Thomson's gazelles form small herds but are socially very flexible (2) (3). Herds of females overlap with other herds, and movement between herds is common. Within their shared home range the females rest, move between pastures and visit waters (2). Males are a little less flexible and mature males fight to obtain and defend territories within the female's favourite pastures (2). They denote the boundaries of their territory with dung and by marking grass stems and twigs with secretion from the scent glands beneath their eyes (2). Territoriality in males' peaks during mating periods when frequent fights and stand-offs occur between neighbouring males, and males attempt to mate with any receptive female that enters their area (2) (3). Lambs may be born at any time of the year, but birthing often occurs towards the end of the rainy season (3). Females are pregnant for 188 days, after which a single lamb weighing two to three kilograms is born (3). Thomson's gazelles feed on fresh green grass whenever possible, but during the dry season, feeding on seeds and the foliage of shrubs is necessary (2). Thomson's gazelles need to drink water every day or two, and in its dry grassland habitat this sometimes requires making round trips of ten miles or more (4).