Avian flight without visual reference: preflight spinning produces spatial disorientation.

INTRODUCTION

Birds regularly fly in conditions of reduced visibility where they cannot see the horizon, whereas human pilots under similar conditions are subject to spatial disorientation (SD) and must, therefore, rely on instruments to maintain safe flight. We surmised that pigeons whose eyes were covered and that were rotated in a centrifuge before flight might show signs of SD.

METHODS

We built a small centrifuge ("ornifuge") that allowed us to spin a bird around the vertical axis of its head at 1 cps for a specified number of turns and then release it instantly through a trap bottom to fly free. We studied 67 cull racing pigeons once each under four conditions: 1) static with normal vision (Static-See, n = 13); 2) static with eyes covered (Static-Cover, n = 17); 3) spin with normal vision (Spin-See, n = 15); and 4) spin with eyes covered (Spin-Cover, n = 22). Flight behavior immediately on release was observed by the investigators and photographed to document the occurrence of initial hovering, direction of spontaneous rotation if any, and staggering after landing. Birds released with eye-covers flicked them off within a few moments.

RESULTS

Both Static-See and Static-Cover birds flew normally. For Spin-See, most flew normally, but 27% hovered momentarily before flying away. Among Spin-Cover birds, abnormal flight was seen in 50% and 72% staggered after landing.

DISCUSSION

Spinning in the ornifuge produced abnormal flight behavior in the majority of blind-folded birds. This may provide a model for examining certain aspects of SD experienced by pilots under instrument meteorological conditions and studying the mechanisms that make birds relatively resistant to SD.