LOL, ours used to chase gulls on the beach when we took them on holiday. They'd have been great for the job.

There was one time when Mist chased them though and one of them couldn't fly and just legged it along the sand but it was nowhere near fast enough and Mist caught up with it and collided with it at full speed knocking it about 20ft further across the sand. I ran up quick and it was just a heap of feathers and then I saw a head and foot sticking out of them. Other than the fact that it was a little shaken up, it was ok...other than it was still unable to fly. We kept the dogs away and let it go then. It was an immature bird so I'm not sure if that was the reason for it not being able to fly but it did stop our breaths for a few seconds as Mist chased it and collided with it because we expected them all to be able to fly off.

All of our BCs have chased birds. They'd do it for hours so it's no surprising they have utilized this trait. They also use BCs to chase birds off airports so that they don't endanger aircraft and such in flight.