The Checklist

Table 1 lists 39 amphibian and 144 reptile species for mainland Sonora, their scientific and common names, habitats in which species are found, and notes on descriptions, distribution, habits, conservation status, and other topics. Marine species that can be observed on or from the Sonoran coast are included, but island species of the Gulf of California are not (see Grismer 2002 for descriptions of these species). Scientific names for species occurring in the United States mostly follow Crother et al. (2000, 2003). Common names for Arizona species follow Brennan and Holycross (2006), which are largely taken from Crother et al. (2000, 2003). Common names of other species occurring in the U.S. follow Crother et al. (2000, 2003). Names of species occurring entirely outside of the U.S. generally follow Liner (1994) as updated by Liner (1996) and Flores-Villela and Canseco-Márquez (2004). However, many of Liner's (1994, 1996) common names are not widely used in Sonora, where amphibians and reptiles are often known by local names that vary regionally, and the same name may be used for a group of similar species. Where I knew of common names used in Sonora, they are included in Table 1 (see Bogert and Oliver 1945, Zweifel and Norris 1955, Schwalbe and Lowe 2000, Grismer 2002, Secretaría de Medio Ambiente y Recursos Naturales 2002, Nabhan 2003, and Campbell and Lamar 2004 for additional Spanish common names). Scientific names vary from the above authors for newly described species, cases in which subspecies have recently been elevated to species status, and other recent taxonomic revisions. For example, the checklist uses the genus name “Plestiodon” for skinks (Brandley et al. 2005) and “Craugastor” for Sonoran barking frogs (Crawford and Smith 2005), and follows Mulcahey et al. (2006) regarding the taxonomy of the Sonoran horned lizard (Phrynosoma goodei), Faivovich et al. (2005) for the lowland burrowing treefrog (Smilisca fodiens) and dwarf Mexican treefrog (Tlalocohyla smithii), Smith et al. (2005a) for the file-tail ground snake (Procinura aemula), and Peters and Orejas-Miranda (1970) for Clifton's lizard eater (Mastigodryas cliftoni). Nomenclature changes for amphibians as proposed by Frost et al. (2006) are not reflected in the checklist, as the scientific community has not yet had time to evaluate those proposals. For this same reason, Collins' (2006) reclassification of snake families was also not adopted. Unresolved taxonomic issues are noted in the third column of Table 1.

Included in Table 1 are seven species that likely occur or occurred historically in Sonora, but for which no museum specimens or published accounts are known. All occur just outside of Sonora in contiguous habitats (Plains spadefoot, Spea bombifrons; Plains leopard frog, Rana blairi; shortnose skink, Plestiodon brevirostris; red-backed whiptail, Aspidoscelis xanthonota; New Mexico threadsnake, Leptotyphlops dissectus; Plains black-headed snake, Tantilla nigriceps; and massasauga, Sistrurus catenatus [see Degenhardt et al. 1996, Campbell and Lamar 2004, Lemos-Espinal et al. 2004, Brennan and Holycross 2006]). Stephanie Meyer (pers. comm. 2005) reported loud, chirping geckos from a hotel in Navojoa that may be the common house gecko (Hemidactylus frenatus), a widely introduced species in the tropics; however, that report has not been investigated and the species was not included in the checklist. The status of the marbled toad (Bufo marmoreus) in Sonora is unresolved, as well. UNAM contains six Sonoran specimens labeled as marbled toads – three from 43 km southeast of Alamos, and three from near San Nicolás on Highway 16. In 2006, George Ferguson (pers. comm.) reported three toads that may have been this species in Arroyo Santa Bárbara, approximately 24 km east of Alamos. However, the marbled toad can be easily confused with juvenile cane toads (Bufo marinus) and Sinaloa toads (B. mazatlanensis), and thus is not included in Table 1. Specimen LACM 65154, which was until recently labeled as a marbled toad from southeastern Sonora, was actually a misidentified juvenile cane toad (R Feeney, pers. comm. 2006).

Habitats in the second column of Table 1 correspond to biotic communities. “Highlands” refers to Chihuahuan Desertscrub/grasslands and/or oak-pine forests and woodlands depicted in Figure 1. Conservation status of species according to the World Conservation Union (IUCN) Red list and the “Lista de Especies en Riesgo” (Secretaria de Medio Ambiente y Recursos Naturales 2002) is provided in the third column.

Figure 1.

Vegetation communities of Sonora and adjacent areas. Drawn by Alberto Búrquez Montijo.

It is beyond the scope of this paper to provide keys, descriptions, or photographs of all 183 amphibian and reptile species in Table 1. However, photographs of 144 Sonoran species shared with Chihuahua and/or Arizona can be found in Lemos-Espinal et al. (2004) and Brennan and Holycross (2006), respectively. Additionally, keys to all species present in Chihuahua are presented in Lemos-Espinal et al. (2004), and Brennan and Holycross (2006) include brief descriptions of each Arizona species. Photographs, descriptions, keys, and species accounts for all five marine turtles and the yellow-bellied sea snake (Pelamis platurus), as well as other species found in Baja California and islands of the Gulf of California can be found in Grismer (2002). Together, these three readily available documents contain photographs and descriptions of 154 of the 183 species in Table 1. Appendix 1 contains photographs of nine more species not found in these references, as well as images of other representative Sonoran amphibians and reptiles. In the first column of Table 1 the reader is referred to recent and available literature that contain photographs, descriptions, or keys for most species; and also indicate if a photo is included in Appendix 1. For the remaining species, the third column of Table 1 provides comparisons to similar taxa and brief descriptions that should be useful for preliminary field identifications. More comprehensive descriptions, keys, and photographs can be found in Smith and Taylor (1966), Hardy and McDiarmid (1969), Iverson (1992), Degenhardt et al. (1996), Rossman et al. (1996), Duellman (2001), Sherbrooke (2003), Stebbins (2003), Van Devender and Ferguson (2003), Campbell and Lamar (2004), images at < http://www.desertmuseum.org/center/research.php>, and other references listed in the Literature Cited herein.

Consistent with the predictions of Bogert and Oliver (1945) that their list of 110 species was likely no more than two-thirds of the actual herpetofauna, the checklist in Table 1 contains 183 species, 176 of which have been confirmed with specimens and/or published accounts. Although access to remote locations is now far better, and much work has occurred since Bogert and Oliver's (1945) classic preliminary herpetofauna was published, many areas of Sonora are still poorly explored herpetologically. As more field and taxonomic work is conducted, numbers of species will no doubt continue to grow and distributions will change from those portrayed in Table 1. In addition, there are likely museum collections not examined herein that would improve information in Table 1. As a result, this paper is no more than an introduction to the herpetofauna of Sonora. A comprehensive description of Sonora's amphibians and reptiles will have to wait until further work can be conducted.

Conservation and Management

Table 1 reveals that 73 (40%) of Sonora's 183 amphibian and reptile species are ascribed special status on either México's “Lista de Especies en Riesgo” or the IUCN's Red List. Some are included on these lists because of threats elsewhere within their ranges, and although from that broader perspective they may warrant special status, in Sonora these species may be fairly secure. Examples include the zebra-tailed lizard (Callisaurus draconoides), common kingsnake (Lampropeltis getula), coachwhip (Masticophis flagellum), and the larger rattlesnakes as well as the sidewinder (Crotalus cerastes). In Sonora, these species are well-represented within their ranges and their populations are fairly robust to various kinds of human disturbance. Many of these are “Pr” species, which is a category on México's list indicating possible threat, but not enough information is available to categorize the species as threatened or endangered. Two Pr species, the Río Grande leopard frog (Rana berlandieri) and spiny softshell turtle (Apalone spinifera), are only represented as introduced species, and in Sonora do not warrant protection. The tiger salamander, listed as Pr, occurs as both a native subspecies (Ambystoma tigrinum stebbinsi) only known in Sonora from Rancho Los Fresnos northwest of Cananea, and an introduced subspecies (A. t. mavortium) in the Arizona/Sonora borderlands. Protection of the introduced form is also not warranted.

Other species not provided special status may deserve such status in Sonora. The narrow-headed and West Coast gartersnakes (Thamnophis rufipunctatus and T. valida, respectively) are both aquatic habitat specialists that could be affected by introduction of non-native fishes or other potential predators. The montane streams where the narrow-headed gartersnake occurs have been impacted by logging, while the coastal habitats of the West Coast gartersnake have been largely converted to agriculture. Another sensitive species, the sheep frog (Hypopachus variolosus), was eliminated from one of very few sites known in Sonora when its breeding pond west of Alamos was altered by chicken farming operations (Schwalbe and Lowe 2000). Sheep frogs have only been observed at a single locality in recent years. The Sonoran green toad (Bufo retiformis) has likely declined due to drought and conversion of desert lands to agriculture (Santos-Barrera and Pacheco-Rodriguez 2004). If the Plains leopard frog exists in northeastern Sonora, then based on its declining status in Arizona, it should probably be considered a special status species in Sonora, as well.

Five taxa in Table 1 are intentional or accidental introductions and additions to Sonora's herpetofauna (barred tiger salamander, Ambystoma tigrinum mavortium; Río Grande leopard frog; American bullfrog, Rana catesbeiana; spiny softshell turtle; and Mediterranean gecko). Only one species has likely been extirpated from the state in recent times – the American crocodile (Crocodylus acutus) occurred on the coast as far north as the mangrove lagoon at Punta Sargento, and possibly on occasion to the Río Colorado delta (Mead and Baez 2003). It was last observed in January 1973 in El Ciego estuary near Guaymas (Navarro 2003). American crocodiles were presumably extirpated due to habitat destruction (Mead et al. 2006) and probably hunting.

Sea turtles stand out as a particularly threatened group. All five of Sonora's sea turtles are listed as in danger of extinction by the Mexican government and as endangered or critically endangered on the IUCN's Red List. All have declined substantially off the coast of Sonora. A long history of harvesting turtles as well as incidental catch in fish and shrimp nets and longlines in the Gulf of California have contributed to that decline (Seminoff and Nichols 2007). But threats to sea turtles in the Gulf are only part of the conservation context of these populations, because all five species breed exclusively or largely on beaches as far away as southern México and Japan (Resendiz et al. 1998, Seminoff and Nichols 2007). When they leave the Gulf, Sonora's sea turtles die from pollution-related disease; intentional harvest for food, aphrodisiacs, and the jewelry and souvenir industry; incidental capture in nets; boat strikes; destruction or disturbance of beaches where sea turtles nest; ingestion of trash and debris; and predation of nests by people and dogs. Nets of shrimp trawlers can be particularly efficient at catching and drowning sea turtles in the Gulf, but turtle excluder devices are now required on all trawlers. Shrimp aquaculture on the coast is an increasingly popular alternative to catching wild shrimp; over 100 shrimp farms exist on about 24,000 ha of the Sonoran coast. Although not yet documented in Sonora, pollution from shrimp farms is thought to kill sea turtles in the Mediterranean Sea.

In 1991 all sea turtles in México and its waters were protected by presidential decree; however, the law is difficult to enforce. Some intentional harvest of turtles still occurs despite the law, and some trawlers are probably still operating without turtle excluder devices (Grismer 2002, Nabhan 2003, Seminoff and Nichols 2007). For such prohibitions to be effective, an understanding of the need for conservation must be promoted at the community level. Several organizations and groups are working to develop community-based conservation programs targeting sea turtles and other imperiled species of the Gulf of California. An example can be found on the north-central Sonoran coast, where sea turtles have played an important role in the diet, legends, songs, and cultural identity of the native Seri (Coomcáac) people. The Seri recognize sea turtles are declining and that their extinction would represent a great cultural loss. With the help of Drs. Gary Nabhan and Jeffrey Seminoff, and staff from the Arizona-Sonora Desert Museum, the Seri have recruited local fisherman and villagers into sea turtle conservation (see Nabhan 2003). A training session co-taught by biologists and Seri elders for Seri youth “para-ecologists” introduced conservation techniques and simple monitoring protocols to promote conservation of Sonora's sea turtles. On the Baja peninsula, Grupo Tortuguero de las Californias – an alliance of communities, fishing cooperatives, NGOs, tourism outfitters, scientists, government agencies, and others – is also working to promote the ecological, economic, and cultural role of sea turtles in the Gulf of California. In the upper Gulf, CEDO (El Centro Intercultural de Estudios de Desiertos y Océanos), located in Puerto Peñasco, and staff at the Reserva de la Biósfera Alto Golfo de California y Delta del Río Colorado, conduct public and community outreach to promote conservation of sea turtles and other sensitive resources. Efforts such as these can contribute significantly to a global sea turtle conservation program, which is needed to ensure the continued existence of these species in the Gulf of California and elsewhere. Seminoff and Nichols (2007) are cautiously optimistic that sea turtles can be successfully conserved in the Gulf of California, and believe that populations off the coast of Sonora may be slowly recovering.

Another particularly threatened group is the native ranid frogs, including most leopard frogs, the Tarahumara frog (Rana tarahumarae), and cascade frog (R. pustulosa). The endangerment of the group is due largely to their dependence on permanent or nearly permanent water, which in an arid land such as Sonora is invariably used or altered by human activities. Native ranid frogs are particularly vulnerable to predation by introduced species, such as the American bullfrog, sport fishes, and crayfish (Orconectes virilis and Procambarus clarkii). The apparent disappearances of lowland leopard frogs (R. yavapaiensis) from the Río Colorado and lowland and Chiricahua (R. chiricahuensis) leopard frogs from the Río San Pedro are probably largely due to these introduced predators. Ranid frogs have also been affected by a fungal skin disease – chytridiomycosis or “Bd” – which may have been spread around the globe by introductions of infected African clawed frogs (Xenopus laevis; Weldon et al. 2004). In Sonora, the disease has been documented in several populations of Tarahumara frogs, as well as lowland and northwest México (R. magnaocularis) leopard frogs, and the cascade frog (Hale et al. 2005), and it has likely been a primary cause in some declines and disappearances of these and other ranid frog populations. Wetlands are often the ultimate sinks for a variety of environmental contaminants, and amphibians in general are sensitive to pollution. Until recently, airborne pollution from copper smelters in southeastern Arizona and northeastern Sonora resulted in acidic rainfall and high levels of cadmium that may have been toxic to Tarahumara frogs and other ranid frogs, and may have made frogs more susceptible to disease (Hale et al. 1995, 2005). These smelters are now closed or are equipped with pollution control scrubbers, so this threat should be waning. Toxins in agricultural chemicals used in the Río Colorado valley, in the extensive agricultural fields in southwestern Sonora, and elsewhere, likely affect some species, as well. Declines of ranid frogs are occurring within the context of a global loss of amphibian biodiversity that has become very apparent over the last 15 years (Stuart et al. 2004). The status of amphibians in general, but particularly highly aquatic forms, should be monitored closely in Sonora. Declines of amphibians may serve as an indicator of environmental degradation that could affect a variety of species, including Sonora's human inhabitants.

Livestock grazing is probably the most widespread human use of Sonora's landscapes. Grazing by cattle, goats, and other livestock has reduced vegetation cover and helped change grasslands to shrublands. Rangelands are often heavily grazed, with effects particularly apparent during drought. In some areas of northeastern Sonora, it is estimated ranchers run as many as two to five times as many cattle as their ranges can support in the long term (Walker and Pavlakovich-Kochi 2003). The effects of overgrazing are many, but precisely how amphibians and reptiles are affected is poorly studied. A study in Arizona showed that the number of lizard species and abundance of lizards declined significantly in heavily grazed areas (Jones 1981). Species dependant upon wetlands, streams, rivers, and ponds can be especially affected because cattle often congregate near water, trampling and eating streamside vegetation, and fouling water quality. In recent decades, ranchers have embarked on a campaign to improve rangelands by planting buffelgrass (Pennisetum ciliare), which was imported from Africa or the Middle East. These habitat conversions, coupled with subsequent fires that buffelgrass fuels, destroy native plant communities and are changing vast areas of Sonoran Desert, thornscrub, and to a lesser extent, tropical deciduous forest, into open African-like savannas. Buffelgrass has invaded more than two-thirds of Sonora, and 1.6 million ha may have been deliberately cleared and seeded with the species (Búrquez-Montijo et al. 2002). Again, although the effects on Sonora's herpetofauna have not been well-studied; many species are probably adversely affected; especially arboreal lizards and snakes, but also those not adapted to fire such as the desert tortoise (Gopherus agassizii). In addition, dense stands of buffelgrass may impede the movement of some species, such as horned lizards (Phrynosoma).

A variety of other human activities affect Sonora's herpetofauna. Conversion of much of the southwestern coastal plain, an area southeast of Bahía Kino, and the Río Colorado Valley to agriculture has benefitted a few species, including some amphibians, but much of the reptile fauna and several amphibian species have been eliminated from these areas. A few, mostly habitat generalists such as common kingsnakes and gophersnakes (Pituophis catenifer), persist in good numbers in agriculture. Mining has caused localized severe impacts to habitats in some areas, such as the copper mines at Cananea, and revisions to Mexican mining laws in 1992 made it simpler and less expensive for mining companies, including foreign firms, to operate in Sonora. Logging in the Municipio de Yécora increased dramatically after the completion of México 16, and by 2003, most of the commercial timber had been cut in the Yécora area (Van Devender and Ferguson 2003). Most of the wooded, higher montane areas of Sonora are too difficult to access for commercial logging, but that could change in the future if new roads are constructed. Finally, many people in Sonora are superstitious or have unfounded fears of amphibians and reptiles, and many animals are killed indiscriminately.

Although human activities are affecting Sonora's herpetofauna, in many ways habitats are less altered than in neighboring Arizona, where non-native predators are comparatively numerous, diverse, and widespread; most major rivers are dammed or dried up; and forests are subject to catastrophic fire due to climate change coupled with a long history of fire suppression that has lead to a build up of woody fuels. Significant opportunities exist in Sonora for working with landowners, ejidatarios, communities, conservation organizations, government agencies, and others to build support for amphibian and reptile conservation before problems such as those in Arizona fully manifest. Protected areas, such as the El Bosque Nacional y Refugio de Vida Silvestre Los Ajos-Bavispe, which covers eight mountain ranges in northeastern Sonora, the Reserva de la Biósfera Alto Golfo de California y Delta del Río Colorado, Reserva de la Biósfera Pinacate y Gran Desierto de Altar, El Área de Protección de Flora y Fauna Sierra de Alamos-Río Cuchujaqui, and others can be key to protecting Sonora's herpetofauna and other flora and fauna (Solís-Herrera 2000, Búrquez and Martínez-Yrízar 2007). However, designation of such areas needs to be followed up with development and implementation of management plans, working with landowners and ejidatarios within and near the reserves, and staffing the reserves adequately to implement plans, monitor species and habitats, and provide enforcement. In most protected areas much work is yet to be done.

There is a growing awareness of the special nature of Sonora's remarkable herpetofauna and the need to protect this legacy. The conservation work of state (CEDES - La Comisión de Ecología y Desarrollo Sustentable del Estado de Sonora) and federal (e.g. CONANP - La Comisión Nacional de Áreas Naturales Protegidas) agencies, and non-governmental organizations such as BIDA (Biodiversidad y Desarrollo Armónico), Naturalia, Pronatura, The Nature Conservancy, and others, is gaining momentum, and there is reason to be optimistic about maintaining Sonora's herpetofaunal biodiversity. As with the successful initial work with sea turtle conservation, a critical need is to work with local communities, ejiditarios, and landowners to foster conservation values for amphibians and reptiles, whether those values be economic or cultural. If the people of Sonora see value in conserving amphibians and reptiles, then maintaining herpetofaunal biodiversity into the future will become a much easier goal to achieve.