by Joseph DeSisto
During my trip to the Southwest I had the chance to spend a day at White Sands National Monument, one of the most ecologically bizarre places in North America. White Sands is located in the dry lowlands of Tularosa Basin, in southern New Mexico. Due to a geological oddity, the sand here is made up of sparkling white gypsum crystals.
This fact has shaped the evolution of White Sands’ animal inhabitants, the most conspicuous of which are lizards. Although few large predators can handle the debilitating heat and drought of this habitat, birds of prey pose a serious threat to reptiles that must spend part of their days basking in the sun. Against a white background, lizards should be easy for a cruising hawk to pick out.
During my walk I found two lizards, each of which had a different solution to their avian problem. The first, and most obvious, was the little striped whiptail. Whiptails are handsome but poorly camouflaged, with blue heads and tails and black spots above their forearms.
The whiptail above is an adult, around 8 inches in length. The juveniles are far more striking, with electric blue tails and striped bodies.
Little striped whiptails are obvious, but nearly impossible to catch by hand. Almost always, by the time I saw one, it was already vanishing in a flash of blue, zooming across the sand like the Road Runner cartoon. I saw perhaps forty whiptails during my time at White Sands. The two shown above are the only ones I could photograph before they disappeared into a burrow, usually at the base of a shrub or cactus.
After half an hour of chasing whiptails, with little more than sunburnt skin to show for my efforts, I started to notice a second lizard in my patch of sandy scrub. These lizards were slower and easier to photograph, but a little harder to spot.
The lesser earless lizard is almost synonymous with White Sands — certainly it is the most famous reptile in the park. The species to which it belongs is wide-ranging, found from South Dakota west to southern California and south through central Mexico. In most places, earless lizards are some combination of brown and black — only the populations at White Sands have evolved pure white scales to help them camouflage with the gypsum sand. Their scales even shimmer, to help the lizard mimic the sand’s reflective crystal grains.
The White Sands earless lizards are called “bleached” earless lizards, for obvious reasons. Many animals at White Sands have evolved white coloration to match the substrate: both lizard predators (e.g., the Apace pocket mouse) and prey (insects). None are quite as effective as the bleached earless lizard, but all are powerful examples of evolution in action.