On the CBC count with Jo-Anne on Saturday I witnessed this extreme attack on a group of gulls on the ice at Lake Aquitaine.
Notice (after the fact) the falcon is banded. He flew in over my head for a fairly good closeup.
He made several straffing runs over the gulls but in the end left empty taloned
I beleive there were a few ( 4 or 5) immature Black-backed gulls mixed in with the ring-billed.
They were much lager and I notice the pink legs and dark spot on the lower mandible