The Sea Around Us (15 page)

No less than the water, the winds and the air currents play their part in bringing inhabitants to the islands. The upper atmosphere, even during the ages before man entered it in his machines, was a place of congested traffic. Thousands of feet above the earth, the air is crowded with living creatures, drifting, flying, gliding, ballooning, or involuntarily swirling along on the high winds. Discovery of this rich aerial plankton had to wait until man himself had found means to make physical invasion of these regions. With special nets and traps, scientists have now collected from the upper atmosphere many of the forms that inhabit oceanic islands. Spiders, whose almost invariable presence on these islands is a fascinating problem, have been captured nearly three miles above the earth's surface. Airmen have passed through great numbers of the white, silken filaments of spiders' ‘parachutes' at heights of two to three miles. At altitudes of 6000 to 16,000 feet, and with wind velocities reaching 45 miles an hour, many living insects have been taken. At such heights and on such strong winds, they might well have been carried hundreds of miles. Seeds have been collected at altitudes up to 5000 feet. Among those commonly taken are members of the Composite family, especially the so-called ‘thistle-down' typical of oceanic islands.

An interesting point about transport of living plants and animals by wind is the fact that in the upper layers of the earth's atmosphere the winds do not necessarily blow in the same direction as at the earth's surface. The trade winds are notably shallow, so that a man standing on the cliffs of St. Helena, a thousand feet above the sea, is above the wind, which blows with great force below him. Once drawn into the upper air, insects, seeds, and the like can easily be carried in a direction contrary to that of the winds prevailing at island level.

The wide-ranging birds that visit islands of the ocean in migration may also have a good deal to do with the distribution of plants, and perhaps even of some insects and minute land shells. From a ball of mud taken from a bird's plumage, Charles Darwin raised eighty-two separate plants, belonging to five distinct species! Many plant seeds have hooks or prickles, ideal for attachment to feathers. Such birds as the Pacific golden plover, which annually flies from the mainland of Alaska to the Hawaiian Islands and even beyond, probably figure in many riddles of plant distribution.

The catastrophe of Krakatoa gave naturalists a perfect opportunity to observe the colonization of an island. With most of the island itself destroyed, and the remnant covered with a deep layer of lava and ash that remained hot for weeks, Krakatoa after the explosive eruptions of 1883 was, from a biological standpoint, a new volcanic island. As soon as it was possible to visit, scientists searched for signs of life, although it was hard to imagine how any living thing could have survived. Not a single plant or animal could be found. It was not until nine months after the eruption that the naturalist Cotteau was able to report: ‘I only discovered one microscopic spider—only one. This strange pioneer of the renovation was busy spinning its web.' Since there were no insects on the island, the web-spinning of the bold little spider was presumably in vain, and except for a few blades of grass, practically nothing lived on Krakatoa for a quarter of a century. Then the colonists began to arrive—a few mammals in 1908; a number of birds, lizards, and snakes; various mollusks, insects, and earthworms. Ninety percent of Krakatoa's new inhabitants, Dutch scientists found, were forms that could have arrived by air.

Isolated from the great mass of life on the continents, with no opportunity for the crossbreeding that tends to preserve the average and to eliminate the new and unusual, island life has developed in a remarkable manner. On these remote bits of earth, nature has excelled in the creation of strange and wonderful forms. As though to prove her incredible versatility, almost every island has developed species that are endemic—that is, they are peculiar to it alone and are duplicated nowhere else on earth.

It was from the pages of earth's history written on the lava fields of the Galapagos that young Charles Darwin got his first inkling of the great truths of the origin of species. Observing the strange plants and animals—giant tortoises, black, amazing lizards that hunted their food in the surf, sea lions, birds in extraordinary variety—Darwin was struck by their vague similarity to mainland species of South and Central America, yet was haunted by the differences, differences that distinguish them not only from the mainland species but from those on other islands of the archipelago. Years later he was to write in reminiscence: ‘Both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on earth.'

Of the ‘new beings' evolved on islands, some of the most striking examples have been birds. In some remote age before there were men, a small, pigeonlike bird found its way to the island of Mauritius, in the Indian Ocean. By processes of change at which we can only guess, this bird lost the power of flight, developed short, stout legs, and grew larger until it reached the size of a modern turkey. Such was the origin of the fabulous dodo, which did not long survive the advent of man on Mauritius. New Zealand was the sole home of the moas. One species of these ostrich-like birds stood twelve feet high. Moas had roamed New Zealand from the early part of the Tertiary; those that remained when the Maoris arrived soon died out.

Other island forms besides the dodo and the moas have tended to become large. Perhaps the Galapagos tortoise became a giant after its arrival on the islands, although fossil remains on the continents cast doubt on this. The loss of wing use and even of the wings themselves (the moas had none) are common results of insular life. Insects on small, wind-swept islands tend to lose the power of flight—those that retain it are in danger of being blown out to sea. The Galapagos Islands have a flightless cormorant. There have been at least fourteen species of flightless rails on the islands of the Pacific alone.

One of the most interesting and engaging characteristics of island species is their extraordinary tameness—a lack of sophistication in dealings with the human race, which even the bitter teachings of experience do not quickly alter. When Robert Cushman Murphy visited the island of South Trinidad in 1913 with a party from the brig
Daisy,
terns alighted on the heads of the men in the whaleboat and peered inquiringly into their faces. Albatrosses on Laysan, whose habits include wonderful ceremonial dances, allowed naturalists to walk among their colonies and responded with a grave bow to similar polite greetings from the visitors. When the British ornithologist David Lack visited the Galapagos Islands, a century after Darwin, he found that the hawks allowed themselves to be touched, and the flycatchers tried to remove hair from the heads of the men for nesting material. ‘It is a curious pleasure,' he wrote, ‘to have the birds of the wilderness settling upon one's shoulders, and the pleasure could be much less rare were man less destructive.'

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.'