Plains
Zebra (Equus burchelli)
Subspecies: The Grant's zebra (Equus burchelli boehmi) is the most common of the plains zebra subspecies. It has broad black stripes on a white background. (see figure 1.1) The Chapman's zebra (Equus
burchelli antiquorum) is characterized by a pattern of broad, dark stripes alternating with
thin, light shadow-stripes. The stripes fade into the brownish
color of the body on the hindquarters and are absent altogether
on the legs. Life
span can extend to 20 years.
Habitat: The
Plains zebra inhabit savannas, from treeless grasslands to open woodlands. |
figure 1.1: Grants Zebra |
Their
body design is specialized for running and eating tough siliceous grasses.
They have excellent hearing and eyesight and can run at speeds of up to
35 miles per hour (56 kilometers per hour). They also have a powerful kick
that can cause serious injury to a predator.
Height and weight: Shoulder height varies from 120 to 140 centimeters
(45-55 in.), and a mature male may weigh 300 kilograms (770 - 990 lbs.).
Stripes:
Zebras have shiny coats that dissipate over 70 percent of
incoming heat. The black and white stripes are a form of camouflage called
disruptive coloration that breaks up the outline of the body. Although
visible during daytime, at dawn or in the evening when their predators
are most active, zebras look indistinct and may confuse predators by distorting
true distance.
|
Figure 1.2: Zebra Stripe pattern |
Broad vertical stripes on the sides bend on the flanks to become horizontal across the rump. (see figure 1.2)
The pattern of stripes on all zebras is unique to each
individual, with the variation greatest in the shoulder region. This
aids foals imprinting and allows adult zebras of a given harem in
identifying each other in the large grazing herds.
Zebras have black skin underneath their hair. |
Diet
and feeding patterns:
Zebras
are herbivores and mostly graze on grasses and shrubs, although they
also might browse on bark, roots and stems if necessary.
They graze for 2/3 of the day and have teeth built for grinding and cropping
grass. They use their strong front teeth to clip off the tips of
the grass and then crush and grind the food using their back teeth.
Spending so much time chewing wears the zebra's teeth down, so their
teeth keep growing all their lives. |
Figure 1.3: Zebra Skull |
Zebras
can be either sedentary or migratory. Where food is mostly plentiful year-round,
they lead a sedentary life, with a home range about 11 mi square (30 km square).
In seasonally dry areas small families of plains zebra gather to form large
herds that migrate in search of food. Staying together as a family group
within large herds, they migrate up to 500 miles (800 km) per year. Plains
zebra are extremely dependent on water and never wander far from waterholes,
where they usually drink at least once a day.
Dry
Season Diet Changes:
As the dry
season arrives and the grasses die
back, zebra herds travel to find more food and water holes for drinking. They
can live on coarse, dry grass only if they are within a short distance (usually
no farther than 20 miles away) of water holes. Most zebras are considered
nomadic, always on the move, without specific territories.
Digestive System:
Although they are not ruminants, Zebras carry
microorganisms in their intestines, which help them to break down their
nutrition. Their digestive system can process coarse, low-quality plant matter
due to a long hindgut. The intestines are 17 times the body length.
Pioneer Species:
Their tolerance for taller grasses and more wooded savanna
gives the zebra much greater geographical range than other herbivores like
wildebeest. They are a pioneer in
the grazer community, first to enter tall or wet pastures, followed by
wildebeests and gazelles after zebras have trampled and cropped the grass
shorter; also crops short green flush with its matched set of incisors and
mobile lips much more efficiently than wildebeests and most other ruminants.
Zebra are more active in daylight, spending nights
preferably on short pasture relatively safe from ambush. Zebras graze
individually an hour or so at a time at night but move about very little.
Resting zebras often steep soundly, but at least one herd member remains
standing and alert. At daybreak in warm weather, herds begin filing to pastures
of longer grass and may cover over 10 mi (17 km) before settling for another
night. Mass movements between
pastures and sleeping grounds, and to water at midday, are also peaks of
social activity.
Behavior and Social Organization:
Plains
zebra are social animals. Although they may live alone, they usually form
bachelor groups and small families (harems) of five to 20 animals, consisting
of a dominant male, mares and offspring.
Harems:
Harem masters have exclusive mating rights with 2 to 6
mares. Harems are so stable that mares remain associated for life; HaremÕs
and the dominant stallion will protect their foals against all threats,
which increases their survival-and his reproductive success. When members
of the
herd
become separated, the family stallion goes looking and calling for them,
and the whole harem will adjust its pace to accommodate sick or crippled
members.
Harem ownership:
When breeding male gets killed, severely injured, or too
old to outface challengers, some lucky stallion stands to inherit his whole
harem. But with a potential life span of over 20 years, most stallions stay
fighting-fit for some 15 years.
Starting a Harem:
The normal way to become a harem stallion is by abducting
fillies in heat, one at a time. Resident mares do not welcome newcomers. The
latest wife must keep her distance, protected and herded by her consort, during
a probation of several weeks.
Harem Hierarchy:
A strict rank hierarchy is enforced, the first mare to join the harem and her offspring taking precedence over the second, the second over the third, and so on down to the latest conquest. This order is strictly enforced when a herd is filing. The stallion's usual position is behind his family, from where he can still direct the herd's movements when he sees fit.
Bachelor Herds:
Colts leave their families on their own initiative usually
between 2 and 3 years to join an all male bachelor group, there to remain until
mature and ready to start a harem at 5 years. Bachelor herds include 2 to 15 males,
are usually led by a young adult, and are quite stable, with a rank order based
simply on age.
Courtship and Reproduction:
Signs of Estrus:
Between I and 2 years of age, fillies begin ovulating and
advertise estrus by adopting a distinctive posture. She urinates frequently,
her tail and neck are extended, ears back, lips retracted and open-mouthed
chewing. Female has a swollen, everted labia and mucous discharge;
Male response to Estrus:
Up to 18 stallions gather around a harem with an estrus
filly and chase the female away from her family group, nipping and attempting
to mount her. They often test her urine and urinate on the spot afterwards.
They also nuzzle, and social groom the female.
Abducting a filly from her father's herd is just the beginning of the ordeal. They have to fight for her with the herd stallion and one another. Even he stands up to the father, she may not mate with him straight away. The filly will stay with the inseminating stallion, starting his new harem. After foaling, subsequent estrous periods are advertised more discreetly so that rivals stay away-as long as the herd stallion is there to repel intruders.
Birth
and Caring for the Young:
Zebra's
reproduce slowly, gestation lasts 12 months and usually produce one foal
every other year. Sexual maturity is at 2 for females and 3 for males.
Foals born
in most
months but a definite annual birth/mating peak early in the rains (Dec.-Jan.
in East Africa.
Size at birth: 55 to 88 pounds (25 to 40 kilograms)
Zebra foals are dark brown and white at birth. They can
stand within 15 minutes and run and suckle in an hour. The mother keeps all
other zebras away for several days to allow the foal to imprint on her
(learning to recognize her by sight, voice and smell).
Although a foal may graze within a week of birth, they
continue to suckle for up to 16 months. The average juvenile mortality is about
50%, mostly due to predation by lions and hyena. There is no adoption and
mothers will only feed their own offspring.
Predators:
Lions,
hyenas, hunting dogs, leopards, and cheetahs are the main predators.
Behavior:
Communication:
Zebras communicate with one another with facial expressions
and sounds. Mother zebras whiney when separated from their foals, and bark to
warn of danger. The position of their ears, how wide open their eyes are, and
whether their mouths are open or their teeth are bared all mean something.
(Ears flat back, for example, means trouble, or you better follow orders)
Grooming:
Mutual grooming reinforces bonds within family groups.
Zebras stand together and nibble the hair on each other's neck and back.
Play:
Running games, and play fighting are common among young and
bachelors. It is a way to develop important skills like running in groups and
fighting.
Greeting/ritual challenge ritual:
Greeting of equals features nasal contact and sniffing,
rubbing of cheeks, moving into head-to-tail position, sniffing of penis,
pressing and rubbing of sides. Both approach with heads outstretched and ears
cocked, or 1 stands in erect posture watching other approach.
Aggressive behavior:
Standing in erect posture with head high, ears pricked,
tail arched. Biting using canine teeth of ears, neck, and body of opponent.
Short squeals, kick threats, and kicking out with hind feet, which can break a
leg or jaw. Kicking with front feet (not at each other), often displayed just
before parting.
Response to Predators:
Alert posture: standing with head high staring in one
direction, stamping and snorting. They run from large predators like lions, but
often close ranks around young to protect them from hyenas and wild dogs. Both
herd stallions and bachelors will line up to chase smaller predators away from
young.
Dominance display.
High stepping (prancing), Broadside display and Head-low
threat (ears back, snaking head movements).
Submission:
A bachelor declines the challenge of harem stallion by
displaying the submission behavior of laidback ears, making open-mouthed
chewing motions and moving away from threatening superior. This resembles the
display of a mare in heat. Ears back suggest threat but chewing is
submissive-an intention movement to nibble groom.
Maintenance Activities:
Dust-bathing, rubbing against trees, rocks, termite mounds,
etc.
Sources:
Web
Sites:
http://www.imh.org/imh/bw/zebra.html
http://www.alumni.caltech.edu/~kantner/zebras/
http://www.nature.ca/notebooks/english/zebra.htm
http://www.awf.org/wildlives/151
http://www.sandiegozoo.org/animalbytes/t-zebra.html
http://www.zoo.org/educate/fact_sheets/savana/zebra.htm
http://sailfish.exis.net/~spook/zebratxt.html
Video:
National
Geographic, Patterns in the Grass
Books
and magazines:
(You should have at least 2 sources that are books or magazines)
Sources of Images:
Figure 1.1:http://www.creative-me.dk/Besoegt/besoegt/besoegt-kbhzoo02-zebra.jpg
Figure
1.2:
Figure 1.3: http://zebrarug.com/images/zebraskull_copy.JPG