Doves appear frequently in the Bible in a favorable context, e.g. they were a Temple sacrifice if you couldn't afford a bigger animal. But that would mean they were clean animals. Also the Holy Spirit appeared as a dove, Noah sent out doves and ravens to look for land, and Elijah was fed by a raven when he was hiding. I know that both gulls and ravens would cheerfully eat a plump dove, but it is spooky that this gull in the city would attack.