hear call (57.6K RM file)

[call details here]

The following account is modified from Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo (©2005 by the Regents of the University of California), used with permission of University of California Press. The book is available from UC Press.

Pseudacris cadaverina (Cope, 1866[a])
            California Treefrog

Edward L. Ervin¹

            This account is dedicated to the memory of the late Dr. Boris I. Kuperman, my friend and mentor.

1. Historical versus Current Distribution.  The geographic distribution of California treefrogs (Pseudacris cadaverina) extends from coastal southern California, to Baja Norte, Baja California, Mexico.  Within the United States, California treefrogs are restricted to California, ranging southward along the Coast Ranges from San Luis Obispo County, to and across the Transverse Ranges, extending east to Joshua Tree National Park, and south along the Peninsular Ranges to the Mexican border.  California treefrogs occur from near sea level to around 2,290 m (7,500 ft).  They have a discontinuous distribution within their range but are often locally abundant (Gaudin, 1979; Stebbins, 1985).  A previous report of an isolated population of California treefrogs occurring in the Granite Mountains, Granite Mountains Preserve in the East Mojave Desert (Greene and Luke, 1996), is unconfirmed and considered questionable (G. Stewart, personal communication).

2. Historical versus Current Abundance.  Jennings and Hayes (1994a) reviewed the data on 80 amphibian and reptile species native to California to assess the possible need for special listing and/or protection.  Data were assembled from individuals having experience with each species, the scientific literature, museum collections, unpublished field notes, field reconnaissance, and archival records.  Jennings and Hayes concluded that California treefrogs did not warrant any state-level status or legal protection.  Since that time, no information or findings have become available that would suggest the overall status of this species has changed.  However, California treefrogs are difficult to find in presumably high-quality habitat along stream segments where populations of non-native predatory fish (i.e., green sunfish [Lepomis cyanellus]) have become established, suggesting that some populations may be experiencing declines (R. Fisher, unpublished data; personal observations).

3. Life History Features. 

            A. Breeding.  Reproduction is aquatic.

                        i. Breeding migrations.  Unknown.

                        ii. Breeding habitat.  Oviposition takes place in pools of still or slow moving water usually surrounded by large water-worn rocks and boulders (Storer, 1925; Stebbins, 1951).  California treefrogs and Pacific treefrogs are often syntopic, with California treefrogs generally calling from banks and islands and rarely from the water; Pacific treefrogs call from shallow water, often in contact with emergent vegetation (Littlejohn, 1971; personal observations).

            B. Eggs.  The mean measurement of 15 eggs preserved on 5% formalin was 1.95 mm (vitellus; range 1.83–2.10) and 4.39 (envelope; range 4.14–4.68; Storer, 1925).

                        i. Egg deposition sites.  Eggs are deposited in the quiet pools of intermittent and perennial streams.  Egg capsules are surrounded by a colorless gelatinous envelope with adhesive properties that secures most to stationary debris on or near the bottom of the pool (Storer, 1925; Stebbins, 1951; Gaudin, 1965).  Eggs are exuded singly and have a tendency to adhere together.  Breeding and eggs deposition occur from early February to early October (Stebbins, 1985), after high flows from seasonal storms have begun to subside.  During rainfall events and the subsequent increase in stream flow, eggs that dropped into interstitial pockets of the substrate are less susceptible to displacement.  A photograph showing eggs attached singly to a sycamore leaf appears in Storer (1925, plate 13, fig. 39).

            Anzalone et al. (1998) conducted experiments investigating the effects of solar UV-B on the survivorship and hatching success of California treefrog embryos.  The study demonstrated that the groups of embryos shielded from UV-B displayed a significant increased survival rate, while embryos directly exposed to solar UV-B had a decreased survival rate.  Laying eggs individually lower in the water column, as opposed to egg masses or strings close to the surface, provides protection from the deleterious effects of direct solar radiation and the unpredictable hydrologic conditions of lotic environments of the southwest. 

                        ii. Clutch size.  Unknown.

            C. Larvae/Metamorphosis. 

                        i. Length of larval stage.  The larval period ranges from 40–75 d (Stebbins, 1951). 

                        ii. Larval requirements.  Larvae are found in pools of still or slow-moving water usually surrounded by large water-worn rocks and boulders (Storer, 1925; Stebbins, 1951).  As a result of rainfall and the subsequent increased velocity of water, tadpoles are occasionally redistributed downstream.  Tadpoles are most abundant in fishless pools and stream reaches (Hemphill and Cooper, 1984; personal observations). 

                                    a. Food.  California treefrog larvae are classified as generalists and typically feed on detritus, periphyton from algal crusts and mats, and from the surface of submerged objects such as leaves, sticks, and rocks (Duellman and Trueb, 1986; Stebbins and Cohen, 1995). 

                                    b. Cover.  When not actively foraging, tadpoles often seek out the warmer water found along shallow pool margins.  When disturbed or threatened, they quickly retreat to deeper waters and seek cover among algae mats, submergent vegetation, leaf litter, or gaps between cobble stones.  Tadpoles possess robust tail musculature that reaches almost to the tail tip and are consequently strong swimmers (Cunningham, 1964; Gaudin, 1964; personal observations). 

                        iii. Larval polymorphisms.  None reported.

                        iv. Features of metamorphosis.  Metamorphosis has been observed in California from June–August (Stebbins, 1951). 

                        v. Post metamorphic migrations.  Cunningham (1964) wrote: "Immediately after metamorphosing, juveniles are extremely common, sometimes numbering several individuals per square yard for distances of 6.1 m (20 ft) or more surrounding the pond from which they emerged.  In mid August, however, in such sites as along the Mojave River, juveniles suddenly become quite uncommon.  Mortality may be high or the toads [sic] may simply change their habitats and become difficult to find." 

            D. Juvenile Habitat.  Recently metamorphosed individuals are often found aggregated under and between small rocks and cobble and at the base of annual plants growing along the margins of breeding pools.  Newly metamorphosed animals show average daily movements of 1 m (range 0.5–2 m) and move from refugia in pursuit of prey (Harris, 1975).  One exceptional juvenile was discovered beneath damp leaves in a small depression 46 m (150 ft) from water (Cunningham, 1964).

            E. Adult Habitat.  During active periods, adults most commonly are found in close proximity to and along stream channels.  During the daytime, individuals seek refuge in cavities or small depressions on the surfaces of the boulders lining streams, often fully exposed to direct sunlight.  These perches are usually within a few jumps from the nearest pool.  Stebbins (1951) writes: "Typical habitat includes clean rock surfaces, crevices, shade, and during the breeding season, quiet, clean water."  Lillywhite and Light (1975) discovered that while California treefrogs bask in direct sunlight, they discharge a clear, non-viscous fluid onto their integument to prevent the underlying epithelium from drying.  Minimal loss of water from the whole animal nevertheless occurs by evaporation and renewal of the mucous film.  Outside the breeding season, these treefrogs spend little time in the water. 

            Individuals are discovered occasionally in upland habitats far from the drainage during the autumn and winter (S. Sweet, personal communication).  In April, two individuals were observed approximately 46 m (50 yd) almost vertically from a small stream; in mid June, an individual was discovered in a rodent burrow located in dry soil approximately 46 m (50 yd) from a small stream (Cunningham, 1964).  As cited in Stebbins (1951), "Klauber has found it on granite boulders to about 100 feet horizontally and 50 feet vertically from the nearest stream (Storer ms.)."  No male/female differences in habitat characteristics or utilization have been reported. 

            F. Home Range Size.  California treefrogs occupy relatively small portions of the streamside habitat available to them during the spring and summer (Dole, 1974; Harris, 1975).  Adult treefrogs move an average distance of 3 m (1–5 m)/d while juveniles move less, an average of 1 m (0.5–2 m)/d.  Adult movements are associated with foraging and breeding, while juvenile activities are primarily in pursuit of prey (Harris, 1975).  Dole (1974) showed that adults rarely moved > 3–4 m in higher quality habitat. 

            Five females that Dole (1974) studied were recaptured in the same area that each had occupied the previous year.  Two of them were recaptured in the same location while three others were within 2 m of their original locations.  One treefrog was captured six times over a 593-d period spanning two winters.  This individual was always found to be within 2 m of her original capture location.  Movements of the four other females captured in both years were greater.  One of these females, originally captured in July, was recaptured 80 m downstream the following March, but by June she had returned to her previous spot.  The three others had moved downstream.  By the following summer all three had returned 91–218 m upstream to where they had been observed originally.

            Of the male treefrogs recaptured during both years of the study, the first moved 13 m, the second moved 6 m in 8 mo, and the third moved 75 m upstream.  Diminishing levels of pooled water and available moisture were suspected to be the reason some adults made extensive downstream movements to an area containing deeper pools and a greater tree canopy. 

            California treefrogs will move long distances (Kay, 1989).  These movements tend to occur between areas of favorable habitat characteristics such as boulders and pooled water and are not thought to be related to population density (Kay, 1989).

            G. Territories.  The first report of a California treefrog encounter call (sensu McDiarmid and Adler, 1974) appeared in Littlejohn (1971), although no details were provided.  Male California treefrogs have been reported to warn male intruders and maintain territories with encounter calls, and if necessary, defend their calling sites with male–male aggressive encounters (F.T. Awbrey, cited in Wells, 1977a; Fellers, 1979a).

            The following observations are noteworthy in that they serve as examples of site-specific territoriality for California treefrogs.  Male aggressiveness has been observed in the field on two separate occasions with both encounters being similar in nature (personal observations).  On the evening of 18 May 1999 (1725 hr) in Hot Springs Canyon (Orange County, California), a vocal response was elicited from a vocalizing male California treefrog by imitating his advertisement call.  While this in itself is not unique, this individual also reoriented toward the call and hopped up onto a partially buried, 50 cm high, granite boulder.  While slowly being approached from 3 m away, imitation calls were again presented to him.  He quickly responded by hoping about 20 cm in a single leap to the highest point of the rock, remained trained on the "intruder," and began to return calls with greater intensity.  The second encounter occurred on the afternoon of 21 March 2000 (1310 hr) in Tenaja Canyon (Riverside County, California).  A male California treefrog responded to the imitation calls in much the same manner.  However, this individual approached from the water's edge with a series of hops across the bedrock towards the observer.  This treefrog traveled approximately 2 m to within 30 cm of the observer while continuing to respond to the imitation calls, also with increased intensity.  The vocalizations reported here have been interpreted as encounter calls because they were accompanied by territorial behavior (i.e., approaching the intruder) and were acoustically distinct from the typical advertisement call (i.e., greater intensity).

            These observations suggest that the drive to defend a preferred site or territory can be strong.  Most likely, this aggressive behavior is restricted to the breeding season.  At this time, no one has analyzed or described the entire call repertoire of California treefrogs.

            H. Aestivation/Avoiding Dessication.  The distribution of California treefrogs suggests that they have adapted to a variety of weather conditions.  Desert populations must aestivate in late summer and early autumn to avoid the hot dry conditions, and high elevation populations must hibernate in the winter months to avoid freezing temperatures (Miller and Stebbins, 1964; Ball and Jameson, 1970; also see "Torpor [Hibernation]" below).

            I. Seasonal Migrations.  Seasonal habitat usage patterns can be summarized from Harris (1975) as follows.  During spring (mid March to mid June) and summer (mid June to mid September), individuals aggregate on granitic boulders along stream and river courses associated with pools of water.  In the fall (mid September to November) and winter (December to mid March), individuals move to crevices located on higher ground bordering the drainages.  The migration from summer habitats to winter habitats appears to function in avoiding desiccation, predation, and high water from unpredictable and occasional heavy rains during the winter season (Dole, 1974).  During the transition from late winter to early spring (i.e., March–April), individuals begin to reappear along the stream and river courses in greater numbers.

            J. Torpor (Hibernation).  By late fall (mid November) the great majority of California treefrogs have moved to higher ground.  From December to mid March, California treefrogs are seldom encountered (Harris, 1975; unpublished data).  Adults seek deep moist crevice microhabitats located on hillsides (Cunningham, 1964; Harris, 1975) and occasionally in damp portions of mine adits (R. Fisher, D. Stokes, personal communication).  High concentrations of urea accumulate in the body fluids (140 mM) during dehydration or periods of reduced water turnover.  This increases the body water potential to levels where net cutaneous water uptake is possible and reduces the gradient for the net loss of water to the environment (Jones, 1982). 

            K. Interspecific Associations/Exclusions.  California treefrogs occur across a wide elevational range and therefore are associated with a diverse herpetofauna.  For example, riparian woodlands along lower gradient stream segments, whether in valley bottoms or at the foot of mountainous terrain, support species such as Coast Range newts (Taricha t. torosa), California toads (Bufo boreas halophilus), arroyo toads (B. californicus), Pacific treefrogs (Pseudacris regilla), California red-legged frogs (Rana draytonii), foothill yellow-legged frogs (R. boylii), two-striped gartersnakes (Thamnophis hammondii), and southwestern pond turtles (Emmys marmorata pallida).  Co-existence with these species often occurs in ecotones, or transitional zone habitats that include stream reaches bordered by rocks and boulders that are favored by California treefrogs (Schoenherr, 1976; DeLisle et al., 1986; personal observations). 

            The channel of steeper gradient streams in the mountains and foothills are characterized by a stair-step watercourse forming a series of riffles, runs, and still to slow-flowing pools, often confined to rocky canyons.  Coast Range newts, mountain yellow-legged frogs (Rana muscosa), two-striped garter snakes, and southwestern pond turtles are found in these habitat conditions.  Where the distributional ranges of these species overlap with California treefrogs, they often co-occur (Schoenherr, 1976; DeLisle, 1985; Anzalone et al., 1998).  Red-spotted toads (Bufo punctatus) and California treefrogs co-occur in wetlands, including canyons, springs and oases, of desert regions (Miller and Stebbins, 1964; Glaser, 1970). 

            California treefrogs are known to share the same stream reaches and macrohabitats with several native fish species including rainbow trout (Oncorhynchus mykiss, freshwater form), southern steelhead (Oncorhynchus mykiss, sea-run form), threespine stickleback (Gasterosteus aculeatus), Santa Ana sucker (Catostomus santaanae), arroyo chub (Gila orcutti), and speckled dace (Rhinichthys osculus; R. Fisher, unpublished data; personal observations).  These associations are possible because these fish are thought to feed primarily on invertebrates and aquatic vegetation and are presumably less reliant on amphibian eggs or larva (Moyle, 1976, 2000; McGinnis, 1984).  However, California treefrogs are often most abundant in streams lacking fish fauna (Hemphill and Cooper, 1984; Cooper et al., 1986; personal observations).  Strategic placement of eggs and the availability of refugia and structurally complex tadpole foraging areas may be important factors determining these interspecific associations with California treefrogs.

            A variety of introduced species are well established in the aquatic habitats utilized by California treefrogs.  The most widespread of these are red swamp crayfish (Procambarus clarkii), African clawed-frogs (Xenopus laevis), American bullfrogs (Rana catesbeiana), black bullheads (Ameiurus melas), mosquitofish (Gambusia affinis), hatchery stock rainbow trout, largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus), green sunfish (Lepomis cyanellus), and European carp (Cyprinus carpio; Gamradt and Kats, 1996; Stephenson and Calcarone, 1999; R. Fisher, unpublished data; personal observations).  The relative impact of introduced aquatic species on California treefrog populations has not been determined.  Interspecific exclusions are currently unknown.

            Probable natural adult hybrids between California treefrogs and Pacific treefrogs have been reported (Brattstrom and Warren, 1955; Gorman, 1960).  However, attempts to hybridize these species in the laboratory have resulted in the production of inviable crosses that failed at the earliest stages of development (Maxon and Jameson, 1968; Ball and Jameson, 1970; Gaudin, 1979).

            L. Age/Size at Reproductive Maturity.  Storer (1925) concluded that California treefrogs reach their adult size and breed when 2 yr old.  This interpretation is based on finding no more than two size classes among metamorphosed individuals.

            M. Longevity.  Unknown.

            N. Feeding.  A stomach content analysis of 15 adult California treefrogs recovered the following prey types: grasshoppers (Orthoptera), spiders (Arachnida), ants (Hymenoptera), beetles (Coleoptera), moths (Lepidoptera), sowbugs (Isopoda), true bugs (Hemiptera), and lacewings (Neuroptera; Cunningham, 1964).

            O. Predators.  Cooper et al (1986) conducted field experiments to investigate predation by rainbow trout and demonstrated that they have the capacity to completely eliminate California treefrog larvae from stream pools.  Introduced non-native green sunfish have been shown to prey on adult California treefrogs (Ervin et al., 2001a).  Established populations of this predatory fish occur in many coastal southern California drainages that currently support California treefrog populations (Stephenson and Calcarone, 1999; personal observations).  Highly aquatic two-striped garter snakes, which have a geographic distribution similar to California treefrogs (Rossman et al., 1996), prey on larvae and metamorphosed individuals (Cunningham, 1959; Schoenherr, 1976; personal observations).

            P. Anti-Predator Mechanisms.  The pigmentation patterns of the California treefrog larva, ranging from light to dark brown and with varying amounts of gold flecking (Gaudin, 1965), closely resembles the appearance of the sand and rocky stream substrates.  This cryptic coloration, in combination with the tendency of larvae to seek refuge in the presence of trout, would likely reduce or delay predation (Cooper, 1988).

            Juvenile and adult California treefrogs possess coloration and marking patterns on the dorsum that resemble those of the rocks and boulders they inhabit (Storer, 1925; Stebbins, 1951).  Their ability to remain undetected is enhanced by the tendency to remain virtually still when approached (Storer, 1925; Stebbins, 1951; Cunningham, 1964).  Most diurnal perches are within 1 m from water's edge, enabling a rapid escape requiring one or two jumps to the nearest still pool or, occasionally, a swift current (Storer, 1925; Stebbins, 1951; Cunningham, 1964).  Noxious and or toxic properties in eggs, larvae, and adults are currently unknown. 

            Q. Diseases.  Unknown.  There is a single record of a California treefrog exhibiting gross morphological abnormalities associated with limbs, and it is one of the few reports to document an extra-legged frog from lotic habitat (E.L.E. and P.T.J. Johnson, unpublished data).  This specimen possessed three normal extremities with two malformed hindlimbs on the right side.  The primary limb, the femur and surrounding musculature were greatly reduced and the tibiofibula folded back upon itself to form a distinct bony triangle (taumelia).  The foot extended anteriorly and exhibited only one clearly defined digit (ectrodactyly).  The supernumerary right limb (polymelia), which was independent of and ventral to the primary limb, was also poorly developed with a truncated femur and only three digits.  Trematode metacercariae, which have been shown to cause developmental abnormalities in the rear limbs of other species of frogs, were not found in this specimen.

            R. Parasites.  The larval stage of chiggers (Hannemania hylae; Acarina: Trombiculidae) has been shown to embed in the skin of adult California treefrogs (Welbourn and Loomis, 1975).  Approximately 98.9% of the treefrogs in this study had a mean of 21.4 chiggers/treefrog.  While Welbourn and Loomis (1975) determined that one life cycle is completed each year, unengorged larvae were found on treefrogs throughout the summer.

            Goldberg and Bursey (2001) examined the helminth communities in California treefrogs and found the trematode Langeronia burseyi and metacercariae of Alaria sp., Fibricola sp., and Gorgoderina sp.; the cestode Distoichometra bufonis; and two species of nematodes (Rhabdias ranae and larvae of Physaloptera sp.).  They also provided a breakdown of the infection site, number of helminths, prevalence, and mean intensity for helminths from California treefrogs from three counties in southern California.

            Fifteen adult California treefrogs from Cedar Creek (San Diego County, California) were examined and found to be infected by three groups of parasites.  Hannemania hylae were located in the abdominal skin and the bottom surface of the front and rear feet.  Prevalence was 100%, while mean intensity was 28 (range 4–57).  Ribeiroia sp. (Trematoda) metacercariae were found encysted and excysted in the musculature of the rear feet and pelvic area with 87% prevalence and a mean intensity of 34 (range 7–92).  Finally, two protozoans were found in the intestines, the flagellate Opalina sp. and the ciliate Balantidium sp., with a prevalence of 60% and 37%, respectively (B. Kuperman and V. Matey, unpublished data).

4. Conservation.  While Jennings and Hayes (1994a) concluded that California treefrogs did not warrant any state-level status and/or legal protection, California treefrogs are difficult to find in presumably high-quality habitat where populations of non-native predatory fish have become established, suggesting that some populations may be experiencing declines (R. Fisher, personal communication; personal observations).

¹Edward L. Ervin
U.S. Geological Survey
Biological Resource Discipline
Western Ecological Research Center
San Diego Field Station
5745 Kearny Mesa Road, Suite M
San Diego, California 92123
eervin@usgs.gov

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Apr 2024.

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