SANTA CRUZ, Calif. – Recent data showing an increase in lead exposure and deaths among critically endangered California condors seems to fly in the face of decades of conservation measures, including bans on lead bullets and public-education campaigns about the plight of this once-vanishing raptor.
But new research by an environmental toxicologist at the University of California, Santa Cruz and her team, shows that the unfortunate rise is despite the clear efficacy of the lead bans and outreach efforts. The study , which analyzed nearly three decades of almost-daily observational data, found that condors are eating less of the lead-free carcasses provided by conservation workers. Instead, they are foraging farther from their release sites into areas where the impact of lead-ammunition bans and education campaigns might not be as strong.
Another likely reason for the increase in lead poisoning is that more wild pigs are being shot in California due to their expanding numbers. The authors of the new study, published in the journal Nature Communications, say these dynamics are masking the continued effectiveness of the lead-bullet bans and outreach—a clear pattern that emerged after accounting for foraging and hunting changes.
"We feel this is critically important research that reveals the lead bans and outreach in California have been effective at reducing condor lead poisoning risk," said the study's senior author, Myra Finkelstein, an adjunct professor of microbiology and environmental toxicology at UC Santa Cruz. "Together, our results show that multiple factors have influenced condor blood-lead levels, including changes in wild behavior by condors and shooting behavior by humans."
Finkelstein and her team were the first to definitively link lead bullets to the poisoning that slowed the recovery of condors in California. Her pioneering research on lead poisoning in California condors helped bolster a 2019 state ban on the use of lead ammunition in hunting. A partial ban within the vulture's geographic home range was enacted 12 years earlier.
A bird that's hard to miss
The California condor is the largest land bird in North America, with an adult's wings spanning about 9.5 feet. Their feathers are mostly black, and they boast a bald, red-orange head. They are estimated to live at least 60 years, making them one of the longest-living raptors. They are also monogamous and reproduce slowly, typically laying just one egg every two years.
Condors, eagles, and other scavenger species are poisoned by ingesting bullet fragments when they feed on the remains of animals shot with lead-based ammunition. Enormous resources have been spent over the past three decades to recover condors in California, where two of the oldest and largest reintroduced flocks reside, in the central and southern part of the state. At the end of December 2025, about 600 California condors were alive, with about 65% in the wild and the remainder in captivity. They were at their lowest in the mid-1980s, numbering in the 20s.
All free-flying condors are wing-tagged and many have telemetry tags for GPS tracking, with behavioral monitoring occurring on a near-daily basis and resulting in extremely rich long-term datasets covering 1996 to 2023.
Troubling trends in the data
To better understand the paradox of rising condor lead exposures, despite decades of conservation actions, the team used computer models to dissect the different and sometimes opposing influences—including the behavior of condors and hunters, outreach efforts, and post-ban time periods—on condor blood-lead levels.
Consistent with previous studies, they found that lead poisoning was the biggest cause of death among condors in the central and southern flocks, at 62% and 44%, respectively. The team also found that the number of birds with potentially lethal levels of lead in their blood almost doubled in the past five years.
But a closer look at the data revealed a pattern of "wilder behavior" over the 27-year study period: Condors fed less often on the lead-free carcasses proffered at feeding stations, respectively declining by 52% and 85% for condors in the central and southern flocks. They also spent less time near release sites where outreach and enforcement of the lead-ammo bans is most likely strongest, with the data showing declines of 42% and 70%.
"Thanks to the heroic efforts to bring condors back from near-extinction and track their recovery, we have a uniquely complete data set for this species," noted the study's lead author, Victoria Bakker, a quantitative conservation biologist at Montana State University. "It was this decades-long record of behavior and health for every individual condor that allowed us to account for the multiple drivers of lead exposure and measure the true effectiveness of outreach and lead-ammunition bans."
The team lacked data to determine direct links between condor lead risk and the shooting of wild pigs for population control. But the researchers hypothesized that was a major driver given the ongoing range sprawl of wild pigs in California, coupled with their findings of increased lead risk associated with pig hunting, plus the strong correlation between pig hunting and pig control.
The study also points out that just a few contaminated meals can explain increased lead exposure in condors. Fewer than 10 feedings on carcasses containing lead over the course of a year are enough to tip the scales from condors being self-sustaining to conservation reliant, based on analyses of blood lead levels.
"The good news is non-lead ammunition for pig hunting is reasonably available and through effective outreach and free giveaways, we can solve this problem while supporting the heritage of hunting and ranching," said Kelly Sorenson, a recovery partner at the Ventana Wildlife Society.
Beware the Red Queen
Looking ahead, the authors suggest that additional outreach to those who shoot wild pigs and deer about the risk of lead poisoning to condors could increase their survival rates. California is currently the only U.S. state to ban lead bullets for shooting wildlife, and the success of conservation actions can serve as a beacon for addressing lead poisoning of wildlife elsewhere—like in the U.K., European Union, and several U.S. states where legislation on the use of lead ammunition have recently passed or are under consideration.
To drive home a main point in the paper, the authors reference the organizational theory known as the "Red Queen dynamic," which occurs when system changes require increasing effort and innovation to sustain the same level of success. The term stems from Lewis Carroll's classic Through the Looking Glass, where the Red Queen explains the chaos of her kingdom to Alice: "Now, here, you see, it takes all the running you can do, to keep in the same place."
"Running to stand still is the exact scenario our results have uncovered for condor recovery actions implemented amidst changing ecological conditions," Finkelstein said. She and Bakker collaborated with a wide array of agencies on this study, including Pinnacles National Park, the Ventana Wildlife Society, U.S. Fish and Wildlife Service, U.S. Geological Survey, and the San Diego Zoo Wildlife Alliance.
"Our findings are a reminder to watch for Red Queen dynamics when evaluating conservation measures in today's complex settings that can mask effectiveness," Bakker added. "Otherwise, successful policies and actions could be abandoned."
