New distribution records for amphibians and reptiles in eastern Chihuahua , Mexico

Distributions of amphibian and reptile species in northern Mexico are poorly understood when compared to adjacent areas of the southwestern United States. To address this gap in knowledge, we conducted a series of surveys in eastcentral Chihuahua, Mexico in 2014–2016. We documented 40 new municipality records for amphibian and reptile species by means of high quality digital photos. Photographic surveys offer a low-cost, highly accessible technique for accumulating distributional information.


Introduction
The distributions of species of herpetofauna are poorly understood in Mexico when compared to the United States and Canada.For example, while the northern Mexican state of Chihuahua has a large and diverse herpetofauna, distributional records for many species in Chihuahua are sparse and patchy.This large state in particular has not experienced intensive collection efforts when compared to adjacent regions (Lemos-Espinal and Smith 2007).This is likely due in large part to the remote and rugged nature of the region and its distance from scientific institutions in Mexico and the United States.This explanation may not be wholly sufficient, though, and despite the close proximity of several U.S. institutions to the borderlands of northern Chihuahua, these areas remain the least surveyed in the state.This may be a result of the perceived danger of fieldwork in the borderlands of northern Mexico, or with perceived difficulties in obtaining collecting permits in Mexico.This situation has left large areas of Chihuahua's border region unexplored and poorly studied (Lemos-Espinal 2015).
The paucity of herpetofaunal distribution records is particularly striking in the northeast corner of Chihuahua.The 2 large municipalities of Ojinaga and Manuel Benavides sit opposite the Rio Grande from Presidio and Brewster counties in Texas.These 4 adjacent subdivisions are collectively home to Big Bend Ranch State Park and Big Bend National Park (USA), and the Santa Elena Canyon Flora and Fauna Protection Area (Mexico).Together, these 3 protected areas form the proposed Big Bend International Peace Park (King and Wilcox 2008).Despite this proposed transboundary protected status, the well-surveyed Presidio and Brewster counties contrast sharply with the poorly understood municipalities to the south.
To address this gap in our knowledge of herpetofaunal distributions, we organized a series of surveys in this area beginning in 2014.This work has already generated important distribution information, including the first record of the Texas Alligator Lizard (Gerrhonotus infernalis) in the state of Chihuahua, and the first documentation of the Trans-Pecos Black-headed Snake (Tantilla cucullata) in Mexico (Hernandez et al. 2017, Herr et al. 2017).
In this paper we present a full account of our activities and report 40 new records of amphibians and reptiles within the study area.We established new records at the level of Mexican municipalities.Municipalities are analogous to the U.S. counties that have long been used to delineate new records at a fine geographic scale (Graham et al. 2007(Graham et al. , 2009)).Furthermore, we demonstrate the ease with which such studies can be conducted by documenting all new records with high quality digital photographs and audio recordings, which are increasingly used as vouchers for distribution records when physical specimens are unavailable (Graham et al. 2010).
Survey methods.We conducted several surveys in most available habitats within the study areas.Most were visual encounter surveys, consisting of 2-4 researchers walking slowly through habitat, turning cover objects, and searching for amphibians and reptiles.Most specimens were found after turning either rocks or dead agaves, although some were located active on the surface.We also employed road-cruising-driving slowly along paved highways at night looking for live or road-killed amphibians and reptiles.There are few paved roads in the study areas, and therefore road-cruising records were generated primarily along the El Chapo-La Hacienda Highway (Chihuahua-200), a 2-lane paved road originating from the town of Manuel Benavides and running west for 60 km to the intersection with the Ojinaga-Camargo Highway (Chihuahua-67).
Identification and disposition of records.Herpetofauna encountered during surveys was identified to species using published keys and field guides (Lemos-Espinal andSmith 2007, Dixon 2013).All identifications were independently verified by Toby Hibbitts (Texas A&M University, College Station, Texas, USA).Specimens were documented as digital photograph vouchers and accessioned in the Sul Ross State University James F. Scudday Vertebrate Collections (SRSU-D).
Lemos-Espinal and Smith (2007) produced a comprehensive guide to the distribution of Chihuahua's herpetofauna to the municipality level.We consulted that work to verify the record-status of our finds, and conducted further literature searches for any records published subsequently.We used a hand-held GPS unit and the World Topographic Basemap (ESRI) to determine municipality boundaries in the field.

Results
We documented 40 new municipality records over the course of our work: 10 in Ojinaga Municipality and 30 in Manuel Benavides.We present the distribution information for all new records below in systematic order.Nomenclature follows the SSAR standard for common and scientific names (Bonett et al. 2017).
First record for Manuel Benavides Municipality: recently metamorphosed individuals found along Playa Bombifrons within Llano Amapolas (29.01779°N, 104.15959°W; WGS84), Sean P. Graham, Mark W. Herr, Tomas Hernandez, and Noah Fields, 21 October 2016 (SRSU-D 61).Remarks.Remarks.A chorus of about 5-7 calling males heard; 1 was recorded calling and photographed.There are only a handful of records for this explosively-breeding frog from Chihuahua; this record extends the species' range in the state some 200 km from the nearest populations to the west (Municipality of Chihuahua) and southwest (Municipality of Camargo).There are also closer records to the north from Presidio and Brewster County, Texas (Dixon 2013, Graham andKelehear 2014).First record for Manuel Benavides Municipality: 500 m SE of Rancho La Victoria, along SE-SW road between Manuel Benavides and Providencia (28.98799°N, 103.54901°W; WGS84), 6 November 2016, Sean P. Graham,Fabiola Baeza,Lauren Garrett,.

Sceloporus bimaculosus
Additional record for Manuel Benavides Municipality: large adult seen along road between Providencia and Santa Elena (28.92926°N, 103.45056°W; WGS84), 6 November 2016, Sean P. Graham,Fabiola Baeza,Lauren Garrett,.Remarks.Only a handful of records exist for this species within Chihuahua, all of which are found in the western half of the state; these records constitute a range extension of approximately 250 km from the nearest record in the Municipality of Namiquipa (Lemos-Espinal and Smith, 2007).However, a much closer record exists approximately 20 km to the north in Big Bend Ranch State Park, Presidio County, Texas (Dixon, 2013).Remarks.Four Tantilla hobartsmithi were found during 2016, all of which were located by turning over dead and decaying Agave havardii.

Discussion
In this study, we offer a series of interesting herpetological records, and demonstrate the ease with which such new records can be documented in poorly studied areas of Mexico.Despite the close proximity of this region to the well-studied Big Bend region of Texas, many common species were not formally documented from this region until now.This region of Mexico is home to many species characteristic of the Chihuahuan Desert, and we documented their presence in our surveys.For example, we provide new records for Chihuahuan Desert endemics such as Bogertophis subocularis, Sceloporus bimaculosus, and Phrynosoma modestum.
Over the course of our surveys in these 2 municipalities, we encountered 4 major herpetological assemblages associated with distinctive plant communities and elevational zones: (1) a low-elevation Chihuahuan Desert scrub community, with characteristic species such as Aspidoscelis marmorata, A. tesselata, Uta stansburiana, Coleonyx brevis, Phyrnosoma modestum, Sceloporus bimaculosus, and Crotalus scutulatus; (2) a higher-elevation Chihuahuan Desert scrub foothills community, with characteristic species such as Aspidoscelis scalaris, Plestiodon obsoletus, Sceloporus cowelsi, S. poinsettii, S. merriami, Urosaurus ornatus, and Tantilla hobartsmithi; (3) a riparian community, with characteristic species such as Hyla arenicolor, Anaxyrus punctatus, Lithobates berlandieri, Gastrophryne olivacea, and Diadophis punctatus; and (4) a grassland community, with characteristic species such as Aspidoscelis inornatus, Phrynosoma cornutum, Holbrookia maculata, and Spea bombifrons.The presence of this last herpetofaunal assemblage, and the close proximity of Llano Amapolas to the other habitats, makes this region particularly rich in amphibians and reptiles.For example, no extensive grassland occurs within the boundaries of nearby Big Bend National Park (BBNP), Big Bend Ranch State Park, or Black Gap Wildlife Management Area in Texas.Therefore, many of these grassland associates present in the vicinity of Santa Elena Canyon Protected Area (Manuel Benavides municipality) are absent from adjacent preserves in the United States.
Our targeted surveys in the Sierra Rica produced mixed results.Although our survey program previously documented key records for Gerrhonotus infernalis (first record for Chihuahua; Hernandez et al. 2017) and Tantilla cucullata (first record for Mexico; Herr et al. 2017), we were unable to confirm the presence of Eleutherodactylus guttilatus, Pantherophis bairdii, and Lampropeltis alterna.These species are present in the nearby Chisos Mountains of Texas, and all would represent new state records in Chihuahua (Lemos-Espinal and Smith 2007).A specimen of Lampropeltis alterna was recently found in Chihuahua (W.Hansen pers.comm.to MWH) and we await the publication of that record.
Despite reaching similar elevations, the Chisos Mountains and Sierra Rica appear to differ in terms of habitats available.For example, the Chisos Mountains support high-elevation stands of Ponderosa Pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), and Arizona Cypress (Cupressus arizonica).Although we reached the summit of the Sierra Rica during the course of our surveys, we did not observe any such high-elevation trees.The Chisos Mountains also support multiple mesic canyons with diverse trees, shrubs, and wildflowers.Although we accessed only one such mesic canyon within the Sierra Rica, other remote canyons were visible from high elevation and merit future exploration.
Traditionally, surveys for reptiles and amphibians have focused on collecting specimens and depositing them in natural history collections.Such specimens offer an unparalleled amount of information to current and future researchers, and collection-based surveys should be pursued whenever possible.Unfortunately, collectionbased surveys are often subject to bureaucratic and financial hurdles that can make them impractical.In this study, we document dozens of new distribution records without the need for expensive equipment, or collection and exportation permits.Students, tourists, and citizenscientists who are unable to collect specimens can still generate and publish relevant distributional information, and we encourage them to do so.

Figure 1 .
Figure 1.A map of the study area in the Big Bend region.Triangles represent the locations of new municipality records reported in this study.The state of Chihuahua is highlighted in cream and protected areas are shown in green.Abbreviations are BBNP: Big Bend National Park (Texas, USA); BBRSP: Big Bend Ranch State Park (Texas, USA); SECFFPA: Santa Elena Canyon Flora and Fauna Protected Area (Chihuahua, MX).