The Downtown office of the Make-A-Wish Foundation, on the 37th floor of the Gulf Tower, was a little louder than normal for a Tuesday morning. Instead of the gentle hum of fingers on keyboards, shrill screeches of two baby peregrine falcons filled the air.

This was not a real-life version of Alfred Hitchcock's famous movie. It was the Pennsylvania Game Commission and the National Aviary joining forces to band the birds for tracking and identification purposes.

Peregrine falcons were once one of the most prevalent species of birds in the world. But the use of pesticides such as DDT caused females to produce thin eggshells, leading to a crash in their population in the 1960s. In 1974, peregrine falcons were one of the first species on the U.S. Endangered Species Act. A nationwide ban on DDT and recovery programs such as the one happening here led to the birds being removed from the endangered list in 1999.

"Peregrine falcons are an effective tool to show our impact on wildlife," said Todd Katzer of the National Aviary. "But also [it shows] our positive impact as well."

Two peregrines have been using the Gulf Tower window nest box since 1991, and 61 chicks have hatched and fledged (a Cathedral of Learning nest box has produced 26 chicks since 2002; four birds will be banded there Tuesday). The female peregrine lays three to six eggs each year, and this year two of five Gulf Tower eggs hatched in April.

These chicks are considered "branchers" at this point in their lives -- they cannot fly yet, but they latch onto branches and practice flapping their wings to build their flight muscles. The Gulf Tower birds hop onto sticks protruding from their nest. Erin Estell, a spokesperson for the National Aviary, said the pair should be flying in one to two weeks.

"That is why we do the banding now," said Estell of the timing of the catch-and-release mission. "We must band them before they get too strong. Otherwise we might scare them, resulting in their trying to fly away and plummeting to the ground."

Both chicks were considered healthy and, based on their large size, assumed to be females. Each bird was fitted with a lightweight aluminum band around one talon, and the birds were returned to their nest after a little less than an hour.