By Ryan Collister
Mexico’s herpetofauna is among the most diverse and exciting of any country in the world, and its proximity to my home state of Texas has always been tantalizing to herp enthusiasts here, myself included. Having spent a large part of my career working with Mexican species in a captive zoological setting, I found it was time to take the next step and encounter some of these truly special animals on their home turf. I cut my teeth in field herpetology within a stone’s throw of the border in west and south Texas as well as the mountains of southeastern Arizona, where most, if not all, of the species present there can be found on both sides of our arbitrary man-made boundaries. So, when I was offered the opportunity to accompany a group expedition to the northern border states of Coahuila, Nuevo León, and Tamaulipas, I was immediately on board.
The northern Sierra Madre Oriental, the mountain range that runs up much of eastern Mexico, is mostly arid terrain, with more mesic conditions at higher elevations, including small portions of cloud forests a bit further south from our destinations. May of 2016 found us beginning our trip before sunrise, where a private shuttle service conveniently picked us up in Del Rio, Texas, where our cars were left in a public parking lot, and took us across the border to our rental car in Ciudad Acuña, which boasted Mexican plates that greatly increased our safety while traveling. For obvious reasons, this is not a subject to be taken lightly in this part of the world and was a frequent topic of conversation before and during the trip.
After experiencing the chaos of Mexico’s highways for a few hours, we stopped to stretch our legs on a rocky mountainside just off the road, where one of our crew found our first animal, a juvenile Lugo’s alligator lizard (Gerrhonotus lugoi). This little lizard could easily be called the rarest find of the entire trip and was a personal highlight for me, after a childhood encounter with a Texas alligator lizard (Gerrhonotus infernalis) forever cemented my interest in this genus and its relatives. The next morning, on the extreme southern side of the state near the border of Nuevo León, we combed some hillsides in search of an uncommon locality of Tamaulipan rock rattlesnakes (Crotalus morulus), but to no avail. Luckily, the first two snakes of the trip did show themselves – immaculate specimens of Mexican black-tailed rattlesnake (Crotalus molossus nigrescens) and Mexican pine snake (Pituophis deppei jani), the latter of which was a literal last-minute find that was waiting for us back at the car! This habitat was still fairly arid, and was interspersed with a variety of interesting cacti, including some form of giant barrel cactus and a smaller one with hot pink spines. Unfortunately, some of these spines made their way into me after I took a tumble on some sliding rocks, a constant possibility on this type of terrain.
Moving southwest into higher elevations in Nuevo León, we explored a grassy area surrounded by tall pines, entering the elevational range of eastern twin-spotted rattlesnakes (Crotalus pricei miquihuanus). It didn’t take too long before one was found in a pile of small boulders, along with the first of many imbricate alligator lizards (Barisia ciliaris) that we would see under rocks. Next on the list was an area near the little mountain town of Pablillo, which greeted us with a thick layer of morning fog and the greenest habitat we would visit on this trip. Epiphytic vegetation covered the branches of the many old oaks, including some interesting Mexican varieties of Tillandsia that happened to be in bloom. A large variety of spiny lizard (Sceloporus torquatus) could be seen frequently here among the rock piles, and a surprise encounter with a yellow-throated garter snake (Thamnophis pulchrilatus) had us scratching our heads, as we had never heard of this species which so closely resembled the black-necked garter snakes back home. After a pleasant run-in with the landowner, who actually distantly knew a member of our party and decided to accompany us for a bit, we finally found two examples of our main target species, the Tamaulipan rock rattlesnake. One of them required some assistance shedding (this was done extremely carefully and without using bare hands!) and was revealed to be an absolute stunner, almost appearing to be made of silver, nicely complimenting another find we would make later.
Later that night, some nocturnal road-cruising of some mid-elevation hills and lowland deserts yielded many common Chihuahuan desert species that are easily found back in Texas. Unfortunately, most of these were roadkills, including a desert kingsnake (Lampropeltis splendida), Texas coral snake (Micrurus tener), and a Baird’s rat snake (Pantherophis bairdi), a species which appears much different in color and pattern down in Mexico than it does north of the border. Our specimen resembled a yellow rat snake from Florida with the head of a green rat snake from Arizona, a far cry from the gray and black stripes and orange highlights of Texas specimens.
The next morning we concluded our trip with a quick jaunt just across the state border into Tamaulipas into a remote canyon deep in the mountains, with a small village and its surrounding agricultural fields nestled deep within the valley. A rare species of montane garter snake, Thamnophis exsul, could be found nearby, but did not turn up for our group. However, another Mexican black-tailed rattlesnake and eastern twin-spotted rattlesnake appeared during a stop on the way in, both of which were stunning and quite different in appearance from the ones seen days prior.
Once we arrived in the valley, another variety of spiny lizard, Sceloporus minor, was often seen flitting back and forth between the massive agaves dotting the landscape. Specimens at this locality exhibited orange bodies, blue bellies, and green tails, but are often solid blue in color in other parts of their range. Ultimately, our team scoured the valley surrounding the little town and turned up a total of thirteen Tamaulipan rock rattlesnakes! The prettiest of which were brought back to the car to be photographed by the group before release, including my personal favorite, a knockout gold specimen with crisp black bands that remains one of the most beautiful wild snakes I’ve ever seen, and a nice contrast to the silver specimen found earlier. Each individual looked vastly different from the last, with various levels of clean or messy patterns, and some combination of greens, grays, pinks, and yellows. Following this epic day in the field, some final meals of street tacos and pollo asado sent us back home happy, if not exhausted, and hungry to return to this heartbreakingly beautiful and dangerous region.
Expeditions such as this are imperative to collecting scientific data and are at the backbone of the Highlands & Islands mission. By documenting, studying, and raising awareness for these amazing animals and their declining populations we hope to maintain a future for them and their habitats. To learn more about Highlands & Islands Conservatory, follow us on social media or visit our website at https://www.highlandsandislandsconservatory.org/
