Skylight polarization as perceived by desert ants and measured by video polarimetry

North African desert ants belonging to different genera and inhabiting diff erent areas (sand dunes, salt pans, inundation flats and gravel plains) exh ibit different ways of skylight navigation: some rely especially on the pol arized light in the sky, others depend more effectively on the position of the sun. Are these differences due to species- or genus-specific idiosyncra sies of the ant's skylight compass, or are they caused by differences in th e overall degree of polarization prevailing in the celestial hemisphere tha t vaults the different kinds of habitat? Theoretically, such differences ar e to be expected, as various parameters known to influence the degree of po larization in the Earth's atmosphere - such as the albedo of the ground and the content of water vapour, dust and haze in the airlayers above the grou nd - do vary between the different types of habitat mentioned above. The fi rst wide-field, video-polarimetric study of skylight polarization presented here clearly shows that at any particular locality the temporal (day-to-da y) variations of the degree of skylight polarization are much more pronounc ed than the differences recorded at the same local time at different locali ties. In contrast, the angle of polarization is unaffected by atmospheric d isturbances and accords well with the predictions of Rayleigh scattering. C onsequently, differences in behavioural performances of navigating North Af rican desert ants are due to interspecific and intergeneric differences in the ants' navigational systems rather than to general differences in the sk ylight stimuli experienced by the ants during navigation.