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The '''dromedary''' ({{IPAc-en|ˈ|d|r|ɒ|m|ə|d|ɛ|ɹ|i}} or {{IPAc-en|-|ə|d|r|i}}), also called the '''Arabian [[camel]]''' or the '''Indian camel''' (''Camelus dromedarius''), is a large, [[even-toed ungulate]] with one hump on its back. First described by [[Aristotle]], the dromedary was given its binomial name by Carl Linnaeus in 1758. The dromedary is the next largest member of the camel family after the [[Bactrian camel]]{{Citation needed|date=November 2013}}. The oldest known ancestor of the dromedary is the ''[[Protylopus]]''. Males are {{convert|1.8|–|2|m|ft|abbr=on}} tall and females are {{convert|1.7|–|1.9|m|ft|abbr=on}} tall. Males range from {{convert|400|–|600|kg|lb|abbr=on}}, while females weigh {{convert|300|-|540|kg|lb|abbr=on}}. They vary in colour from a light beige to dark brown. The notable hump, measuring {{convert|20|cm|in|abbr=on}} high, is composed of fat bound together by fibrous tissue.
The '''dromedary''' ({{IPAc-en|ˈ|d|r|ɒ|m|ə|d|ɛ|ɹ|i}} or {{IPAc-en|-|ə|d|r|i}}), also called the '''Arabian [[camel]]''' or the '''Indian camel''' (''Camelus dromedarius''), is a large, [[even-toed ungulate]] with one hump on its back. First described by [[Aristotle]], the dromedary was given its binomial name by Carl Linnaeus in 1758. The dromedary is the next largest member of the camel family after the [[Bactrian camel]]{{Citation needed|date=November 2013}}. The oldest known ancestor of the dromedary is the ''[[Protylopus]]''. Males are {{convert|1.8|–|2|m|ft|abbr=on}} tall and females are {{convert|1.7|–|1.9|m|ft|abbr=on}} tall. Males range from {{convert|400|–|600|kg|lb|abbr=on}}, while females weigh {{convert|300|-|540|kg|lb|abbr=on}}. They vary in colour from a light beige to dark brown. The notable hump, measuring {{convert|20|cm|in|abbr=on}} high, is composed of fat bound together by fibrous tissue.


Their diet includes foliage and desert vegetation, like thorny plants which their extremely tough mouths allow them to eat. These camels are active in the day, and rest together in groups. Led by a dominant male, each herd consists of about 20 individuals. Some males form bachelor groups. Dromedaries show no signs of territoriality, as herds often merge during calamities. Predators in the wild include wolves, lions, and tigers. Dromedaries use a wide set of vocalizations to communicate with each other. They have various adaptations to help them exist in their desert habitat. Dromedaries have bushy eyebrows and two rows of long eyelashes to protect their eyes, and can close their nostrils to face sandstorms. Their ears are also lined with protective hair.<ref>http://enchantedlearning.com</ref> When water-deprived, they can fluctuate their body temperature by 6°C, changing from a morning minimum of 34° to a maximum of 40° or so in the afternoon. This reduces heat flow from the environment to the body and thereby water loss through perspiration is minimised. They have specialized kidneys, which make them able to tolerate water loss of more than 30% of their body mass; a loss of 15% would prove fatal in most other animals.<ref>http://www.science.smith/edu</ref> Mating usually occurs in winter, often overlapping the rainy season. One calf is born after the gestational period of 15 months, and is nurtured for about two years.
Their diet includes foliage and desert vegetation, like thorny plants which their extremely tough mouths allow them to eat. These camels are active in the day, and rest together in groups. Led by a dominant male, each herd consists of about 20 individuals. Some males form bachelor groups. Dromedaries show no signs of territoriality, as herds often merge during calamities. Predators in the wild include wolves, lions, and tigers but because of the large range the main predators of dromedaries varies greatly. Dromedaries use a wide set of vocalizations to communicate with each other. They have various adaptations to help them exist in their desert habitat. Dromedaries have bushy eyebrows and two rows of long eyelashes to protect their eyes, and can close their nostrils to face sandstorms. Their ears are also lined with protective hair.<ref>http://enchantedlearning.com</ref> When water-deprived, they can fluctuate their body temperature by 6°C, changing from a morning minimum of 34° to a maximum of 40° or so in the afternoon. This reduces heat flow from the environment to the body and thereby water loss through perspiration is minimised. They have specialized kidneys, which make them able to tolerate water loss of more than 30% of their body mass; a loss of 15% would prove fatal in most other animals.<ref>http://www.science.smith/edu</ref> Mating usually occurs in winter, often overlapping the rainy season. One calf is born after the gestational period of 15 months, and is nurtured for about two years.


The dromedary's origin is unclear, but it was probably domesticated in Somalia or Arabian Peninsula about 4000 years ago, with a general agreement among experts about the domestication of the one-humped camel.<ref>{{cite book |author=Richard, Suzanne |title=Near Eastern Archaeology: A Reader |year=2003 |url=http://books.google.co.uk/books?id=khR0apPid8gC&pg=PA120|publisher=Eisenbrauns |page=120 |isbn=}}</ref> The [[domestication|domesticated]] form occurs widely in Horn of Africa, North Africa, South Asia, and the Middle East. Today, almost 13 million dromedaries are domesticated. They are beneficial as [[Working animal|beasts of burden]], and their docility and toughness compared to cattle are additional advantages. The hair is a highly regarded source material for woven goods. Another useful feature is their dung which can be used as fertiliser and fuel.
The dromedary's origin is unclear, but it was probably domesticated in Somalia or Arabian Peninsula about 4000 years ago, with a general agreement among experts about the domestication of the one-humped camel.<ref>{{cite book |author=Richard, Suzanne |title=Near Eastern Archaeology: A Reader |year=2003 |url=http://books.google.co.uk/books?id=khR0apPid8gC&pg=PA120|publisher=Eisenbrauns |page=120 |isbn=}}</ref> The [[domestication|domesticated]] form occurs widely in Horn of Africa, North Africa, South Asia, and the Middle East. Today, almost 13 million dromedaries are domesticated. They are beneficial as [[Working animal|beasts of burden]], and their docility and toughness compared to cattle are additional advantages. The hair is a highly regarded source material for woven goods. Another useful feature is their dung which can be used as fertiliser and fuel.

Revision as of 08:00, 13 June 2014

For the world music group, see Dromedary (band).

Dromedary camel
Scientific classification Edit this classification
Missing taxonomy template (fix): Camelus dromedarius
Binomial name
Camelus dromedarius
Domestic dromedary range
Synonyms
Species synonymy[1]
  • *Camelus aegyptiacus Kolenati, 1847
  • *Camelus africanus Gloger, 1841
  • *Camelus arabicus Desmoulins, 1823
  • *Camelus dromas Pallas, 1811
  • *Camelus dromos Kerr, 1792
  • *Camelus ferus Falk,1786
  • *Camelus lukius Kolenati, 1847
  • *Camelus polytrichus Kolenati, 1847
  • *Camelus turcomanichus J. Fischer, 1829
  • *Camelus vulgaris Kolenati, 1847

The dromedary (/ˈdrɒmədɛri/ or /-ədri/), also called the Arabian camel or the Indian camel (Camelus dromedarius), is a large, even-toed ungulate with one hump on its back. First described by Aristotle, the dromedary was given its binomial name by Carl Linnaeus in 1758. The dromedary is the next largest member of the camel family after the Bactrian camel[citation needed]. The oldest known ancestor of the dromedary is the Protylopus. Males are 1.8–2 m (5.9–6.6 ft) tall and females are 1.7–1.9 m (5.6–6.2 ft) tall. Males range from 400–600 kg (880–1,320 lb), while females weigh 300–540 kg (660–1,190 lb). They vary in colour from a light beige to dark brown. The notable hump, measuring 20 cm (7.9 in) high, is composed of fat bound together by fibrous tissue.

Their diet includes foliage and desert vegetation, like thorny plants which their extremely tough mouths allow them to eat. These camels are active in the day, and rest together in groups. Led by a dominant male, each herd consists of about 20 individuals. Some males form bachelor groups. Dromedaries show no signs of territoriality, as herds often merge during calamities. Predators in the wild include wolves, lions, and tigers but because of the large range the main predators of dromedaries varies greatly. Dromedaries use a wide set of vocalizations to communicate with each other. They have various adaptations to help them exist in their desert habitat. Dromedaries have bushy eyebrows and two rows of long eyelashes to protect their eyes, and can close their nostrils to face sandstorms. Their ears are also lined with protective hair.[2] When water-deprived, they can fluctuate their body temperature by 6°C, changing from a morning minimum of 34° to a maximum of 40° or so in the afternoon. This reduces heat flow from the environment to the body and thereby water loss through perspiration is minimised. They have specialized kidneys, which make them able to tolerate water loss of more than 30% of their body mass; a loss of 15% would prove fatal in most other animals.[3] Mating usually occurs in winter, often overlapping the rainy season. One calf is born after the gestational period of 15 months, and is nurtured for about two years.

The dromedary's origin is unclear, but it was probably domesticated in Somalia or Arabian Peninsula about 4000 years ago, with a general agreement among experts about the domestication of the one-humped camel.[4] The domesticated form occurs widely in Horn of Africa, North Africa, South Asia, and the Middle East. Today, almost 13 million dromedaries are domesticated. They are beneficial as beasts of burden, and their docility and toughness compared to cattle are additional advantages. The hair is a highly regarded source material for woven goods. Another useful feature is their dung which can be used as fertiliser and fuel.

Etymology

The scientific name of the dromedary is Camelus dromedarius, which could be based on the Greek δρομὰς κάμηλος (dromas kamelos), meaning 'running camel'.[5] The Babylonians and Assyrians were the first to refer to the dromedary as gammalu, similar to the word gâmâl used in the Hebrew Bible (e.g. Gen 24:64Gen 31:34), and the Arabic word Jimal.[6]

The term "dromedary" comes from the Old French word dromedaire, or the Latin word dromedarius, which means 'swift'. It is based on the Greek word dromas (GEN dromados), meaning "runner".[7][8] An early variant of this word was 'drumblediary' (used in the 1560s).[9] The term "camel" is derived via Latin and Greek from Hebrew or Phoenician gāmāl, possibly from a verb root meaning 'to bear/carry' (related to Arabic ǧamala).[10] A northern oïl dialect, such as Old Norman or Old Picard, could have also been an intermediate, where the word for "camel" was camel (compare Old French chamel, modern French chameau).[11] The word "dromedary" has been used in English since the 14th century CE.[12] Aristotle called the dromedary "the camel of the Arabians".[13]

Taxonomy and genetics

The dromedary is a member of the genus Camelus and the family Camelidae. Macedonian philosopher Aristotle was the first to describe two species of camel, the dromedary and the Bactrian camel. He defined them as one-humped and two-humped respectively in his book History of Animals.[6][14] The dromedary was given its current binomial name Camelus dromedarius by Carl Linnaeus, a Swedish botanist, physician, and zoologist, in his 1758 Systema Naturae.[1]

British veterinarian Arnold Leese had classified dromedaries on the basis of their habitat into three groups: hill camels, plains camels, and camels that could survive in conditions between the hills and the plains.[15] Today, as both the dromedary and the Bactrian camel interbreed successfully, some authors have considered merging them into one species with two varieties on the basis of hybrid fertility.[15] However, mitochondrial analysis shows the species are differentiated by 10.3%.[16] Some evidence also indicates the onset of speciation in Camelus started in the early Pliocene.[16]

The dromedary has 74 chromosomes, the same as other camelids. No karyotypic differences exist among the camels.[15] The autosomes consist of five pairs of small to medium-sized metacentrics and submetacentrics, in which the X chromosome is the largest. There are 31 pairs of acrocentrics.[17]

Hybrids

The origin of camel hybridization dates back to as early as the first millennium BCE.[18] Some hybrids have been formed with the dromedary, but none proved to be viable.

For about 1000 years, though, Bactrian and dromedary camels have been successfully bred to form hybrids which are characterized by either a long and slightly lopsided hump, or two humps - one small and one large. These hybrids are larger and stronger than their parents — they can bear more load and thus are more useful.[17][18] A cross between a first-generation female hybrid and a male Bactrian camel also produces a useful hybrid. Other types of hybrids, though, tend to be bad-tempered or runts.[17]

Evolution

The extinct Protylopus, which occurred in the upper Eocene in North America, is both the oldest and the smallest camel known. In the transitional period from Pliocene to Pleistocene, the Camelus species migrated across the Bering Strait and dispersed widely to Asia, eastern Europe, and Africa.[17] By the Pleistocene, ancestors of the dromedary came to be known from the Middle East and North Africa.[19]

The ancient fossils of C. sivalensis and C. antiquus have been traced in the Shiwalik Hills in India. Fossils of subgenus Paracamelus were found in western Siberia, China, near the Sea of Azov, and the northern coast of the Black Sea. In the Pliocene, Camelus species ranged much farther south in Africa, and in northern Africa, remains of C. thomasi have been found. The dromedary possibly had origins in Arabia and is therefore sometimes referred to as the Arabian camel. A jawbone of a dromedary, whose radiocarbon date was 8200 BP and calibrated 7100-7200 BC, was found on the southern coast of the Red Sea in Saudi Arabia.[20][21]

History

This woodcut is an illustration of the dromedary camel from the book The History of Four-Footed Beasts and Serpents by Edward Topsell.

The Book of Genesis implies the dromedary was used by nomadic tribes in the second millennium BCE, but the book was composed at a later time, so the information cannot be corroborated.[6] Scholars have dated the spread of dromedaries to the first centuries AD, before the arrival of the Romans.[22] The Persian invasion of Egypt under Cambyses in 525 BC introduced domesticated camels to the area. The Persian camels, however, were not particularly suited to trading or travel over the Sahara; rare journeys made across the desert were made on chariots pulled by horses.[23]

The dromedaries became common after the Islamic conquest of North Africa. While the invasion was accomplished largely on horseback, the new links to the Middle East allowed camels to be imported en masse. These camels were well-suited to long desert journeys and could carry a great deal of cargo, allowing substantial trade over the Sahara for the first time.[24][25] In Libya, they were used for transportation within the country, and their milk and meat constituted the local diet.[26]

In the mid-seventh century, the dromedary was first used in warfare when the Achaemenid king, Cyrus the Great, made use of these animals while fighting with King Croesus of Lydia in 547 BC. Since then, the Persians, Seleucideans, Alexander the Great, Parthians, and Sasanians also used dromedaries in warfare. They were also used for the same means in the eastern provinces of Egypt, Arabia, Judaea, Syria, Cappadocia, and Mesopotamia.[6]

Domesticated camel calves in Dubai

In 1840, about six camels were shipped from Tenerife to Adelaide, but only one survived the trip, arriving on October 12, 1840. He was called Harry and was owned by the explorer John Ainsworth Horrocks. Although Harry had proved to be bad tempered, he was still used in the following year's expedition because of his load-carrying capability. However, a month into this trip, Horrocks had dismounted from the supine camel to shoot a prized bird. As he was loading his gun alongside him, Harry lurched against him, catching his pack against the gun lock, making it discharge and shooting Horrocks in the finger, the bullet then entering his cheek. He died some three weeks later from his infected injuries.[27] The next major group of camels were imported in 1860 and between 1860 and 1907 some 10 to 12 thousand were imported.[28] These were used mainly for riding and transportation.[29] An estimated one million feral camels now live in Australia.[29]

Domestication

Dromedaries were first domesticated in central or southern Arabia, thought to be around 4000 years ago. In the 9th or 10th century BCE, the animal became popular in the Near East. Today, almost 13 million domesticated dromedaries exist, found mainly from western India via Pakistan through Iran to north Africa.[30][31]

Description

Skeleton
The skeleton structure of a dromedary
Body
Dromedary body for comparison with skeleton

The dromedary is the largest camelid, next to the Bactrian camel. Adult male dromedaries grow to a height of 1.8–2 m (5.9–6.6 ft) and females to 1.7–1.9 m (5.6–6.2 ft). Their weight is usually in the range of 400–600 kg (880–1,320 lb) for males and 300–540 kg (660–1,190 lb) for females. The dromedary broadly overlaps in size with the Bactrian, though is perhaps slightly smaller on average, as male Bactrian camels regularly exceed 600 kg (1,300 lb). Very large male dromedaries, however, can weigh as much as 1,000 kg (2,200 lb).[32][33]

Their coats can range from dark brown to a much lighter sandy beige colour, and hair is concentrated more on the neck, hump, and shoulder. The male dromedary has a soft palate, called dulaa in Arabic, which it inflates to produce a deep pink sac. This palate is often mistaken for the tongue, as it hangs out of the side of the male's mouth to attract females during the mating season. Dromedaries are also noted for their thick eyelashes and bushy eyebrows. The hump, which can be 20 cm (7.9 in) tall or more, is made up of fat bound together by fibrous tissue.[17] The dromedary has long and powerful legs with two toes on each foot, which resemble flat, leathery pads. Unlike many other animals, camels move both legs on one side of the body at the same time, giraffes also move like this, which results in a swaying motion. They can adapt their body temperature from 34°C to 41.7°C, to conserve water.[34] The dromedary camel exhibits sexual dimorphism, as both sexes are quite different in their appearance.[34] They have sharp eyesight and a good sense of smell.[21] The cranium has a well-composed sagittal crest, long facial part, and an indented nasal bone.[17] They have an average lifespan of 40 years,[32] which can be extended to 50 years in captivity.[34]

Anatomy

The dromedary has 22 milk teeth, which are eventually replaced by 34 permanent teeth.[35] The lenses of their eyes contain crystallin, which constitutes 8-13% of the total protein present there.[36] The epidermis is 0.038–0.064 mm (0.0015–0.0025 in) thick, and the dermis is 2.2–4.7 mm (0.087–0.185 in) thick. Though glands are absent on the face, males have glands 5–6 cm (2.0–2.4 in) below the neck crest, on either side of the midline of the neck. These seem to be modified apocrine sweat glands which secrete a smelly, coffee-coloured fluid during rut. The females have mammary glands, four-chambered and cone-shaped, which are 2.4 cm (0.94 in) in length and 1.5 cm (0.59 in)in diameter at the base. They can continue to lactate even during dehydration, with the water content exceeding 90%.[17]

The heart is 5 kg (11 lb) in weight, and has two ventricles with the apex curving to the left. Its pulse rate is 50 beats per minute. The normal blood volume is 0.093 L (0.025 US gal). The lungs are not lobed, and a dehydrated camel has a lower breathing rate. The kidneys each have a volume of 858 cm3, and can produce urine with high chloride concentrations. It is the only mammal with oval red blood corpuscles, and it lacks a gall bladder. The liver is divided into four parts and is triangular; the dimensions are 60×42×18 cm (23.6×16.5×7.1 in) and has a mass of 6.5 kg (14 lb). The spinal cord averages 213.6 cm (84.1 in) in length, ending at the second and third sacral vertebrae.[17]

The ovaries, present in females, are reddish in colour, circular, and flattened. They are enclosed in a conical bursa, and have a size of 4×2.5×0.5 cm (1.57×0.98×0.20 in) during anestrus. The oviducts are 25–28 cm (9.8–11.0 in) in length. The uterus is bicornuate. The vagina is 3–3.5 cm (1.2–1.4 in) in length. The vulva is 3–5 cm (1.2–2.0 in) deep and contains a small clitoris. The placenta is diffuse and epitheliochorial with a crescent-like chorion. The scrotum, present in males, is located high in the perineum with testicles in separate sacs. Testicles are 7–10 cm (2.8–3.9 in) long, 4.5 cm (1.8 in) deep and 5 cm (2.0 in) in width. The right testicle is often smaller than the left.[35] During the rut, the mass of both testicles ranges from 165–253 g (0.364–0.558 lb), otherwise it is less than 140 g (0.31 lb). The prostate gland is dark yellow, usually disc-shaped and divided into two lobes. The Cowper's gland is white, shaped like an almond, and lacks seminal vesicles. The penis is covered by a triangular penile sheath opening backwards,[37] and is about 60 cm (24 in) long.[17]

Diseases and parasites

The dromedary is prone to trypanosomiasis, a parasitic disease caused by various species of the genus Trypanosoma and transmitted by the tsetse fly. The main symptoms are recurring fever, anemia, and weakness, which usually ends with the camel's death.[17] Brucellosis is another disease of dromedaries. In an observational study, the seroprevalence of the disease was usually low (2-5%) in nomadic or loosely confined dromedaries, while it was high (8-15%) in those kept closely together. Brucellosis is caused by different biotypes of Brucella abortus and Brucella melitensis.[38] Other internal parasites include Fasciola gigantica, a trematode (flatworm); two types of cestode (tapeworm), and various nematodes (roundworms). Among external parasites, Sarcoptes species cause sarcoptic mange.[17] In a study in Jordan, 83% of the 32 camels tested positive for sarcoptic mange, and 33% of the 257 examined specimens were seroprevalent for trypanosomiasis.[39] In another study, following the rinderpest outbreak in Ethiopia, dromedaries were found to have natural antibodies against rinderpest virus and ovine rinderpest virus.[40]

Fleas and ticks are common and widespread causes of physical irritation. In a study in Egypt, 2,545 ticks (1491 adults and 1054 nymphs) were collected from dromedaries. The range of the number of ticks per camel was broad (6 to 173). A species of Hyalomma specific to the dromedary was predominant, with 95.6% of the adult ticks belonging to this species. Other ticks found were also species of Hyalomma. In Israel, the number of ticks per camel ranged from 20 to 105. Nine camels in the date palm plantations in Arava Valley were injected with ivermectin, but it was not effective against Hyalomma tick infestations.[41]

Larvae of Cephalopsis titillator known as the camel nasal fly, can cause brain compression and nervous disorders, which can prove fatal. Illnesses that can affect dromedary productivity are pyogenic diseases and wound infections due to Corynebacterium and Streptococcus; pulmonary disorders caused by Pasteurella (like hemorrhagic septicemia), and Rickettsia ; camelpox caused by the camelpox virus; anthrax due to Bacillus anthracis, and cutaneous necrosis due to Streptothrix and dietary salt deficiency.[17]

In 2013 the dromedary was identified as a potential source of infection with Middle East Respiratory Syndrome Coronavirus (MERS-CoV), a recently discovered respiratory virus that can cause severe lower respiratory tract infection in humans. MERS-CoV was identified in 3 camels in a herd in Qatar in a barn, which was linked to two confirmed human cases who have since recovered. The presence of MERS-Cov in the camels was confirmed by the National Institute of Public Health and Environment (RIVM) of the Ministry of Health and the Erasmus Medical Center (WHO collaborating center), the Netherlands. None of the camels showed any sign of disease when the samples were collected. The Qatar Supreme Council of Health advised that people with underlying health conditions, such as heart disease, diabetes, kidney disease, respiratory disease, the immunosuppressed, and the elderly, avoid any close animal contacts when visiting farms and markets, and to practice good hygiene, such as washing hands.[42]

Ecology

Herd of dromedaries in Israel

In summers, the dromedaries, usually diurnal, rest together in closely packed groups. Generally, herds consist of about 20 individuals, led by a dominant male and consisting of several females. Females also lead in turns.[17] Some males either form bachelor groups or roam alone. Groups are not territorial, and form herds of over hundreds of animals, joining other herds during natural calamities and when searching for water.[32] During the breeding season, males become very aggressive, sometimes snapping each other and wrestling, while defending the females with them. The male declares his success in the fight by placing the rival's head between his legs and body. Free-ranging camels face the large predators typical of their regional distribution, which include wolves, lions, tigers, and humans. Camels are often injured or killed by moving vehicles.[43]

Behavior

Some special behavioral features of the camel include snapping each other without biting, showing displeasure by stamping its feet, and running and occasionally vomiting cud when hurt or excited. They prefer walking in a single file[citation needed]. Camels find comfort in scratching parts of their bodies with their front or hind legs or with their lower incisors. They are also seen rubbing against tree bark and rolling in the sand. Their main vocalizations include a sheep-like bleat used to locate individuals and the breeding gurgle of males, while a whistling noise is produced as a threat noise by males by grinding the teeth together.[34] They are not usually aggressive, with the exception of rutting males. The males of the herd prevent their females from interacting with other bachelor males by standing or walking between them and driving other males away. Camels seem to remember their homes; females in particular remember the place they first gave birth or suckled their offspring. They do not defecate in any special posture, and marking behavior is common.[17]

A 1980 study found androgen levels in the blood of males influenced their behavior. Between January and April, when these levels are high due to their being in rut, they become difficult to manage, blow out a palate flap from the mouth, vocalize, and throw urine over their backs with their tails.[44]

Diet

Dromedaries are herbivores.

The diet of the camel mostly consists of foliage, dry grasses, and available desert vegetation, mostly thorny plants growing in the camel's natural habitat.[45] These comprise 70% of their diet in summer and 90% in winter. In the Sahara, 332 plant species have been recorded for the dromedary. The dromedary will feed on Acacia, Artiplex, and Salsola plants whenever available.[17]

They keep their mouths open while chewing thorny food. They use their lips to grasp the food, then chew each bite 40-50 times. Features like long eyelashes, eyebrows, lockable nostrils, caudal opening of the prepuce and a relatively small vulva help the camel avoid injuries, especially while feeding.[45]

Adaptations

Dromedary footprint on dry sand

Dromedaries have several adaptations for their desert habitat. Bushy eyebrows, a double row of eyelashes, and the ability to close their nostrils assist in water conservation and prevent sand and dust from entering, even in a sandstorm. Dromedaries can conserve water by fluctuating their body temperature throughout the day from 34.0 to 41.7°C, which saves water by avoiding perspiration at the rise of the external temperature. The kidneys are specialized so that not much water is excreted. Groups of camels also avoid excess heat from the environment by pressing against each other.[32] The dromedary can tolerate greater than 30% water loss, which is impossible for other mammals. In temperatures of 30-40°C (86-104°F), they need water every 10 to 15 days, and only in the hottest temperatures do they take water every four to seven days. They have a very fast rate of rehydration and can drink at the speed of 10–20 L (2.6–5.3 US gal) per minute.[17] Maintaining the brain temperature within certain limits is critical for animals; to assist this, dromedaries have a rete mirabile, a complex of arteries and veins lying very close to each other which uses countercurrent blood flow to cool blood flowing to the brain.[46]

The hump stores up to 80 lb (36 kg) of fat, which a camel can break down into water and energy when sustenance is not available. If the hump is small, the animal can show signs of starvation. In a 2005 study, the mean volume of adipose tissues (in the external part of the hump that have cells to store lipids) is related to the dromedary's unique mechanism of food and water storage.[47] In case of starvation, they can even eat fish and bones, and drink brackish and salty water.[21] The hair is longer at the throat, hump and shoulders. The pads widen under its weight when it steps on the ground.[34][48] This prevents the dromedary from sinking much into the sand. When the dromedary walks, it moves both the feet on the same side of the body at the same time. This way of walking makes the dromedary's body swing from side to side as it walks, hence its nickname: "the ship of the desert". Its thick lips help in eating coarse and thorny plants.[32]

Reproduction

Camel calf feeding on her mother's milk

Females reach sexual maturity around three years of age and mate around age four or five. Males begin to mate at around three years of age, too, but still are not sexually mature until six years of age. Mating occurs in winters, but peaks in the rainy season. The onset of the breeding season is believed to be cued by nutritional status of the camel and the daylength.

If mating does not occur, the follicle, which grows during estrus, usually regresses within a few days.[49] In one study, 35 complete estrous cycles were observed in five nonpregnant females over a period of 15 months. The cycles were about 28 days long, in which follicles matured in six days, maintained their size for 13 days, and returned to their original size in eight days.[50] In another study, ovulation could be best induced when the follicle reaches a size of 0.9–1.9 cm (0.35–0.75 in).[51] In another study, pregnancy in females could be recognized as early as 40 to 45 days of gestation by the swelling of the left uterine horn, where 99.52% of pregnancies were located.[52]

During the reproductive season, males splash their urine on their tails and nearer regions. Males also extrude their soft palate. Copious saliva turns to foam as the male gurgles, covering the mouth.[34] Males threaten each other for dominance over the female by trying to stand taller than the other, making low noises and a series of head movements including lowering, lifting, and bending their necks backwards. A male tries to defeat other males by biting at his legs and taking the opponent's head in between his jaws.[34] Copulation begins with a necking exercise. The male smells the female's genitals, and often bites her in this region or around her hump. The male makes the female sit, and then grasps her with his forelegs. Normally, three to four ejaculations occur. The camelmen often aid the male to enter his penis into the female's vulva, though the male is considered able to do it on his own. Copulation time ranges from 7–35 minutes, averaging 11–15 minutes.[53]

A single calf is born after a gestational period of 15 months. Calves move freely by the end of their first day. Nursing and maternal care continue for one to two years.[34] In a study to find whether young could exist on milk substitutes, two male young camels, one month old, were separated from their mothers and were fed on milk substitutes prepared commercially for lambs. For the initial 30 days, the changes in their weights were marked. Each gained 0.400 kg (0.88 lb) and 1 kg (2.2 lb), respectively, per day. Finally, they were found to have grown properly and weighed normal weights of 135 kg (298 lb) and 145 kg (320 lb).[54]

Habitat and distribution

Dromedary camels in dunes of Genipabu Beach (Brazil)

The dromedary occupies arid regions, notably the Sahara Desert in Africa. The original range of the camel’s wild ancestors was probably south Asia and the Arabian peninsula.[32] They inhabit the dry, hot regions of North Africa, Ethiopia, the Near East, and western to central Asia.[55] All African camels are dromedaries, of which 84% occur in Somalia, Ethiopia, Sudan, Djibouti and Kenya,[17] which constitutes 60.1% of the world's whole camel population.[56] In the Horn of Africa, the dromedary can occur as far south as 2°S, where the annual rainfall may be 550 mm (22 in). The dromedary overlaps in distribution with the Bactrian camel in Afghanistan, Pakistan, and southwest Asia.[57] Richard Bulliet has observed that dromedaries exist where the Bactrian camel do not, and Bactrian camels exist where dromedaries do not. He concluded this can be because the nomads of Syrian and Arabian deserts valued the dromedary more, whereas Asiatic people preferred the Bactrian camel.[56]

Commonly found in African, Arabian, Indian, and Middle Eastern deserts, where all dromedaries are domesticated, they number about 15 million.[32] The dromedary camel is also found in feral populations in northern Australia, where it was introduced in 1840.[32][58] Populations survive in the Canary Islands, where they were exported in 1405. Attempts had been made to introduce dromedaries into the Caribbean, Colombia, Peru, Bolivia, and Brazil; some were imported to the western United States in the 1850s and some to Namibia in the early 1900s, but today they exist in none of these areas.[17] Short-term home ranges of feral camels in Australia are 50-150 square km, and annual home ranges are estimated to be several thousand kilometres.[17]

Uses

Dromedaries at Bait al-Faqih market, Yemen

Dromedaries are used as beasts of burden in most of their domesticated range. Unlike horses, they kneel for the loading of passengers and cargo. A camel can carry an estimated 159–295 kg (351–650 lb) for 24 km (15 mi) for a long time. Camels can be trained to bear loads from five years of age, but must not be given a large load until six years old. Camels are usually patient animals, easier to train and tougher than cattle. Camels can also be used to pull carts, plows, and draw wheels. A dromedary can plow at a speed of 2.5 km (1.6 mi) per hour, but must not be worked for more than six hours a day. Their hair is durable and light, so it is used as a source material for woven goods, ranging from Bedouin tents to garments. The hair is clipped off using hand shears, or sometimes simply pulled, after which the camel's body is oiled. Juveniles less than two years of age have a fine undercoat, which is also used for these purposes. They also give wool. The wool produce of a herd of 4300 dromedaries in Russia in 1970 and 1974 was 557 kg (1,228 lb) and 576 kg (1,270 lb), respectively.[59]

Dairy products

Dromedary milking in Niger
Main article: Camel milk

Camel milk is a staple food of desert nomad tribes. According to a study, it consists of 11.7% total solids, 3% protein, 3.6% fat, 0.8% ash, 4.4% lactose, and 0.13% acidity (pH of 6.5). The quantities of sodium, potassium, zinc, iron, copper, manganese, niacin and vitamin C were relatively higher than the amounts in cow's milk. At the same time, levels of thiamin, riboflavin, folacin, vitamin B12, pantothenic acid, vitamin A, lysine, and tryptophan were lower than those in cow's milk. The molar percentages of the fatty acids in milk fat were 26.7% for palmitic acid, 25.5% oleic acid, 11.4% myristic acid, and 11% palmitoleic acid.[60] Camel milk has higher heat stability compared to cow's milk.[61]

Daily yield generally varies from 3.5–35 kg (7.7–77.2 lb) and from 1.3 to 7.8% of the body weight.[62] Amount of milk yield and milking frequency in dromedaries varies geographically, and depends upon their diet and living conditions. For example, Adal camels yield a maximum of 10.4 kg (23 lb) a day, while the Pakistani dromedary, considered a better milker and bigger, can yield 9.1–14.1 kg (20–31 lb). Dromedaries in Murrah (Arabia) can be milked once a day, while those in Afar (Ethiopia) may be milked six or seven times a day. A healthy female can give 9 kg (20 lb) of milk per day during the peak of lactation. Lactational yield can vary with species, breed, and the general factors like region, diet, and lactating stage.[63]

Dromedary milk was studied to find its ability to form curd, in which catalysts were noted. Milk coagulation did not show actual curd formation, and had a pH of 4.4. It was much different from that of cow's milk, and had a fragile and heterogeneous structure perhaps composed of casein flakes.[64] Still today, cheese, even hard cheese, and other dairy products can be made out of the camel's milk. J. P. Ramet of the FAO has also succeeded in making cheese in 1987. A special factory has been set up in Nouakchott to pasteurize and make cheese out of camel's milk.[65]

Meat

Meat of dromedary served as food

Dromedary meat is a good source of food, composed of 78% water, 19% protein, 3% fat, and 1.2% ash. The carcass is composed of 57% muscle, 26% bone, and 17% fat. Seven- to eight-year-old camels can produce a carcass of weight of 125–400 kg (276–882 lb). The meat is a raspberry red to a dark brown or maroon, while the fat is white in colour. It tastes like beef and has the same texture.[66] Dromedaries can increase their weight by 500 g (1.1 lb) every day. In modern times, camel meat is processed into food items such as burgers, patties, sausages, and shawarma.[66]

In a study of the fatty acid composition of raw meat taken from the hind legs of seven young males (one to three years old), 51.5% were saturated fatty acids, 29.9% were monounsaturated, and 18.6% were polyunsaturated fatty acids, in chains. The major fatty acids in the meat were palmitic acid (26.0%), oleic acid (18.9%), and linoleic acid (12.1%). In the hump, palmitic acid was dominant (34.4%), followed by oleic acid (28.2%), myristic acid (10.3%), and stearic acid (10%).[67]

A 2005 report, issued jointly by the Saudi Ministry of Health and the United States Centers for Disease Control and Prevention, details five cases of bubonic plague in humans, resulting from the ingestion of raw camel liver. Four of the five patients had severe pharyngitis and submandibular lymphadenitis. Yersinia pestis was isolated from the camel's bone marrow, as well as from the jird (Meriones libycus) and also from fleas (Xenopsylla cheopis) captured at the camel's corral.[68]

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