|
|||||||
 ·Wester Lowland Gorilla |
|||||||
|
Description: Western lowland gorilla males can weigh 300-600 pounds, and stand 5-6 feet tall. Females are significantly smaller and weigh about half that of males; they stand up to 5 feet tall. A gorilla’s arms are longer than their legs, and a male’s arm span can reach 7-9 feet. They walk on all fours, using the knuckles of their hands to support and pivot their weight. Their back feet are flat on the ground (plantigrade). Both the male’s and female’s bodies are covered in grey, brown, or black hair, with the exception of the face and chest. Until males are about ten years old, they are hard to distinguish from females. At this time, male secondary sexual characteristics quickly develop. They include the development of a wide, protruding bone above their eyes (supraorbital ridge) and protusions on their head and neck (sagittal and nuchal crests). Grey or white hair develops on their lumbar region giving them the silverback name. The average life span is around 30 in the wild and longer in captivity, about 40-50 years. The oldest gorilla in captivity was recorded at 54 years by “ Massa” in the Philadelphia Zoo. Diet: The western lowland gorilla is primarily an herbivore, eating over 200 types of plants, fruits, stems, shoots, bulbs, bark, leaves, pith. Less frequently, they may also feed on invertebrates such as termites and ants in the wild. Gorillas prefer fruit, but their large size prevents them from harvesting great quantities. They will not eat fallen fruit because it is tainted by fermentation. Younger gorillas will climb trees to feed and might throw down fruit laden branches to adults on the ground. Some populations consume such a large amount of succulent herbs that they do not need to drink much water. In the zoo they are fed a commercial diet, oranges, apples, pears, carrots, grapes, various greens, yams, peppers, corn, nuts and raisins. Behavior: Gorillas are shy and gentle creatures living in bands, or troops, of 5-30 gorillas. A typical troop includes a silverback (dominant male), 1 or 2 sub-dominant males, several females, and young. The silverbacks regulate this structured family group’s behavior, such as sleeping patterns, eating and traveling. Young males are driven out of the troop at maturity and may form all male groups or loosely attach themselves to other bands. Sometimes the males may even start their own groups with females that leave their troop. The silverback will eventually be defeated by a challenger and then move on to live a solitary life. Females will leave their band and join another troop. This prevents inbreeding. There is a hierarchy among the females within the troop, and a female’s rank is passed on to her offspring. Females stay in proximity with one another to stay near the silverback. Related females and those that have been together since they were youngsters get along better than unrelated females. Females new to the group have low status and the silverback stops female bickering when new females enter the group. Gorillas will usually build a nest twice daily. Before dusk, each gorilla makes its own nest, or bed, for the night, which is probably a learned behavior. The height above the ground at which the gorillas build their nightly nests varies with their weight, with the silver backs usually being on or close to the ground. The females and young will sleep in the trees on nests made of small branches and leaves. The older males will nest in drier grass at the base of trees. Of all the primates, only gorillas commonly sleep on the ground. Communication among gorillas includes facial expressions, body posture, vocal communication, and tactile means such as grooming and play. All gorillas beat their chests. Laryngeal sacs extend into the pectoral region resonate the beating (like drums), so that it can be heard a mile away. The males do this to display power or intimidate others; it also serves as a bluff to scare off intruders. When gorillas are being aggressive, they growl and may produce a series of pants. Silverbacks roar to threaten humans and gorilla intruders instead of immediately fleeing from them. They have no natural enemies except humans and rare attacks from leopards. The male leader will charge all intruders while the females and young will flee to a safe distance. Mildly alarmed and curious adults emit question barks and hiccup barks. Often they will silently slip away when they are extremely afraid. Distressed infants emit a variety of screeches, sobs, wails, and other noises. Contented gorillas produce deep, prolonged, soft belching sounds. If they are threatened, a hooting sound is uttered to alert the rest of the troop. Other sounds are sharp grunts for invoking discipline and low growls for expressing pleasure. Breeding: The gorilla’s sexual cycle is somewhat similar to humans. The female menstruates about every 28 days and has a gestation period of 8-9 months. The female gives birth to one young, and occasionally twins. Depending on infant survival rates, a female will give birth every 3.5-4.5 years. The females become sexually mature around seven years of age, but usually do not breed until after ten years. Males are sexually mature around ten years of age. Gorillas are not seasonal breeders and females will mate with any male in any season. Aggression is the main tactic used by silverbacks to keep other males away from his females. Males must be fully mature in order to retain females and reproduce. When young are born, they weigh about 4-5 pounds and are pinkish grey with brown and/or black hair. The newborn gorilla clutches belly-to-belly for close contact until strength and coordination develops. After two or three months, the baby gorillas begin to crawl around and cling to mother’s back, and will walk at 30-40 weeks. Gorillas may nurse up to four years although weaning occurs anywhere from 1-4 years of age. The baby will nest with the mother until around three years of age. Although the mother provides primary care to the young, the male silverback will “baby-sit” his offspring while the female forages for food without the hindrance of the playful young. Silverbacks also may take care of abandoned or orphaned youngsters. Adaptations: Most often the gorilla is seen on all fours, using the knuckles of its hands to pivot and support its large size. Gorillas, like humans, have binocular vision. This is when both eyes are used together, creating a wide field of view. The gorilla has a well developed brain; it is able to learn from experience and has the ability to reason. A gorilla is more likely to perform a task out of interest than to earn a reward. At Stanford University in 1972 a female gorilla, Koko, was taught how to use sign language and uses several hundred different signs. The male’s large canine teeth are mainly used as a visual display warning others, and are also used for ripping into tough fruits and nuts. The canines are not used for ripping into flesh as some may suspect. They are primarily vegetarian. Threats to Survival: Currently gorillas are classified as endangered due to destruction of their habitat, hunting, (for the bush meat trade and pet trade) and trapping (sometimes caught in traps meant for other animals). The forests are being cut down for wood. Although gorillas are protected in all of the countries they inhabit, their future still remains uncertain. Gorillas are important in the wild because they feed on fruits and disperse seeds in their dung as they travel throughout the forest. Plant growth occurs in bright sunlight, and gorillas like to forage in areas cleared by elephants, storms, and even people. They leave behind seeds that generate new growth. Sources: www.bj4hs.bj.edu.cn/chinese/animal/gorillaa.htm www.cattales.org/gorilla.html www.selu.com/-bio/gorilla/info/nh.html Estes, Richard Despard, The Behavior Guide to African Mammals. University of California Press, 1991. Tuttle, Russell H. Apes of the World. Noyes Publications, 1986. Preston-Mafhan, Rod and Ken. Primates of the World Facts on File, 1992. wwwgpz.org/album/gorillas/index_g.html www.animaldiversity.ummz.umich.edu www.bagheera.com/inthewild/van_anim_gorilla.htm
|
|||||||
 |
|||||||
