|Common Name||White Antelope and Screwhorn Antelope|
The Addax, (Addax nasomaculatus), also known as the white antelope and the screwhorn antelope, is an antelope of the genus Addax, that lives in the Sahara desert. It was first described by Henri de Blainville in 1816. As suggested by its alternative name, this pale antelope has long, twisted horns - typically 55 to 80 cm (22 to 31 in) in females and 70 to 85 cm (28 to 33 in) in males. Males stand from 105 to 115 cm (41 to 45 in) at the shoulder, with females at 95 to 110 cm (37 to 43 in). They are sexually dimorphic, as the females are smaller than males. The colour of the coat depends on the season - in the winter, it is greyish-brown with white hindquarters and legs, and long, brown hair on the head, neck, and shoulders; in the summer, the coat turns almost completely white or sandy blonde.
The addax is a very large desert antelope found only in the remotest parts of the southwestern Sahara Desert. Small herds of addax once roamed the whole desert, but now there are just a few - about 200 animals in total. The addax has been hunted for its meat and skin. Because of its size, this antelope is not capable of great speed.
The addax mainly eats grasses and leaves of any available shrubs, leguminous herbs and bushes. These animals are well-adapted to exist in their desert habitat, as they can live without water for long periods of time. Addax form herds of five to 20 members, consisting of both males and females. They are led by the oldest female. Due to its slow movements, the antelope is an easy target for its predators: lions, humans, african wild dogs, cheetahs and leopards. Breeding season is at its peak during winter and early spring. The natural habitat of the addax are arid regions, semideserts and sandy and stony deserts.
The addax is a critically endangered species of antelope, as classified by the IUCN. Although extremely rare in its native habitat due to unregulated hunting, it is quite common in captivity. The addax was once abundant in North Africa, native to Chad, Mauritania and Niger. It is extinct in Algeria, Egypt, Libya, Sudan and western Sahara. It has been reintroduced in Morocco and Tunisia.
The addax has 27 male chromosomes and 28 female chromosomes. All chromosomes are acrocentric but the first pair of autosomes, which is submetacentric. The X chromosome is the largest acrocentric, and the Y chromosome a medium-sized one. The short and long arms of the pair of submetacentric autosomes correspond respectively to the 27th and first chromosome. In a study, the banding patterns of chromosomes in addax were found to be much similar to those in four other species of the subfamily Hippotraginae. Karyotypes of caprine and bovine species also highly resemble the banding patterns in addax.
Behavior and EcologyEdit
These animals are mainly nocturnal, particularly in summers. In the day, they dig into the sand in shady locations and rest in these depressions, which also protect them from sandstorms. Addax herds contain both males and females, and have from five to 20 members. They will generally stay in one place and only wander widely in search of food. The addax have a strong social structure, probably based on age, and herds are led by the oldest female. Herds are more likely to be found along the northern edge of the tropical rain system during the summer and move north as winter falls. They are able to track rainfall and will head for these areas where vegetation is more plentiful. Males are territorial, and guard females, while the females establish their own dominance hierarchies.
Due to its slow movements, the addax is an easy target for predators such as lions, humans, african wild dogs, cheetahs and leopards. caracals, hyenas and servals attack calves. The addax are normally not aggressive, though individuals may charge if they are disturbed.
The addax are amply suited to live in the deep desert under extreme conditions. They can survive without free water almost indefinitely, because they get moisture from their food and dew that condenses on plants. Scientists believe the addax has a special lining in its stomach that stores water in pouches to use in times of dehydration. They also produce highly concentrated urine to conserve water. Pale colour of the coat reflects radiant heat, and the length and density of the coat helps in thermoregulation. In the day the addax huddle together in shaded areas, and in cool nights rest in sand hollows. These practices help in dissipation of body heat and saving water by cooling the body through evaporation.
In a study, eight addaxes on a diet of rhodes grass. were studied to determine the retention time of food from the digestive tract. It was found that food retention time was long, taken as an adaptation to a diet including a high proportion of slow fermenting grasses; while the long fluid retention time could be interpreted to be due to water-saving mechanisms with low water turnover and a roomy rumen.
The addax live in desert terrain where they eat grasses and leaves of what shrubs, leguminous herbs and bushes are available. Their staple foods are the Aristida, Artemisia, Citrullus and Acacia grasses; perennials which turn green and sprout at the slightest bit of humidity or rain. The addax eat only certain parts of the plant and tend to crop the Aristida grasses neatly to the same height. By contrast, when feeding on Panicum grass, the drier outer leaves are left alone while they eat the tender, inner shoots and seeds. These seeds are important part of the addax diet, being their main source of protein.
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Females are sexually mature at two to three years of age and males at about two years. Breeding occurs throughout the year, but it peaks during winter and early spring. In the northern Sahara, breeding peaks at the end of winter and beginning of spring; in the southern Sahara, breeding peaks from September to October and from January to mid-April. Each estrus bout lasts for one or two days.
In a study, the blood serum of female addax was analyzed through immunoassay to know about their luteal phase. Estrous cycle duration was of about 33 days. During pregnancy, ultrasonography showed the uterine horns as coiled. The maximum diameters of the ovarian follicle and the corpus luteum were 15 mm (0.59 in) and 27 mm (1.1 in). Each female underwent an anovulatory period lasting [tel:39 10 131 39 10 131] days, during which there was no ovulation. Anovulation was rare in winter, which suggested the effect of seasons on the estrous cycle.
Gestation period lasts 257–270 days (about 9 months). Females may lie or stand during the delivery, during which one calf is born. A postpartum estrus occurs after two or three days. The calf weighs 5 kg (11 lb) at birth and is weaned at 23–29 weeks old.
Threats and ConservationEdit
Decrease in the population of the addax has begun notably since the mid-1800s. More recently, addax were found from Algeria to Sudan, but due mainly to overhunting, they have become much more restricted and rare.
Addax are easy to hunt due to their slow movements. Roadkill, firearms for easy hunting and nomadic settlements near waterholes (their dry-season feeding places) have also decreased numbers. Moreover, their meat and leather are highly prized. Other threats include chronic droughts in the deserts, habitat destruction due to more human settlements and agriculture. Less than 500 individuals are thought to exist in the wild today, most of the animals being found between the Termit area of Niger and the Bodélé region of western Chad.
Today there are over 600 addax in Europe, Yotvata Hai-Bar Nature Reserve (Israel), Sabratha (Libya), Giza Zoo (Egypt), North America, Japan and Australia under captive breeding programmes. There are 1000 more in private collections and ranches in United States and the Middle East. Addax is legally protected in Morocco, Tunisia, and Algeria; hunting of all gazelles is forbidden in Libya and Egypt. Although enormous reserves, such as the Hoggar Mountains and Tasilli in Algeria, the Ténéré in Niger, the Ouadi Rimé-Ouadi Achim Faunal Reserve in Chad, and the newly established Wadi Howar National Park in Sudan cover areas where addax previously occurred, some do not keep addax any more due to less resources. The addax has been reintroduced in Bou Hedma National Park (Tunisia) and Souss-Massa National Park (Morocco). The first reintroduction in the wild is ongoing in Jebil National Park (Tunisia), Grand Erg Oriental (Sahara) and another is planned in Morocco.