The social structure of Grant’s gazelles depends on habitat and season. On the plains of the Serengeti, Grant’s live mostly in mixed herds of males and females, numbering up to 400. As a herd moves throughout its home range, it occasionally enters a region belonging to a territorial male who becomes dominant over the herd’s males and takes charge of the females. In woodland areas, mixed groups are much less common. In this habitat, Grant’s tend to form groups of females with a single male, while other males live on their own. Woodland herds do not have more than 40 individuals. The number of mixed herds increases during the dry season, when there is little territoriality. During the wet season, territoriality increases, and herds tend to split into smaller groupings, the largest of which are the breeding herds. No matter the habitat, Grant’s gazelle herds are loosely composed; individuals join and leave with ease, especially during migration. The only exception is a harem group, made up of about 10 to 25 females and a territorial male. These herds are “half-open,” meaning that females can easily join but have a harder time leaving the male’s area.
Most communication between Grant’s gazelles is visual. Smell also factors into communication, as territorial males use scent to mark their territories. Grant’s gazelles also emit noises during courtship and to send up an alarm.
Though they are often found near each other, the Grant’s gazelle and the Thomson’s gazelle belong to different genera and have remarkably distinct territorial behavior. A territorial male Grant’s gazelle tears up grass with his horns and marks the boundary of his area with urine. In contrast, a territorial male Thomson’s gazelle marks his boundary with secretions from glands near his eyes. A territorial Grant’s male is easier to spot, as he stands in plain view to publicize his status. While Thomson’s territorial males engage in fights along their borders, their Grant’s counterparts simply keep a constant eye on neighboring activities.
Poaching and competition with livestock are the biggest threats to Grant’s gazelle populations. Of the three species within the Nanger genus, Grant’s are fairly stable, as a high percentage of these gazelles resides within protected regions, such as the Serengeti and the Maasai Mara.