The parent falcons, particularly mom, did not like it one bit, as she flew to get a closer look from a nearby Center City building.
"She's a very aggressive bird and we like that because that means she's very protective of her young," Dr. Arthur McMorris of the Pennsylvania Game Commission said.
RELATED: See a slideshow of the mother and baby falcons.
The chicks, three female and one male, are 30 days old.
They hatched in a manmade nest box that was first placed on the ledge in 1995.
The bird experts banded and examined all four in their efforts to save the Peregrine species, which is still on the state's endangered list.
"The ones we've looked at so far are very healthy, and I'm really happy with the way it's turning out." Dr. Keith Hinshaw of the Philadelphia Zoo said.
Peregrine Falcons are so protective of their young that they've been known to go after small airplanes if they deem them a threat.
The banding will help the Game Commission track the location, size of the peregrine population, and its typical life expectancy.
"The only reason we're doing this is to help the population recover, and once it's recovered, we'll stop doing this," McMorris said.
The Pregrine Facon is known as the fastest animal in the world with a diving speed of 200 miles per hour.
You can bet the parents were glad to see the chicks' safe return 15 stories above one of the biggest cities in the country.
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