Like taxes, they come every April. But this arrival is fun and free. I'm talking about the peregrine falcon chicks and the launch of the exciting time on falcon cam, the annual nature show atop the Rachel Carson DEP building in Harrisburg.

This year the two mating peregrine falcons have four healthy chicks, who we hear are constantly nagging their parents with demands for food.

Almost driven to extinction by the toxic pesticide DDT, peregrine falcons have made a comeback, including in large cities where they tend to nest on skyscrapers and bridges, much like their native cliff dwellings.

In a wonderfully symbolic coincidence, the falcons came to nest on the new Rachel Carson building in 1997, named for the famous native Pennsylvania biologist who sounded the warning call about DDT in her 1958 landmark book "Silent Spring." Falcon pairs have been successfully nesting on a small bed of gravel here, known as a scrape, 10 stories above the busy downtown Harrisburg streets and the city's rail yard.

Watch all the action live here.

(Photo: File/Clem Murray/Inquirer)