Known wild peregrine falcon nests in Pennsylvania in the past 50 years.

"Crippled reproductively by the pesticide DDT, peregrine falcons stopped nesting in Pennsylvania in the late 1950s," said Carl Roe, executive director of the Pennsylvania Game Commission. "With the banning of DDT in the early '70s and reintroduction efforts in several northeastern states -- including Pennsylvania -- through the '80s and '90s, peregrines slowly began to reclaim their nesting range throughout the Northeast."

About two dozen peregrine nests have been artificially established on Pennsylvania skyscrapers including Downtown's Gulf Tower and Oakland's Cathedral of Learning. Peregrine falcons are considered endangered in Pennsylvania.

Source: Pennsylvania Game Commission