Scimitar oryx

Taxonomy and naming

The scimitar oryx is a member of the genus Oryx and the family Bovidae. The German naturalist Lorenz Oken first described it in 1816, naming it Oryx algazel. The nomenclature has undergone various changes since then, with the introduction of names like Oryx tao, O. leucoryx, O. damma, O. dammah, O. bezoarticus and O. ensicornis. In 1826, Philipp Jakob Cretzschmar used the name Oryx ammah for the species. A year later, the name Oryx leucoryx came into use, but as this was a synonym of the Arabian oryx (then called Oryx beatrix), it was abandoned, and Oryx algazel was accepted once more. Over 100 years later in 1951, Sir John Ellerman and Terence Morrison-Scott found that the name Oryx algazel was also ineligible for use. Finally, in January 1956, the International Trust for Zoological Nomenclature accepted Oryx dammah as the scientific name. There have been no more changes since then, though many papers published after 1956 created confusion by using names like O. gazella tao.

Its scientific name, Oryx dammah, is derived from: Ancient Greek ὄρυξ (orux), meaning a gazelle or antelope (originally a pickaxe); Latin damma (fallow deer or antelope); and Arabic dammar (sheep). The scimitar oryx is named for its horns, which resemble scimitars. Its common name in English is "scimitar-horned oryx", or simply "scimitar oryx".

Genetics and evolution

The scimitar oryx has 58 chromosomes. It has one pair of large submetacentric autosomes and 27 acrocentric autosomal pairs. The X and Y chromosomes are the largest and smallest acrocentrics. The first molecular study of this species (published in 2007) observed genetic diversity among European, North American and some other captive groups. Divergence was found within the mitochondrial DNA haplotypes, and was estimated to have taken place between 2.1 and 2.7 million years ago. Population increases occurred approximately 1.2 and 0.5 million years ago.

In another study, intended to note genetic differences between Oryx species, karyotypes of Oryx species and subspecies – namely O. gazella, O. b. beisa, O. b. callotis, O. dammah and O. leucoryx – were compared with the standard karyotype of Bos taurus. The number of autosomes in all karyotypes was 58. The X and Y chromosomes were conserved in all five species.

Physical description

The scimitar oryx is a straight-horned antelope that stands just over 1 m (3.3 ft) at the shoulder. The males weigh 140–210 kg (310–460 lb) and the females 91–140 kg (201–309 lb). The body measures 140–240 cm (55–94 in) from the head to the base of the tail. The tail is 45–60 cm (18–24 in) long and ends with a tuft. They are sexually dimorphic with males being larger than females.

Its coat is white with a red-brown chest and black markings on the forehead and down the length of the nose. The coat reflects the sun's rays, while the black portions and the tip of the tongue provide protection against sunburn. The white coat helps to reflect the heat of the desert. Calves are born with yellow coats and lack distinguishing marks, which appear later in life. Their pelage changes to adult coloration at 3–12 months old.

Both male and female oryxes have horns, with the females' being more slender. The horns are long, thin, and symmetrical; curve backward (a distinctive feature of this species); and can reach 1.0 to 1.2 m (3 ft 3 in to 3 ft 11 in) in both sexes. The hollow walls of the horns are so thin that they can easily break. The female has four nipples. The large, spreading hooves are well adapted to allow these antelopes to walk on the sand of their dry habitats. A scimitar oryx can live as long as 20 years. At Smithsonian National Zoo, a female oryx died at 21, an exceptional age since females generally have a lifespan of about 15 years.

Diseases and parasites

The scimitar oryx can be infected with cryptosporidiosis, a parasitic disease caused by protozoan parasites of the genus Cryptosporidium in the phylum Apicomplexa. A study in 2004 revealed that C. parvum or similar organisms infected 155 mammal species, including the scimitar oryx. An analysis in 2005 found Cryptosporidium parasites in stool samples from 100 mammals, including the scimitar oryx. Oocysts of a new parasite, Eimeria oryxae, have been discovered in the feces of a scimitar oryx from Zoo Garden in Riyadh. In France, Streptococcus uberis was isolated for the first time in an oryx. It had caused vegetative endocarditis in the animal, leading to fatal congestive heart failure.

A 1983 study examined the blood serum chemistry of blood samples taken from the jugular veins of 50 scimitar oryxes ranging from neonates to adults over 13 years old. The study concluded that the higher eosinophil counts of the juveniles and adults might reflect larger internal parasite burdens in them as compared with the neonates.

Ecology and behavior

The scimitar oryx was a very sociable animal and traveled in herds of between two and 40 individuals, generally, led by a dominant bull. This species once gathered in groups of several thousand for migration. During the wet season, they migrated north into the Sahara. Scimitar oryx are diurnal. In the cool early mornings and evenings, they rest under trees and shrubs, or if neither are available, they dig depressions in the soil with their hooves and rest there. Males fight often, but not for long and not violently. Predators, such as lions, leopards, hyenas, cheetahs, golden jackals, vultures and Cape hunting dogs, mostly kill weak and young oryxes.

The play activity of eight calves in captivity was observed in a 1983 study. Male calves played for longer than females calves did. Mixed sex play was usual; selection of partners depended on age, but not on sex or genetic relatedness. Results suggested that size dimorphism was an important factor responsible for sex differences in play.

Adaptations

With a metabolism that functions at the high temperatures prevalent in their habitats, scimitar oryxes need less water for evaporation to help conduct heat away from the body, enabling them to go for long periods without water. They can allow their body temperature to rise to almost 46.5 °C (115.7 °F) before beginning to perspire. In times of ample supply, oryx can use fluid loss through urination and feces to lower their body temperature to below 36 °C (97 °F) at night, giving more time before reaching maximum body temperature the following day. They can tolerate high temperatures that would be lethal to most mammals. They have a network of fine blood vessels that carry blood from the heart to the brain, passing close to the nasal passage and thus allowing the blood to cool by up to 3 °C (5 °F) before reaching the brain, which is one of the most heat-sensitive organs of the body.

Diet

The habitat of the scimitar oryx in the wild was steppe and desert, where they ate foliage, grass, herbs, shrubs, succulent plants, legumes, juicy roots, buds, and fruit. They can survive without water for nine to 10 months because their kidneys prevent water loss from urination – an adaptation to desert habitats. They can get water from water-rich plants such as the wild melon (Citrullus colocynthis) and Indigofera oblongifolia and from the leafless twigs of Capparis decidua. In the night or early morning, they often search for plants such as Indigofera colutea, which produce a hygroscopic secretion that fulfills water requirements. They eat tuft grasses such as Cymbopogon schoenanthus after it has rained, but they normally prefer more palatable grasses, such as Cenchrus biflorus, Panicum laetum and Dactyloctenium aegyptium. When the dry season begins, they feed on the seedpods of Acacia raddiana, and during the dry season, they rely on perennial grasses of genera such as Panicum (especially Panicum turgidum) and Aristida, and browse plants such as Leptadenia species, Cassia italica and Cornulaca monacantha.

Reproduction

Both males and females reach sexual maturity at 1.5 to 2 years of age. Births peak between March and October. Mating frequency is greater when environmental conditions are favorable. In zoos, males are sexually most active in autumn. The estrous cycle lasts roughly 24 days, and females experience an anovulatory period in spring. Periods between births are less than 332 days, showing that the scimitar oryx is polyestrous.

Courting is done by means of a mating circle: the male and female stand parallel to one another, facing in opposite directions, and then circle around each other until the female allows the male to mount from behind. If the female is not ready to mate, she runs away and circles in the reverse direction. Pregnant females leave the herd for a week, give birth to the calf and conceive again during their postpartum estrus; thus they can produce a calf a year. Gestation lasts about nine months, after which a single calf is born, weighing 10–15 kg (22–33 lb). Twin births are very rare - only 0.7% of the births observed in one study. Both mother and calf return to the main herd within hours of the birth. The female separates herself from the herd for a few hours while she nurses the calf. Weaning starts at 3.5 months, and the young become fully independent at around 14 weeks old.

Habitat and distribution

The scimitar oryx once inhabited grassy steppes, semideserts and deserts in a narrow strip of central north Africa (Niger and Chad). It was widespread on the fringes of the Sahara, mainly in subdesert steppe, the grassy zone between the real desert and the Sahel, an area characterized by an annual rainfall of 75–150 mm (3.0–5.9 in). In 1936, a single herd of 10,000 scimitar oryx was seen in the steppe area of Chad. By the mid-1970s, Chad was home to more than 95% of the world population of this species.

Status and conservation

Following the Neolithic Subpluvial, around 7500 to 3500 BCE, the "green Sahara" became dry and the scimitar oryx's population began to decline due to a loss of suitable habitat. This was further exacerbated by humans who hunted the scimitar oryx for both its meat and horns. The northern population was already almost lost before the 20th century. With the introduction of horses and firearms during the 20th century, nomadic hunters were able to decimate populations. The decline of the southern population accelerated as Europeans began to settle the area and hunt them for meat, hides and horn trophies. French involvement in World War II and the civil war in Chad that started in the 1960s are thought to have caused heavy decreases of the species through an increase in hunting for food. Roadkill, nomadic settlements near watering holes (the oryx's dry-season feeding places), and introduction of cattle and firearms for easy hunting have also reduced numbers.

The IUCN lists the scimitar oryx as regionally extinct in Algeria, Burkina Faso, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Nigeria, Senegal, Sudan, Tunisia and the Western Sahara, and has assessed it as extinct in the wild since 2000. Reports of sightings in Chad and Niger remain unsubstantiated, despite extensive surveys carried out throughout Chad and Niger from 2001 to 2004 in an effort to detect antelopes in the Sahel and the Sahara. At least until 1985, 500 scimitar oryx were estimated to be surviving in Chad and Niger, but by 1988, only a few individuals survived in the wild.

There is now a global captive breeding program for the scimitar oryx. In 2015, about 1,750 captives were managed as part of breeding programs; at the program's peak, up to 11,000 were kept in Texas farms and 4,000 were held in the Arab states of the Persian Gulf. Reintroduction plans involve fenced-in herds in Bou-Hedma National Park (1985), Sidi Toui National Park (1999) and Oued Dekouk National Park (1999) in Tunisia; Souss-Massa National Park (1995) in Morocco; and Ferlo Faunal Reserve (1998) and Guembeul Wildlife Reserve (1999) in Senegal.

Chad is currently leading a project to reintroduce the species in Ouadi Rimé-Ouadi Achim Game Reserve, with the support of the Sahara Conservation Fund and the Environment Agency of Abu Dhabi. At 78,000 km² – equivalent to the size of Scotland- Ouadi Rimé Ouadi Achim is one of the world's largest protected areas. The first group was released at the beginning of 2016 in an acclimation enclosure and then fully released in the wild in the rainy season. That group was made of 21 animals, which by the beginning of 2017 had already produced a calf, the first birth in the wild for more than 20 years. A second group comprising six males and eight females was placed in the acclimation enclosure on 21 January 2017.

The Marwell Zoo in Hampshire and the Edinburgh Zoo have also worked in partnership with ZSL to help reintroduce captive-bred scimitar oryx to their former natural ranges. The Tunisian reintroductions began in 1985 with 10 scimitar oryxes from the Marwell and Edinburgh Zoos (co-ordinated by ZSL). In 1999 and 2007, Marwell co-ordinated the release of scimitar oryxes into three more protected areas within their former historic range.