A pair of California condors have produced a baby, surprising wildlife experts who said on Friday the endangered raptors had managed to secretly mate outside their careful monitoring.

Late last month, biologists noticed a "mystery" juvenile condor at a wildlife sanctuary in Big Sur, California, according to the Ventana Wildlife Society, a group that helps protect and observe the birds in their natural habitat.

The young bird was seen with two adult condors presumed to be its parents - and the bundle of joy, about 9-months-old, had been hatched and raised without the knowledge of biologists monitoring the region, the group said.

"This pair of condors is suspected of nesting in a remote portion of the Ventana Wilderness in the Arroyo Seco drainage," the group said in a statement. "Biologists have never entered the nest because of the area's inaccessibility."

This was only the third unobserved pairing of condors in the wild since 1997, the San Francisco Chronicle reported.

The parents were identified as "Shadow" and "Wild 1," the group said. Shadow, the suspected father, has been active in the population, having produced two other chicks, the group said.

"This is truly exciting to witness as it offers another example of condors surviving on their own," said Kelly Sorenson, executive director of the Ventana Wildlife Society.

Condors, the largest flying birds in North America, once populated an area from Canada to Mexico but nearly became extinct in the 1980s due to factors such as poaching, lead poisoning and habitat destruction.

The total condor population now stands at 425 birds, both captive and wild, of which 116 are living in the wilderness of California, the Ventana Wildlife Society said.

Get the Monitor Stories you care about delivered to your inbox. By signing up, you agree to our Privacy Policy

One of the longest-living raptors in the world, condor populations are also found in Mexico, Arizona and Utah.

(Reporting by Victoria Cavaliere in Seattle; Editing by Cynthia Johnston and Andrew Hay).