A functional role of the sky's polarization pattern for orientation in the greater mouse-eared bat

Abstract

Animals can call on a multitude of sensory information to orient and navigate. One such cue is the pattern of polarized light in the sky, which for example can be used by birds as a geographical reference to calibrate other cues in the compass mechanism. Here we demonstrate that the female greater mouse-eared bat (Myotis myotis) uses polarization cues at sunset to calibrate a magnetic compass, which is subsequently used for orientation during a homing experiment. This renders bats the only mammal known so far to make use of the polarization pattern in the sky. Although there is currently no clear understanding of how this cue is perceived in this taxon, our observation has general implications for the sensory biology of mammalian vision.

Figure 1. Vanishing bearings of the bats.

North (0°) is always at the top of the circles, except for a. The dashed circle depicts the Rayleigh significance threshold (P=0.05) and the arrows are the mean vector. The axial distribution of PS is shown by a double arrow. The triangle on the outside of the circles indicates the home direction. a is a 360° view of the sky with sunset and the experimental conditions. The dark bars represent the band of maximum polarization, mimicked by the filters. PN presents a natural polarization direction pattern, which is shifted 90° in PS. The bars on top of the experimental boxes symbolize the axis of vertical polarization in the windows. b are the control bats for RS1 (CC) that were untreated. c and d show the PN and PS data for release site 1 (RS1) and e and f for release site 2 (RS2).

Figure 2. Experimental boxes.

On the left is the outer box (polarization box) with two different layers of filters. On the outside is a pseudo-depolarizing filter and on the inside a polarizing filter. The direction of polarization is indicated with arrows. On the right is the inner box (holding box) with its meshed windows.