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Sierran Treefrog - Pseudacris sierra
Other Names:  Hyliola sierra, Pseudacris regilla [misapplied, not present in MT]

Native Species

Global Rank: G5
State Rank: S4

Agency Status


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Copyright by Canadian Amphibian and Reptile Conservation Network
General Description
The Sierran Treefrog is a small frog found across western Montana in suitable habitat. Often heard but not seen, the species can be quite abundant in some areas. This species and the closely related Pacific Treefrog (Hyla regilla) are distinguishable only through genetics, and until 2021 uncertainty as to which species was present in Montana existed. Genetic testing has confirmed that the species present in Montana is the Sierran Treefrog (Pseudacris sierra which is synonymous with Hyliola sierra (Jadin et al. 2021). Note that materials published prior to 2022 will refer to this species as Pacific Treefrog.

Although individual females are known to lay 500 to 750 eggs (Smith 1940), eggs are usually deposited in a number of clutches a few centimeters in size containing 18-119 eggs (X = 68, SD = 26.5, N = 25 across 4 sites in northwest Montana) (Werner et al. 1998a, Maxell et al. 2009). Each ovum is dark gray to tan above, white to cream below, and is surrounded by two jelly layers (Gaudin 1965, Maxell et al. 2009). Ovum diameters are approximately 1.3 mm (0.05 in), but total egg diameters, including the two jelly layers are 4.6-6.7 mm (0.18-0.26 in) (Gaudin 1965).

Eyes are outside the outline of the body when viewed from above (Maxell et al. 2009). Tail musculature and dorsal portion of the body are tan with brown mottling and metallic gold flecks. Iridescent copper color laterally and a clear to whitish color ventrally (Maxell et al. 2009). The dorsal and ventral tail fins are clear with numerous brown and metallic gold flecks (Maxell et al. 2009). Total length (TL) of 8-55 mm (0.3-2.2 in) (Maxell et al. 2009).

Toes are long, have large disks or pads at the end, and there is very little webbing. Virtually all individuals have a black stripe extending from the snout through the nostril, eye, and tympanum to just above the front leg (Maxell et al. 2009). Dorsal color is commonly tan mottled with dark brown spots, but individual coloration can vary from solid green or green with black spots, reddish, or bronze are also found (Schaub and Larsen 1978, Maxell et al. 2009). A dark “Y” or triangular shaped brown patch is usually present on the head between the eyes (Maxell et al. 2009). Ventral color is creamy white. Snout-vent length (SVL) of 12-49 mm (0.47-1.9 in) (Gaudin 1965, Werner et al. 1998a).

This species has a loud call that can carry a distance of 400 m (1,312 ft) (Bryce Maxell, personal communication). It is an audible "ribbet-ribbet" with variable intervals that are intermixed with longer trills, and deafening in large choruses. Males will also make a single and low "krreck" during the active season, but away from the breeding site (Werner et al. 2004).

Diagnostic Characteristics
Except for the Boreal Chorus Frog (Pseudacris maculata), adults of all other frogs and toads in Montana have webbing between their hind toes. Additionally, besides Boreal Chorus Frogs, the eyes of the tadpoles of all other frogs and toads in Montana do not stick out beyond the body outline when viewed from above (Werner et al. 2004). The geographic range of Boreal Chorus Frog does not overlap with the geographic range of Sierran Treefrog (see sections on the distribution).

Species Range
Montana Range Range Descriptions


Range Comments
This species ranges from California through central Oregon into eastern Washington, Idaho and Montana (Jadin et al. 2021). Previously this and the closely related Pacific Treefrog (H. regilla) were recognized as a single distinct species ranging from southern British Columbia through the Pacific Northwest and western Great Basin to the tip of Baja Mexico at elevations up to 3,536 m (11,600 ft) (Stebbins 2003). In Montana, Sierran Treefrog has been documented with continuous distribution north of the Missoula and Mineral County lines and west of the Mission, Swan, and Livingston Ranges. In addition, isolated populations are present in the southern Bitterroot Valley near Lake Como, and at several locations along the Blackfoot River between Missoula and the junction of the Clearwater River and on the upper Clark Fork River between Missoula and Drummond.

Maximum elevation: 1,753 m (5,750 ft) (Maxell et al. 2003)

Observations in Montana Natural Heritage Program Database
Number of Observations: 629

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Usually not found far from forested habitats (Maxell et al. 2009). Adults are freeze tolerant and are presumed to overwinter in underground rodent burrows, underneath thick vegetation or debris or in the crevices of rocks and logs (Brattstrom and Warren 1955, Croes and Thomas 2000). During the active season, juveniles and adults take shelter during the day in dense vegetation, under rocks/logs, or in rodent burrows (Nussbaum et al. 1983). Sierran Treefrogs are regularly found in the water only during the breeding period. They announce their presence during the spring calling frequently at night and sporadically throughout the day. Breeding takes place in shallow, warm, fishless waters which may or may not have emergent vegetation (Maxell et al. 2009).

Sierran Treefrogs move into adjacent uplands and are rarely seen after breeding. Individuals are known to use terrestrial habitats several hundred meters away from their breeding pond and are known to travel as much as 1,000 m (3,281 ft) in order to return to a breeding site they have been removed from (Brattstrom and Warren 1955, Jameson 1956, 1957). In western Montana they breed in temporary ponds at lower elevation forests and intermountain valleys shortly after snowmelt. In northwestern Montana an individual was found at 1,456 m (4,774 ft) elevation and more than 3.25 km (2 mi) from the nearest breeding site (Maxell et al. 2009).

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
Tadpoles feed on algae, diatoms, detritus, and pollen (Kupferberg et al. 1994, Wagner 1986). Adults and juveniles feed on a variety of arthropods, but mostly rely on smaller insects (Brattstrom and Warren 1955, Johnson and Bury 1965).

Severe droughts can affect populations (Schaub and Larsen 1978). Primarily nocturnal and move along ground or in low shrubs at night (Black 1970a).

Reproductive Characteristics
Breeding takes place in April and May in shallow, quiet waters (Maxell et al. 2009). Females deposit eggs on emergent vegetation at depths usually less than 20 cm (7.9 in) in ponds that do not have a closed canopy (Maxell et al. 2009) Eggs usually hatch in 10 to 14 days and tadpoles metamorphose in two or three months during mid-summer (Maxell et al. 2009).

In northern ID, males arrive in breeding ponds early to mid-April and females arrive mid- to late April. Eggs are lain April to mid-May and hatch early to mid-May. Metamorphose occurs around mid-Jul to mid-September. Treefrogs prefer warmer, more open ponds, but observed calling in water at 2 °C (35.6 °F) and air temperature of 0.5 °C (32.9 °F) (Schaub and Larsen 1978).

The following was taken from the Status and Conservation section for the Pacific Treefrog account (now recognised as Sierran Treefrog) in Maxell et al. 2009

Pacific Treefrogs are commonly heard calling, and larvae are commonly found, in standing water bodies at lower elevations north of the Missoula and Mineral County lines and west of the Mission, Swan, and Livingston Mountain Ranges. However, they appear to be present in only a few isolated populations at the southern end of Bitterroot Valley near Lake Como, at several locations around the Blackfoot River between Missoula and the junction of the Clearwater River and around the upper Clark Fork River between Missoula and Drummond. Risk factors relevant to the viability of populations of this species are likely to include all the general risk factors described above except for harvest and commerce. Individual studies that specifically identify risk factors or other issues relevant to the conservation of Pacific Treefrogs include the following. (1) The eggs (Licht 1969b) and larvae (Bryce Maxell, pers. obs.) of Pacific Treefrogs are readily eaten by a number of trout species (Salvelinus sp., Salmo sp., or Oncorhynchus sp.) and fish may be expected to exclude Pacific Treefrogs from habitats they occupy through predation. In the Palouse region of northern Idaho, Monello and Wright (1999) found the presence of Pacific Treefrogs to be highly negatively correlated with the presence of a variety of fish species, including Largemouth Bass (Micropterus salmoides), Bluegill (Lepomis macrochirus), Channel Catfish (Ictalurus punctatus), and Goldfish (Carassius auratus). Bradford (1989) found that Pacific Treefrogs were not found in any of the 123 lakes where trout have been introduced for 173 lakes examined in the Sierra Nevada Mountains. Similarly, Yoon (1977) found that meadow pools occupied by trout were rarely if ever occupied by Pacific Treefrogs or other amphibians in the Sierra Nevada. (2) Jameson (1956) reported that he felt that exotic American Bullfrogs (Lithobates catesbeianus) had excluded Pacific Treefrogs from several breeding sites and found that where American Bullfrogs were common in the Willamette Valley, Pacific Treefrog choruses, egg masses, or larvae were never found. Kupferberg (1993) also documented the decline of Pacific Treefrog populations behind the invasion front of exotic American Bullfrog. Kupferberg (1997a) found that American Bullfrogs significantly reduced growth and larval survival of Pacific Treefrogs. Finally, Kupferberg (1994) observed that when American Bullfrogs replaced native Pacific Treefrogs, native Gartersnakes (Thamnophis sp.) were not able to forage on the larger American Bullfrog tadpoles as efficiently as they had on the native Pacific Treefrogs. (3) Johnson (1980) found that when three week old Pacific Treefrog tadpoles were exposed to the insecticides temephos, fenthion, methyl parathion, chlorpyrifos, and malathion for 24 hours at lower concentrations than are applied in the field for mosquito control they became thermally stressed at lower temperatures than tadpoles in a control group. Furthermore, tadpoles exposed to methyl parathion at 100 ppb or malathion at 500 ppb reduced their activity levels compared to tadpoles in the control group, possibly reducing their foraging efficiency and growth and increasing the time required to reach metamorphosis. Also, as has been noted by other studies, Schuytema et al. (1995) found that two pesticides containing the active ingredient Guthion had very different effects on Pacific Treefrog larvae because of the presence of different “inactive” ingredients in the pesticide formulation. Tadpoles were 5 times more sensitive to one formulation than another because of the differences in “inactive” ingredients. The relationship of the inactive and active ingredients in these pesticides to commonly applied pesticides in Montana is not known, but it is likely that both pesticides and herbicides may represent lethal and/or sublethal threats to Pacific Treefrog populations. (4) Several studies in the western United States have reported rear limb deformities in Pacific Treefrogs (Hebard and Brunson 1963, Reynolds and Stephens 1984, Johnson et al. 1999). Hebard and Brunson (1963) found rear limb deformities in 20-30 percent of metamorphosing frogs at a pond in the Flathead Valley in the late 1950s and early 1960s. More recently hind limb deformities have been found at the same site and appear to be the result of infection with the nematode parasite Ribeiroia which has been found to be responsible for limb deformities in a number of amphibians throughout the western United States (Johnson et al. 1999, Pieter Johnson, Claremont Mckenna College, personal communication). Deformities apparently result from the amphibian larvae s response to the mechanical perturbation of the cysts the parasites form after they burrow through the larvae’s body wall because mechanical implants of resin beads result in almost identical deformities (Sessions and Ruth 1990, Johnson et al. 1999) Animals that breed in ponds, including the one reported by Hebard and Brunson (1963) and recently revisited, which are eutrophic as a result of organic inputs from livestock or agricultural activities may support high numbers of Planorbid Snails (the first host of Ribeiroia), thereby increasing the rate of parasite infection and deformities (Johnson et al. 1999). (5) Several studies have found that Pacific Treefrog embryos seem to be particularly resilient to exposure to ambient and enhanced UV-B radiation levels, apparently as a result of the presence of high levels of photolyase, and enzyme that is known to repair UV-B damage to DNA (Blaustein et al. 1994d, Kiesecker and Blaustein 1995, Davis et al. 2000, Hays et al. 1996, Ovaska et al. 1997, Anzalone et al. 1998, Blaustein et al. 1998). However, lab studies have shown that tadpoles and metamorphs that are chronically exposed to enhanced UV radiation have deformities and suffer higher mortality rates than those shielded from UV radiation or exposed to ambient levels of UV radiation (Hays et al. 1996, Ovaska 1997). (6) Pacific Treefrog embryos are apparently less likely than other amphibians to be infected and suffer mortality from the fungus Saprolegnia ferox because of their habit of laying eggs in small isolated clumps rather than in communal masses (Kiesecker and Blaustein 1997a). (7) Bradford et al. (1994) found that the LC50 pH for Pacific Treefrog embryos and hatchlings exposed for 7 days averaged 4.3 and that pH levels greater than or equal to 5.0 had no significant lethal or sublethal effects. (8) Weitzel and Panik (1993) reported that feral house cats either predated or mauled several Pacific Treefrogs.

  • Literature Cited AboveLegend:   View Online Publication
    • Anzalone, C.R., L.B. Kats and M.S. Gordon. 1998. Effects of solar UV-B radiation on embryonic development in Hyla cadaverina, Hyla regilla, and Taricha torosa. Conservation Biology 12: 646-653.
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    • Bradford, D.F. 1989. Allotopic distribution of native frogs and introduced fishes in high Sierra Nevada lakes of California: Implication of the negative effect of fish introductions. Copeia 1989(3): 775-778.
    • Bradford, D.F., C. Swanson, and M.S. Gordon. 1994. Effects of low pH and aluminum on amphibians at high elevation in Sierra Nevada, California. Canadian Journal of Zoology 72: 1272-1279.
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    • Cocroft, R.B. 1994. A cladistic analysis of chorus frog phylogeny (Hylidae: Pseudacris). Herpetologica 50(4): 420-437.
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    • Johnson, C.R. 1980. The effects of five organophosphorus insecticides on thermal stress in tadpoles of the Pacific tree frog (Hyla regilla). Zoological Journal of the Linnean Society 69: 143-147.
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    • Licht, L.E. 1969b. Palatability of Rana and Hyla eggs. American Midland Naturalist 82: 296-298.
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  • Additional ReferencesLegend:   View Online Publication
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