Individual Group Flight of European Starlings and Budgerigars in a Wind Tunnel Without a Horizon Reference

I studied the ability and willingness of European Starlings (Stumus vulgaris) and Budgerigars (Melopsittacus undulatus) to fly under different lighting conditions in a wind tunnel. My observations indicate that these birds can fly under conditions that supply no visual reference points, but their flight ability is more proficient when some light is available. The addition of a single horizon line to dark conditions improved the birds\u27 flight ability and willingness, as indicated by an increase in the number of birds that took flight after landing. When small flocks were flown in the wind tunnel there was contact between birds in all lighting conditions. The collisions did not cause major disruptions of flight, but the birds seemed to be limited by the small space of the flight chamber. I conclude that (a) mechanisms in addition to sight may influence flock structure and (b) lack of visual cues may affect the primary orientation of birds enough to cause behavioral effects