have been a function of zebra stripes in a 1981 study. A 2014 study found a correlation between striping and overlap with horse and tsetse fly populations and activity. Other studies have found that zebras are rarely targeted by these insect species. Caro and colleagues (2019) studied captive zebras and horses and observed that neither could deter flies from a distance, but zebra stripes kept flies from landing, both on zebras and horses dressed in zebra print coats. There does not appear to be any difference in the effectiveness of repelling flies between the different zebra species; thus the difference in striping patterns may have evolved for other reasons. White or light stripes painted on dark bodies have also been found to reduce fly irritations in both cattle and humans. How the stripes repel flies is less clear. A 2012 study concluded that they disrupt the polarised light patterns these insects use to locate water and habitat, though subsequent studies have refuted this. Stripes do not appear to work like a barber pole against flies since checkered patterns also repel them. There is also little evidence that zebra stripes confuse the insects via aliasing. Takács and colleagues (2022) suggest that, when the animal is in sunlight, temperature gradients between the warmer dark stripes and cooler white stripes prevent horseflies from detecting the warm blood vessels underneath. Caro and colleagues (2023) conclude that the insects are confused by the high colour contrast and relative thinness of the patterns. Ecology and behaviour Zebras may travel or migrate to wetter areas during the dry season. Plains zebras have been recorded travelling between Namibia and Botswana, the longest land migration of mammals in Africa. When migrating, they appear to rely on some memory of the locations where foraging conditions were best and may predict conditions months after their arrival. Plains zebras are more water-dependent and live in moister environments than other species. They usually can be found from a water source. Grévy's zebras can survive almost a week without water but will drink it every day when given the chance, and their bodies maintain water better than cattle. Mountain zebras can be found at elevations of up to . Zebras sleep for seven hours a day, standing up during the day and lying down during the night. They regularly use various objects as rubbing posts and will roll on the ground. A zebra's diet