How bees analyse the polarization patterns in the sky

Summary

Polarized light from the blue sky exhibits an extensive pattern which in terms of both direction and degree of polarization is linked to the position of the sun (Fig. 1). Honeybees, among other animal species, are able to perceive skylight polarization and to use it as compass in both foraging flights and communication dances.

• 1. From our previous work it is known that bees orient by means of a simplified e-vector map when their view of the sky is restricted to single e-vector directions (Fig. 2). Nothing is known, however, regarding how navigating bees analyse the polarization pattern as a whole.

• 2. To study this, dancing bees were presented large parts of the natural e-vector patterns, and their orientation performance with respect to known feeding stations was analysed (Fig. 4A, 5A, 6A).

• 3. The results show that bees make mistakes, and these are consistent with the hypothesis that they invariably apply their simplified e-vector map to any polarization pattern they are exposed to (Figs. 3, 4B, 5B, 6B).

• 4. Based on these findings it is suggested that information processing in the bee's visual system does not elaborate a detailed image of the polarization patterns. Rather, it is hypothesized, a simplified version of the pattern, as the one deduced experimentally (Fig. 2), is determined and mimicked by the spatial layout of polarization analysers in the bee's retina (Fig. 7). For the model to work, the insect then has to rotate about its vertical body axis and in doing so perceives celestial polarization in the form of temporal brightness and/or colour modulations (Fig. 8).

• 5. It is explained how the bee could use these modulations to derive the orientation of the celestial sphere and subsequently the direction of the intended compass course.