Rana chiricahuensis: Platz and Mecham, 1979
Chiricahua Leopard Frogs
Michael J. Sredl1
Randy D. Jennings2
1. Historical versus Current Distribution. Chiricahua leopard frogs (Rana chiricahuensis) are found in Arizona, New Mexico, and Mexico (Platz and Mecham, 1979). The range of this species is divided into two areas. The first includes northern montane populations along the southern edge of the Colorado Plateau (= Mogollon Rim) in central and eastern Arizona and west-central New Mexico. The second includes southern populations located in the mountains and valleys south of the Gila River in southeastern Arizona and southwestern New Mexico, and extends into Mexico along the eastern slopes of the Sierra Madre Occidental (Platz and Mecham, 1979). The distribution of this species within its range is fragmented due to the aridity of this region (Mecham, 1968c). Populations in the northern portion of the range may soon be described as a new species (J. Platz, personal communication).
Historical records for Chiricahua leopard frogs are known from Coconino, Yavapai, Gila, Navajo, Apache, Greenlee, Pima, Santa Cruz, Graham, and Cochise counties, Arizona; and Catron, Soccoro, Sierra, Grant, Hidalgo, and Luna counties, New Mexico (Jennings and Scott, 1991; Sredl et al., 1997). A single specimen collected from Rio Arriba County, New Mexico, is sufficiently distant from the established range to suggest that it was likely mis-mapped (Fritts et al., 1984). Historical records for Chiricahua leopard frogs also exist from Chihuahua, extreme northern Durango, and northern Sonora, Mexico (Platz and Mecham, 1979). Elevations of Chiricahua leopard frog localities range from 1,000–2,710 m (Platz and Mecham, 1979; Sredl et al., 1997).
During surveys conducted in Arizona between 1983 and 1987, Clarkson and Rorabaugh (1989) found Chiricahua leopard frogs at only 2 of 36 historical sites and at 2 new sites. Sredl et al. (1997) conducted 871 surveys within the northern portion of the Chiricahua leopard frog range and confirmed their presence at 4 of 25 historical sites and at 11 new sites. They also conducted 656 surveys within the range for southern populations and found frogs at 17 of 84 historical sites and at 44 new sites. In New Mexico, R.D. Jennings (1995a) found Chiricahua leopard frogs at 6 of 50 historical sites and 5 of 22 new sites. The status of populations in Mexico is unknown.
2. Historical versus Current Abundance. Little is known of historical abundance. Zweifel (1968b) characterized leopard frogs (cf. R. chiricahuensis) as “abundant” in well-watered sites in valleys such as at San Bernardino Ranch on the Mexican border in southeastern Arizona. In other parts of southeastern and east-central Arizona, frogs that were likely Chiricahua leopard frogs were more abundant and widespread than they are at present (Wright and Wright, 1949; J.T. Bagnara, personal communication). These frogs can be locally abundant (10–20 frogs jump with each step along the shoreline) or can be scarce. This variation seems to be associated with environmental conditions found in different types of habitats. It is likely that similar patterns of abundance occurred historically.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding migrations described for some amphibians have not been noted in Chiricahua leopard frogs. In most populations, breeding usually follows springtime emergence after a period of winter inactivity and may continue through the summer and into the fall.
Male Chiricahua leopard frogs typically call above water, but may also advertise underwater (Degenhardt et al., 1996). Proximate cues that stimulate mating have not been well studied. Using data collected from a long-term captive colony, Fernandez (1996) states that oviposition may be stimulated by rainstorms. Platz (1997), studying wild populations of the closely related Ramsey Canyon leopard frog (Rana subaquavocalis), noted that oviposition in that species does not appear to be correlated with rain, but instead may be correlated with changes in water temperature. Oviposition occurred on 10 of 11 nights shortly before or slightly after a decrease in water temperature. Altig et al. (1998) describe the tadpoles of Chiricahua leopard frogs.
Egg masses of Chiricahua leopard frogs have been reported in all months except January, November, and December, but reports of oviposition in June are uncommon (Zweifel, 1968b; Frost and Bagnara, 1977; Frost and Platz, 1983; Scott and Jennings, 1985; M.J.S., unpublished data). Zweifel (1968b) noted that breeding in the early part of the year appeared to be limited to sites where the water temperatures do not get too low, such as spring-fed sites. Frogs at some of these sites may oviposit year-round (Scott and Jennings, 1985).
Frost and Platz (1983) studied populations of Chiricahua leopard frogs in Arizona and New Mexico and noted egg masses in March–August. They divided egg-laying activity into two distinct periods with respect to elevation. Populations at elevations below 1,800 m tended to oviposit from spring through late summer, with most activity taking place before June. Populations above 1,800 m bred in June–August.
Scott and Jennings (1985) found a similar seasonal pattern of reproductive activity (February–September) as Frost and Platz (1983), although they did not note elevational differences. Additionally, they noted reduced oviposition in May–June.
ii. Breeding habitat. Chiricahua leopard frogs are habitat generalists and breed in slack waters in a variety of natural and manmade aquatic systems (Mecham, 1968c; Zweifel, 1968b; Frost and Bagnara, 1977; Scott and Jennings, 1985; Sredl and Saylor, 1998). Natural systems include rivers, permanent streams, permanent pools in intermittent streams, beaver ponds, cienegas (= wetlands), and springs. Manmade systems in which they have been recorded include earthen cattle tanks, livestock drinkers, irrigation sloughs, wells, abandoned swimming pools, ornamental backyard ponds, and mine adits. The year-round flow, constant water temperature that permits year-round adult activity and winter breeding, and depauperate fish community of thermal springs make these sites particularly important breeding habitat for Chiricahua leopard frogs in New Mexico (Scott and Jennings, 1985).
In the Sulfur Springs Valley of southeastern Arizona, egg masses were found most frequently between late March and late May, although occasional egg masses were found in the summer and early fall (Frost and Bagnara, 1977).
Jennings (1988, 1990) studied five populations of Chiricahua leopard frogs in New Mexico from 1987–'89. Populations in warm springs have a reproductive period more than twice as long as a population in a cold stream and likely reproduce year-round (Scott and Jennings, 1985). Jennings (1990) also found a great deal of annual and site-specific variation in all breeding activities.
i. Egg deposition sites. Females deposit spherical masses attached to submerged vegetation. Jennings and Scott (1991) found egg masses to be suspended within 5 cm of the surface, attached to vegetation. Zweifel (1968b) found the minimum–maximum temperatures for Chiricahua leopard frog embryos to be 12.0–31.5 ˚C. Zweifel (1968b) reported the highest temperature at which an egg mass was found in the wild was 27.8 ˚C. In New Mexico, egg mass temperatures ranged from 12.6 ˚C, recorded from a stock tank at 2,385 m elevation, to 29.5 ˚C, recorded at a warm spring at 1,885 m (R.D.J., personal observations).
ii. Clutch size. Estimates of the number of eggs per egg mass ranged from 300–1,485 (Jennings and Scott, 1991). Vegetation associated with egg masses included Potamogeton spp., Rorippa sp., Echinochloa sp., and Leersia sp.
C. Larvae/Metamorphosis. Hatching time of egg masses in the wild has not been studied in detail. Eggs of the closely related Ramsey Canyon leopard frog hatch in approximately 14 d depending on temperature (Platz, 1997); hatching time may be as short as 8 d in geothermally influenced springs (R.D.J., unpublished data).
Tadpoles are known to overwinter (Frost and Platz, 1983). Length of larval period may be as short as 3 mo or as long as 9 mo (Jennings, 1988, 1990). Jennings (1990) found that tadpoles in warm springs appear to grow continuously, while growth of those in cold water sites appeared to be arrested or retarded during the winter. Tadpole activity has been observed under ice in water at 5.0 ˚C (R.D.J., personal observations). Tadpoles from stream habitats have more contrasting melanic patterns on the tail, thicker dorsal fins, and somewhat larger tail muscles than tadpoles from ponds (Jennings and Scott, 1993).
D. Juvenile Habitat. Not well studied, but some spatial and temporal separation of Chiricahua leopard frog adults and juveniles may enhance survivorship. Seim and Sredl (1994) studied the association of juvenile–adult stages and pool size in the closely related lowland leopard frog (Rana yavapaiensis) and found that juveniles were more frequently associated with small pools and marshy areas while adults were associated with large pools. Fernandez (1996) speculated that lack of cover and cannibalism was the reason for low juvenile survival in a captive colony of Chiricahua leopard frogs. Jennings (1988) noted that juveniles were more active during the day, adults more active at night.
E. Adult Habitat. Habitats in which Chiricahua leopard frogs are found range from perennial to near perennial. Mechanisms by which Chiricahua leopard frogs survive the loss of surface water are unknown. However, other species of leopard frogs in the southwestern United States have been observed to survive drought by burrowing into mud cracks (Howland et al., 1997).
Although no studies examining habitat use by adult Chiricahua leopard frogs have been conducted, these frogs are known to be habitat generalists and occupy a variety of natural and manmade aquatic systems within their range. The role of habitat heterogeneity within the aquatic and terrestrial environment is unknown, but is likely to be important. Shallow water with emergent and perimeter vegetation provide tadpole and adult basking habitats, while deeper water, root masses, and undercut banks provide refuge from predators and potential hibernacula (M.J.S., unpublished data). Most perennial water supporting Chiricahua leopard frogs possess fractured rock substrata, emergent or submergent vegetation, deep water, root masses, undercut banks, or some combination of these features that frogs may use as refugia from predators and extreme climatic conditions (R.D.J., unpublished data).
Occupation of natural and artificial aquatic systems presents interesting opportunities and dilemmas for conservation of native leopard frogs. Sredl and Saylor (1998) found artificial aquatic systems such as earthen cattle tanks to be important for the continued viability of populations of Chiricahua leopard frogs and other members of the leopard frog complex in Arizona. Of the nine extant populations of Chiricahua leopard frogs on the Mogollon Rim in Arizona, one is a natural aquatic system and the remainder are artificial or highly modified aquatic systems (Sredl et al., 1997). In New Mexico, only 5 of 33 known, extant populations persist in stock tanks (three earthen tanks and two concrete storage tanks). Streams and springs appear to be the most important habitats for Chiricahua leopard frogs in New Mexico (R.D.J., personal observations).
Severe fragmentation and alteration of aquatic habitats in the southwestern United States has likely constricted many wide ranging aquatic species into isolated pockets, and maintenance of aquatic corridors may be critical in preserving organisms in the arid Southwest (Jennings and Scott, 1991). Sredl and Howland (1995) speculated that distribution of extant Chiricahua leopard frog populations in Arizona may be reflective of habitat fragmentation and extinction without recolonization, as well as habitat quality.
Effects of livestock grazing on amphibian populations may be positive or negative (Jennings, 1988; Rosen and Schwalbe, 1998; Sredl and Saylor, 1998). In the late 1800s and early 1900s, construction of earthen cattle tanks in upland drainages became a common range management practice (U.S. General Accounting Office, 1991), one that continues to this day. Because these tanks were primarily built to water livestock, a positive secondary benefit of these systems is the water and aquatic habitat they provide to many species of wildlife, including amphibians.
Overgrazing negatively impacts amphibian habitat by removing bankside cover, increasing ambient ground and water temperatures, destroying bank structure (e.g., eliminating undercut banks), trampling egg masses, and adding high levels of organic wastes (Jennings, 1988). Overgrazing in upland habitats may degrade amphibian habitat by increasing runoff and sedimentation rates (Jennings, 1988; Belsky and Blumenthal, 1997).
Although the relationship between the Chiricahua leopard frog and non-native predators (e.g., American bullfrogs [Rana catesbeiana], crayfish, and predatory fishes) has not been studied in detail, there is a negative co-occurrence between them (Rosen et al., 1995; Fernandez and Rosen, 1996). Jennings and Scott (1991) questioned the importance of American bullfrogs as a factor leading to regional declines of native amphibians in the southwestern United States, arguing that many populations that have declined in New Mexico were not impacted by bullfrogs or were impacted by factors other than bullfrogs.
F. Home Range Size. Male home range sizes (dry season mean = 161.0 m2; wet season mean = 375.7 m2) tended to be larger than those of females (dry season mean = 57.1 m2; wet season mean = 92.2 m2). The largest home range size documented for the species was that of a male who used approximately 23,390 m2 (2,339 m x 10 m) of an intermittent, low elevation canyon (1,775 m) in New Mexico during July–August 1999. Another male moved 3.5 km (> 2 mi) in one direction during that same time period. The largest home range size documented for a female frog was about 9,500 m2 (950 m x 10 m). Male frogs tended to expand home range size to a greater degree than females when ranges during the dry season (early July) were compared to wet season (late July to August; R.D.J., unpublished data).
G. Territories. Calling male Chiricahua leopard frogs will engage in fisticuffs with other males, presumably defending calling sites. This site defense appears to be transient, however. Other forms of territorial defense are not known (R.D.J., unpublished data).
H. Aestivation/Avoiding Dessication. Unknown.
I. Seasonal Migrations. Jennings and Scott (1991) noted that maintenance of corridors used by dispersing juveniles and adults that connect disjunct populations may be critical to preserve populations of frogs and other aquatic organisms.
J. Torpor (Hibernation). Although post-metamorphic Chiricahua leopard frogs are generally inactive from November–February, a detailed study of wintertime activity or habitat use has not been done. Jennings (1988, 1990) studied five populations of Chiricahua leopard frogs in New Mexico from 1987–'89. Among sites, the number of frogs observed during diurnal surveys was best predicted by month of the year, diurnal air temperature, and time of day. Time of day was negatively associated with frog numbers, indicating frogs were more numerous early in the day before temperatures elevated. Number of frogs observed during nocturnal surveys among sites was best predicted by nocturnal water temperature and amount of wind. Frogs were most abundant when water temperatures were warmer and when winds were calmer. The number of egg masses observed during diurnal surveys of all sites was best predicted by the number of frogs observed during diurnal surveys. Only diurnal water temperature provided predictive power of number of egg masses at any single site included in the study.
Jennings (1990) found that populations in warm springs exhibited prolonged activity (year-round at one site) and reproductive patterns, while ponds without geothermal input exhibited relatively brief periods of activity and reproduction (also in Jennings, 1988). Chiricahua leopard frogs exhibit greater variation in activity than has been reported for any other species of leopard frog (Jennings, 1990). Chiricahua leopard frogs likely overwinter near breeding sites, although microsites for these “hibernacula” have not been studied.
K. Interspecific Associations/Exclusions. Throughout their range, Chiricahua leopard frogs occur with tiger salamanders (Ambystoma tigrinum), Tarahumara salamanders (A. rosaceum), southwestern toads (Bufo microscaphus), red-spotted toads (B. punctatus), Woodhouse’s toads (B. woodhousii), canyon treefrogs (Hyla arenicolor), Arizona treefrogs (H. wrightorum), striped chorus frogs (Pseudacris triseriata), plains leopard frogs (Rana blairi), northern leopard frogs (R. pipiens), Tarahumara frogs (R. tarahumarae), and lowland leopard frogs (Frost and Bagnara, 1977; Hale and May, 1983; Platz and Frost, 1984; Clarkson and Rorabaugh, 1989; Jennings, 1990; M.J.S., unpublished data).
Of interest has been sympatry between Chiricahua leopard frogs and four members of the Rana pipiens complex: northern, lowland, and plains, and one undescribed species of leopard frog (Platz and Mecham, 1979). In east-central Arizona, Mecham (1968c) found northern leopard frogs to predominate in meadow-like habitats and Chiricahua leopard frogs to predominate in rocky streams. In the Sulfur Springs Valley of southeastern Arizona, Frost and Bagnara (1977) found plains leopard frogs to predominate in non-permanent and most semi-permanent tanks and sloughs, while Chiricahua leopard frogs predominate in permanent tanks and streams. In New Mexico along Cuchillo Negro Creek, plains leopard frogs and Chiricahua leopard frogs were observed along the same stretch of stream, in similar microhabitats and in similar numbers (R.D.J., personal observations).
Rosen et al. (1995) noted a strong negative co-occurrence between Chiricahua leopard frogs and introduced American bullfrogs. Jennings and Scott (1991) questioned the role that American bullfrogs have played in declines of native amphibians in New Mexico, where several local extinctions did not involve the presence of American bullfrogs.
L. Age/Size at Reproductive Maturity. Age and size at reproductive maturity are poorly known. In southeastern Arizona, juvenile frogs and late-stage tadpoles introduced to an outdoor enclosure in May–June 1994 reproduced in September 1994 (Rosen and Schwalbe, 1998). The smallest males to exhibit secondary sexual characteristics from study sites in Socorro and Catron counties, New Mexico, were 53.5 mm and 56.2 mm SUL, respectively (R.D.J., unpublished data). Size at which females reach sexual maturity is not known.
M. Longevity. Although scoring of annuli in Chiricahua leopard frogs is more difficult than in lowland leopard frogs (Collins et al., 1996), preliminarily, skeletochronology of Chiricahua leopard frogs indicate that they can live ≤ 6 yr (Durkin, 1995).
N. Feeding Behavior. No comprehensive studies of the feeding behavior or diet of Chiricahua leopard frog larvae or adults have been conducted. Larval Chiricahua leopard frogs are herbivorous. Available food items at one site examined within the range of this species include bacteria, diatoms, phytoplankton, filamentous green algae, water milfoil (Myriophyllum sp.), duckweed (Lemna minor), and detritus (Marti and Fisher, 1998). Captive larvae eat spinach, romaine lettuce, cucumber slices, frozen trout, duckweed, spirulina-type fish foods, and rabbit pellets. Captive juvenile frogs will eat crickets (Demlong, 1997).
The diet of Chiricahua leopard frog adults likely contains a wide variety of insects and other arthropods (Degenhardt et al., 1996). Stomach analyses of other members of the leopard frog complex from the western United States show a wide variety of prey items including many types of aquatic and terrestrial invertebrates (e.g., snails, spiders, and insects) and vertebrates (e.g., fish, other anurans [including conspecifics], and small birds; Stebbins, 1951).
O. Predators. Detailed studies of predators of Chiricahua leopard frogs have not been conducted. Tadpoles are likely preyed upon by aquatic insects, including belostomatids, notonectids, dytiscids, and anisopterans, and vertebrates including native and non-native fishes, garter snakes (Thamnophis spp.), great blue herons (Ardea herodias), and other birds. Predators of juvenile and adult frogs likely include native and non-native fishes, American bullfrogs, garter snakes, and great blue herons, and mammals including rats, coyotes, gray foxes, raccoons, ringtail cats, coatis, black bears, badgers, skunks, bobcats, and mountain lions.
P. Anti-Predator Mechanisms. Adult and juvenile Chiricahua leopard frogs avoid predation by hopping to water (Frost and Bagnara, 1977). Among members of the Rana pipiens complex, Chiricahua leopard frogs possess the unusual ability to profoundly darken their ventral skin under conditions of low albedo (reflectance) and low temperature (Fernandez and Bagnara, 1991; Fernandez and Bagnara, 1993). In the clear, swiftly moving streams they inhabit (low albedo environments), this trait is thought to aid in escape from predators by reducing the amount of attention that bright flashes of white ventral skin would bring. At low temperatures, poikilotherms (cold-blooded animals) are unable to flee swiftly. Under these conditions, crypsis may be the most effective form of predator avoidance. Other anti-predator mechanisms have not been identified, but deep water, vegetation, undercut banks, root masses, and other cover sites have been mentioned as being important retreats.
Q. Diseases. Post-metamorphic death syndrome was implicated in the extirpation of Chiricahua leopard frog populations in New Mexico in the late 1980s (Anonymous, 1993). This syndrome affected earthen cattle tank populations, which became extirpated over a 3-yr period. The syndrome was characterized by the death of all post-metamorphic or adult-form frogs over winter. Dead or moribund frogs were often found during, or immediately following, winter dormancy or unusually cold periods. The syndrome appeared to spread among adjacent populations causing regional loss of populations or metapopulations.
In 1998, chytrid fungus was implicated in declines of amphibians in Australia and Panama (Berger et al., 1998). That same year, it was first identified in Arizona (Milius, 1998). Presently in Arizona, one salamander species, Sonoran tiger salamanders (Ambystoma tigrinum stebbinsi), seven species of ranid frogs (Rio Grand leopard frogs [Rana berlandieri], plains leopard frogs, American bullfrogs, Chiricahua leopard frogs, Ramsey Canyon leopard frogs [R. subaquavocalis], Tarahumara frogs, and lowland leopard frogs), and one treefrog, Canyon treefrogs (Hyla arenicolor), have been affected by this fungus. All outbreaks have been a cool season phenomena, and the pathogen is well distributed in central and southeastern Arizona (Sredl et al., 2000). In southwestern New Mexico in 2000, the presence of chytrid fungus was confirmed in a population of Chiricahua leopard frogs exhibiting declines . It is possible that chytrid fungus was responsible for population declines observed in the late 1980s in New Mexico, including those characterized as Post-metamorphic Death Syndrome (R.D.J., personal observations).
R. Parasites. Goldberg et al. (1998b) examined parasites of Chiricahua and lowland leopard frogs and American bullfrogs collected in Arizona. Chiricahua leopard frogs were found to be infected with six species of trematode (Cephalogonimus brevicirrus, Glypthelmins quieta, Gorgoderina attenuata, Haematoloechus complexus, Megalodiscus temperatus, and Clinostomum sp.) and one species of nematode (Physaloptera sp.). None of the helminths identified from the two native species were found in American bullfrogs.
4. Conservation. Because of documented declines and extirpations at historical localities, Chiricahua leopard frogs were added to the list of Category 2 candidate species (U.S.F.W.S., 1991). Beginning with the 28 February 1996, candidate notice of review, the U.S. Fish and Wildlife Service discontinued the designation of multiple categories of candidates, and only those taxa meeting the definition for the former Category 1 candidate were considered candidates (U.S.F.W.S., 1996a). In that 28 February 1996 notice, Chiricahua leopard frogs were listed as a candidate species (U.S.F.W.S., 1996a). In 2000, they were proposed for Federal listing as Threatened (U.S.F.W.S., 2000a), and Chiricahua leopard frogs are now federally listed as Threatened (http://ecos.fws.gov.tess_public/TESSSpeciesReport).
1Michael J. Sredl
Arizona Game and Fish Department
2221 West Greenway Road
Phoenix, Arizona 85023-4399
2Randy D. Jennings
Department of Natural Sciences
Western New Mexico University
P.O. Box 680
Silver City, New Mexico 88062
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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