Apparently it's called "mobbing" and is common in some bird species. The Red-Winged Blackbird will summon other males to assist in warding off larger predators and I have been attacked by small groups of what I think was three or four but never anything like The Birds. Still, it's very scary the first time it happens and you don't realize what is happening. There are several videos of birds mobbing cyclists on Youtube that you can show your wife.