Biologists suspect two possible causes. The first is absence of predation. Having left their natural enemies behind on the mainlands, island animals can afford to dispense with flight and devote their metabolic resources to other anatomical or behavioral needs. The second factor is that flightlessness tends to keep individual creatures (plant or animal) in the particular island’s gene pool. Those seeds or birds or insects that can fly well are exactly the ones most likely to disappear, heading back out over the ocean; those that fly poorly are most likely to stay and breed. Neither of the two causes has been experimentally verified, but together they probably account for the widespread pattern.
Size change is another island phenomenon, this one especially familiar in the Galápagos context. Evolution tends to dictate that insular species be either bigger or smaller than their mainland relatives. Most species of land snails on Pacific islands are unusually small. The beetles of Hawaii are small. So are the beetles of St. Helena. Nosy Bé off Madagascar harbors a chameleon the size of an ant. By contrast, St. Helena also offers the world’s largest (and therefore most disgusting) earwig, more than three inches long. Those extinct moas of New Zealand stood twelve feet tall, and the Madagascan elephant birds, not quite so tall but heftier, probably reached weights of a thousand pounds. (Sheer magnitude like that is no doubt another good reason they didn’t fly.) And finally now we come to Geochelone elephantopus, the species that gives the Galápagos Islands their name and their famous image. “Galápagos” is the Spanish for tortoise, and no living thing represents this place so vividly as the giant tortoises.
The Galápagos tortoises are, like the Egyptian pyramids, a marvel of which the dramatic effect can’t be spoiled even by overfamiliarity. No matter how many zoo specimens you have seen, no matter how many photographs, these animals are still magically impressive in their native land. They are huge, they are gentle, and as a half dozen of them munch their way through a field of pangola grass in the highlands of Santa Cruz Island, they are astounding. What they are not, however, is incomparable.
Part of understanding island biology—and part of appreciating, therefore, the Galápagos—is to recognize that those Galápagos giants aren’t alone. On the island of Aldabra in the Indian Ocean survives a related tortoise species called Geochelone gigantea, roughly the same size as the Galápagos animals and produced (insofar as biologists can guess) by the same evolutionary conditions. Having escaped mainland predators and mainland competitors, these island tortoises were free to become enormous, moving into the large-herbivore niche that elsewhere is occupied by moose, rhino, wildebeest.
Isolation and escape are what give island ecosystems their peculiarity. Isolation and escape are the preconditions that allow those other characteristic conditions (impoverishment, disharmony, the arrival of good-traveler lineages, the retention of bad-traveler offspring, changes of size) to appear. The isolation compels an inbreeding population to shape themselves, genetically, toward the new challenges of this new island habitat; and the escape from predators and competitors allows that same population a great latitude of experiment, transformation, aggrandizement. A tortoise grows huge. A finch takes on the life-style of a woodpecker. A prickly pear cactus stiffens and raises itself into a stout tree.
The exceptional becomes routine. An observer as keen as Darwin might even see an iguana fly through the air.
• • •
No sensible person travels all the way to the Galápagos just to sit on one pile of lava rock, staring at iguanas. And neither have I. Leaving behind that stretch of coastline on Santa Cruz, I board a boat and spend seven days cruising around the archipelago.
To visit a number of these islands in brisk succession, taking note of the differences in vegetation and wildlife from one to another, the differences in relative concentration of those various species, the differences in physical terrain, is an essential part of the experience. Just as it was for Darwin: “I have not as yet [noted] by far the most remarkable feature in the natural history of this archipelago; it is, that the different islands to a considerable extent are inhabited by a different set of beings.” My own week of island cruising will pass too quickly, too full of amazing sights for adequate appreciation of each, but at least I have come prepared. Despite having already destroyed my binoculars (in a maneuver so clownish as not to bear recounting), I am equipped with a field guide, a snorkel mask with prescription lenses, a packet of seasickness medicine, a silly hat, a Royal Robbins shirt that washes well in salt water, and a paperback copy of The Voyage of the Beagle. Most helpful of all, I am accompanied by my own personal consulting biologist, with whom I share a fondness for homely arthropods and a wedding anniversary. She is here mainly to scout for new species of fiddler crab, but consents also to show an interest in birds, plants, reptiles. After a day at sea we reach Española Island, nesting site for virtually the world’s entire population (twelve thousand pairs) of the waved albatross.
In a quiet bay off another island, Santa Fe, we see spotted eagle rays, their leopard-pattern fins swirling out of the water as they frolic (or possibly mate) near the surface. On the island called South Plaza we see land iguanas, fat mustard-colored lizards that are cousins to Amblyrhynchus cristatus but even larger, and that sustain themselves on this arid slab with a diet of prickly pear pads. On Tower Island, far up in the northeast corner of the archipelago, we see male frigate birds with their scarlet throat pouches inflated for mating display, and red-footed boobies roosting in bushes, webbed feet wrapped clumsily over the thin branches. Just off the shore of James Island we witness a feeding frenzy of blue-footed boobies, falling out of the sky in formation to make their plunge dives—whop, whop, whop, whop—like a mortar attack hitting the water. On Seymour we see prickly pears that grow horizontally, resting their pads on the ground, an indulgence they can afford partly because Seymour has no tortoises to feed on them. And then already the boat tour, this dizzying pageant of exotica, is over.
After such a spectacle, almost anything would seem anticlimactic. But the biologist wants more time at the Darwin Research Station, and I want more time communing with iguanas, so we return to the bay on the south coast of Santa Cruz.
• • •
There is still that one other point from Joseph Hooker’s lecture: extinction.
The drawback for any species in having evolved on an island, under conditions of isolation and escape, is that eventually the isolation is breached and the escape comes to a rude end. This fate is almost inevitable. Just as surely as “pioneers” found their way to the island once, “invaders” will find their way later. Suddenly, then, forms of anatomy and behavior that have served well for a million years may become, instead, under new conditions, disastrous. “Tameness” may prove suicidal. Flightlessness may prove fatal. Gigantism may prove to be a dire handicap. All at once there are unfamiliar predators (or competitors, or maybe just parasites or disease organisms) sharing the island, and those newcomers present a threat with which the native species are not prepared to cope. No species offers a more vivid example of this sorry truth than Geochelone elephantopus, the Galápagos tortoise.
For millennia their huge size and slow metabolism allowed them to endure droughts and famines that occasionally struck the islands, while their stately, trustful behavior was no disadvantage. They had a low reproductive rate, but each adult was likely to live a hundred years or more, so it didn’t matter. The populations (fifteen distinct races, isolated from each other among the different islands) were stable.
Then humankind arrived.
There had been no aboriginal humans in the Galápagos. But beginning late in the seventeenth century, whalers and other forms of sea-borne human predator stopped on the islands for fresh water and plundered the tortoises for meat and oil. The tortoises were defenseless; still worse for them, their reptile metabolism allowed them to survive months of storage in the hold of a ship, making fresh meat available without refrigeration. In two centuries possibly 200,000 adult tortoises were butcher
ed. Even Darwin helped eat them.
Meanwhile goats and pigs and dogs and rats (all brought to the islands by humans) did their share of damage also, preying on tortoise eggs and young hatchlings or competing with the adults for limited grazing resources. By gracious fortune, protective laws were enacted before every race of the tortoises was extinct. Eleven of the races survive. Many of those, though, are still threatened by feral mammals.
Elsewhere in the world, the dodo wasn’t so lucky. The great auk wasn’t so lucky. The moas and the elephant birds and the Guam broadbill weren’t so et cetera—and likewise with the rest of a whole dreary litany of unluckies. Since 1680, by one estimate, 127 species or races of birds have gone extinct, of which 116 lived on islands. Most of those extinctions were caused by humankind, but not all. In truth, humanity’s role in destroying island species only accelerates (grossly and cataclysmically, yes) what is otherwise in some sense inevitable. Island species come to an end, almost invariably, without ever rejoining the mainstream of evolution. They are bad travelers. They are adapted for life in a relative biological vacuum which Nature herself abhors. In the long run, therefore, they are goners.
But then in the long run we’re all goners, and the Earth itself is just another doomed biological island. It’s a truism that death and entropy await everybody, everything. That certainly doesn’t mean Homo sapiens shouldn’t, in the somewhat shorter run, scramble like hell to survive—or that we shouldn’t do all possible to minimize our baneful impact on island species.
• • •
Back on the south coast of Santa Cruz, the iguanas seem profoundly uninterested when I reappear.
They don’t flee. They glance at me and continue basking. They allow me to rejoin the group.
Most wild animals would be spooked by a human approaching so close. Not these. These singular lizards are products of isolation and escape. Evolution has forged in them the once-accurate, now-foolhardy assumption that they have no enemies on land; that the sharks cruising offshore are the only sort of beast they need fear. If I grab one by the tail, swing him around, throw him into the water, scientific precedent says he will probably swim straight back to shore and allow me to catch him again. Three hundred years’ acquaintance with humanity hasn’t been long enough, evidently, to teach caution. Maybe Darwin was right. Maybe they are stupid.
But I prefer to see them as recklessly, lavishly, forgivingly trustful. And I hope they can afford to stay that way a bit longer.
IV
THE MORAL ECOLOGY OF A DESERT
THE BEADED LIZARD
Sanctuary in Tucson: 1984
The beaded lizard is part of the landscape. Seldom is it also part of the scenery. A distinction to bear in mind. Scenery is what you look at. Landscape is where you live and die.
Most often the beaded lizard is invisible within its favored habitat, this land of dearth and stress called the Sonoran Desert—invisible even when present. It tends to be reclusive, shy, nocturnal. Also there are tricks of perspective involved, ambiguities of the optical sort, figure-and-ground confusions. In dim light, against a dark background, the animal’s black beading may blend away and the paler pink and orange markings stand forward like bleached desert sticks, leaving no lizard outline whatsoever. And vice versa against a pale background. In daylight it retreats to a burrow. Feeds ploddingly on bird and reptile eggs, rodents, young rabbits. The venom is truly potent but the reputation of lurking menace is fantasy. The beaded lizard is notorious under its more common name, and scientifically familiar as Heloderma suspectum, but it can be blamed, unequivocally, for few if any human fatalities. Unlike a mad dog or a man, a Gila monster evidently won’t bite or kill without good reason.
So it’s not really very monstrous. There are tricks of perspective involved.
Scenery is an apparition in two dimensions but landscape is a matrix for destiny. And the story in question here—this particular tangled matter of exodus, murder, thorny plants, law versus policy, ideals versus betrayal of ideals, barbed wire, religious faith, and invisible venomous reptiles—that story plays itself out, by no accident, on a harsh landscape. It begins along a remote stretch of road in the desert hills of northern Mexico, when a car pulls to a sudden stop.
• • •
Seven people climb quickly out, carrying heavy day-packs loaded with water and food. Immediately the car drives away. The people clamber over a guard rail, adults hoisting the two little children, and skid down the steep hillside into a gulch, where they will be out of sight from the road above. Beneath mesquite bushes, they pause for breath. Four of these people are Salvadorans, a young family, and they are literally running for their lives. Two others are U.S. citizens, from a certain small group up in Tucson, who are about to risk jeopardy of twenty-year prison sentences under U.S. law. One of the seven is a craven but curious journalist.
That one doesn’t share so much as a language with the four Salvadorans. He is not politically and morally pellucid, like the two young guides. He is merely a dilettante with a strong interest in predation, modes of survival, landscape.
For the moment, together, they are all safe. But the border is still a mile away, and much of that mile is open ground.
The children—a boy of five, a girl of at most four—show only a hint of terror behind their stolid faces. They are silent, obedient, stalwart. Possibly they don’t comprehend the stakes. More likely they have already seen enough in their brief lives to make these moments of danger unexceptional. As the group begin picking their way down the gulch, boulder to boulder, mesquite to mesquite, staying low in the tangled brush to avoid exposure, the little boy takes a hard fall, slamming his tailbone down on a rock shelf. While his mother applies a gentle rub, he furrows his face to a scowl, but doesn’t so much as whimper.
They move on, trying to leave no more footprints than necessary. The young Anglo man—call him Jeff—leads the way. He has hiked this particular backcountry trail before. The Anglo woman—call her Helen—walks at the rear, keeping watch behind for traffic on that stretch of road. Her large floppy straw hat gives her the look of an innocent American schoolteacher out for a day’s hike in the Sonoran hills, attentive to birds and wild-flowers. A veteran of these border crossings, like Jeff, she has cultivated the image. She brushes the others’ footprints away with a mesquite branch—idly, as though she were doodling in gouache.
The first half mile is tense but uneventful.
They have been listening carefully for distant guttural rumbles, then taking cover each time a truck rolls by on the road behind them. Finally they make their turn from the gulch into a wider canyon, this one running due north, which leads them out of eyeshot, at last, from that Mexican road. But now a different rumble of engine comes up on them too suddenly and too near. In Spanish, Helen hisses: “Avion!” They dive under the thickest clumps of mesquite, smashing themselves into the dry branches, flattening down against leaf litter and gravel, cowering there, as a small plane passes low over the canyon. Border Patrol, most likely. One glimpse, a radio call to land forces nearby, and the whole enterprise will unravel in disaster.
Still, it all seems so much like a game, so much like a television melodrama, that the journalist has to remind himself consciously: This isn’t hide-and-seek. People could go to jail. People could die. Very possible. These four people here. They could be caught, and deported, and then murdered. Very possible. He has to remind himself that the invisible menace out here today is not fantastical, and not herpetological. This isn’t a nature hike.
While the others climb out of the brush and move on, the journalist takes an extra moment to rip off his right boot and pull out the cactus spine that has been driven into his big toe. Then he scrambles to catch up with the family who are running for their lives, and with the two gringos who are smuggling them into Arizona.
• • •
“I first became involved on May 4 of 1981,” says Jim Corbett, a mild and middle-aged Quaker with hands badly twisted by arthritis. Corbett ra
n a cattle ranch here in southern Arizona until the arthritis made that sort of work impossible; before the ranching, he had taken a master’s degree in philosophy at Harvard. Since Jim Corbett is one of the founders of the latter-day underground railroad that moves Central Americans to sanctuary in the United States, May 4 of 1981 marks an important beginning.
On that date a friend of Corbett’s, driving back up toward Tucson from the border town of Nogales, had picked up a hitchhiker who turned out to be Salvadoran. Almost immediately, Corbett’s friend and the passenger came to one of the routine Border Patrol checkpoints that are common in southern Arizona. The Salvadoran had no papers; in the view of the Border Patrol, he was an illegal alien. So the Patrol agents took him, to be jailed and eventually deported back to El Salvador. “That night, when my friend came over,” says Corbett, “we talked about what might happen to that refugee.”
Corbett already knew something about the conditions in E1 Salvador, where hundreds of unarmed civilians were dying each month, most of them evidently killed by government security forces and those right-wing paramilitary groups known as los escuadrones de la muerte—the infamous “death squads.” He knew that people were disappearing, their mangled bodies turning up on street corners; that men and women were being jailed and tortured for any hint of “subversive” sympathies, or for the crime of remaining neutral in a polarized country; that children were being murdered to eliminate witnesses. And there was more. “We had heard reports that an entire planeload of deportees had been shot down at the airport in E1 Salvador, in December 1980. So we were concerned about what might happen to that hitchhiker.” The next morning Corbett woke up having decided, he says, that he ought to find out.
The Flight of the Iguana Page 17
