Nestled among the red-rock cliffs of Zion national park and the Grand Canyon, California condor chicks No 1,000 and 1,001 blinked into this world. Their birth signalled success for a decades-long program to bring North America’s largest bird back from the brink of extinction.

As a result of hunting, diminishing food and dwindling territory, the number of birds in the wild numbered just 22 in the early 1980s. Lead poisoning was also a major killer, caused by inadvertently ingesting bullets that hunters left inside dead animals that the enormous birds, which have a wingspan of 9.5ft and weigh up to 25lb, scavenged for food.

Facing imminent extinction, the few remaining wild birds were placed into a captive breeding program in 1987 and slowly released back into the wild starting in the early 1990s. Biologists estimate that the 1,000th and 1,001st chicks hatched in May this year, but they were only able to confirm their existence over the past several days, because the raptors build their nests inside caves carved into steep, sometimes inaccessible cliffs. “You know, condors can be secretive,” said Janice Stroud-Settles, a wildlife biologist at Zion National Park in Utah.

Facebook Twitter Pinterest Zion national park biologists confirmed a California condor chick in a nest on the cliffs near the north rim of the Grand Canyon. Photograph: Zion National Park

After noticing that one condor couple seemed to be taking shifts scavenging for food, “we suspected that they’d hatched a new chick”, Stroud-Settles said. Field researchers eventually captured a photo of the 1,000th chick after rappelling off a cliff across from the birds’ nest cave. “When we confirmed it … it was just this feeling of overwhelming joy,” she said.

The 1,000th hatchling’s parents were both born in captivity, and the mother has already lost two chicks. Her firstborn probably died – as many baby condors do – in an initial, unsuccessful attempt to fledge (AKA fly) the nest, park officials say. She found herself unable to properly care for her second chick after her mate died of lead poisoning.

“Now that she’s re-coupled with a new mate, we’re hoping this chick will successfully fledge once it’s old enough to fly – sometime in the fall,” Stroud-Settles said, noting that the nesting site she chose has a large “porch” area where the growing chick can practice flapping before taking its perilous first flight.

The 1,001st chick, which was also born to parents bred in captivity, lives in a nest near the north rim of the Grand Canyon. And researchers are currently searching for up to four more chicks that may have hatched since, said Tim Hauck, who manages the condor program at The Peregrine Fund, a non-profit focused on protecting birds of prey. The government keeps a “Condor Gossip Chart” to help biologists track new couplings and births.

The fact that so many chicks are being born into the wild, “is really special – a sign of progress”, Hauck said.

Facebook Twitter Pinterest The mother of the 1,000th condor chick was born in captivity at the San Diego zoo. Photograph: Zion National Park

But the species is still classified as critically endangered by the IUCN and faces multiple threats, including the ongoing menace of lead poisoning.

A law that went into effect this month has made it illegal to use lead ammunition to hunt any game in California. In Utah and Arizona, however, conservationists have taken a different approach. Because a straight ban could alienate hunters, conservationists are encouraging locals to reduce their use of lead bullets through a voluntary program. “Ink on paper doesn’t necessarily change behavior,” said Chris Parish, the director of global conservation at The Peregrine Fund. “People aren’t inclined to follow rules they don’t understand, so here in Utah and Arizona we’re focusing on education and explaining to hunters why it’s important to cut down on lead bullets.”

The total living population of California condors now numbers more than 500, with more than half in the wild. The oldest bird being tracked in the condor restoration program is 24, but researchers estimate that California condors can live up to 70 years. They are very gregarious animals who get together in large groups and “like humans, tend to mate for life”, noted Stroud-Settles.

“I just love them,” she said. “They might look a little weird, but there’s so much beauty behind the ugliness.”