Notes on the Arizona Herpetofauna


 This website is an effort to summarize what we know about Arizona’s amphibians and reptiles. We have investigated the literature and spent some time in the field watching and photographing frogs, lizards and snakes. We don’t claim this to be an exhaustive treatment of the fauna. It is imperfect and there are likely many gaps in the information, it is likely we have missed some papers, or omitted them because they duplicate information. We also recognize that a missed locality for a favored species, or our use of a scientific or common name may not be agreeable to everyone. However, the changing climate and the growing human population are setting up a perfect storm for the rapid decline of the herpetofauna. This is likely to go un-noticed until it’s too late. Population declines followed by local extirpations, and suddenly a species is gone. We hope this will stimulate awareness and appreciation of the fauna, but also act as stimulus to get more people involved is citizen science.Arizona is 295,000 square kilometers of forests, grasslands, and deserts and a biological diversity that results of the confluence of the Colorado Plateau with the Great Plains, the Mojave, Sonoran, and Chihuahuan deserts.  The differences in topography produce many localized climates and microhabitats.  Lower elevations tend to be desert, with mild winters and hot summers.  Upper elevations tend to be cooler and wetter, with cold winters and mild summers.  Diurnal temperature variations in the deserts and mountains can differ dramatically in 24 hours.  Urban areas have become heat islands, being warmer than the natural environments found around them.Arizona’s average annual rainfall is 32 cm, which falls during two rainy seasons. Pacific cold fronts produce late fall through early spring) rains, with prevailing winds coming from the west.  Winter rains are cool, and rainfall is usually widespread, steady, and light.  During late spring and summer, the wind pattern shifts, coming from the south, initiating the North American monsoon.  Rains come from moisture-laden air from the Gulf of California and the Gulf of Mexico.  Summer storms are spotty, but may be intense, bringing lightning, thunder, wind, and torrential downpours that move over much of the eastern two-thirds of the state.  The western part of the state is much drier and receives fewer monsoonal storms.Historically, the monsoon starts about 4 July and ends sometime in September. However, it may start as early as mid-June and extend into fall.  On occasion, tropical cyclones in the eastern Pacific (e.g., Baja California) may pump large quantities of moisture into the Arizona atmosphere during the fall, thereby extending the functional monsoon into October or even early November.  The additional precipitation is sometimes separated from the monsoons and termed the chubasco.  In the past, the North American monsoon was defined by subsequent days of high dewpoint, but in recent years, the National Weather Service has defined the start as 15 June and the end as 30 September.  While these specific dates are useful for annual record-keeping, the reptiles and amphibians respond to the actual dewpoint.Concern about widespread amphibian declines came to the attention of the herpetological community in 1989.  Follow-up studies revealed the severity of the declines.  At a study site in Costa Rica, 40% of the amphibian fauna disappeared over a short period in the late 1980s.  The sudden disappearance of several species of Neotropical frogs from pristine habitats suggested amphibians were in trouble.Skeptics considered these normal fluctuations in amphibian populations.  Further investigations revealed this was not the case, as the declines were far more widespread and severe than would occur under normal conditions.  Most herpetologists became convinced that amphibian declines were not random.  Stuart et al. (2004) noted 427 species (7.4%) were Critically Endangered, the highest threat category of the IUCN (International Union for Conservation of Nature), as compared with 1.8% of birds and 3.8% of mammals.  They suggested the level of threat to amphibians is undoubtedly much greater than previously thought because 1,300 species (22.5%) were too poorly known to assess, i.e., data deficient, as compared to only 0.8% of birds and 5.3% of mammals.The first global assessment of extinction risk in reptiles was presented by Böhm et al. (2013).  They used a representative global sample of 1,500 reptiles.  59% of the species in the assessment ranked as being of Least Concern; 5% were considered Near Threatened; 15% were ranked as Threatened (Vulnerable, Endangered, or Critically Endangered); and the last 21% as Data Deficient.  The authors estimated the true percentage of threatened reptiles in the world to be 19% (range: 15-36%).  Another 7% of species were estimated as Near Threatened (range: 5-26%).  Of the 223 species categorized as threatened, about half (47%) were assigned to the Vulnerable category, another 41% Endangered, and 12% regarded as Critically Endangered.  By habitat, threat estimates found 19% of terrestrial species threatened, while 30% of marine and freshwater species were estimated as threatened.  The percentage of threatened species varied greatly among higher-level taxa.  Three of four crocodilian species and 52% of freshwater turtles were estimated as threatened.  Turtles were equally spread among Red List categories, with 51% of species estimated as Threatened and another 22% assessed as Near Threatened. In contrast, only 21% of lizards and 12% of snakes were in the Threatened categories. Sinervo et al. (2010) used modeling and data from numerous studies in Mexico to assess extinction and extirpation (local extinction) likelihoods for lizards.  Many of these species are also found in Arizona.  They estimated about 40% of lizards would be extirpated and 20% of the lizards, worldwide, would be extinct by 2080.Using data for 549 reptile populations representing 194 species from the Living Planet database, Saha et al. (2018) provide the first detailed analysis of this database for a specific taxonomic group. They estimated an average global decline in reptile populations of 54–55% between 1970 and 2012.  Previous estimates suggested 30% of amphibians and 20% of reptiles were at risk of disappearing.  Both these estimates (Bohm et al. 2013 and Saha et al. 2018) suggest amphibians and reptiles are the most endangered vertebrates.  Human-produced toxins, climate change, invasive species, habitat destruction, and disease are the major factors contributing to the decline of amphibians and reptiles.  Unfortunately, amphibians and reptiles are not nearly as well-studied as birds and mammals, and the number of undescribed species is substantial.Arizona had about 8 million people in 2015.  By 2030, it is estimated to increase to just over 10 million inhabitants.  Human population growth will certainly result in less habitat for the fauna and more damage to ecosystems.  Minimizing the damage to biodiversity is important.  On behalf of the Southwest Partners in Amphibian and Reptile Conservation, Jones et al. (2016) provided habitat management guidelines to help land managers and private and public entities reduce the impact of human influence on the habitats and populations of native species.  They also provided a list of species or groups having the greatest conservation need.  Similarly, the Arizona Game and Fish Department maintains a list of Species of Greatest Conservation Need. 

Amphibians, Reptiles, & Climate Change

Amphibians and reptiles are all dependent on temperature for critical physiological processes that range from muscle contraction to food digestion and the timing of reproduction.  Reptiles have a thermal niche; this can be thought of as a thermal envelope the animal can survive in.  Changes in the thermal shell may decrease the animal’s survival ability.  Some reptiles have their sex determined by the temperature the embryo experiences at a critical time during development.  Amphibians are often thermal conformers and can be active at temperatures that are cooler than reptiles.  Their embryonic development, tadpole transformation, and reproductive timing are all linked to the local temperature and rainfall regimes of the area they inhabit.Temperate zone amphibians and reptiles are at risk from the changing climate. Foraging and mating occur during limited times of the year.  If the temperature is to too warm or too cold, the change in weather conditions may result in years when food is not available, or courtship and mating cannot occur.  The result may be a dramatic decrease in the adult population or a failure to reproduce.  Lizard mortality may be linked with warm spells in winter, alterations in the vegetation, fire regimes, or invasive species, and they may face new diseases or be unable to cope with new ones.  Snakes may be affected by these same factors.  Climatic niche models suggest that some rattlesnakes may have reduced the size of their distribution while some ratsnakes have increased activities due to warmer night temperatures.The aquatic nature of most turtles suggests they may find their habitats fragmentated with an altered climate.  Water availability and its temperature may become unsuitable for these species. Turtles (and alligators and crocodiles) have temperature-sensitive sex determination. Cooler temperatures may produce clutches of only males, while warmer temperatures may produce only females. Local temperature changes may alter the sex ratios of populations and have a long-term impact over time.Altered thermal niches for amphibians and reptiles at the northern boundaries of their ranges may produce conditions that are lethal.  The window of time with suitable temperatures for amphibian and reptile activities is changing.  The window is becoming shorter as climate changes in both tropical and temperate zone regions.  Reduction in activity times means the time they must forage for food, locate mates, and reproduce is changing.  If they are active for more extended periods of time, they may require more food.  Habitat may be expanding northward or into mountains for some species.  For other species, increased weather variation may produce conditions that they just cannot tolerate. Extinction will likely be the result for many species.One study in Mexico reports that 12% of local lizard populations have been lost since 1975.  The evidence suggests that these losses are associated with climate change altering thermal niches (Sinervo et al. 2010).  In Alberta, Canada, Greater Short-Horned Lizards, Phrynosoma hernandesi, overwinter at high altitudes, and their survival depends on a persistent snow cover to insulate the lizard from very cold air: lizards become active during warm spells in winter, and they can be ‘caught out’ and die when the temperature drops (Alberta Conservation Association, 2010).  In contrast, thermal niches used by ratsnakes may be expanding with more warmer nights (Weatherhead et al. 2012). Names, Maps, & AbbreviationsCommon and scientific names usually follow Crother et al. (2017) with some exceptions.  Two major exceptions to this are the hylid frogs and the rattlesnakes, where we follow the arrangements of Duellman et al. (2016) and Schuett et al. (2016) respectively. Discussion of subspecies occurs within the species accounts.  Some subspecies may be destined to become full species, while others will fade into history.  They can be confusing and are human constructs, not natural units, but they are important because they are frequently used as units for conservation.In the titles for each species account we have given the name(s) of the people who described that species and the date it was described.  If their name(s) and the date of publication are in parentheses it means the species is now in a different genus from when it was described.  If no parentheses are present it means the generic assignment is the same as it was in the original description.Each account ends with a section on taxonomy. Amphibian taxonomy is primarily based of version 6.0 of Amphibians of the World on the American Museum of Natural History’s website. The reptile taxonomy sections are based mostly on the accounts in the Reptile Database and Wallach et al. (2016). However, in some accounts we have used additional sources. The taxonomy sections are sometimes long and convoluted and may have little bearing on the life history of the animal.  However, applying the correct name to natural history observations and conservation data can have important implications for the legal standing and scientific understanding of species in question.Maps.  Controversy over using specific localities versus shaded areas, using data that has been specifically verified by an “expert,” and using data that has been unfiltered by experts are all topics of contention. In our view maps, like statements, are always best considered hypotheses, subject to revision, and critical analysis – like all other aspects of science.Abbreviations. We have used the following abbreviations: ASL = above sea level, Bd = Batrachochytrium dendrobatidis, km = kilometers, MYA = millions of years ago, mm = millimeters, cm = centimeters, m = meters, SUL = snout-urostyle length, SVL = snout vent length.[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_single_image image=”3004″ img_size=”large”][/vc_column][/vc_row]