The Western Whiptail lizards of the Colorado Plateau appear to have gamed the system, at least in my yard. They are flourishing, and if you are an insect, they are a force to reckon with.
We used to see, with regularity, half a dozen species of lizards gracing our yard and surrounding desert.
The tiny Side-blotched Lizard (Uta stanburiana) was ubiquitous at the bottom of the food chain, the fast food of other, heftier lizards. Leopard Lizards (Gambelia wislizenii), the largest species in these parts, and the striking turquoise-colored Collared Lizard (Crotaphytus collaris), will get up on their hind legs, dinosaur-like, and run down their prey, usually smaller lizards like Side-blotched, Sagebrush or Eastern Fence Lizards.
Watching lizards is akin to viewing a soap opera. Although usually solitary, they do wander about in pursuit of food, mates and choice basking sites, and so intersect with each other on occasion. Depending on circumstances like individual species, size, sex, etc., these run-ins are eventful and entertaining (for the observer). Many of the lizards I’d see would punctuate their encounters with push-ups, a territorial display meant to either attract a mate or repel an interloper. Most often this would result in the smaller lizard racing off, leaving a tiny dust cloud. Sometimes a chase or even a wrestling match would ensue. Another commonality noted was the hunting strategy of many species: lying motionless, usually in dappled shade, waiting, waiting, waiting for a juicy morsel to blunder into range, then … pounce! This was the world of lizards I thought I knew, but things are changing.
Enter the Western Whiptail (Aspidoscelis tigris, formerly Cnemidophorus tigris). Actually, whiptails are not a new species, just newly dominant. Adults are handsomely striped or checkered in black and yellow colors, streamlined, and very fast. As their name suggests, about half their length is composed of tail, which appears integral to locomotion. Not a lizard that sits around under a bush waiting, this one actively prowls, even through the heat of the day. Often you’ll hear one before you spot it, digging in leaves or soil, foraging for ants, a favorite food.
Whiptails do not eat other lizards, they do not do push-ups; they don’t appear to be territorial, wandering as they do over a large range but not defending it. When two whiptails encounter each other, they normally show no obvious signs of aggression or even interest. Could this be because in their world, food is plentiful? After all, there is never a shortage of ants. I have noted, on occasion, two whiptails traveling together, one closely following the other. This may be what whiptail courtship looks like. And speaking of sex, this is a fascinating lizard family (Teiidae) in that a few types, specifically the more southern whiptails of Arizona, Mexico and New Mexico, are unisexual. More on this later.
The interesting thing is that while the whiptail population appears to be expanding, other species like the Side-blotch Lizard are much harder to find. I rarely see any other species in this new “Whiptail Nation.” Is this phenomena a product of my cultivated homestead, whose gardens and paths favor the whiptail’s wandering hunting strategy? Or — heavens to Betsy! — have we somehow created an insect destination that supplies whiptails with an endless food stream? I have watched them take on tomato hornworms. Are whiptails somehow better able to cope with recent rising temperatures? Out in the desert, I do see other lizard species, but even there the whiptails seem to be more populous. Populations do fluctuate for many interconnected reasons and speculation into the why of things is a constant intrigue.
Several whiptail species are unisexual, composed entirely of females. They reproduce by parthenogenesis, an unfertilized egg, always producing more genetically identical females. As with most things, there are pros and cons to this particular strategy. It is efficient — no need to expend energy finding a mate (it is staggering to think of the implications should this scenario ever happen in humans), and if the environment is stable and predictable, the genetic blueprint should guarantee success. But the environment does change, in which case an unchanging genetic code can hinder a specie’s fortune. So, genetic diversity seems like a valuable asset. Is there a lesson here for people?
Alice Drogin is a crotchety NYC transplant living the good life in Castle Valley; a USU alumni; and lover of flowers & lizards.
“Watching lizards is akin to viewing a soap opera.”