Homing behaviour in the sleepy lizard (Tiliqua rugosa): the role of visualcues and the parietal eye

To investigate how visual cues are integrated into a navigational strategy for homing in the Australian sleepy lizard (Tiliqua rugosa), lizards were d isplaced beyond their home range, either with full access to visual cues or with no access to visual cues during the displacement. Homeward orientatio n was significantly worse when lizards were denied visual cues during the d isplacement than when they were not. However when lizards were displaced wi th their field of view restricted to the sky, their homeward orientation wa s equally as good as that of lizards displaced with no visual restriction. These experiments suggest that sleepy lizards use celestial cues to determi ne the compass bearing of the outward journey, and reverse this bearing to orient in the homeward direction (course reversal). In a subsequent experim ent, lizards oriented randomly with respect to home when the parietal eye w as entirely covered with a patch during the displacement and return, while control lizards fitted with a sham parietal eye patch were well oriented to wards home. In both groups, the lateral eyes were unobstructed and had comp lete access to visual cues including celestial cues and landmarks. These re sults suggest that the parietal eye plays a highly significant role in slee py lizard homing, perhaps mediating a sky polarization compass sense.