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).
Tadpoles are relatively large and can reach 30 mm, the length of an adult frog (Green, 2003). The larvae have specialized suctorial mouthparts enabling them to cling to rocks in fast-flowing currents (Green, 2003). Larvae may also 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).
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).