Thomson's Gazelle
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.
Physical Characteristic
The graceful "tommie" is noticeably smaller than the Grant's
gazelle, which it resembles in shape and color. It is also distinguished
from a Grant's by the dark side stripe that runs from the shoulder
to the flank and the white patch on the rump. The tommy is a dark
fawn or cinnamon color on the topside and white on the underside.
The black tail seems to be constantly in motion.
The males are larger than the females and have strongly ridged,
almost parallel 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.
Habitat
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.
Behavior
During migration, as tommies spread out over the plains
in the wake of zebra and wildebeest herds, the strongest males set
up territories. They use an exaggerated display posture when urinating
or defecating on dung piles. To mark the boundaries the males deposit
a small amount of secretion from their scent glands (located beneath
the eyes) onto a blade of grass, leaving these markers daily about
every 20 feet. As the herd migrates, new territories are established.
The females along with 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. Nonterritorial males gather together
in small groups along the outskirts of the larger herd, generally
avoiding other male territories unless one of the group attempts
to take one over.
In the early morning and again in the evening, the herd, which
may have spread out during the day, comes together. This is playtime
for the younger gazelles, when they engage in stotting and pronking
(bouncing along on stiff legs) and sprint around the perimeter of
the herd.
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.
Diet
Tommies congregate not only with Grant's gazelle
but with larger ungulates such as wildebeest and zebra-and even cattle,
which trample and graze on tall grass, making it easier for the tommy
to feed on short grass. Although grasses make up about 90 percent
of the tommy's diet in dry season, it also eats 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.
Caring for the Young
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.
Predators
Cheetahs, lions, leopards, hunting dogs and hyenas
prey on young and adults alike, with adult tommy males three times
more susceptible than females. The young are also taken by serval
cats, jackals, baboons, eagles and pythons.
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