With scratched and bleeding hands, Glenn Stewart picked up a 25-day-old peregrine falcon on Thursday and attached a small band around its leg. The bird squawked and squealed as its parents violently circled their nest — atop a high-rise in downtown San Francisco.

After Stewart, director of the Predatory Bird Research Group at UC Santa Cruz, attached bands to the baby falcons’ two siblings, he stood up and the little birds fell silent. A fluffy, white feather stuck out of a wound on his hand.

The three birds hatched earlier this month outside the 33rd floor of the 34-story Pacific Gas & Electric Building at 77 Beale St., and the bands are marked with numbers that will allow researchers to follow each falcon’s movements and nesting patterns.

The falcons, one male and two females, are part of a long legacy of birds hatched and raised atop the PG&E building and on other skyscrapers nearby.

Stewart and his team set up the current nesting box in 2007. Since then, about 35 baby falcons have taken their first flights from the building.

Skyscrapers are perfect nesting places for the species, which, in the wilderness, usually find their homes atop cliffs, Stewart said.

“They want to be on a site that dominates the landscape,” he said. “These are like cliffs to them.”

If there is an abundance of food in the area, peregrine falcons will nest there. For falcons living in downtown San Francisco, that diet is mostly pigeons.

“The peregrines pick the spot,” Stewart said. “They picked this building. They picked downtown. We don’t just willy-nilly put up nest spots.”

The PG&E nesting box location was carefully selected after Stewart observed that the falcons were already nesting on nearby buildings as early as 1986. He first set up a nest on the north side of the PG&E building, but the falcons used it for only two years before finding a better location.

Stewart worked with PG&E to set up the current nesting box, which has been consistently used since 2007.

“They’ve given us an opportunity to have nature in the city,” Stewart said.

He attributes his work with peregrine falcons to being in the right place at the right time. He learned that the falcon population was nearing extinction in the Bay Area when he was a student at UC Santa Cruz in the 1970s.

Back then, researchers could find only two pairs in the Bay Area.

Stewart worked with teams at UC Santa Cruz to breed, hatch and release falcons, eventually bringing the population to more than 300 pairs that can now be found flying around the region.

The three falcons banded Thursday will stay on top of the building for another three weeks as their flight feathers grow. After that, they will begin to soar around the immediate area before leaving to set up their own nests.

In the meantime, people can watch them grow on a live camera feed at www.pge.com/falconcam and submit suggestions for their names using the hashtag #pge4me on Twitter, or by emailing currents@pge.com by July 7.

Matt Nauman, manager of PG&E corporate relations, said there were more than 200 name submissions for last year’s falcons.

Next spring, Stewart will return to San Francisco and band a new group of baby falcons.

He does this all over the Bay Area, so scratched and bloodied hands are part of the job for him. Through this work, he said, researchers have learned vital information about migration patterns and mating activity in the area and have saved the species from the brink of extinction.

Alison Graham is a San Francisco Chronicle staff writer. Email: agraham@sfchronicle.com Twitter: @alisonkgraham

Live stream

of baby falcons

To watch a live stream of the three baby falcons hatched atop the PG&E building at 77 Beale St. in San Francisco, log on to http://pge.com/falconcam