But man, unhappily, has written one of his blackest records as a destroyer on the oceanic islands. He has seldom set foot on an island that he has not brought about disastrous changes. He has destroyed environments by cutting, clearing, and burning; he has brought with him as a chance associate the nefarious rat; and almost invariably he has turned loose upon the islands a whole Noah’s Ark of goats, hogs, cattle, dogs, cats, and other non-native animals as well as plants. Upon species after species of island life, the black night of extinction has fallen.
In all the world of living things, it is doubtful whether there is a more delicately balanced relationship than that of island life to its environment. This environment is a remarkably uniform one. In the midst of a great ocean, ruled by currents and winds that rarely shift their course, climate changes little. There are few natural enemies, perhaps none at all. The harsh struggle for existence that is the normal lot of continental life is softened on the islands. When this gentle pattern of life is abruptly changed, the island creatures have little ability to make the adjustments necessary for survival.
Ernst Mayr tells of a steamer wrecked off Lord Howe Island east of Australia in 1918. Its rats swam ashore. In two years they had so nearly exterminated the native birds that an islander wrote, ‘This paradise of birds has become a wilderness, and the quietness of death reigns where all was melody.’
On Tristan da Cunha almost all of the unique land birds that had evolved there in the course of the ages were exterminated by hogs and rats. The native fauna of the island of Tahiti is losing ground against the horde of alien species that man has introduced. The Hawaiian Islands, which have lost their native plants and animals faster than almost any other area in the world, are a classic example of the results of interfering with natural balances. Certain relations of animal to plant, and of plant to soil, had grown up through the centuries. When man came in and rudely disturbed this balance, he set off a whole series of chain reactions.
Vancouver brought cattle and goats to the Hawaiian Islands, and the resulting damage to forests and other vegetation was enormous. Many plant introductions were as bad. A plant known as the pamakani was brought in many years ago, according to report, by a Captain Makee for his beautiful gardens on the island of Maui. The pamakani, which has light, wind-borne seeds, quickly escaped from the captain’s gardens, ruined the pasture lands on Maui, and proceeded to hop from island to island. The CCC boys were at one time put to work to clear it out of the Honouliuli Forest Reserve, but as fast as they destroyed it, the seeds of new plants arrived on the wind. Lantana was another plant brought in as an ornamental species. Now it covers thousands of acres with a thorny, scrambling growth—despite large sums of money spent to import parasitic insects to control it.
There was once a society in Hawaii for the special purpose of introducing exotic birds. Today when you go to the islands, you see, instead of the exquisite native birds that greeted Captain Cook, Mynas from India, cardinals from the United States or Brazil, doves from Asia, weavers from Australia, skylarks from Europe, and titmice from Japan. Most of the original bird life has been wiped out, and to find its fugitive remnants you would have to search assiduously in the most remote hills.
Some of the island species have, at best, the most tenuous hold on life. The Laysan teal is found nowhere in the world but on the one small island of Laysan. Even on this island it occurs only on one end, where there is a seepage of fresh water. Probably the total population of this species does not exceed fifty individuals. Destruction of the small swampy bit of land that is its home, or the introduction of a hostile or competing species, could easily snap the slender thread of life.
Most of man’s habitual tampering with nature’s balance by introducing exotic species has been done in ignorance of the fatal chain of events that would follow. But in modern times, at least, we might profit by history. About the year 1513, the Portuguese introduced goats onto the recently discovered island of St. Helena, which had developed a magnificent forest of gumwood, ebony, and brazilwood. By 1560 or thereabouts, the goats had so multiplied that they wandered over the island by the thousand, in flocks a mile long. They trampled the young trees and ate the seedlings. By this time the colonists had begun to cut and burn the forests, so that it is hard to say whether men or goats were the more responsible for the destruction. But of the result there was no doubt. By the early 1800’s the forests were gone, and the naturalist Alfred Wallace later described this once beautiful, forest-clad volcanic island as a ‘rocky desert,’ in which the remnants of the original flora persisted only in the most inaccessible peaks and crater ridges.
When the astronomer Halley visited the islands of the Atlantic about 1700, he put a few goats ashore on South Trinidad. This time, without the further aid of man, the work of deforestation proceeded so rapidly that it was nearly completed within the century. Today Trinidad’s slopes are the place of a ghost forest, strewn with the fallen and decaying trunks of long-dead trees; its soft volcanic soils, no longer held by the interlacing roots, are sliding away into the sea.
One of the most interesting of the Pacific islands was Laysan, a tiny scrap of soil which is a far outrider of the Hawaiian chain. It once supported a forest of sandalwood and fanleaf palms and had five land birds, all peculiar to Laysan alone. One of them was the Laysan rail, a charming, gnomelike creature no more than six inches high, with wings that seemed too small (and were never used as wings), and feet that seemed too large, and a voice like distant, tinkling bells. About 1887, the captain of a visiting ship moved some of the rails to Midway, about 300 miles to the west, establishing a second colony. It seemed a fortunate move, for soon thereafter rabbits were introduced on Laysan. Within a quarter of a century, the rabbits had killed off the vegetation of the tiny island, reduced it to a sandy desert, and all but exterminated themselves. As for the rails, the devastation of their island was fatal, and the last rail died about 1924.
Perhaps the Laysan colony could later have been restored from the Midway group had not tragedy struck there also. During the war in the Pacific, rats went ashore to island after island from ships and landing craft. They invaded Midway in 1943. The adult rails were slaughtered. The eggs were eaten, and the young birds killed. The world’s last Laysan rail was seen in 1944.
The tragedy of the oceanic islands lies in the uniqueness, the irreplaceability of the species they have developed by the slow processes of the ages. In a reasonable world men would have treated these islands as precious possessions, as natural museums filled with beautiful and curious works of creation, valuable beyond price because nowhere in the world are they duplicated. W. H. Hudson’s lament for the birds of the Argentine pampas might even more truly have been spoken of the islands: ‘The beautiful has vanished and returns not.’
The Shape of Ancient Seas
WE LIVE IN AN age of rising seas. Along all the coasts of the United States a continuing rise of sea level has been perceptible on the tide gauges of the Coast and Geodetic Survey since 1930. For the thousand-mile stretch from Massachusetts to Florida, and on the coast of the Gulf of Mexico, the rise amounted to about a third of a foot between 1930 and 1948. The water is also rising (but more slowly) along the Pacific shores. These records of the tide gauges do not include the transient advances and retreats of the water caused by winds and storms, but signify a steady, continuing advance of the sea upon the land.