Tuesday, 10 July 2012

Addax

The addax (Addax nasomaculatus), also known as the screwhorn antelope, is an antelope of the genus Addax, that lives in the Sahara desert. It was first described by Henri Blainville, a French zoologist and anatomist, in 1816. As suggested by its alternative name, this pale antelope has long, twisted horns. It is closely related to the oryx, but differs from other antelopes by having large square teeth like cattle and lacking the typical facial glands.
It mainly eats grass, 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 twenty members, consisting of both males and females. They are led by the oldest female. Breeding season is at its peak during winter and early spring. The addax can be easily hunted by its predators due to its slow walking pace. The natural habitat of addax are arid regions, semideserts and sandy and stony deserts.
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. They are sometimes hunted as trophies on ranches in the United States.

Etymology

 

It is believed the name “addax” is obtained from an Arabic word meaning a wild animal with crooked horns. The word “nasomaculatus” comes from the Latin words “nasus” (or the prefix “naso”) that means nose and “macula” that means a spot or spotted and the suffix –“atus” refers to the spots and facial markings of the antelope. Bedouins use another name for the addax, that is the Arabic term “bakr” (or “bagr”) “al wahsh”, which literally means the cow of the wild. The name can be used to refer to other ungulates as well.

Physical description

 

Addax at St Louis zoo.

Male addax stand from 105 to 115 centimetres (41 to 45 in) at the shoulder, with females at 95 to 110 centimetres (37 to 43 in). The addax are sexually dimorphic, as the females are smaller than males. The head and body in both sexes measure from 120 to 130 centimetres (47 to 51 in), with a 25 to 35 centimetres (9.8 to 14 in) tail. The weight of males varies from 100 to 125 kilograms (220 to 280 lb), and of females from 60 to 90 kilograms (130 to 200 lb). The coloring of their coat varies with the season. In the winter it is greyish brown with white hind quarters and legs, and long brown hair on the head, neck, and shoulders. In the summer, the coat turns almost completely white or sandy blonde. Their head is marked with brown or black patches that form an ‘X’ over their nose. They have a scraggly beard and prominent red nostrils. Long black hairs stick out between their curved and spiralling horns, ending in a short mane on the neck.
The horns, which are found on both males and females, have two to three twists and are typically 55 to 80 centimetres (22 to 31 in) in females and 70 to 85 centimetres (28 to 33 in) in males, although there have been occasional records of longer horns. The lower and mid portions of the horns are marked with a series of thirty to thirty five ring-shaped ridges. Their tail is short and slender, ending in a puff of black hair. The hooves are broad with flat soles and strong dewclaws to help them walk on soft sand. All four feet possess scent glands. The life span of addax can be extended to 25 years under captivity.

Ecology

 

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 twenty members. They will generally stay in one place and only wander widely in search of food. 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. Addax are able to track rainfall and will head for these areas where vegetation is more plentiful. These herds are led by a dominant male. 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 like lions, human, African hunting dogs, cheetahs and leopards. Caracals, hyenas and servals attack calves. Addax are normally non-aggressive, though individuals may charge if they are disturbed.

Adaptations

They are amply suited to live in the deep desert under extreme conditions. Addax can survive without free water almost indefinitely, because they get moisture from their food and dew that condenses on plants. Scientists believe that 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.

A calf with its mother.
 

Diet

Addax is mainly a herbivore.

Addax live in desert terrain where they eat grass, and leaves of what shrubs, leguminous herbs and bushes are available. Their staple diet 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's diet, being their main source of protein. They rarely drink water but derive moisture from whatever foliage available.

Reproduction

Females are sexually mature at 2 to 3 years of age and males at about 2 years. Breeding occurs throughout the year but it peaks during winter and early spring. Gestation period lasts 257–270 days (about nine months). Females may lie or stand during the delivery, after which one calf is born. A postpartum estrus occurs after two or three days. The calf weighs 5 kilograms (11 lb) at birth and is weaned at 23–29 weeks old.

Habitat and distribution

 

The addax inhabits arid regions, semideserts and sandy and stony deserts, but today are only found in rare pairs or as individuals in the Sahara desert and a few neighboring regions. The addax is extinct in Jordan since 1900 and in Egypt and Morocco by the mid-20th century. It was once abundant in north Africa, native to regions like Chad, Mauritania and Niger. Fossils are known from Egypt, Morocco, Algeria, and Sudan, dating back to the Pleistocene.
By 1972, the addax was found mainly in Rio de Oro, Mauritania; north Mali and Chad; with some in Algeria, South Libya, and North Sudan. It was rare everywhere except in the uninhabited area in Mauritania and Mali in the western Sahara. It is now found in scarce populations in Mauritania, Mali, Chad, Niger and almost extinct in Sudan, Algeria, Egypt, Libyan Arab Jamahiriya and western Sahara.
Some addax are to be found on game ranches in Texas where they are raised for trophy hunting. 

Threats and conservation

 

Herd of addax in Ramat Gan Safari.

In ancient times, addax occurred from Northern Africa through Arabia and the Levant. Pictures from Egyptian tombs show them being kept as domesticated animals in around 2500 BC. More recently, addax were found from Algeria to Sudan, but due mainly to overhunting, they have become much more restricted and rare. The dama gazelle and scimitar oryx are also found in the same region. These are easy to hunt due to their slow movements, particularly using motorized vehicles and automatic weapons. 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. It is believed that less than 500 individuals exist in the wild today, most of the animals being found between the Termit area of Niger and the Bodélé region of Western Chad.
In Israel, the Yotvata Hai-Bar Nature Reserve breeds addax in order to restore them to the wild. Although enormous reserves, such as the Ahaggar National Park and Tasilli in Algeria, the Ténéré in Niger, the Ouadi Rimé-Ouadi Achim 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. Addax have been introduced in Tunisia and Morocco, firstly in Bou Hedma National Park (Tunisia).