BIG SUR, Calif. -- For the first time in more than 100 years, California condors were spotted nesting in the northern part of the state, scientists said.

The condor couple was found Monday displaying typical nesting behavior inside a hollowed-out redwood tree in Big Sur, a mountainous coastal region south of Monterey, the Ventana Wildlife Society said Tuesday.

"For the past 10 years when this sort of thing came up, it turned out to be just in my dreams," Kelly Sorenson, the group's executive director. "Now it is a reality."

The male and female took turns guarding the nest every two or three days, never leaving the nest unattended for more than several minutes, the scientists said.

"Although the view into the cavity is very limited and we can't actually see the egg, we strongly suspect they have an egg based on their behavior at the nest site," said Joe Burnett, a wildlife biologist.

Scientists have worked for years to bring the condor back from the brink of extinction.

Ventana, a nonprofit group, began releasing condors into the wild in 1997 and now monitors a population of 38 condors in Central California.The last known condor egg in Northern California was collected in 1905 in Monterey County.

The condor recovery effort has increased the number of birds tenfold over the past two decades. But about 40 percent of released condors have died from attacks by golden eagles and power lines, among other causes.

Biologists said the mortality rate of condors in Big Sur is much lower.