Off the scale

On the hottest day of the year, a chilly wind whips across the boat speeding south from Ventura. Cathy Schwemm, a veteran of such voyages, keeps her balance on the tilting deck as other spray-dampened passengers grab at railings and poles.

She has come dressed for lizard hunting: brown hair pushed under a sun hat, water bottle strapped to her waist. With bare feet shoved into Tevas instead of hiking boots, she is clearly unfazed by the specter of rampaging lizards.

Only one kind of lizard lives on Santa Barbara Island, and that’s plenty. As many as 1,300 occupy a single acre on the rocky outpost, the highest known density of any ground-dwelling lizard on Earth. Imagine lizards waiting nose to nose to snap up the next available fly. Jammed claw to claw under prickly-pear cactuses. Skittering over sleeping bags in the dark. But Schwemm, a Channel Islands National Park wildlife biologist, repeats the warning of experts: This is not an easy reptile to hunt.

For decades, scientists have traveled 38 miles out to sea to study Xantusia riversiana, or the island night lizard, and each discovery is more peculiar than the last. Like a Lewis Carroll creation, this species is at once familiar and strange.

It’s dramatically bigger than its mainland cousins -- up to 8 inches long, compared with puny 1-inchers in the California desert. It flaunts unusually flamboyant spots or stripes. And while many lizards die after a few years, this one can live to 25 or more. Most curious of all, it bears live young as mammals do.

Despite its name, the island night lizard roams by day and sleeps at night, spending its life within a few square yards. It lives only on three small islands off Southern California. Two are military installations, closed to the public. The third is Santa Barbara Island, visited by public boats only six times a year. Planes and helicopters are banned. The giant tortoises of the Galapagos are easier to visit.

Fortunately for lizard scholars, Channel Islands National Park runs a boat here to deliver supplies and to relieve the island’s only human inhabitant, a ranger who spends seven days on the island and seven days off.

For Schwemm’s research purposes, this mound of volcanic rock is ideal because its communities are simple. It has one reptile, the lizard, which probably washed here on driftwood a million years ago. It has one mammal, a field mouse. And, most important, it is shielded from people.

As the island draws closer, its hills look voluptuous, awash in burnished golds and Gauguin reds. One can picture influential naturalists such as Charles Darwin and Alfred Russel Wallace journeying here to wrestle with the riddles of evolution. Schwemm quashes such romantic drivel.

The golds are invasive grasses brought by early settlers. The reds are an import called crystalline ice plant, which absorbs salt as it grows, turning the soil too saline for many native plants that once flourished here. Sheep brought to the island by ranchers ate more plants. So did rabbits that World War II-era military units imported for food. The rabbits destroyed the shrubs where the Santa Barbara Island song sparrow took cover, driving the bird out of existence. The lizard survived it all.

On a midsummer day on the island, pelicans and cormorants swirl above craggy black cliffs. Sea lions bask on rocks in the green-blue harbor. The scent of the sea drifts to the grassy highlands.

Not a single lizard darts across the path.

Not one is visible in the grass, or even in the boxthorn and prickly pear that it supposedly favors.

Schwemm, undeterred, hikes briskly toward the island’s summit. The breeze grows warmer. Gnats flitter. Giant coreopsis plants that color the island yellow in spring now droop like dusty gray skeletons. Nature is never as simple or as welcoming as we imagine back home.

Besides, this is not a simple lizard, as two scientists determined during eight years here studying its habits. They dipped lizards in plastic bags brimming with fluorescent powders and tracked their trails with ultraviolet light. They equipped them with radioactive tags and tailed them with a Geiger counter. They became caught up in the oddities of this lizard, its riddles, or what another island scholar, biologist Edward O. Wilson, has called the lure of nature’s mysteries. “Without mystery, life shrinks,” Wilson wrote. “Even a laboratory rat seeks the adventure of the maze.”

The two men found that the lizards’ metabolism was low, and that predators were few -- barn owls, burrowing owls, kestrels. They spend most of their days under leaves and thickets and in rocky crevices.

“These lizards don’t really roam. They mostly just sit,” said U.S. Geological Survey biologist Gary A. Fellers, who, along with survey zoologist Charles Drost, conducted the project.

This may help explain why so many lizards can live invisibly in so little space. They inhabit a kind of parallel universe, under bushes and underground. Even the island ranger rarely sees one.

Their larger size may be an example of what some call “gigantism,” a feature found in other island-dwelling species such as jays and foxes. “Everything is a little bit different on the islands. It’s a very Gestalt-type impression,” said Kevin Lafferty, another Geological Survey biologist.

Up ahead, Schwemm crouches and clears off a 1-foot-square piece of weathered wood. This is a monitoring site, meant to lure lizards fond of hiding under prickly pear leaves. She lifts the wood like a trapdoor. No lizard. She moves a few yards away and tries another piece. No lizard. Another, and a mouse leaps out.

The next one yields a lizard. Schwemm gently scoops it up. Delicate claws grasp at her fingers. Tiny beadlike eyes appear guarded but unafraid. The creature’s head is sculpted like that of a dinosaur. Its mottled green-and-tan skin is soft, like some fancy woven fabric dusted with fine glitter.

Schwemm turns it over to see the pale underside. The stomach is slightly swollen. It is a female, due to give birth in September. She sets it down, and it vanishes into the wild.

“For the naturalist,” Wilson wrote, “every entrance into a wild environment rekindles an excitement that is childlike in spontaneity, often tinged with apprehension -- in short, the way life ought to be lived, all the time.”

We leave the island to the lizards.