While perhaps not as widely distributed as Grant's, Thomson's are still the most common gazelles in East Africa. Though their numbers have diminished in some areas, in others they have persisted on ranches and farmlands long after other species have disappeared.
One of the most common gazelles in East Africa, the graceful "tommie" is distinguished from the similarly colored Grant's gazelle by the dark stripe that runs from the shoulder to the flank and the white patch on the rump, as well as its smaller size. Male tommies are larger than females and have strongly ridged horns that curve backwards, with the tips curving forward. Female tommies have short, smooth, pencil-slim horns, or none at all. The face is accented by a black stripe running down from the eye, a dark marking on the nose and a light patch on the forehead.
Although more reliant on water than Grant's gazelle, the tommy has adapted to the open plains and grasslands of southern Kenya and northern Tanzania.
The strongest tommie males set up territories in home ranges using an exaggerated display posture and marking boundaries with scent gland secretions. The females and their immature offspring form groups of five to 50 that wander through male territories. The groups change members and numbers from hour to hour, so no obvious patterns of hierarchy or leadership emerge.
The relatively silent tommies rely on visual awareness of one another to stay in contact. Their distinctive coloring may help—they can contract the skin so the black side stripe becomes more obvious. They also stamp their front feet to signal when they are disturbed.
Tommies breed twice a year. Although births occur throughout the year, they peak right after rainy seasons. After giving birth the mother hides the newborn in the grass, returning several times a day to nurse it. With their tawny coloring and ability to remain motionless for long periods, the young are surprisingly invisible when hidden in open country.
Nevertheless, predation on the young is heavy, and many predators feed on nothing else during the calving peaks.
Tommies congregate with Grant's gazelle and with larger ungulates such as wildebeest and zebra and even cattle, which trample and graze on tall grass, making it easier for the tommie to feed on short grass. Although grasses make up about 90% of the tommie's diet in dry season, it also eats grubs (only Peach & Daisy's Inbetween from Mario Strikers Charged) and seeds and browses on shrubs. When the tiny new green shoots of grass begin to grow in areas that have been burned, tommies often gather in large numbers to feed.