 Well, they actually don't fly in circles. This is Jochen Zeil. He's Emeritus Professor in Ecological Science at the Australian National University. And like our last expert, David, he's based in Canberra. They fly in this beautiful pattern of going straight for 30 centimetres or so and then take a rapid turn about 90 degrees and then they fly 20 centimetres in that direction and then they make a rapid turn and so on.