Rana cascadae Slater, 1939
Christopher A. Pearl 1
Michael J. Adams2
1. Historical versus Current Distribution. Cascade frogs (Rana
cascadae) historically occupied moderate and high elevation (about
400–2,500 m) lentic habitats throughout the Cascade Range, from the very northern
edge of California’s Sierra Nevada to within 25 km of the British Columbia border
(Dunlap and Storm, 1951; Dunlap, 1955; Dumas, 1966; Bury, 1973a; Hayes and Cliff, 1982;
Nussbaum et al., 1983; Fellers and Drost, 1993; Jennings and Hayes, 1994a; K.R.
McAllister, 1995). Population systems occurring in the Olympic Mountains of
Washington and the Trinity Alps, Mt. Shasta, and Mt. Lassen areas of California are
notably disjunct from the main Cascade axis and may warrant investigation for cryptic
taxa (Jennings and Hayes, 1994a; K. Monson and M. Blouin, unpublished data).
Range contractions have been documented in the southern end of their range (Fellers and
Drost, 1993; Jennings and Hayes, 1994a). Jennings and Hayes (1994a) and Fellers
and Drost (1993) estimate that Cascade frogs are extirpated from about 99% of their
southernmost population clusters (Mt. Lassen and surroundings), and 50% of their total
historical distribution in California.
2. Historical versus Current Abundance. Cascade frogs are among the most
commonly encountered lentic breeders in Olympic and Mount Rainier national parks, where
extensive surveys suggest no evidence of declines (Adams et al., 2001; Tyler et al.,
2002). Cascade frogs were among the first amphibians to recolonize sites post
eruption and are now commonly encountered in Mount St. Helens Volcanic Monument in the
southern Washington Cascades (Karlstrom, 1986; Crisafulli and Hawkins, 1998; C.
Crisafulli, personal communication). Some concerns for declines in the central
Oregon Cascade Range have been reported (Nussbaum et al., 1983; Blaustein and Wake,
1990), but other surveys do not suggest exceptionally low site occupancy rates (C. Brown,
1997; C.A.P., B. Bury, and M.J.A., unpublished data). Recent surveys suggest that
Cascade frogs remain present in portions of the Trinity Alps and Marble Mountains, but
are rare to nonexistent in other Californian portions of their historical range (G.
Fellers, H. Welsh, personal communications). Declines have been documented around
Lassen Volcanic National Park in northeastern California, where Cascade frogs were
historically widespread and abundant between 1,450 and 2,480 m (Grinnell et al., 1930;
Badaracco, 1962). In 1991, Cascade frogs were detected at only 1 of 50 sites in
the vicinity of Lassen Volcanic National Park, 16 of which historically supported this
species (Fellers and Drost, 1993). More recent surveys (1992–2002) have
detected Cascade frogs at only 4 of 400 sites (G. Fellers, personal communication).
Population sizes were small at all four sites, and as of 2002, frogs had disappeared from
two of these four sites (G. Fellers, personal communication).
3. Life History Features.
i. Breeding migrations. Available information suggests that Cascade frog adults
overwinter near breeding localities and, because they often become active during ice
thaw, are thought not to make extensive breeding migrations (Briggs, 1976, 1987;
ii. Breeding habitat. Cascade frogs breed in temporary and permanent lentic
waters, often in smaller bodies of water nearer larger lakes (Nussbaum et al., 1983;
Briggs, 1987; Bury and Major, 1997). In Olympic National Park, Washington, Cascade
frog breeding sites generally have silt/mud substrates, lack fish, and have low UV-B
transmission (Adams et al., 2001).
i. Egg deposition sites. First egg masses are deposited in comparatively warm
water along gradually sloping shorelines, often over soft substrates protected from
severe wave action (Sype, 1975; O’Hara, 1981). Breeding is explosive (often
completed in < 1 wk), and egg masses are commonly deposited in aggregations (Sype,
1975; Briggs, 1987). The placement of clusters of egg masses in shallow water soon
after first thaw can make them susceptible to freezing mortality, pathogen transmission
between adjacent masses, or desiccation associated with receding water levels (Blaustein
and Olson, 1991; Kiesecker and Blaustein, 1997b; C.A.P., personal observations).
ii. Clutch size. Egg masses contain between 300–800 ova (O’Hara, 1981;
Nussbaum et al., 1983). Adults appear to be strongly philopatric, using the same
breeding sites for several years (O’Hara, 1981; Olson, 1992). Females breed
no more than once/year, but whether they skip years remains unknown (Sype, 1975; Nussbaum
et al., 1983).
i. Length of larval stage. Water temperatures strongly influence rates of
development, hatching, and time to metamorphosis (Sype, 1975). Metamorphosis is
generally achieved about 2 mo after hatching (Nussbaum et al., 1983; Briggs, 1987).
There is no documentation of overwintering larvae, but the topic warrants further
ii. Larval requirements.
a. Food. Larvae are thought to be primarily benthic feeders, but specific
preferences are not well known (Nussbaum et al., 1983).
b. Cover. Larvae often form loose aggregations near their oviposition sites.
Aggregations usually include kin (O’Hara and Blaustein, 1985) and are generally
associated with flooded vegetation in warm microhabitats (O’Hara, 1981; Wollmuth et
iii. Larval polymorphisms. Not reported. Albino larvae have been observed
three times in the central Cascade Range of Oregon (Altig and Brodie, 1968; B. McCreary,
vi. Features of metamorphosis. In laboratory trials, size at metamorphosis varies
from 15–30 mm SVL and depends on larval density, food availability, and water
temperature (Blaustein et al., 1984). Larvae reared in 23 ˚C lab water averaged
20–21 mm SVL at metamorphosis after 37.5 d (Nussbaum et al., 1983). Larval
growth rate can affect shape (e.g., leg length) at metamorphosis (Blouin and Brown,
v. Post-metamorphic migrations. Specific information is lacking.
Habitat. Similar to adults, especially marshy fringes of lentic environments, but
detailed information is not yet available (C.A.P., personal observation).
Habitat. Cascade frog adults utilize an array of habitat types, but are generally
associated with open wetland habitats at higher elevations (C. Brown, 1997; Bury and
Major, 1997; Bosakowski, 1999; Olson, 2001). Cascade frog adults commonly occupy
moist meadows and can be found in relatively small permanent and temporary ponds (Sype,
1975; O’Hara, 1981; Olson, 1992). Adults are also found along streams in
summer, especially at lower elevations where lentic habitats are less common (Dunlap,
1955; C.A.P., personal observations). Adults generally stay close to water,
particularly along sunny shores, under dry summer conditions, but can be found traversing
uplands during high humidity (Nussbaum et al., 1983). Adults and breeding can
occur in anthropogenic wetland habitats such as pump chances (Quinn et al., 2001).
F. Home Range
Territories. While adults are not considered territorial (Nussbaum et al., 1983),
males will behave aggressively toward one another during breeding (C.A.P., personal
Aestivation/Avoiding Dessication. Not reported; summer is their active season.
Migrations. See "Breeding migrations" and "Juvenile Habitat"
(Hibernation). Cascade frogs hibernate through the long, snowy winters typical of
most of their range (Nussbaum et al., 1983). Frogs have been recovered from mud
beneath 0.3–1.0 m of water and from spring-saturated areas around ponds (Briggs,
Associations/Exclusions. Cascade frogs may share breeding sites with western toads
(Bufo boreas), northwestern salamanders (Ambystoma
gracile), long-toed salamanders (A. macrodactylum),
rough-skinned newts (Taricha granulosa), and Pacific treefrogs
(Pseudacris regilla). They also occur syntopically with Oregon
spotted frogs (Rana pretiosa) at < 10 sites along the Oregon
Cascades and can co-occur with northern red-legged frogs (Rana aurora)
at sites in lower elevations (C.A.P., personal observations). Several researchers
have suggested that Cascade frogs may be reduced in number by introduced sport-fish
(Fellers and Drost, 1993; Jennings and Hayes, 1994a).
L. Age/Size at
Reproductive Maturity. In the Oregon Cascades, males and females are thought to
reach sexual maturity at 2–3 yr (about 35–40 mm) and 4 yr (about 50–55
mm) post metamorphosis, respectively (Briggs and Storm, 1970; Olson, 1992; Jennings and
In the Oregon Cascades, both males and females are thought to live > 5 yr, sometimes
reaching 7 yr (Briggs and Storm, 1970; Olson, 1992).
Behavior. Diet composition of Cascade frogs is poorly known, but adults are thought
to consume a variety of invertebrate prey and will occasionally consume conspecifics
(Rombough et al., 2003).
Native predators of adult frogs include water bugs (Belostomatidae), garter snakes
(especially common garter snakes, Thamnophis sirtalis), mustelid
mammals, raccoons, and several bird species (Briggs and Storm, 1970; Nussbaum et al.,
1983; Nauman and Dettlaff, 1999). Larvae and newly metamorphosed individuals are
taken by invertebrates (Belostomatidae, Dytiscidae, Odonata), and aquatic salamanders
(rough-skinned newts, northwestern salamanders, and long-toed salamanders; Briggs and
Storm, 1970; Peterson and Blaustein, 1991, 1992). Juvenile and adult Cascade frogs
are known to cannibalize larvae and newly metamorphosed animals (Rombough et al.,
2003). Introduced salmonids are now widespread in high lakes throughout the range
of Cascade frogs and may represent a common predator of larvae and small adults (Hayes
and Jennings, 1986; Fellers and Drost, 1993; Jennings and Hayes, 1994a; Simons,
Mechanisms. In laboratory trials, larvae increased activity when exposed to
waterborne chemical cues of injured conspecifics (Hews and Blaustein, 1985).
Chemical cues of predatory leeches can elicit early hatching of eggs (Chivers et al.,
2001). Adult escape behavior often includes a series of rapid bounds into water,
followed by burrowing head-first into unconsolidated substrate (C.A.P., personal
Field experiments suggest that the oomycete fungus, Saprolegnia ferax,
is related to embryonic mortality in Cascade frogs and may be enhanced by other stressors
such as ultraviolet radiation (Kiesecker and Blaustein, 1995, 1997b).
The blood parasite Lankesterella sp. was reported in Cascade frogs by Clark et
al. (1969). Cascade frogs exhibited lower malformation frequencies attributable to
metacercariae of the trematode Ribeiroia ondatrae relative to other
Pacific Northwestern amphibians (Johnson et al., 2002).
4. Conservation. A latitudinal gradient of conservation status apparently
exists for Cascade frogs, with declines documented in the southern portion of their range
but not in study areas to the north (see "Historical versus Current
Distribution" and "Historical versus Current Abundance" above).
Recent surveys in northern California suggest that populations in the region are often
small, and that their abundance and distribution is negatively associated with introduced
salmonids (Fellers and Drost, 1993; H. Welsh, G. Fellers, personal communications).
Declines have been referenced in Oregon (Blaustein and Wake, 1990), but field data from
the northern and central Oregon Cascades suggest the species remains widespread in some
areas and has the capacity to rebound from short-term declines (Olson, 1992; C. Brown,
1997; C.A.P. and colleagues, personal observations). Cascade frogs remain
widespread and common in Olympic and Mount Rainier national parks, and in the Mt. St.
Helens Volcanic Monument in Washington (Karlstrom, 1986; Crisafulli and Hawkins, 1998;
Adams et al., 2001; Tyler et al., 2002). Cascade frogs are considered a Species of
Special Concern in California (California Department of Fish and Game, 1999), and
Sensitive-Vulnerable in Oregon (Oregon Natural Heritage Program, 1995).
Causes of Cascade
frog declines are not fully known, but introduced trout, UV-B radiation, fungal
pathogens, and loss of open meadow habitat due to fire suppression have been suggested
(Hayes and Jennings, 1986; Fellers and Drost, 1993; Blaustein et al., 1994b,c; Kiesecker
and Blaustein, 1995; Fite et al., 1998; Adams et al., 2001). In Oregon, Casacde frog
embryos have low photolyase levels and therefore low capacity to repair UV-B damage; they
demonstrate reduced hatching in unshielded relative to shielded in situ enclosures
(Blaustein et al., 1994c). However, breeding sites in the Oregon and Washington
portions of the species' range may be afforded some protection from lethal UV-B doses by
dissolved organic matter (Palen et al., 2002). One Oregon study failed to detect
short-term changes in breeding phenology that might be attributable to climate change
(Blaustein et al., 2001). Fertilizers such as urea may pose a threat to Cascade
frogs, as juveniles do not appear capable of sensing and avoiding toxic levels in
laboratory studies (Hatch et al., 2001). Nitrites may affect behavior and
metamorphosis of Cascade frog larvae (Marco and Blaustein, 1999). An improved
understanding of microhabitat associations and interactions with introduced fish is
needed to assist with conservation measures for the species (Olson, 2001).
1Christopher A. Pearl
USGS Forest and Rangeland Ecosystem Science Center
3200 SW Jefferson Way
Corvallis, Oregon 97331
2Michael J. Adams
USGS Forest and Rangeland Ecosystem Science Center
3200 SW Jefferson Way
Corvallis, Oregon 97331
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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