National Geographic : 2006 Sep
A spiny-tailed iguana nibbles a cardon cactus flower on Isla San Esteban. The Seri Indians considered these reptiles a valuable food source and spread them among several islands in the Gulf of California to serve as emergency stores for stranded fishermen. of a sea. Salt water surrounds one of the most fascinating portions, which takes in nearly all of the 34 major islands and more than 850 smaller islands and islets in the Gulf of California. Some have labeled this archipelago Galapagos North because so many different species arose from common ancestors as they adapted to island environments, providing a laboratory for the study of evolution. Steep-sided Isla San Pedro Martir, a square mile in size, towers among the remote Midriff Islands at the center of the gulf, shimmering ghostly white from guano, blurred by a haze of wings, and moated by cold, upwelling cur rents where great whales feed on krill and sardines. Large birds, including the world's densest colony of brown boobies and largest colony of blue-footed boobies, rule this strange castle alongside side-blotched lizards, which abound almost a thousand to an acre. The court jesters are striped gnats known as bobitos, or little boobies. While gnat larvae develop in the boobies' droppings, adults sip moist mucus from the birds' eyelids. They're happy to drink around your eyes, too. And in your ears, up your nose, or on any patch of sweaty skin-by the hun dreds, tickling without letup. The green-and turquoise lizards, Utapalmeri, found only on San Pedro Mirtir, are almost as bold. Show a bit of red on your sock, and a dozen emerge from rocks to run up your leg and bite the cloth. Red happens to be the color of a key Utafood: fruit from cardon cactuses, which grow in candelabra forests fertilized by the bird lime. The lizards also dash right in among the birds to snatch fish scraps and gnats. There are 115 kinds of land-dwelling reptiles on the gulf's islands. Forty-eight of them are unique to this region. For example, the Midriff island called San Esteban has produced a rat tlesnake, whipsnake, spiny iguana, and Gila monster-size chuckwalla, all found only within its 16 square miles. Ana Luisa Figueroa of the Mexican resource agency CONANP (Comisi6n Nacional de Areas 140 NATIONAL GEOGRAPHIC * SEPTEMBER 2006 Naturales Protegidas) urged me to add this: By all means, go see the wonders of the gulf's isles. But do it with a guide or, better yet, from a boat circling the shores. The birds nest so close together that a single hiker can put thousands to flight. Before that blizzard settles down, every exposed egg or young chick will have been eaten by gulls or ravens. Many of the gulf islands have native Pero myscus mice. Many host the endemic Mexican fishing bat. But hardly any hold larger predatory native mammals. After seeing me off on my snorkel along San Pedro Martir's shore, Araceli Samaniego, a biologist with the Mexican non profit Grupo de Ecologia y Conservaci6n de Islas, part of a North American island conserva tion network, scrambled up steep cliffs where she noticed a dwindling colony of red-billed tropic birds nesting. She returned fuming, carrying crab shells and infant bird bones, all gnawed. "Rats," she grumbled. "Everywhere!" House mice-Mus musculus-andcats, too, often jump ship to take up island life. At each island we visit, Samaniego sets out a series of baited live traps. A petite, soft-spoken woman of 28 with an easy laugh, she talks to the wild mice she catches, calling them corazn sweetheart-and stroking their little feet before letting them go. If the traps hold rats instead, she carefully weighs and measures them. Then she kills them. She doesn't like it, but she likes the idea of rats gobbling nestlings and rare endemic life-forms even less. Two-thirds of all known extinctions worldwide since the year 1600 have taken place on islands, Samaniego reminds me, and alien species introduced by people are a major cause. Gathering data by trapping is the early stage of a planned effort by the island conservation group and CONANP to eradicate rats on San Pedro Martir. A similar program on nearby Isla Raza in 1995 helped restore the globe's premier breeding colonies of elegant terns and Heermann's gulls, though it came too late for the island's nesting black storm-petrels and Xantus's murrelets.