06/03/2026
For twenty years, a biologist dangled from a helicopter on a hundred-foot line, landed in bald eagle nests on the cliffs of Santa Catalina Island, swapped the real eggs for resin fakes, and flew away before the parents killed him.
The eagles sat on the fake eggs for weeks. The real eggs were incubated in a lab. When the chicks hatched, the biologist flew back, removed the fakes, placed the live chicks in the nest, and left. The parents never knew.
Peter Sharpe did this up to four times a year from 1989 to 2009.
The reason was DDT. The Montrose Chemical Corporation manufactured DDT in Los Angeles from 1947 to 1982 and discharged waste into the sewer system, which emptied into the Pacific Ocean off the Palos Verdes Peninsula. Hundreds of tons of DDT and its metabolite DDE settled into the ocean sediment along the Southern California coast. The contamination entered the marine food web. Fish absorbed it. Bald eagles ate the fish. DDE accumulated in the eagles' tissues and interfered with calcium metabolism during egg formation. The shells came out thin. When a twelve-pound eagle sat on a thin-shelled egg, the egg collapsed.
DDT was banned in the United States in 1972, but the chemical does not leave the environment on a human timeline. DDE persists in ocean sediment and continues cycling through the food web decades after the last drop was manufactured. The eagles on the Channel Islands were eating contaminated fish in 2009 the same way they were eating contaminated fish in 1972. The eggshells were still too thin.
The Institute for Wildlife Studies began reintroducing bald eagles to Catalina Island in 1980. Between 1980 and 1986, thirty-three young eagles raised in captivity were released from hacking towers on the island. The birds matured. They paired. They built nests on the cliff ledges overlooking the Pacific. In 1987, the first eggs were laid. Every one of them broke.
IWS biologist Dave Garcelon analyzed the remains and found DDE concentrations high enough to explain the shell failure. The eggs were too fragile to survive incubation. The adult eagles were healthy, paired, nesting, and doing everything right. Their eggs were killing their own chicks before the chicks could form.
In 1989, the egg manipulation program began. Sharpe and the IWS team developed a protocol that sounds like a heist. They monitored every known nest on the island. When a pair laid eggs, they called in the helicopter. The pilot positioned the aircraft above the nest site, which was typically on an exposed rock ledge on a sea cliff face. Sharpe was lowered on a long line, sometimes a hundred feet, with a box of resin replica eggs. He landed in the nest. The adult eagles were nearby, agitated, sharp-taloned, and fully capable of inflicting serious injury. He removed the real eggs, placed the fakes, secured the real eggs in padded containers, and signaled the pilot to extract him. The whole swap took minutes.
The real eggs were transported to the Santa Cruz Predatory Bird Research Group at UC Santa Cruz or to the Avian Conservation Center at the San Francisco Zoo. There, in temperature and humidity-controlled incubators, the eggs were given the stable conditions their shells could not provide in the wild. The hatching success rate of removed eggs was roughly twenty percent. One in five survived. The rest were too damaged by DDE to develop even under perfect artificial conditions.
The chicks that hatched were flown back to Catalina and fostered into the nests. Sharpe repeated the helicopter descent, removed the fake eggs, placed the live chicks among the nesting material, and left. The adult eagles accepted the chicks as their own. They had been incubating what they believed were their eggs for weeks. When a chick appeared in the nest, their parental behavior activated. They fed it. They brooded it. They raised it to fledging age. They never knew the egg they had been sitting on was made of resin and the chick in front of them had hatched in a building in Santa Cruz.
When IWS could not produce enough viable chicks from the thin-shelled Catalina eggs, the San Francisco Zoo supplemented the program with chicks bred from its own captive bald eagles. Those zoo-bred chicks were also fostered into wild nests on Catalina. The adult eagles did not distinguish between their own biological offspring and a chick that had been born in a zoo enclosure four hundred miles away. If it was small and hungry and in their nest, they raised it.
Between 1989 and 2007, sixty-four chicks were fostered into nests. Twenty-one additional eagles were released through continued hacking. The population grew. Then in 2007, IWS took a chance. They left two pairs of eggs in the nest without swapping them. The adults incubated their own eggs. The eggs held. The chicks hatched. For the first time since DDT contamination began, Catalina Island bald eagles successfully reproduced without human intervention.
By 2024, all of Catalina's eagle pairs were laying, incubating, and hatching their own eggs. The DDE levels in the marine food web had finally declined enough that the shells could support the weight of an incubating parent. The twenty-year helicopter operation was over. Peter Sharpe no longer needed to dangle from a line above a cliff with a box of fake eggs and a prayer that the twelve-pound raptor on the ledge would not tear his hands open before he could make the swap.
Catalina Island now supports a self-sustaining bald eagle population. The program that built it involved thirty-three released eagles, twenty years of egg swaps, a helicopter pilot willing to hover above sea cliffs in Pacific wind, a biologist willing to hang from a rope and reach into an occupied eagle nest, a zoo that bred backup chicks, a university that ran incubators, and a resin egg convincing enough to fool a bird whose species has been incubating eggs for millions of years.
The DDT is still in the ocean floor off Palos Verdes. The eagles are still eating fish from those waters. The shells are thicker now, but the contamination has not gone away. It has diluted. If it concentrates again, the shells will thin again, and someone will have to get back in the helicopter.
Source: Institute for Wildlife Studies / Scientific American / LAist / Catalina Island Marine Institute.
