From Aspidoscelis to Heloderma to Xantusia, Sonora hosts some of Mexico's most impressive lizard diversity, and some of its most rarely encountered. Our primary target was the Tiger Banded Gecko, Coleonyx fasciatus. We needed samples from near the northern edge of its distribution as part of a project examining the genus Coleonyx. Alfonso Forrer had found the first specimen of C. fasciatus in the early 1880’s during his extensive collection efforts in southern Sinaloa and adjacent Durango. The lizard, an adult female measuring just short of four inches, was taken near the now abandoned mining town of Ventanas along the Río Presidio in extreme western Durango and was described by George Albert Boulenger in 1885. Additional specimens turned up in the century that followed, but despite a distribution measuring almost 1000km of thorn and tropical deciduous forest from north to south, the species has only been sighted at a handful of localities. To further complicate matters, no one is really certain whether lizards from these known sites represent the same species.
The HERP.MX Field Team converged on a mining town in northern Sonora with the hope of night-walking C. fasciatus. Unfortunately, our arrival coincided with that of a cold storm system which dropped the temperatures the first night and left us empty-handed. Our conciliatory finds? A large adult Tiger Rattlesnake (Crotalus tigris) and a Green Ratsnake (Senticolis triaspis).
The next morning, while waiting to see how the day’s weather would develop, we took advantage of our proximity to a known location for another of Sonora’s rarest lizards, Ditmar’s Horned Lizard (Phrynosoma ditmarsi). While now documented at several localities across Sonora, Ditmar’s Horned Lizard was once completely lost to science. After the first few specimens were collected in 1890 and 1897, P. ditmarsi virtually disappeared. Thanks to the detective work of some dedicated herpetologists (namely, Chuck Lowe, Vince Roth, and Michael Robinson) the species was rediscovered 73 years later in the hills of northern Sonora.
Now with the luxury of others having laid the groundwork, completed the hardwork, the put in the legwork (and with some direction from The Biodiversity Group’s Scott Tragesar) we lazily climbed a few hundred meters to a relatively barren and sunbaked hillside strewn with sharp reddish rock and peppered with oak trees — the text-book habitat for these rare lizards. A Northern Black-tailed Rattlesnake (Crotalus molossus molossus) made an appearance but herpetofaunal activity was scarce. We’d been carefully monitoring the region's weather and the previous evening’s storm was the first in a month. It had saturated the hillsides, and we’d expected a flurry of activity as herps raced to enjoy the first real monsoonal rain, but it was as if the reptiles hadn’t yet received the news. A handful of Whiptails (Aspidocelis sp.) scurried through still dry grasses, a red-spotted toad (Bufo punctatus) was spotted at the edge of its retreat, and a turned rock near an ant nest revealed a Western Threadsnake (Rena humilis) but otherwise the movements of a handful of invertebrate species were the only signs of life.
With nothing better to do before nightfall, we continued working the hillsides, inspecting each shady bush and tree since the mid-day sun rendered everything else inhospitable. Or at least, so we thought. While making the 10th or 11th pass along a horned lizard buffet line (one of the few trails of Apache Harvester Ants, Pogonomyrmex apache), a single rock among a jumble of jagged rocks in a sea of rocks stood out.
Peeking out from a carpet of similarly textured, colored, and shaped stones was the stone-like head of one of Sonora’s rarest lizards: Ditmar’s Horned Lizard or also and fittingly called, the Rock Horned Lizard (Phrynosoma ditmarsi).
While we’d like to think the ensuing celebration was over the trips’ first target, at least some of the joy could be credited to the newfound license to finally get off the sun-baked slope.
As we did, a set of towering clouds moved into view, grew several shades darker then unleashed a second torrential downpour. With the memory of last-night’s results still fresh, and not eager for a repeat showing, we opted to race south to ‘Site B’ (when planning trips during the monsoon season, it’s best to plan enough backup locations to cover the bulk of the alphabet).
We arrived at ‘Site B’ — a rocky canyon cutting through an ocean of Sonoran thorn forest —shortly after nightfall and set off, headlamps fixed to foreheads and flashlights in hand. Maybe 20 minutes, or about 5,000 face crashing gnats and moths later, a small Sonoran Leaf-toed Gecko (Phyllodactylus homolepidurus) was spotted along the canyon wall. The HERP.MX Field Team had spread out to various points of the wide wash, and while in route to review the gecko, Brandon La Forest spotted the unmistakable banded blur of a fleeing Coleonyx.
With some careful corralling, we had our second, and primary target in hand: a ruby-headed Tiger Banded Gecko (Coleonyx fasciatus).
The remainder of that night, and the following night, would yield an unremarkable mix of Sonoran thorn-forest residents. Green Ratsnakes (Senticolis triaspis), Northern Black-Tailed Rattlesnakes (Crotalus molossus molossus), Thornscrub Hooknosed Snakes (Gyalopion quadrangulare), Sonoran Lyre-snakes (Trimorphodon lambda), and Boa Constrictors (Boa sigma) rounded out the snakes, while Western Narrow-mouthed Toads (Gastrophryne olivacea), Lowland Burrowing Treefrogs (Smilisca fodiens), and Red-Spotted Toads (Anaxyrus punctatus) took advantage of the bump in humidity to move about the surface. A single Sonoran Banded Gecko (Coleonyx variegatus sonoriensis) also made an appearance, but no additional C. fasciatus were to be found.
The final target of the trip, and really more of a way to pass the time before a late afternoon flight, was to track down Sonora’s endemic turquoise beauty: Dickerson’s Collared Lizard (Crotaphytus dickersonae). We arrived near the coast just before dark and started night-driving the desert roads to find a handful of Sonoran Banded Geckos (Coleonyx variegatus sonoriensis), a couple Western Diamondback Rattlesnakes (Crotalus atrox), and a single neonate Sonoran Sidewinder (Crotalus cerastes cercobombus).
The next morning we hit the hills with a makeshift noose in search of collared lizards. A large adult spotted us and disappered into a rocky maze, but a nearby young adult male was a bit more tolerant of our fumbling attempts to photograph and eventually noose him.