Four peregrine falcon chicks hatched over the weekend on a 5-foot building ledge overlooking San Francisco's Financial District, and they will take flight for the first time in a few weeks, researchers said.

Bay Area falcon enthusiasts are thrilled at the new faces nesting on the 33rd floor of 77 Beale St., a Pacific Gas and Electric Co. building.

Falcon fans can keep track of the chicks' progress thanks to a webcam installed outside the nesting site in 2005. Streaming video of the chicks and their mother, Diamond Lil, can be seen at sfg.ly/I0AGgP.

The chicks will fledge, or take their first flight, in about 40 days, said Glenn Stewart, director of the Predatory Bird Research Group at UC Santa Cruz.

Diamond Lil and her mate, Dapper Dan, have nested in the spot since 2008, Stewart said. Researchers decided to put a nest box on the ledge after they saw falcons flying around the area in 1986. The first peregrine pair began nesting on the ledge in 2003. Falcon eggs incubate for about 33 days before hatching. These new chicks' eggs were laid about a month ago.

Since chicks hatch once a year, the 10 days or so they spend learning how to fly is a special occasion. Some devoted falcon observers have taken days off work to camp out on the sidewalk under the chicks' departure point in case they don't figure it out right away. Stewart is on call and ready to carry a fallen chick back up to the nest for a second try.

Even if chicks survive their first flights, some have died after hitting windows or getting buffeted by sudden winds.

"I've seen some babies die," said Glenn Nevill, 59, who often photographs the falcons in flight during his lunch breaks from his Financial District job as an architectural draftsman. "But we love to see them fly."

The UCSC research group also has a livestream camera on a pair of falcons nesting at San Jose City Hall. Those birds are expecting their four eggs to hatch in about a week, Stewart said.

In about two or three weeks, Stewart plans to go onto the ledge and attach an identification band to the San Francisco chicks. The bands include a letter and number big enough to be seen with binoculars, allowing falcon-tracking to be outsourced to birdwatchers who report spottings around the Bay Area to Stewart.

"It's citizen science," Stewart said. "People watch it on camera and then they go out and buy binoculars. ... They spend their leisure time, go out on weekends, look for birds all over the bay."

One of the pair's older male offspring was spotted by birdwatchers currently courting a falcon in Richmond, Stewart said.

Peregrine falcons were close to extinction in the 1960s and '70s, but were taken off the endangered species list in 1999. About 30 peregrine falcon pairs live in the Bay Area and favor urban settings, Stewart said.

"Most of the ones in the Bay Area are on buildings, cranes, bridges," Stewart said. "We built all these cliffs for them."

Cities also have lots of pigeons, a major food source for the peregrines because they don't dive for prey on the ground like other predatory bird species, Stewart said.