WASHINGTON –

By 1982, the number of California condors in the wild had dwindled to 22, an entire species nearly wiped out by, among other threats, lead poisoning from hunters' ammunition.

Though it was difficult to know for sure at the time because few condor carcasses were retrieved, researchers concluded that the big scavengers — whose wingspans can reach nine feet or more — were consuming lead fragments in the carrion that makes up their diet and were rapidly dying off.

Thirty-one years and $60 million later, the state's captive breeding program has brought the bird's population to 424, more than half living in the wild. Yet the main cause of death and illness for the condors remains the same: lead poisoning from ammunition in felled game and "gut piles" left behind by hunters who clean the carcasses in the field.

Today there is little doubt that lead is the primary threat, according to scientists, advocates and conservationists, because captive-bred birds are equipped with radio transmitters, captured and tested annually. The National Rifle Association remains one of the few major groups to deny the connection.

To break the cycle, Gov. Jerry Brown this month signed a ban on lead in hunting ammunition, making California the first state with such a law and settling a dispute that had been fought for decades. The ban will be phased in from 2015 to 2019.

"This is the last major source of lead that we knowingly discharge into the environment," said Jeff Miller, conservation advocate for the Center for Biological Diversity, which campaigned hard for the new law. "We got it out of gasoline, we got it out of paint, we got it out of toys."

Hunters have been using lead ammunition for centuries. But the metal is softer than alternatives such as copper alloys and steel, and it fragments easily, leaving particles in animal tissue that scavengers consume.

Lead's toxicity to humans and animals is well established, and its danger to scavengers has been known since the first article on the subject was published in 1889, according to John McCamman, the California condor coordinator for the U.S. Fish and Wildlife Service.

A 2012 study by a team at the University of California at Santa Cruz found that 30 percent of blood samples taken from condors each year showed levels of lead high enough to cause significant health problems and that 20 percent of the free-flying birds required treatment to remove lead. From 1992 to 2012, the cause of death was established for 123 condors in California, Arizona and Baja California, Mexico; lead was responsible for 42 of the mortalities, according to a 2013 review of the condor's progress by the Fish and Wildlife Service.

"Lead-based ammunition is the [principal] source of lead poisoning in condors," the UC-Santa Cruz researchers wrote, adding that "the only hope of achieving true recovery [is] dependent on the elimination or substantial reduction of lead poisoning rates."

Though there are no similar data for humans, California Assemblyman Anthony Rendon said he sponsored the bill that resulted in the ban because he saw the issue as a public health concern. Rendon said he is worried about hunters and others who might eat meat from deer and other game killed with lead ammunition.

Miller said some states have begun checking for lead in venison donated to feeding sites.

Besides condors and people, the ban will benefit bald eagles, golden eagles, ravens and other raptors, all of which are "very efficient scavengers," Miller said. Waterfowl, including geese and ducks, already are protected by a nationwide ban on lead shot for hunting imposed by the Fish and Wildlife Service in 1991. Before that, the birds ate the tiny lead pellets that littered their habitats, confusing them for pebbles, which they swallow to aid in digestion. Many states have partial bans on lead ammunition.

In 2007, California banned the use of lead bullets in the eight counties that made up the condors' range, but the prohibition has been largely ineffective, both sides agree. They clash, however, about the reasons.

In a long letter urging Brown to veto the statewide ban, the NRA noted that "in the five years since [the law] took effect, there has been no reduction in lead poisoning of condors, and in fact, condor blood-lead levels have actually increased," even though the vast majority of hunters obeyed the ban.

"Thus the evidence clearly shows that hunters' lead ammunition is not the source of lead poisoning in California condors," wrote NRA state liaison Ed Worley.

Other groups opposing the statewide ban included the National Shooting Sports Foundation and the California Fish and Game Wardens Association, which told Brown that "there is insufficient data to justify such a drastic action across the entire state."

Condors could be picking up lead from paint, junkyards or other sources, said Andrew Arulanandam, a spokesman for the NRA. Indeed, one review found that a few condors had been ingesting leaded paint from a fire watchtower.

"The most important point here," Arulanandam said, "is the fact that from our perspective is there isn't a connection that has been proven, yet there is a rush to ban" lead ammunition.

Rendon dismissed that claim as "absolutely ridiculous," and McCamman said the failure of the partial ban reflected its weakness, not the lack of a connection between lead ammunition and condors' deaths. Farmers, ranchers and others still use lead ammunition to kill varmints and other animals, he said, and the condors range over a very large area. Poachers still kill deer with lead bullets as well, he said.

The ban "is great so far as it goes, but it doesn't go far enough," McCamman said.

The NRA says the total ban will be costly to hunters who will have to purchase ammunition made of copper and other metals. But Rendon said he bought similarly priced bullets not far from his office in Sacramento, and other advocates predict that the huge size of the California market will drive down the cost of non-lead ammunition.

Brown said he agreed to sign the bill because it contains protections for hunters, and he said in his signing statement that "it is time to begin this transition and provide hunters with ammunition that will allow them to continue the conservation heritage of California."