DDT Residues Haunt the Endangered Peregrine Falcon, Scientists Warn : Environment: More than 20 years after the pesticide was banned in the United States, its effects linger. It is still used in other parts of the world; when it rises into the atmosphere it falls with rain.

Jeep Pagel rappelled down a spectacular rock cliff to a ledge harboring two peregrine falcon chicks, pulled on a surgical glove and gathered up broken eggshells.

“A toxicologist told me, ‘Don’t touch the eggs. They’re loaded with organochlorine contaminants,’ ” the U.S. Forest Service biologist said afterward.

More than 20 years after DDT was banned in the United States and the peregrine falcon species was put on the endangered list, the deadly pesticide still is causing problems for the bird.

DDT, ingested by the falcons through the birds they prey on, has long been blamed for eggs with shells so thin they often crack before they can be hatched.

Now Pagel is wondering whether DDT or other chemicals could be responsible for an unnatural 2-to-1 proportion of females to males among chicks, and whether they are also causing female behavior in at least one male adult.

“With these contaminants introduced into the system since the 1940s, I may never have seen normal peregrine behavior,” he said.

DDT came into wide use during World War II to control insects such as lice and mosquitoes. Through the 1950s and ‘60s, it was widely used to control crop-eating insects.

But when scientists discovered that birds such as the peregrine and the bald eagle were ingesting the pesticide and were unable to hatch young because of eggshell thinning, DDT was virtually banned in the United States in 1972.

The bald eagle has recovered enough that the government took it off the endangered species list, classifying it instead as a threatened species.

The effects of DDT on wildlife have been dissipating as the chemical gets buried in the sediment of rivers and bays, said D. Michael Fry, a research physiologist at the University of California at Davis.

But storms and dredging stir it up from time to time, and the pesticide still is used in Central America and other parts of the world, where it contaminates migratory birds. In warm weather, the chemical becomes volatile. It is carried into the atmosphere and falls to earth in rain around the world.

“We see it in the snow and ice of Antarctica, as well as the Arctic,” Fry said. “I think the problems with DDT are much reduced in the temperate zones, but it will continue to pose a global risk if it is used in other parts of the world.”

Patricia Zenone, a U.S. Fish and Wildlife Service biologist in Reno, Nev., is analyzing a proposal that the status of the peregrine species in the West be changed from endangered to threatened. After the 1992 breeding season, the Western states counted 591 breeding pairs, compared with estimates of fewer than 50 pairs in 1973.

Still, peregrines in southwestern Oregon, the California coast near Big Sur and West Texas have problems.

Pagel, who keeps watch over 37 nests in Oregon and Northern California, counted an average of one chick per nest. That’s better than the 0.7 count of recent years, but still below the 1.5 needed to maintain a stable population.

Zenone believes peregrines are contaminated by DDT from migrating to Mexico and Central America and from eating birds in North America that have been south of the border.

Pagel said he believes the sources of contamination may be closer to home, in forests that were sprayed for years with chemicals to control weeds and pests.

He is finding that peregrines in Oregon that nest below 2,000 feet elevation don’t travel very far or eat migratory birds in winter. And it is in winter that the falcons form their fat reserves, where DDT is stored.

Pagel also found that in one nest in Oregon, the male is failing to feed his mate while she is brooding and is trying to bump her off the eggs.

“It’s like there’s two females in the nest,” Pagel said.

DDT and other chemicals, such as PCBs, mimic the female hormone estrogen and cause malformed male sex organs in species from sea gulls to alligators.

“We banned DDT basically because of its eggshell-thinning effects,” Fry said. “Its feminizing effects, although reported 13 years ago, really have not been of great interest until the last couple of years. But I think there’s much more danger to wildlife than just eggshell thinning.”

Nobody knows what is skewing the peregrines’ sex ratio. Fry said he doubts it’s DDT. Pagel suggested it could be other unknown or unmeasurable contaminants.