Rio Grande Leopard Frog (Rana berlandieri*)
Rio Grande Leopard Frog, Yuma Co., AZ. Photo by Jim Rorabaugh
Editor’s Note: We follow Amphibiaweb and Yuan et al. (2016: Systematic Biology, doi: 10.1093/sysbio/syw055) in our usage of Rana rather than Lithobates for Arizona’s ranid frogs.
In 1983 I was working as a biologist for the Bureau of Reclamation in Yuma, Arizona. Specifically, I was assisting with a Mule Deer project along and adjacent to the Wellton-Mohawk Canal near Tacna and Wellton in Yuma County. Deer were falling into the canal and drowning, and it was our job to monitor the situation and develop solutions. One of those solutions was the installation of wildlife waters north of the canal, which we hoped would act as alternative watering sites, reducing the need for the deer to come to the canal. In late August of 1983, a huge monsoon storm delivered substantial rainfall to the southern King Valley of Kofa National Wildlife Refuge and adjacent Yuma Proving Grounds, producing heavy flooding in the arroyos leading southward to the Gila River. The canal we were monitoring was located just north of and parallel to the river. On 29 August I accessed a wildlife water about 1.6 km north of the canal on the edge of one of those large arroyos and was amazed to find at least eight sizeable leopard frogs occupying a 35-gallon drinker. I knew from Vitt and Ohmart’s 1978 work that leopard frogs were presumed extirpated from the Colorado River due to competition with or predation by American Bullfrogs (Lithobates catesbeianus) or other causes. But perhaps they had persisted along the Gila River? This discovery led to a collaboration with Rob Clarkson, who at the time worked for the Arizona Game and Fish Department in Yuma, and, I came to learn, in 1981 Rob had observed two leopard frogs on the Colorado River at Yuma during a Bullfrog dietary study (Clarkson and deVos 1986). As we discovered, leopard frogs were fairly common along the Gila River near the Wellton-Mohawk Canal, and those eight frogs in the wildlife drinker had almost certainly dispersed up the arroyo from the river or the canal during or after the storm.
Rob and I eventually contacted Jim Platz at Creighton University in Nebraska who was sorting out the confused taxonomy of southwestern leopard frogs, and in time we came to realize that our leopard frogs represented an introduction of the Rio Grande Leopard Frog (Lithobates berlandieri), which was probably unintentionally brought to our area during the 1960s or 70s as tadpoles or frogs mixed in with loads of warm water sport fishes from a hatchery in New Mexico or Texas (the Federal hatchery in Uvalde, Texas is the most likely source). Over several years, we found leopard frogs to be widespread along wetted reaches of the Gila River and in agricultural ditches and canals in the Gila River Valley from near Buckeye south to Yuma, and then along the Colorado River and in adjacent agriculture south of Laguna Dam to the international boundary (Platz et al. 1990). An interesting side note is that Jim Platz needed tissue samples from other leopard frog species to identify the Gila River frogs, so Rob Clarkson and I made trips to other parts of Arizona to collect native frogs from historical localities. To our surprise, and that of Jim Platz, we encountered much difficulty in finding leopard frogs, and this led to expanded surveys throughout Arizona to determine the status of native leopard frogs. The resulting work (Clarkson and Rorabaugh 1989) was the first to ring the alarm bells that Arizona leopard frogs were declining precipitously, and often for unknown reasons.
Most of the diversity within leopard frogs has been recognized only within the last four decades. However, L. berlandieri is an exception – it was described as a species distinct from the broad-ranging Lithobates pipiens in 1859 by Spencer F. Baird. Hillis and Wilcox (2005) placed berlandieri in the berlandieri subgroup of the pipiens group, and found that the Mexican species, Rana (Lithobates) tlaloci and neovolcanica, were most closely related to it. Frost et al. (2006) proposed use of the genus Lithobates, rather than Rana, for berlandieri and other leopard frogs, a proposal that was accepted by the Society for the Study of Amphibians and Reptiles (Crother 2012), but is still controversial (e.g. Pauly et al. 2009). Lithobates forreri and L. brownorum have, at times, been considered conspecific with L. berlandieri.
Description and Similar Species
The Rio Grande Leopard Frog is a relatively large leopard frog (<114 mm SVL) with dorsolateral folds that are discontinuous and inset posteriorly. The dorsum typically has dark spots on a background of brown, grayish, bronze, green, olive green, or a combination of these colors, and usually no spots are present on the head anterior to the eyes (Fig. 1). I observed one frog near Gila Bend that lacked dark spots on the dorsum. The pattern on the rear of the thighs is a bold, open dark and light reticulation (Fig. 2), sometimes with a bluish or turquoise tint. The venter is an immaculate cream, sometimes with yellow coloration in the groin.
Of the other leopard frogs in Arizona, the Rio Grande Leopard Frog is most similar to the Lowland Leopard Frog (Lithobates yavapaiensis), the Relict Leopard Frog (Lithobates onca), and the Plains Leopard Frog (Lithobates blairi). In fact, at least some areas now occupied by the Rio Grande Leopard Frog were once inhabited by the Lowland Leopard Frog. The current distributions of L. yavapaiensis and L. berlandieri are nearly adjacent at Lake Pleasant, but are not known to overlap anywhere. The Lowland and Relict Leopard frogs are considerably smaller (<87 mm SVL and < 89 mm SVL, respectively), males lack prominent vocal sacs (large and often floppy in the Rio Grande Leopard Frog, especially in the breeding season – see Figure 3), and the pattern on the rear of the thigh is typically a tight brown or gray-brown reticulation that is darker than in the Rio Grande Leopard Frog, and never with a bluish or turquoise tint. The Lowland Leopard Frog is usually a brown or brown-gray frog, sometimes with some green on the head; its dorsal coloration is not as variable as that of the Rio Grande Leopard Frog. The Relict Leopard Frog is similar in appearance to the Lowland Leopard Frog, but its hind legs are proportionally shorter. It is colored and patterned like the Lowland Leopard Frog, but some individuals are a charcoal color dorsally. The Relict Leopard Frog is limited to a few small sites in extreme northwestern Arizona and adjacent portions of Nevada and Utah.
In Arizona, the Plains Leopard Frog only occurs at a few places in eastern Cochise County, well outside the current Arizona range of the Rio Grande Leopard Frog. It is nearly as large (<111 mm SVL) as the Rio Grande Leopard Frog, but has a complete light stripe on the upper lip (incomplete in the Rio Grande Leopard Frog). It is typically a tan or olive frog dorsally, the rear of the thigh is a dark and light reticulation similar to the Rio Grande Leopard Frog, except it usually has a fuzzy or out-of-focus appearance, there are usually one or more spots atop the head anterior to the eyes, and it almost always has a prominent light spot on the tympanum (variable in the Rio Grande Leopard Frog). Males of the Plains, Relict, and Lowland Leopard frogs lack vestigial oviducts, whereas male Rio Grande Leopard Frogs possess these structures.
The calls of these four species vary as well. The advertisement call of the Rio Grande Leopard Frog is a series of loud grating snores with each snore note lasting about 0.5 second and consisting of 6-15 pulses (Platz et al. 1990). The calls of the Lowland and Relict Leopard frogs are much softer and the snore has a stuttering quality to it, often more of a chuckle than a snore. The call of the Plains Leopard Frog is a stuttering chuckle. After a bout of snores or chuckles, all four species may produce sounds resembling someone rubbing an inflated balloon (Davidson 1996, Elliott et al. 2009).
Distribution and Habitat Use
The introduced distribution of the Rio Grande Leopard Frog, as currently documented, runs from the wetlands on the Salt River beneath the 101/202 Freeway interchange in Phoenix, downstream to the Gila River, the Agua Fria River and adjacent agriculture from just downstream of Lake Pleasant to the Gila River, a short stretch of the Hassayampa River immediately upstream of the Gila confluence, and downstream in the Gila River Valley to the Colorado River confluence, upstream in the Colorado River Valley to Mittry Lake, and downstream into Sonora and Baja California to at least the Ciénega de Santa Clara (Platz et al. 1990, Rorabaugh et al. 2002, Rorabaugh and Servoss 2006). Two localities near Mobile suggest the species has colonized the Rainbow Valley southwest of Phoenix. The Rio Grande Leopard Frog also extends into the Imperial Valley of California, where it was first reported in 1990 (Jennings and Hayes 1994). It may have reached that valley via dispersal along the All-American Canal or through agriculture in the Mexicali Valley of Baja California (Rorabaugh et al. 2002). In 2007, the species was found in the southern Coachella Valley, as well (Lovich et al. 2008), and probably arrived there via the Coachella Canal. It almost certainly occupies the Mexicali Valley of Baja California (Figure 4). The spread of this species has not been followed recently in Arizona, and it is possible it may have continued its invasion upstream on the Salt River and potentially to the Verde River. Large dams in a narrow river canyon are likely to stymie its upstream progress on the Salt River, but Horseshoe and Bartlett dams on the Verde are probably much less of a barrier. Similarly, the Rio Grande Leopard Frog seems poised to colonize the Agua Fria River and its many tributaries above Lake Pleasant.
Within its native range, the Rio Grande Leopard Frog occurs in the lower Pecos River drainage of southeastern New Mexico, portions of Texas, and south through the eastern part of Chihuahua, Coahuila, Nuevo León, Tamaulipas, and the extreme eastern parts of San Luis Potosí, Querétaro, and Hidalgo. It occurs throughout the lowlands of Veracruz except for the southern portion of the state.
In Arizona, the species is restricted to artificial or natural wetlands within Sonoran desertscrub at elevations of 28-426 m. The species can be abundant in cattail or bulrush marshes, but occurs as well along open banks of rivers, in backwaters and off-channel ponds, in dirt or concrete-lined canals and ditches, agricultural sumps, and, less commonly, cattle tanks. Where this species occurs along rivers, agriculture often is nearby, and in rivers such as the Gila, many portions of which in southwestern Arizona are intermittent, agricultural ditches and canals may provide a buffer against desiccation in the river bottom. Unlike native leopard frogs, the Rio Grande Leopard Frog usually occurs with non-native fishes, crayfish, turtles, and the American Bullfrog. At least 29 species of non-native fishes have been recorded from the vicinity of Yuma (Minckley and Marsh 2009), two species of crayfish (Procambarus clarki and Orconectes virilis) occur within the Arizona range of the Rio Grande Leopard Frog (Inman et al. 1998), as well as several introduced turtles (Brennan and Holycross 2006). Where the Rio Grande Leopard Frog occurs, the American Bullfrog is almost always nearby. The Rio Grande Leopard Frog occurs naturally with a similar suite of species in the eastern portions of its native range, and presumably evolved mechanisms to avoid predation and/or competition with them to a degree that it can persist (e.g. Feder 1983). That said, the species has apparently failed to move upstream of Imperial Dam on the Colorado River, where the river is much deeper and wider than below the dam, and non-native predators, particularly larger fishes, are common.
Activity and Reproduction
The Rio Grande Leopard Frog has been found active every month of the year in Arizona. It is most easily observed at night, but is often active during the day, as well. Although most breeding occurs in the spring and then again in the late summer or fall, the species probably breeds nearly year-round in Arizona. Calling has been heard as early as 10 February and as late as 29 October in Arizona. A pair was found in amplexus near Yuma on 28 October (Rorabaugh 2005). Eggs masses, 7-9 cm in diameter (Degenhardt et al. 1996), are attached to vegetation within 15 cm of the water’s surface. The tadpole is gray with dark speckling on the back, but is lighter on the ventral surface (see photo gallery). The tail fin is heavily mottled and may include golden spots. Tadpoles grow to about 95 mm TL prior to metamorphosis (Scott and Jennings 1985) and overwintering has been documented near Yuma and in Texas (Rorabaugh 2005). Size at maturation is not well studied, but likely occurs at 55-60 mm SVL, based on similarly-sized ranid frogs. The largest males are smaller than the largest females, and males have prominent, paired vocal sacs and enlarged thumbs during the breeding season. Metamorphs resemble adults but measure 27-32 mm SVL.
As demonstrated by their rapid colonization of a wildlife drinker about 1.6 km up a normally dry arroyo from the Wellton-Mohawk Canal, the Rio Grande Leopard Frog is surprisingly good at dispersing. It moves through the uplands as well as along drainages. Platz et al. (1990) estimated the species moved 15-16 km/year along the Gila River from its initial point of introduction, although illegal human transport and release cannot be ruled out as a contributing dispersal mechanism.
Examination of stomach contents of 85 Rio Grande Leopard Frogs from western and southern Texas suggested the species is an opportunistic generalist whose diet strongly matches prey availability (Parker and Goldstein 2005). The most common identifiable prey items in spring were grasshoppers (Acrididae), tiger beetles (Cincindelidae), katydids (Tettigonidae), and spiders (Arachnida). In fall, the most common identifiable items were owlet moths (Noctuidae), grasshoppers, and darkling beetles (Tenebrionidae). In Texas, Platz et al. (1990) noted that small leopard frogs were frequently found in Rio Grande Leopard Frog stomachs.
A die off of Rio Grande Leopard Frogs was noted in a Phoenix area pond in 1992-93 (Sredl et al. 2002). Frogs were symptomatic for “red leg” and subsequent histology revealed frogs were infected with Batrachochytrium dendrobatidis, the pathogen that causes the disease chytridiomycosis. The disease was also documented in two Rio Grande Leopard Frogs collected from near Mecca in the Coachella Valley in 2007 (Lovich et al. 2008). However, no widespread, disease-related declines of the Rio Grande Leopard Frog have been noted anywhere within its range.
To the best of our knowledge, the Rio Grande Leopard Frog has only colonized aquatic sites unoccupied by other native ranids. Its appearance on the Gila and Colorado rivers almost certainly occurred after the Lowland Leopard Frog had been extirpated (Rorabaugh 2010). The Rio Grande Leopard Frog may feed upon small Checkered Gartersnakes (Thamnophis marcianus) and occasional native anurans, but these species already tolerate predation by a suite of other non-natives and the increment represented by the presence of the Rio Grande Leopard Frog is probably inconsequential. However, the Rio Grande Leopard Frog could move upstream in the Agua Fria drainage or the Verde River and its tributaries and colonize habitats where it could adversely affect native wetland herpetofauna. In particular, the species could fairly easily move into sites currently occupied by the Lowland Leopard Frog. This smaller frog would likely be susceptible to predation and the two species could potentially hybridize. Once into the Agua Fria River above the dam at Lake Pleasant or into Verde River, few apparent barriers exist to colonization northward perhaps into the Bradshaw Mountains and the Verde Valley. Rio Grande Leopard Frogs could even potentially move into habitat occupied by the Chiricahua Leopard Frog in the Buckskin Hills of the Coconino National Forest, which is in the headwaters of Fossil Creek, a tributary to the Verde River. The Central Arizona Project’s Tucson Canal, a potential dispersal corridor, runs from Lake Pleasant through Phoenix to its terminus southwest of Tucson. However, the canal is concrete-lined and portions of it run underground, providing poor habitat for leopard frogs. Thus, the likelihood that the Rio Grande Leopard Frog would colonize the Tucson area via that canal is very low. However, the species could appear in Tucson or elsewhere in Arizona through illegal human transport and introduction.
Rorabaugh and Sredl (2002) recommended development and implementation of a fully-funded, comprehensive action plan to stem the continued invasion of the Rio Grande Leopard Frog; however, no action has been taken on their proposal. In fact, as of the summer of 2013, monitoring of the spread of this invasive exotic frog has all but halted.
Baird, S.F. 1859. Reptiles of the boundary, with notes by the naturalists of the Survey. U.S.-Mexico Boundary Survey (Emory) 3(2):1-35.
Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.
Frost, D.R., et al. 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History 297:1-370.
Clarkson, R.W. and J.C. deVos Jr. 1986. The bullfrog, Rana catesbeiana Shaw, in the Lower Colorado River, Arizona–California. Journal of Herpetology 20:42–49.
Clarkson, R.W., and J.C. Rorabaugh. 1989. Status of leopard frogs (Rana pipiens Complex) in Arizona and southeastern California. The Southwestern Naturalist 34(4):531-538.
Crother, B.I. 2012. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding, seventh edition. Society for the Study of Amphibians and Reptiles, Herpetological Circular (39):1-92.
Davidson, C. 1996. Frog and Toad Calls of the Rocky Mountains. Library of Natural Sounds, Cornell Laboratory of Ornithology, Ithaca, New York.
Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996. Amphibians and reptiles of New Mexico. University of New Mexico Press, Albuquerque.
Elliott, L., C. Gerhardt, and C. Davidson. 2009. The Frogs and Toads of North America. Houghton Mifflin Harcourt, Boston, MA.
Feder, M. 1983. The relation of air breathing and locomotion to predation in tadpoles, Rana berlandieri, by turtles. Physiological Zoology 56(4): 522–531.
Hillis, D.M., and T.P. Wilcox. 2005. Phylogeny of New World true frogs (Rana). Molecular Phylogenetics and Evolution 34:299-314.
Inman, T.C., P.C. Marsh, B.E. Bagley, and C.A. Pacey. 1998. Survey of crayfishes of the Gila River basin, Arizona and New Mexico, with notes on occurrences in other Arizona drainages and adjoining states. Unpublished report to the Bureau of Reclamation, Phoenix Area Office, AZ, Order # 5-FG-32-00470.
Jennings, M.R., and M.P. Hayes. 1994. Decline of native ranids frogs in the desert Southwest. Pages 185‑213 in: Brown, P.R. and J.W. Wright (editors). Herpetology of the North American Deserts, Proceedings of a Symposium. Southwestern Herpetologists Society, Special Publication Number 5.
Lovich, R., M.J. Ryan, A.P. Pessier, and B. Claypool. 2008. Infection with the fungus Batrachochytrium dendrobatidis in a non-native Lithobates berlandieri below sea level in the Coachella Valley, California, USA. Herpetological Review 39(3):315-317.
Minckley, W.L., and P.C. Marsh. 2009. Inland Fishes of the Greater Southwest, Chronicle of a Vanishing Biota. University of Arizona Press, Tucson.
Parker, M.L., and M.I. Goldstein. 2004. Diet of the Rio Grande Leopard Frog (Rana berlandieri) in Texas. Journal of Herpetology 38(1):127-130.
Pauly, G.B., D.M. Hillis, and D.C. Cannatella. 2009. Taxonomic freedom and the role of official lists of species names. Herpetologica 65:115–128.
Platz, J.E., R.W. Clarkson, J.C. Rorabaugh, and D.M. Hillis. 1990. Rana berlandieri: Recently introduced populations in Arizona and southeastern California. Copeia 1990(2):324-333.
Rorabaugh, J.C. 2005. Rana berlandieri Baird, 1854(a), Rio Grande leopard frog. Pages 530-532 in: M.J. Lannoo (editor), Amphibian Declines: The Conservation Status of United States Species. University of California Press, Berkeley.
Rorabaugh, J.C. 2010. Conservation of amphibians and reptiles in northwestern Sonora and southwestern Arizona. Pages 181-204 in: W. Halvorson, C. Schwalbe, and C. van Riper III (editors). Southwestern Desert Resources. University of Arizona Press, Tucson.
Rorabaugh, J.C., and J.M. Servoss. 2006. Rana berlandieri (Rio Grande leopard frog). Mexico: Sonora. Herpetological Review 37(1):102.
Rorabaugh, J.C., and M.J. Sredl. 2002. Continued invasion by the Rio Grande leopard frog in Arizona, California, and Mexico: Implications and opportunities for management. Pages 112-113 in: W.L. Halvorson and B.S. Gebow (editors). Creative Cooperation in Resource Management: Fourth Conference on Research and Management in the Southwestern Deserts, extended abstracts. USGS Sonoran Desert Field Station, University of Arizona, Tucson.
Rorabaugh, J.C., M.J. Sredl, V. Miera, and C.A. Drost. 2002. Continued invasion by an introduced frog (Rana berlandieri): Southwestern Arizona, southeastern California, and Rio Colorado, Mexico. The Southwestern Naturalist 47(1):12-20.
Scott, N.J., and R.D. Jennings. 1985. The tadpoles of five species of New Mexican leopard frogs. Occasional Papers for the Museum of Southwestern Biology 3:1-21.
Sredl, M.J., K.J. Field, and A.M. Peterson. 2002. Understanding and mitigating the effects of chytrid fungus to amphibian populations in Arizona. Nongame and Endangered Wildlife Program Technical Report 208. Arizona Game and Fish Department, Phoenix.
Vitt, L.J. and R.D. Ohmart. 1978. Herpetofauna of the lower Colorado River: Davis Dam to the Mexican border. Proceedings of the Western Foundation of Vertebrate Zoology 2:35–72.
Author: Jim Rorabaugh
Published in the Sonoran Herpetologist, September 2013 (26(3):56-61)