Diurnal and nocturnal African dung beetles use celestial cues, such as the sun, the moon, and the polarization pattern, to roll dung balls along straight paths across the savanna. Although nocturnal beetles move in the same manner through the same environment as their diurnal relatives, they do so when light conditions are at least 1 million-fold dimmer. Here, we show, for the first time to our knowledge, that the celestial cue preference differs between nocturnal and diurnal beetles in a manner that reflects their contrasting visual ecologies. We also demonstrate how these cue preferences are reflected in the activity of compass neurons in the brain. At night, polarized skylight is the dominant orientation cue for nocturnal beetles. However, if we coerce them to roll during the day, they instead use a celestial body (the sun) as their primary orientation cue. Diurnal beetles, however, persist in using a celestial body for their compass, day or night. Compass neurons in the central complex of diurnal beetles are tuned only to the sun, whereas the same neurons in the nocturnal species switch exclusively to polarized light at lunar light intensities. Thus, these neurons encode the preferences for particular celestial cues and alter their weighting according to ambient light conditions. This flexible encoding of celestial cue preferences relative to the prevailing visual scenery provides a simple, yet effective, mechanism for enabling visual orientation at any light intensity.he blue sky is a rich source of visual cues that are used by many animals during orientation or navigation (1, 2). Besides the sun, celestial phenomena, such as the skylight intensity gradient or the more complex polarization pattern, can serve as references for spatial orientation (3-5). Polarized skylight is generated by scattered sunlight in the atmosphere, and to a terrestrial observer, the resulting alignment of the electric field vectors extends across the entire sky, forming concentric circles around the position of the sun (Fig. 1A). A similar distribution of brightness and polarization pattern is also created around the moon (6). Although this nocturnal pattern is 1 million-fold dimmer than the daylight pattern (6), some animals, such as South African ball-rolling dung beetles, can use this lunar polarization pattern for orientation (7). To avoid competition for food at the dung pile, these beetles detach a piece of dung, shape it into a ball, and roll it away along a straightline path. For this type of straight-line orientation, nocturnal beetles seem to rely exclusively on celestial cues (8), such as the moon or polarized light.As with all nocturnal animals, night-active beetles have to overcome a major challenge: They need to maintain high orientation precision even under extremely dim light conditions. Indeed, recent experiments have shown that nocturnal dung beetles orient at night with the same precision as their diurnal relatives during the day (9), an ability partly due to the fact that their eyes are considerably more sensiti...

Here we investigate the counting ability in honeybees by training them to receive a food reward after they have passed a specific number of landmarks. The distance to the food reward is varied frequently and randomly, whilst keeping the number of intervening landmarks constant. Thus, the bees cannot identify the food reward in terms of its distance from the hive. We find that bees can count up to four objects, when they are encountered sequentially during flight. Furthermore, bees trained in this way are able count novel objects, which they have never previously encountered, thus demonstrating that they are capable of object-independent counting. A further experiment reveals that the counting ability that the bees display in our experiments is primarily sequential in nature. It appears that bees can navigate to food sources by maintaining a running count of prominent landmarks that are passed en route, provided this number does not exceed four.

No abstract