Decades after peregrines came back from the brink, a new threat emerges—comments from Prof. David Bird

After DDT use nearly wiped out peregrine falcons in the 20th century, numbers are collapsing again in many countries, the Guardian reports.

Though scientists have yet to determine a definite cause, many—including McGill Professor Emeritus David Bird, who formerly led the University's Avian Science and Conservation Centre—think highly pathogenic bird flu may be largely to blame.

In North America, the decline seems most pronounced along the coasts. Bird suspects falcons could be picking up avian influenza after preying on shorebirds, seabirds and waterfowl—transitory populations that may have been infected on poultry farms.