During their first year of life young peregrines wander, looking for places where prey is abundant. A full grown peregrine needs to catch just one good-sized bird or a couple of small ones (blackbird size) each day to satisfy its hunger. Locations where thousands of birds gather on migration is prime hunting ground. That’s why young peregrines gravitate to the shore.
Shorebirds gather in the thousands at the water’s edge on migration. To protect themselves against peregrines they fly up in a very tight ball so the peregrine can’t pick out a single bird. If any shorebird breaks out of the ball the peregrine will catch it.
With thousands of potential prey items, the peregrine needs to catch just one.
p.s. If you think the shorebirds’ evasive flight uses up a lot of energy you’d be right. Peregrine pressure on shorebirds keeps them fit. Read more in this vintage blog: Peregrines as a Fitness Program.
(photo of Zoetic with prey by Chad+Chris Saladin. Zoetic is the first female fledgling from the Cleveland Metroparks Zoo site)