Tortuga de la Sierra Madre

December 1, 2013


By Robert A. Villa

My Encounter with a Cryptic and Elusive Turtle: Near the end of a weeklong biological reconnaissance in 2012, I encountered one of North America’s least known chelonians on the eastern bank of the Río Yaqui in northern Sonora.

Spotted box turtle2After graduating from high school, I made my first journey beyond the border town of Nogales. As we drove south into the state of Sonora, I first encountered the Sonoran Desert Tortoise (Gopherus morafkai), now recently described as a distinct species, inhabiting tropical deciduous forest rather than its typical desert home. Stopping at the Río Yaqui bridge, I imagined all the mysterious verdant canyons descending from the wild Sierra Madre. As we approached the magical land surrounding the small town of Alamos – in all of her tropical splendor – I was awestruck at finally arriving at this epicenter of reptile diversity.

Around 23 million years ago the Sierra Madre Occidental cordillera was lifted by tectonic and volcanic force from tropical lowlands, creating the physio-climatic setting for Sonoran biodiversity. Over the past million years, recurrent ice ages and interglacials expanded and contracted the various desert, temperate and tropical biomes.

The modern Sonoran ecosystem has predominantly tropical affinities, but desert and temperate mountain biomes intermix, all within a few hours’ drive of the U.S. border. Most notable are the temperate and tropical species reaching their extreme geographical limits via biotic corridors on and along the Sierra Madre Occidental and the adjacent lowlands. These corridors are deep, north-south canyons, or barrancos, that act as tropical shelters from seasonally cold winter storms from the north.

Alamos is a charming colonial town but also a “hot spot” destination for turtle lovers where a variety of species may be encountered in a small geographic area. In addition to the forest dwelling Desert Tortoise, Mexican Wood Turtles (Rhinoclemmys pulcherrima), Sonoran Sliders (Trachemys nebulosa hiltoni) and three Mud Turtle species (Kinosternon alamosae, K. hirtipes, K. integrum) can be found. Here too, resides one of the most elusive North American species: the Spotted Box Turtle (Terrapene nelsoni).

Probably the first specimen of the Spotted Box Turtle collected for science was by the Nelson-Goldman expedition of the Smithsonian Institution in 1897. The Spotted Box Turtle was named after Dr. E.W. Nelson in honor of his epic biological expeditions across Mexico when Norwegian-born zoologist Leonhard Stejneger described the species in 1925.

In July of 2012 I had the pleasure of assisting with a biological rafting expedition of the Río Aros and surrounding wilderness. The purpose was to help monitor the spectacular Los Pavos/Northern Jaguar Project Reserve and surrounding properties for possible acquisition by the reserve, which are flanked by the Aros. Rafting is the only practical route of entry to the interior of these large remote properties, and travel by river is not easy as there are difficult rapids in places. The particularly lush foothill thornscrub we were entering led me to entertain the hope of establishing new locality records of the known range of Beaded Lizards and other tropical herps. On the forefront of my mind was the chance I might find what has been described as the holy grail of North American turtles, the Northern Spotted Box Turtle, that had been reported on previous rafting trips to this region. Since learning of this secretive creature, I knew I had to find this precious gem of North American chelonians in the Mexican back of beyond.

The launch site was at Natora – a two-day drive from Tucson, with the second day taken up by driving over mountainous dirt roads 62 miles from the nearest town. This little village is the last outpost before entering some of the most wild and inaccessible terrain in the Sonoran region. In the chaotic assembly of the rafts, gear and supplies, we were drenched by a chubasco (monsoonal downpour), which left us shivering in the middle of July. The locals had more ammunition for the theory that gringos are crazy, and as the river rose I began to agree. Among the gathering crowd, I managed to buy a liter of home-distilled bacanora from a local drunk. This regional mezcal (agave liquor) made from the Narrow-leaved Agave (Agave angustifolia) would be a most appreciated purchase later on. It was getting late and the spectators now included young men hoping we could get them and/or their clandestine goods to el otro lado (the other side [of the border]) if we hired them as helpers. They offered us anything we wanted within their recreational pharmacopeia. We launched without them and landed just a couple miles downstream before dark.

We had reached the point of the trip where the Aros meets the Bavispe to form the Yaqui. It was all smooth sailing from here, and I was relieved, since I’d had enough whitewater by this point! But I was admittedly dismayed not to have seen the more impressive reptiles known from this river, including Indigo Snakes and Spotted Box Turtles. Every day we’d wake early to explore canyons in search of biota before breaking camp. I should have seen something new by now…

Toward the end of the trip we were in a lovely canyon with seeps from which we filtered drinking water. Going to the raft for a tool, I noticed a log worth inspecting for reptiles. Hot and somewhat depressed, I lifted it, and realizing it was heavier than I thought, dropped it on my foot, scraping off a gnarly bit of skin.

PUTA MADRE! Cursing my rookie move, I looked up and became instantly joyous. There in her quizzical silence a Spotted Box Turtle beheld a most peculiar ape. The ape was bleeding, in pain and dancing. I had found one of North America’s most secretive and little known chelonians. Photos were taken, gratuitous and documentary, and all was good.

In the thrill of the moment I neglected my duty as a naturalist to observe anything of importance relating to the animal in its natural setting.

Like other box turtles, the Spotted Box Turtle is active during the summer rainy season (July to September). The apparent difficulty in finding this turtle may be due to a combination of its remote, densely vegetated habitat and effective camouflage. The few specimens reported have been found in a variety of habitats and corresponding elevational gradients including foothills thornscrub, tropical deciduous forest, oak woodland, pine-oak woodland and mixed conifer forest.

This turtle has been documented to eat beetles and cactus fruit, as evidenced by crimson, juice-stained beaks. One can surmise that they will likely be as opportunistic as other box turtles and eat carrion, bird eggs and nestlings, other fruits, and scavenge through scat.

Much of the range of this turtle lies within mountainous regions where socially volatile and clandestine activities occur. The heart of its range is controlled by the Sinaloa Cartel, and being mixed up with narcotraficantes could, in part, explain the paucity of specimens and locality records. However, within the last few years, new records of the Spotted Box Turtle have augmented its poorly known distribution. The discovery of populations by American and Mexican biologists near Nácori Chico, Sonora, and Quila, Jalisco, significantly extended the range limits of the Spotted Box Turtle.

Today a variety of threats face the Spotted Box Turtle in Sonora. Most directly is the practice of slashing and burning of habitat to plant Buffelgrass (Pennisetum ciliare) for cattle. Northern Mexico shares the deep-rooted romanticism for cattle ranching and the cowboy with the U.S., so it’s not surprising that in 2003 government figures showed cattle (largely subsidized by the government) occupied 83 percent of the state of Sonora. There are few formal protected areas in the state, and these cover less than six percent of the land area. Over its entire range, the Spotted Box Turtle only occurs in four wilderness preserves. There are continuing threats to the species’ survival from logging, agricultural, urban and highway expansion, and climate change.

Among a few local names given to the Spotted Box Turtle, one that stands out is from Alamos where some elders refer to it as tortuga de chispitas (turtle of little sparks) in reference to the many yellow spots on the shell and skin. Indeed, sparks will fly whenever I lay my eyes on this chelonian.

Robert Villa is a field biologist and musician from Tucson, Arizona with a love of chelonians. He is keenly interested in the cultural and natural histories of the Sonoran region and Mesoamerica. He is currently president of the Tucson Herpetological Society, which is dedicated to conservation, education, and research of amphibians and reptiles of Arizona and Mexico.