Almost all the 17 million adult birds on Christmas Island in the mid-Pacific have been killed or fled, leaving their nestlings to starve to death, according to a report presented to the National Science Foundation yesterday.
The "population crash" is probably the largest of its kind ever recorded, and the first near-total disappearance of a major bird population recorded on a tropical island, said Ralph W. Schreiber, curator of ornithology at the Natural History Museum of Los Angeles County.
The ecological disaster may have been caused by "El Nino," the same ocean currents and disastrous weather that have hit California and the west coast of South America in recent weeks. The birds fled not because of storms, but because El Nino's ocean currents forced the birds' food supply into deeper water or swept it away from the island.
Schreiber, who traveled to the island last November after an absence of some months, was surprised to find evidence of the mass death and evacuation that probably occurred in October.
He examined the nesting places of terns, shearwaters, frigates and other marine birds, and found only devastation--thousands of dead nestlings and a few dead adults.
Schreiber said that many of the adult birds probably died of starvation as they went out in search of food that was no longer there. But the seabirds are gliders, coming to land only to breed, and can remain aloft literally for months at a time. The birds would probably not fly to the nearest island, Schreiber said, because they stay aloft most of their lives.
Of the 19 species that were on the island, 18 are gone, including the world's largest single population of sooty terns, a gull-like black and white sea bird. Fourteen million of them have disappeared.
The disaster provides new information about how the vast El Nino weather systems recur and alter weather and currents across the Pacific every three to eight years, Schreiber said. They cause storms along the coasts of the Americas from Tierra del Fuego to San Francisco. (The name El Nino, which means "the child" in Spanish, comes from Peruvian fishermen who recognized that the winds and currents occur around the Christmas season.)
The events on Christmas Island also demonstrate "that when we study ecology, it is probably no use studying short periods of time," Schreiber said. Scientists once believed that animal and plant populations were stable for extremely long periods, changing only very slowly. But now it is clear that "population crashes" occur.
Schreiber said this fact has direct implications for humans, who must guard against such rare events. For example, El Nino storms in 1972 wiped out nearly 90 percent of the anchovy fishing industry along South America's west coast. The fish might have survived and repopulated the area had man not overfished it. The fishing industry has never recovered.
El Nino weather patterns occur when surface currents and winds normally moving westward stop and sometimes reverse themselves completely, heading eastward throughout a huge wedge-shaped area of the Pacific Ocean from the international dateline at the equator to the Americas.
The shift can last up to 18 months and create havoc with marine and bird life, as local conditions change.
For example, the shift warms waters two to eight degrees Fahrenheit higher than normal. More important, the wind shift causes the usual "upwelling" of nutrient chemicals from several hundred feet to stop. Thus, green plants and small animals near the ocean surface cannot get the nutrients they need, their populations are thinned and fish must move to other waters.
Such a mass migration of fish may have forced the birds to leave the area of Christmas Island.