut timber harvest on the movement patterns of Tailed Frogs (Ascaphus truei) in southwestern British Columbia. M.Sc. thesis, Department of Forest Sciences, University of British Columbia.
Matsuda, Brent M., David M. Green and Patrick M. Gregory. 2006. Amphibians and reptiles of British Columbia. Royal British Columbia Museum, Victoria.
Nielson, M., K. Lohman and J. Sullivan. 2001. Phylogeography of the Tailed Frog (Ascaphus truei): implications for the biogeography of the Pacific Northwest. Evolution 55: 147-60.
Richardson, J.S., and W.E. Neill. 1998. Headwater amphibians and forestry in British Columbia: Pacific giant salamanders and tailed frogs. Northwest Science 72: 122-123.
Van Horne, B. 1983. Density as a misleading indicator of habitat quality. Journal of Wildlife Management 47: 893-901.
Wahbe, T.R., and F.L. Bunnell. 2003. Relations among larval tailed frogs (Ascaphus truei), forest harvesting, stream microhabitat, and site parameters in southwestern British Columbia. Canadian Journal of Forest Research 33: 1256-1266.
http://linnet.geog.ubc.ca/efauna/Atlas/Atlas.aspx?sciname=Ascaphus%20truei&ilifeform=1
http://www.canadianherpetology.ca/species/species_page.html?cname=Coastal%20Tailed%20Frog
https://www.naturewatch.ca/frogwatch/tailed-frog/
https://www2.gov.bc.ca/gov/content/environment/plants-animals-ecosystems/wildlife/wildlife-conservation/amphibians-reptiles/amphibians-in-b-c/frogs-toads
http://a100.gov.bc.ca/pub/eirs/finishDownloadDocument.do?subdocumentId=1304
https://species-registry.canada.ca/index-en.html#/documents/1550