Peregrines are still threatened by chemicals
By Jeff Barnard
Associated Press Writer
MEDFORD, Ore. -- 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 was put on the endangered species 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 hatch.
Now Pagel is wondering whether DDT or other chemicals are responsible for an unnatural 2-to-1 proportion of females to males among newborn chicks and whether they are also causing at least one male to act like a female.
"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 is taking it off the endangered species list and listing it instead as a threatened species.
The effects of DDT in 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, it becomes volatile and is carried up into the atmosphere, falling around the world in rain.
"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 to upgrade peregrines in the West from endangered to threatened species. After the 1992 breeding season, Western states counted 591 breeding pairs, compared with estimates of fewer than 50 in 1973.
Still, peregrines in southwestern Oregon, the California coast near Big Sur and western 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 in 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 this country that have been south of the border.
Pagel thinks 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 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 when 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, causing 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 sex ratio among peregrines. Fry said he doubts it's DDT, and Pagel suggested it also could be other unknown or unmeasurable contaminants.