I think that's different. I'd guess the cat was unknowningly getting near the bird's nest + kids so mother was panicking.
But I have seen a cat trotting along a wire fence with a concrete base. On that base, which was about the cat's height there was a hooded crow happily scuttering behind the cat and grabbing at its tail from time to time.
The cat mostly ignored it but it was apparent that it judges the chances of catching the pesky bird.