You can take advantage of a "state" variable on your crow object. Use different events to control the behavior according to the state.
For example, add an instance boolean variable "attacking", default false.
For your events:
1. if "attacking" is false -> fly in specified area.
2. Trigger once, compare two values distance(player.x, player.y, crow.x, crow.y) < specified distance -> set "attacking" to true.
3. If "attacking" is true -> attack player