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The San Lorenzo Peregrine Falcon

San Lorenzo Peregrine FalconThe "San Lorenzo" Peregrine

On 8 May 1984 Predatory Bird Research Group staff and volunteers climbed to a peregrine falcon eyrie on the North American wall of El Capitan in Yosemite Valley. The mission was to remove thin-shelled eggs from the nest before they broke, and replace them with young hatched safely in incubators at our facility. The three eggs collected that day ranged from 13.5-19.5% thinner than normal, and two were already dead when collected.

The climbers spent a day fixing ropes for the climb and then returned the following day for a rapid ascent to foster the young peregrines into the eyrie high on the wall. Among the two chicks was a female that hatched from the only remaining egg left of a clutch collected in northern California for captive incubation. The other eggs had all been crushed by the incubating falcons due to eggshell thinning.

That particular female chose the San Lorenzo River mouth in Santa Cruz as a place to winter that fall. She returned every subsequent winter through 2003. She could be observed on one of several perches overlooking the River between October and March. She was one of the oldest peregrines we know of in California, and presumably left in spring to breed at a high elevation eyrie she vacated in the winter, probably in the Sierras where she fledged as a youngster.