Maybe this is a good reason to wear a bike helmet. From Tom Vanderbilt, who’s visiting Australia.

About that magpie. It turns out they can be rather fierce enemies of those on bikes, swooping down from trees to land on their helmets and peck at their ears. As a countermeasure, riders will strap plastic twist-tie-like things to their helmets, virtually sprouting of their heads like gangly antennae. It was a bit unnerving to find a couple of these fellows coming toward me, the shock troops of some alien two-wheeled race. I’m not sure if this sort of thing happens elsewhere, but it was the first I had seen in such active preparation for avian attack

Here’s another video where a magpie attacks a little girl on a bike.