Figure 1.

Experimental apparatus used to reproduce astronomical orientation under artificial light conditions. (a) external view: a, white Plexiglas dome (80 cm in diameter); b, Plexiglas plate; c, optical fibre bundle used to simulate astronomical orientating cues (the sun and the moon). (b), internal view: a, glazed Plexiglas dome; b, Plexiglas plate with c, a central part of transparent Plexiglas; d, optical fibre bundle with a negative lens to illuminate the inner part of the dome (=artificial sky). e, transparent Plexiglas bowl in which the sandhoppers were released.