What do the ants know about the rotation of the sky?

Animals which use a celestial compass to navigate in a particular direction are able to compensate for the movement of the Sun1–3. It has generally been assumed4–8 that this compensation is exact even though the rate of change of the position of the Sun's azimuth is not constant but varies according to the time of day, the date and the latitude. However, what can be deduced at best even from the most comprehensive studies of birds9, fishes10, spiders11,12 and bees13–16 is that the animals do not simply use the Sun's average rate of azimuth movement (15° h−1). The scatter in most data and methodological shortcomings (for example, see ref. 17) prevent a more specific conclusion. A further possibility, supported by recent experiments with bees18, is that animals do not use long-term information about the rate of movement of the Sun's azimuth at all but just extrapolate from the most recently observed rate of movement. Here, we show that ants do indeed compensate for the variable rate of movement of the Sun's azimuth even if they have not seen the sky for several hours. Small but consistent errors further suggest that the ants might acquire their knowledge of the Sun's azimuth movement by interpolation between successive memorized positions of the azimuth.