E-Vector orientation in bees

Abstract

If an insect is able to determine the direction of polarization in any point of the sky, this ability does not in itself guarantee that the insect can orientate unambiguously. Such would only be the case, if every point in the sky had its own exclusive direction of polarization. In thee-vector pattern of the sky, however, each direction of polarization is found at many different points. For compass orientation the insect has therefore to use some information on the geometry of thee-vector pattern in the sky. In general, eache-vector occurs twice at a given elevation (Fig. 1). The angular separation ω between the positions of identicale-vectors depends on the elevations of thee-vectors above the horizon and on the height of the sun. Except at sunrise and sunset, ω ≠ 180°. If a bee is trained to fly in a certain direction to a food source, the direction of its waggle dance on a horizontal comb points directly towards the goal (provided that the bee is able to view the sky). However, if the bee is only allowed to view a singlee-vector in the sky (or a single artificially adjustede-vector), it should perform ambiguous orientation. One expects the bee to prefer two dance directions separated by the proper angular distance ω. One of these two dance directions should point at the food source. The bees indeed dance in two directions. However, there are two unexpected results: (1) The angular distance between the two preferred directions invariably amounts to ω=180°. (2) One of the preferred directions points closely, but not exactly at the goal. What one can deduce from these single-e-vector tests is that the bee uses a rather generalized internal representation of thee-vector pattern in the sky. This paper describes the generale-vector characteristic applied by a dancing bee that only views a singlee-vector in the sky (diameter of the celestial patch or the artificially polarized light source ≦10°). This generale-vector characteristic of the bee (Fig. 9) more closely fits the meane-vector distribution near the zenith thane-vector distributions in other parts of the sky (Fig. 11).