Fig. 2.

Flies maintain a straight flight course using polarized skylight. (A) Flies were glued to a steel pin and placed in a magnetic tether in which they were free to rotate about their yaw axis. During flight, they could see a 28 deg patch of sky but not the sun or visual landmarks. (B) An example of a fly actively rotating its flight orientation to maintain a straight heading in global coordinates (i.e. relative to the sky). During a 24 min flight, the arena was rotated by 90 deg every 3 min (changes in shading). The fly adjusted its local heading in arena coordinates (top panel) by ∼90 deg to compensate for each rotation (bottom panel). (C) When a circular polarizer was placed over the arena (red trace), flies no longer adjusted for arena rotations as they did with no filter (black trace). Adapted from Weir and Dickinson (2012).