This is apparently a major problem in Sydney Australia when the Australian Magpie is nesting, leading people to try various helmet adornments as a deterrent (with varying degrees of effectiveness):

http://www.youtube.com/watch?v=9wHreVKgOT4

Hey Bojack that's up in my neck of the woods. I just set up my own shop in Boardman, Oregon. The largest town in Oregon without an attorney. No longer. Those freakin' birds are scary and they do that stuff all the time. They are HUGE! Magpies will try the same thing but they just get shot.

There's an app for that.

A few years back, I used to bike along a lonely stretch of road, and regularly passed underneath a light pole favored by the biggest female red-tailed hawk you've ever seen. Nearly every day, she'd watch me go by, and then drop and swoop down on me. It wasn't malicious intent: she was apparently fascinated by my red bike helmet, and would try to scrape her talons on the helmet without my spotting her. If I turned at the wrong time and saw her, she'd back off and fly back to her perch, apparently grumbling "Next time." It got to be quite the game for the both of us: my pretending that I didn't see her on her perch, and her pretending that I couldn't see her in my rear-view helmet mirror.

Sadly, she disappeared about two years ago: I don't know if West Nile virus got her (an increasingly common fate for a lot of local birds), she died of old age, or if she just found a better hunting territory. Since then, I've moved, and have a drastically different route to work. Every time I go through that vicinity, though, I keep hoping that she's returned, and I'd be willing to go waaaaaay out of my way to play the game again once or twice.