Decades after peregrines came back from the brink, a new threat emerges

DDT use nearly wiped out the raptor by the 1970s. Now peregrine numbers are collapsing again in many countries and no one is quite sure why

For the past six years, Gordon Propp, who builds sets for British Columbia's film industry, has kept a close watch over 13 peregrine falcon nests in and around Vancouver, including 10 on the city's bridges.

A self-described wildlife enthusiast and citizen scientist, Propp has had a lifelong fascination with these raptors. To see a creature that high up the food chain adapting to an urban environment, to me, that's quite remarkable," says Propp.