A Day in the Life of a Horned Gecko

A dusty-brown lizard wakes to the sight of a young star shining as it rises between two distant mountain peaks. The reptile hauls itself out of its little crevice in the gravelly soil and into a patch of well-lit earth, allowing Apterra's sun to heat its body. Only five centimeters from its nose to the tip of its stubby tail, it's imperative that the gecko (a member of the species Sentisaurus polycornus) keeps totally still until it's warm enough to run quickly. Indeed, once its metabolism has been jump-started, it is capable of impressive speed for short periods, a trait that usually keeps it well-protected from predators. 

It can smell that one has been here during the night, and soon it can see the footprints of the mid-sized kiwi trailing off into the distance. Good luck and a well-placed hiding spot have kept the lizard safe through the night. This wasn't the first brush it's had with this particular hunter; they've crossed paths at least a dozen times so far, though only once has the bird noticed and attempted to eat the lizard, leaving it with a nasty scar on its belly in the process. The arms race between gecko and kiwi in this environment has been escalating for hundreds of thousands of generations now; this individual's Correlophus spinatus ancestors faced Apteryx gekkovenator, just as it now cowers from the Thrasherbird (Terojactus confractospinus).

Life is harder for the horned gecko than ever before; despite the equatorial location of its island, extreme elevation and global cooling have resulted in the mountains becoming more sparse than in ages past. Worse, with the extinction of hydrostalks, stable sources of water are now nearly nonexistent. Relict populations of thorny-baskets are common here, providing much-needed shelter as the lizard scuttles along the still-cool land. Sweeping away some dead leaves that broke off the basket-grass during a storm a few days ago, it finds a group of woodlice that make for a nice breakfast, snapping them up in a series of bites from its strong, wide jaws. 

Emerging from the shade of the basket-grass, the insectivorous reptile seeks out another warm place to sit and digest its food. It approaches a dark grey rock, feels that it is warm to the touch, but passes it over; it would stand out against a background so different from its own body color, so it keeps moving in search of a better spot to sun itself. Climbing higher up the slope, it eventually settles on a small outcrop that matches the pattern of its scales. It sprawls out, letting the light hit every inch of its body, and peacefully sleeps while the isopods dissolve in its stomach. Others of its species begin to congregate as the morning progresses; while not especially social, this species doesn't mind grouping together around rare sites like this. It soon joins the other females at a high vantage point as the males begin to form a lek.

Battles for mating rights are intensely physical, though injuries beyond minor scratches are rare. Two males circle each other, flashing their cherry-red throats. This equally serves to intimidate their rivals and entice females, who find the color irresistible. Other indicators of fitness include the length of their horizontally-projecting horns, which are possessed by both sexes to fend off predators and are, therefore, a sure sign that a male will father well-defended and healthy offspring. The primary determining factor, though, is the fight. Both contenders push against each other, attempting to flip their opponent on its back. They slam the sides of their bodies together, each raking its sharp spines across the other's flank. A flurry of bites follows as the two lizards lash out at one another's horns, feet, and tails. Before long, one has the other pinned to the ground. The victor allows its defeated competitor to scurry off into a thicket of buttress-barrels below the ledge where the fight took place. 

After an hour or so, the pool of nearly a hundred males that originally gathered on this sunning-rock has been narrowed down to a handful of champions; exhausted and seeing dozens of females eagerly awaiting them, they don't feel the need to continue fighting until only one remains. After watching from afar, the scarred female greets one of the winners, and following a brief union, the two go their separate ways. She'll mate with a dozen or more males before her next clutch, which she'll lay in a few days in some secluded spot where she thinks they'll be safe from predators. For now, she leaves the meeting place, climbing higher on the peak to look for something else to eat. 

The very tops of these mountains are a tough place for any plants to live, as ultraviolet radiation scorches anything that remains in the sunlight too long without adequate protection. The only grass that's common here is the Isle Mountain Sodstalk (Microsaccharus compacta), which grows in short mats that keep it insulated from the elements. The sodstalk carpet is so thick that the gecko can easily walk on top of the blades, but she knows that her meal can be found within. Pushing her way through the miniature jungle with her wedge-shaped head, she spots a pill bug weaving its way between the tiny stalks. She gives chase, hoping to pounce on the crustacean before it sees her. The dense foliage, though, slows her progress, and she nearly finds herself entangled in the layers of stems, which are coated in sticky, wool-like hairs that protect the plant against the harsh light.

The lizard soon gives up, climbing out of the sodstalk colony and catching her breath as she rests in the sand nearby. It takes nearly an hour to lick all the sap off her rough skin, though the sugary woodlouse-grass secretions are a welcome source of energy. Embracing this strategy, she laps up more nectar from the sodstalks and, feeling satisfied, descends back to her normal territory. The sun is setting now, and she knows she must find a place to hide before night falls and the thrasherbirds come out to hunt once more. She spots a bed of loose soil between two thorny-barrels that seems safe - perhaps when she's ready to lay her eggs, she'll return to bury them here. She ignores it for now, instead scouting out a small pocket in a rock face. Too high off the ground for a kiwi to reach, it should offer ample protection while she sleeps. Her toes grip the smooth stone as she climbs, dragging herself into the alcove and lying down to await the next sunrise.