Ecology: Fighting for Aldabra

Almost 10% of the wildlife on the tiny raised atoll of Aldabra, 400 miles east of Africa, can be found nowhere else on earth. Owing to its isolation, Al-dabra’s ecosystem has remained unique. Soaring with 7-ft. wingspreads at altitudes of more than half a mile, hundreds of thousands of frigate birds, which use Aldabra as their major Indian Ocean nesting site, blot out the rays of the sun. Thousands of rare giant land tortoises, some 4-ft. across and weighing as much as 600 Ibs., creep across the pitted coral and ridged limestone surface of the island. Tiny flightless rails nestle amidst Aldabra’s bushy scrub and mangrove forests, while above them swoop red-footed boobies, sacred ibises and fruit-eating bats. Twenty of the island’s plant species are nonexistent elsewhere in the world; so are a host of its insect inhabitants.

Aldabra, with only a tiny human colony on one of its islands, is to scientists a unique natural laboratory for the study of evolution; as early as 1874, Charles Darwin fought successfully to keep the atoll unsullied by man. Now British scientists once again have to fight for Aldabra. The opposing force: Her Majesty’s Defense Ministry, which late last year announced that Britain was weighing the possibility of developing the island as a major airbase and satellite tracking station in cooperation with the U.S.

Collision Hazard. Building such a base on Aldabra would be an ecological disaster, said Britain’s Royal Society of scientists in a memorandum to Defense Minister Denis Healey last May. Healey responded noncommittally, so the society mounted an eleven-man midsummer expedition to the island to prove its point.

This month, seven members of the group returned after studying Aldabra’s wildlife and the hazards posed to it by the construction of such a base. To establish an airstrip on Aldabra would require dredging and damming the atoll’s 18-mile-long lagoon, creating a harbor and building a 13-mile causeway from the harbor to the airstrip. Such an invasion of bulldozers, concrete mixers and men, said the scientists, would irreversibly damage the ecosystem of the island. They added that the frigate birds would constitute one of the worst aircraft-collision haz ards in the world. The frigate is a sea bird that spends its adolescent years far from the island, returning to mate only after it is mature. Each year, a new crop of adults arrives for the mating ritual, thus posing a problem to aircraft that could last longer than a decade even if an extermination program were undertaken.

Healey has remained noncommittal. “No decision has yet been made on the use ^L Aldabra for defense purposes,” he said. But the scientists were obvious ly unwilling to settle for bureaucratic vagueness. One biologist dryly noted that, of course, the giant land tortoise could always survive in the London Zoo. “The Union Jack flying over Aldabra is evidence of our custodianship of a biological treasure house,” the magazine New Scientist reminded Healey. “It is not a license to kill.”