North America’s largest bird, the California condor (Gymnogyps californianus), was declared extinct in Mexico in 1939, but a two-decade effort to return the enormous raptor to Mexico’s skies has been making impressive—though painstaking—progress. “Species can disappear in no time at all, but to establish a population in the wild requires a lifetime of dedication,” says Mexican biologist Juan Vargas, fieldwork director for Mexico’s condor-reintroduction program.

There are now 47 California condors living in the wild in and around the state of Baja California’s Sierra de San Pedro Mártir National Park. The park is home to the 21-year-old Mexican reintroduction program, which has been managed with the help of agencies and institutions both in Mexico and the United States.

Three of these birds were among the first six to be freed at the start of the program in 2002, an indicator their Baja habitat is healthy. Fifteen were born in the wild, and some have reproduced successfully. The Mexican program’s goal, ultimately, is to have 150 California condors living in the wild in Baja California.

“The reintroduction program is considered a great success because the starting point was zero and now there is even a second generation born in the wild, which in itself is a great achievement,” says Vicente Rodríguez of Mexico’s National Commission for the Knowledge and Use of Biodiversity (Conabio).

The California condor is the lesser-known cousin of the Andean condor (Vultur gryphus), which is revered by Andean cultures as a symbol of immortality and power. The Andean condor, whose wingspan exceeds three meters, once was found from Venezuela to Tierra del Fuego. Today it is classified as vulnerable by the International Union for the Conservation of Nature (IUCN), with the most recent survey, conducted in 2020, estimating that only 6,700 adults remain in the wild.

Like the slightly smaller California condor, the Andean condor also has been the focus of conservation efforts, among them a binational Argentine and Chilean initiative called the Andean Condor Conservation Program (PCCA). Established in 1991, the initiative has rescued more than 370 of the birds and has hatched and released over 80 Andean condors in Patagonia and elsewhere in South America.

PCCA scientists use GPS-equipped collars to track condors after they are released. The data is used to identify their habitats, which, in turn, helps inform policymakers on conservation priorities. Some of the key habitats in Patagonia where Andean condors have been reintroduced are earmarked for the possible development of wind farms, drawing warnings from conservationists that turbines could pose a threat to the birds.

The California condor’s original habitat is believed to have run the length of the U.S. Pacific Coast, with a small percentage extending onto the Baja California peninsula of northwest Mexico. But the bird has faced many of the same pressures as its Andean cousins, including toxins from bullets or poisons in the carcasses it feeds on, flight-path obstructions such as power lines, and occasional poaching.

The most recent census of California condors living in the wild in the United States, conducted in 2022, reported 310 birds. Added to Mexico’s population of 47, overall numbers are still so low that the species remains classified as critically endangered by the IUCN. The two countries collectively keep some 200 condors in captivity for breeding.

In 1982 there were only 22 California condors living in the wild in the United States. Subsequent research revealed that the consumption of toxic lead-bullet fragments when feeding on the carcasses of animals that had been shot was the main cause of condor deaths. Eventually, the last six wild U.S. condors were captured to begin a breeding program that allowed the U.S. Fish and Wildlife Service to reintroduce the birds into the wild in California in 1992, Arizona in 1996 and on the Oregon-California border in 2022.

These three populations collectively account for all California condors in the United States. The fact that they are geographically separate helps protect the species from threats such as highly pathogenic avian influenza (HPAI), which killed 21 members of the Arizona California condor population in 2022 alone. That die-off recently prompted the U.S. Fish and Wildlife Service to begin administering HPAI vaccinations to all U.S. California condors being released into the wild.

Reintroduction efforts in Mexico have been undertaken in close coordination with those in the United States. The San Diego Zoo provided the first six California condors to be released into the wild south of the border, with Vargas and a binational team of colleagues setting them free in 2002. The then-nascent binational condor initiative has become increasingly sophisticated over time.

Among the collaborators from the start were the Mexican Environment and Natural Resources Secretariat (Semarnat), the U.S. Fish and Wildlife Service, and Mexico’s National Commission for Natural Protected Areas (Conanp), the agency for which Vargas works.

“The U.S.-Mexico binational effort to reintroduce the condor in Mexico is an example of collaboration to be followed and replicated with other species,” says Conabio’s Rodríguez. “Collaboration has successfully transcended all levels, from zoos and institutions all the way up to national levels of government.”

Vargas recalls that when his country began condor-reintroduction efforts, “there was no information or research available on the California condor in Mexico.”
Says Vargas: “We did not even know why Baja’s population had disappeared. We built an aviary to receive the first six specimens and developed reintroduction, tracking and monitoring methods from scratch in response to local geographical challenges and economic limitations.”

Budgetary pressures have challenged Mexico’s reintroduction program since its birth. While the U.S. Fish and Wildlife Service calculates that over US$50 million has been spent on California condor recovery in the United States, Vargas has had to keep Mexico’s program going amid near-constant funding uncertainty.

There are also important differences in the reintroduction work itself in the two countries. Scientists, for instance, point to the bird’s relatively urbanized United States habitat as compared to its largely remote, mountain-canyon surroundings in Baja California.

An early hurdle for Vargas was popular myth. Some Baja Indigenous communities viewed condors as evil, blaming them for killing their cattle’s young even though experts say such incidents were likely the work of coyotes or wolves.

“I had to get close to the communities and elders to explain that condors’ feet are not prehensile,” says Vargas, who promotes public education about California condors in visits to schools and community groups. “They are not designed to kill. Condors only eat carrion.”

Adds Vargas: “I tell the children that condors are the equivalent of a garbage truck that covers huge expanses of the wild, eating every last bit of flesh on a carcass that would otherwise be a source of infection and disease. They even turn the bones and expose them to the UV rays, which sterilize them and reduce the risks of infection.”

The aviary for Mexico’s reintroduction program is located in San Pedro Mártir National Park. Most of the birds it receives come from captive-bred populations in the United States. They typically occupy the aviary in the summer before being released into the wild in the fall. The process, however, can be complicated by onerous customs restrictions.

“Conservation efforts and customs laws do not have the same goals,” says biologist Ashleigh Blackford, California condor coordinator for the U.S. Fish and Wildlife Service. “We need to find smoother ways to get the specimens to where we need them.”

California condors, which can weigh up to 10 kilograms (22 pounds) and whose wingspan can measure three meters, are a highly social species organized in complex hierarchies. Scientists say that to survive in the wild, reintroduced condors must understand social structure before being released.

Weight gain is a key indicator that an individual can navigate social hierarchies to secure adequate access to food. Once condors demonstrate this ability, as well as adequate socialization skills and an awareness of dangers, they are deemed ready for release.

Timing the releases to boost the odds of survival has become particularly tricky on account of climate change.

“In the old days the weather was so predictable, but nowadays we can’t be sure of anything,” Vargas says. “Climate change has made the weather a real risk factor in releases. Sometimes we prefer to hold birds back rather than risk them facing extreme conditions such as blizzards. We have to be very astute.”

The birds can live up to 70 years, are monogamous, and typically stay with their partner for life, breeding from the age of five or six. They produce one egg every one to two years, and they take turns incubating it for nearly 60 days. Once the chick has hatched, they feed and care for it in the six months before it leaves the nest, and for at least a year after that.

The length of the reproductive process requires extraordinary patience on the part of reintroduction-program organizers as they work to build the bird’s Mexican population to reach the goal of 150.

The project faces other challenges, among them lead poisoning—a leading cause of mortality among condors. The birds can be exposed to lead when they eat the carcasses of animals shot by hunters.

“Bullet fragments in the carcass taint most of the meat in the animal,” says Blackford of the U.S. Fish and Wildlife Service. “Since condors eat in groups, a single carcass can kill several specimens at once.”

Vargas says lawmakers must address the problem by banning lead in bullets: “If only we could do away with the risk of lead poisoning, the future of the condor would be assured.”

Reintroduction-project personnel try to limit the lead-poisoning danger by leaving lead-free animal carcasses for wild condors to feed on. Lead poisoning, however, is not as pervasive a threat to Mexico’s California condors as it is to the U.S. population of wild condors, which live in greater proximity to humans.

Blackford says the population of California condors in the United States has to be supplemented with captive-raised birds each year to compensate for a lead-poisoning death rate of approximately 50%.

“The Mexican population is in a unique position to help us learn about condors and what they can do because they are not impacted by lead in the way the U.S. population is,” Blackford says. “The Mexican [California condor] population is growing naturally, not just because it is supplemented.”

Vargas cites a Mexican project he is participating in, one whose objective is to identify viruses and bacteria to which California condors have natural resistance.

“No one bothers about carrion-eating species, but the facts outstrip any fiction,” he says. “Condors can eat a carcass that contains anthrax and survive. If we can decipher how the condor’s immune system works, we could apply the knowledge in human medicine, for example, against pandemics.”