SAN FRANCISCO (Map, News) - Two peregrine falcon chicks were found dead in a nest Monday on the Bay Bridge by rescue workers who had scaled the span in hopes of moving the birds to a safer location.

The Santa Cruz Predatory Bird Research Group at UC Santa Cruz has been raising transported chicks on the mainland since the early ’90s, when it was discovered that young birds nesting under the bridge were not strong enough to make the one-mile flight to solid ground, according to the organization’s program director, Glenn Stewart.

“It’s always disheartening to see any peregrine falcons die, because they’re such a rare and iconic species,” Stewart said.

The workers were unable to determine exactly why the two chicks died under the Bay Bridge’s central anchorage, which has been a site for peregrine falcon nests since 1988.

Stewart said it was possible the chicks died either because their parents abandoned them or they perished themselves following the birth of the baby birds three weeks ago.

The chicks likely lived for a few days before dying, Steward said. A necropsy will be performed on them this week.

Peregrine falcons were on the United States Endangered Species List until 1999, when their federal status was upgraded, but they remain on California’s Endangered Species List and are fully protected in the state, Stewart said. There are approximately 250 pairs of the species in California, and eight to 10 in the Bay Area, he said.

Peregrine falcons usually nest on sea cliffs or mountainsides, but they’ve also been known to take advantage of urban structures, according to Stewart. A pair of falcons recently hatched eggs in a perch atop a 19-story tower at San Jose’s City Hall.

Monday’s operation to transport the baby chicks did not affect traffic on the bridge, according to Bart Ney of Caltrans.

wreisman@sfexaminer.com