Every year from September to November the Australian cyclists have to beware of magpie attacks.
This video is an example of a magpie that has attempted to attack me when I was riding to work in the morning. I can remember that there were Magpies around at the same area last year. It seems they make their nests around the same areas every year.
There is no much you can do to avoid an attack, unless you plan your route to skip the areas where you have seen them already.