AmphibiaWeb - Ascaphus montanus


(Translations may not be accurate.)

Ascaphus montanus Mittleman & Myers, 1949
Rocky Mountain Tailed Frog, Inland Tailed Frog, Eastern Tailed Frog
family: Ascaphidae
genus: Ascaphus
Species Description: 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: 147.160.
Ascaphus montanus
© 2011 Michael E. Jorgensen (1 of 5)
Conservation Status (definitions)
IUCN Red List Status Account Least Concern (LC)
NatureServe Use NatureServe Explorer to see status.
National Status None
Regional Status None
conservation needs Access Conservation Needs Assessment Report .


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Ascaphus montanus adult males range from 30 to 50 mm in SVL, while the females are slightly larger (Green, 2003). The "tail" (actually an extension of the cloaca used for internal fertilization) is a distinguishing feature of adult males in this genus (Duellman and Trueb, 1994). The head is wide, with nostrils widely spaced (Green, 2003). Pupils are vertical and in the shape of a diamond (Green, 2003). There is a skin fold from the eye back to the corner of the mouth (Green, 2003). The tympanum is not visible (Green, 2003). Dorsally, the skin is tuberculate (Green, 2003). Hind toes are short and webbed, with the outermost toe being thickest (Green, 2003). The lungs are small, with most gas exchange occurring via the skin (Green, 2003). Dorsally, adult Ascaphus montanus frogs are brown on the dorsal surfaces, occasionally with faint black bands extending from the shoulder across the eye and over the nostril to the upper jaw; ventrally, they are whitish (Metter, 1964). There is a pale patch between the eyes, extending forward across the snout (Green, 2003). Breeding males appear to have rougher skin, because the tubercles on the back and legs increase in size during mating season (Metter, 1964). Breeding males also have a line of dense small tubercles along the edge of the lower jaw, and cloacal spines (Metter, 1964). Nuptial pads develop on breeding males, on the inner palmar tubercle and forearm and as a patch on each side of the pectoral region (Metter, 1964).

Ascaphus montanus and A. truei frogs have nine presacral vertebrae. Of these, the third, fourth, and fifth vertebrae bear closely associated but free (not fused) ribs. Among living frog species, these vertebral characteristics are shared only by frogs in the genus Leiopelma; all other frog species have eight or fewer presacral vertebrae, with ribs fused to the vertebrae (Duellman and Trueb, 1994).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Canada, United States

U.S. state distribution from AmphibiaWeb's database: Idaho, Montana, Oregon, Washington

Canadian province distribution from AmphibiaWeb's database: British Columbia

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These frogs can be found in the Rocky Mountains and Columbia Mountains of Idaho, western Montana, northeastern Oregon, and southeastern Washington to southeastern British Columbia. They inhabit small, fast-flowing, high-gradient, mid-elevation mountain streams, in mature, old-growth forests (Green, 2003; Nielson et al., 2001).

Life History, Abundance, Activity, and Special Behaviors

Rocky Mountain Tailed Frogs are primarily nocturnal, and live in fast-flowing headwater streams in old-growth forests (Nielson et al, 2001). During the day, at least in the summer, they shelter beneath stream-bed rocks (Metter, 1964). These frogs have been reported to be generally most active from April to October, but activity depends on the site and the conditions (Hallock and McAllister, 2005). They are found either in the water or generally close by, not more than 150 yards away (Metter, 1964). Mating takes place in early fall (Metter, 1964). During breeding season, males develop black nuptial pads on their hands as well as black tubercles on their sides and arms (Green, 2003). These frogs lack tongues and vocal sacs and do not vocalize, so there are no mating calls (Green, 2003). Amplexus is inguinal (Duellman and Trueb, 1994). Ascaphus montanus and Ascaphus truei are the only species of frogs with internal fertilization, an adaption to living in fast-flowing streams (Nielson et al., 2001). The male's "tail" is actually a copulatory organ (Green, 2003). Although mating takes place in early fall, egg deposition is delayed into the next year (Metter, 1964). During the following mid-summer, when the water flow in streams has subsided somewhat, females lay long strings of 45 to 75 unpigmented eggs, attaching them to the underside of large rocks underwater (Metter, 1964; Duellman and Trueb, 1994). Females apparently lay eggs only every other year (Metter, 1964). Eggs take approximately a month to hatch into larvae (Metter, 1964).

This species does not reach sexual maturity until seven to eight years of age (Green, 2003). These frogs have a relatively long life-span, up to 15 to 20 year (Green, 2003). The adult diet consists primarily of arthropods and other terrestrial invertebrates (including collembolans, caterpillars, spiders, and snails), with aquatic insects playing a lesser role as prey (Mitter, 1964). Ascaphus montanus are in turn preyed on by snakes (Thamnophis elegans, which consume both larval and adult Ascaphus montanus), fish (trout, which also consume both larvae and frogs), larger frogs, birds, invertebrates, and small mammals (Metter, 1964; Green, 2003).

The larvae are relatively large, growing to 30 mm, the length of an adult frog, with specialized suctorial mouthparts enabling them to cling to rocks in fast-flowing currents (Green, 2003). Tadpoles are dark slate gray with wide heads, with a large ventral sucker surrounding the mouth, and up to 16 rows of denticles (Green, 2003; Duellman and Trueb, 1994). Small glands are scattered over the body (McDiarmid and Altig, 1999). There is a single spiracle, which is located midventrally (McDiarmid and Altig, 1999). The tail tip is rounded, with a white spot bordered by black (Hallock and McAllister, 2005).

With their specialized suctorial mouthparts, tadpoles may be found in riffles and pools within the stream (Green, 2003). At night, larvae have been observed climbing above the water on rocks drenched with stream spray (Metter, 1964). When the tadpoles first hatch (13-15 mm in total length). they are unpigmented and appear white (Metter, 1964). Pigmentation is complete when animals reach 18 mm, but not until the animals are 20-21 mm are the beaks fully developed and the yolk completely resorbed (Metter, 1964). Larvae do not leave the aquatic nest site under a large rock until the yolk is fully used, as late as early spring (Metter, 1964). Tadpoles may take up to three years to metamorphose (Metter, 1964). During the first year, the tadpoles remain without legs (Metter, 1964). At the end of the second year, the hind legs appear, a full year before transformation is complete (Metter, 1964). Near the beginning of July of the third year, the front legs break through (Metter, 1964). Tail resorption is completed in September of the third year (Metter, 1964).

The larval diet consists primarily of diatoms, scraped from rocks, as well as a very small amount of filamentous algae, desmids, and minute insect larvae (Metter, 1964). Interestingly, Ascaphus montanus tadpoles were also found to consume a large amount of pollen during the month of June (Metter, 1964). Metter (1964) also reported that 30-40% of all A. montanus gut contents were fine sand grains, presumably accumulated while scraping diatoms from rocks.

Parasites found in this species include the gut ciliate Protoopalina, in younger feeding larvae, and metacercariae (flukes), encysted in the skin of both larvae and adults (Metter 1964).

Trends and Threats

Ascaphus montanus is vulnerable to changes in its stream habitat, such as stream bank integrity, sediment load, and stream temperature (Hallock and McAllister, 2005). Of particular importance is the protection of headwater streams (Hallock and McAllister, 2005).

This species is thought to be relatively common in Idaho and Montana (IUCN, 2006). However, within the state of Washington it is known from only nine localities, all within the Blue Mountains, and only two of those reports have occurred since 1985 (Hallock and McAllister, 2005). Since these frogs are restricted to stream habitat, low dispersal rates may hinder recovery for populations that have declined (Nielson et al., 2001).

Possible reasons for amphibian decline

Habitat modification from deforestation, or logging related activities
Subtle changes to necessary specialized habitat

Tailed frogs (Ascaphus montanus and Ascaphus truei) are some of the most primitive frogs, along with the genus Leiopelma (Duellman and Trueb, 1994). These frogs all resemble the earliest known frogs from the Jurassic in their skeletal anatomy (Duellman and Trueb, 1994). They retain many primitive morphological features which have been lost in all other living anuran lineages (Ford and Cannatella, 1993).

Ascaphus montanus is found inland while the closely related species Ascaphus truei is distributed along the coast (Nielson et al., 2001). The isolation of the two lineages is thought to date back to the late Miocene or early Pliocene, most likely due to the rise of the Cascade Mountains (Nielson et al., 2001).

This species was featured in News of the Week 29 October 2023:

Measurements of organismal maximum heat tolerance, such as critical thermal maximum (CTmax), are often used to partly assess a species’ vulnerability to warming temperatures. However, the usefulness of CTmax for vulnerability assessments has been questioned, with two major concerns. First, these assessments assume that experimental measurements of CTmax are transferable to a natural setting. The second major concern is the perception there is insufficient variation in CTmax among populations and species for CTmax to evolve in response to increasing temperatures. Recently, Cicchino and colleagues (2023) addressed these concerns by testing the assumption that CTmax estimates are related to heat stress tolerance (mortality) in natural conditions among populations of the Rocky Mountain Tailed Frog (Ascaphus montanus). They found that CTmax was strongly related to mortality from thermal stress in temperatures mimicking natural conditions among populations, demonstrating the relevance of experimental estimates of CTmax. They also showed that relatively small differences in CTmax can have large impacts on mortality from thermal stress. This result emphasizes the potential for observed existing variation in CTmax to play a role in mediating the consequences of warming temperatures. Overall, their results provide compelling evidence that experimental measurements of CTmax can be used in assessments of vulnerability to warming temperatures. (Written by Amanda Cicchino)


Duellman, W. E., and Trueb., L. (1994). Biology of Amphibians. Johns Hopkins University Press, Maryland.

Green, D. M. (2003). ''Rocky Mountain tailed frog, Ascaphus montanus.'' Grzimek's Animal Life Encyclopedia, Volume 6, Amphibians. 2nd edition. M. Hutchins, W. E. Duellman, and N. Schlager, eds., Gale Group, Farmington Hills, Michigan.

Hallock, L.A. and McAllister, K.R. 2005. Rocky Mountain Tailed Frog. Washington Herp Atlas. Accessed 18 July 2007.

McDiarmid, R. W., and Altig, R. (1999). Tadpoles: the Biology of Anuran Larvae. The University of Chicago Press, Chicago and London.

Metter, D. E. (1964). ''A morphological and ecological comparison of two populations of the tailed frog, Ascaphus truei Stejneger.'' Copeia, 1964, 181-195.

Nielson, M., Lehman, K., and Sullivan, J. (2001). ''Phylogeography of the Tailed Frog (Ascaphus truei): Implications for the Biogeography of the Pacific Northwest.'' Evolution, 155(1), 147-160.

Originally submitted by: Peera Chantasirivisal (first posted 2005-11-14)
Edited by: Kellie Whittaker, Michelle S. Koo (2023-10-29)

Species Account Citation: AmphibiaWeb 2023 Ascaphus montanus: Rocky Mountain Tailed Frog <> University of California, Berkeley, CA, USA. Accessed Jul 20, 2024.

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Citation: AmphibiaWeb. 2024. <> University of California, Berkeley, CA, USA. Accessed 20 Jul 2024.

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