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In addition to their elongated cervical vertebrae, giraffes have their point of articulation between the cervical and thoracic vertebrae is shifted to lie between [[Thoracic spinal nerve 1|T1]] and [[Thoracic spinal nerve 2|T2]], the first and second [[thoracic vertebrae]], rather than between [[Cervical spinal nerve 7|C7]] and T1, as in most other ruminants.<ref name=bada/><ref name=van/> This allows C7 to contribute directly to increased neck length, and has sparked the suggestion that T1 is actually C8, and giraffes have added an extra cervical vertebra.<ref>Solounias, N. (1999). [http://www.ikhebeenvraag.be/mediastorage/FSDocument/73/download.pdf "The remarkable anatomy of the giraffe's neck"]. ''Journal of Zoology'' '''247'''(2):257–268 [[doi]]:[http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1999.tb00989.x/abstract 10.1111/j.1469-7998.1999.tb00989.x]</ref> However, this proposition is generally not accepted, as T1 has other morphological features, such as an articulating [[rib]], deemed diagnostic of thoracic vertebrae. Also, the exceptions to the mammalian [[vertebral column|constraint]] of seven cervical vertebrae are generally characterized by increased [[neurological disorder|neurological anomalies]] and maladies, symptoms that have not been observed in giraffes.<ref name=bada/> Because of its long neck, the giraffe inhales a lot of air that is not used for respiration and the windpipe contains a mix of inhaled and exhaled air with corresponding low oxygen levels. As such the giraffe must breath more regularly than expected for an animal of its size and takes more than 20 breaths a minute when resting.<ref name = "anatomy"/>{{rp|77}}
In addition to their elongated cervical vertebrae, giraffes have their point of articulation between the cervical and thoracic vertebrae is shifted to lie between [[Thoracic spinal nerve 1|T1]] and [[Thoracic spinal nerve 2|T2]], the first and second [[thoracic vertebrae]], rather than between [[Cervical spinal nerve 7|C7]] and T1, as in most other ruminants.<ref name=bada/><ref name=van/> This allows C7 to contribute directly to increased neck length, and has sparked the suggestion that T1 is actually C8, and giraffes have added an extra cervical vertebra.<ref>Solounias, N. (1999). [http://www.ikhebeenvraag.be/mediastorage/FSDocument/73/download.pdf "The remarkable anatomy of the giraffe's neck"]. ''Journal of Zoology'' '''247'''(2):257–268 [[doi]]:[http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1999.tb00989.x/abstract 10.1111/j.1469-7998.1999.tb00989.x]</ref> However, this proposition is generally not accepted, as T1 has other morphological features, such as an articulating [[rib]], deemed diagnostic of thoracic vertebrae. Also, the exceptions to the mammalian [[vertebral column|constraint]] of seven cervical vertebrae are generally characterized by increased [[neurological disorder|neurological anomalies]] and maladies, symptoms that have not been observed in giraffes.<ref name=bada/> Because of its long neck, the giraffe inhales a lot of air that is not used for respiration and the windpipe contains a mix of inhaled and exhaled air with corresponding low oxygen levels. As such the giraffe must breath more regularly than expected for an animal of its size and takes more than 20 breaths a minute when resting.<ref name = "anatomy"/>{{rp|77}}


There are two main hypotheses regarding the evolutionary origin and maintenance of elongation in giraffe necks.<ref name=sim2010>{{Cite journal | doi = 10.1111/j.1469-7998.2010.00711.x | last = Simmons | first = R. E.| coauthors = Altwegg, R. | title = Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe | journal = Journal of Zoology | volume = 282 | issue = 1 | pages = 6–12 | year = 2010}}</ref> The "competing [[browsing (predation)|browsers]] hypothesis" was originally suggested by [[Charles Darwin]] and only challenged recently. It suggests that competitive pressure from smaller browsers, such as [[kudu]], [[steenbok]], and [[impala]], drove the elongation of the neck so giraffes could reach nutrients competitors could not. This advantage is real – giraffes can and do feed up to 5&nbsp;m, while most of their competitors, [[kudu]], can only feed up to about 2&nbsp;m (7&nbsp;ft).<ref name=dt1990>{{Cite journal | doi = 10.1111/j.1365-2028.1990.tb01136.x | last = du Toit | first = J. T. | title = Feeding-height stratification among african browsing ruminants. | journal = African Journal of Ecology | volume = 28 | issue = 1 | pages = 55–62 | year = 1990}}</ref> There is also research suggesting that browsing competition below 2&nbsp;m is intense, and giraffes feed more efficiently (gaining more leaf biomass per bite) higher in the canopy.<ref>{{Cite journal|author= Cameron, E. Z.; du Toit, J. T. | title = Winning by a Neck: Tall Giraffes Avoid Competing with Shorter Browsers| journal = American Naturalist | volume = 169| issue = 1| pages = 130–135| year = 2007| doi = 10.1086/509940 |pmid= 17206591}}</ref><ref>{{Cite journal|author= Woolnough, A. P.; du Toit, J. T. | title = Vertical zonation of browse quality in tree canopies exposed to a size-structured guild of African browsing ungulates| journal = Oecologia | volume = 129| issue = 1| pages = 585–590| year = 2001}}</ref> However, scientists disagree about just how much time giraffes spend feeding at levels unreachable to other browsers.<ref name=sim2010/><ref name=dt1990/><ref name=sexdiff>{{Cite journal|doi= 10.1111/j.1439-0310.1991.tb01190.x |author= Young, T. P.; Isbell, L. A. | title = Sex differences in giraffe feeding ecology: energetic and social constraints| journal = Ethology | volume = 87| issue = 1-2| pages = 79–89| year = 1991 |dio = 10.1007/s004420100771}}</ref> Although giraffes can feed as low as 0.5&nbsp;m and as high as 6&nbsp;m off the ground, it appears that they most often feed between 2 and 4&nbsp;m (7–14&nbsp;ft).<ref name=sexdiff/>
There are two main hypotheses regarding the evolutionary origin and maintenance of elongation in giraffe necks.<ref name=sim2010>{{Cite journal | doi = 10.1111/j.1469-7998.2010.00711.x | last = Simmons | first = R. E.| coauthors = Altwegg, R. | title = Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe | journal = Journal of Zoology | volume = 282 | issue = 1 | pages = 6–12 | year = 2010}}</ref> The "competing [[browsing (predation)|browsers]] hypothesis" was originally suggested by [[Charles Darwin]] and only challenged recently. It suggests that competitive pressure from smaller browsers, such as [[kudu]], [[steenbok]], and [[impala]], drove the elongation of the neck so giraffes could reach nutrients competitors could not. This advantage is real – giraffes can and do feed up to 5&nbsp;m, while most of their competitors, [[kudu]], can only feed up to about 2&nbsp;m (7&nbsp;ft).<ref name=dt1990>{{Cite journal | doi = 10.1111/j.1365-2028.1990.tb01136.x | last = du Toit | first = J. T. | title = Feeding-height stratification among african browsing ruminants. | journal = African Journal of Ecology | volume = 28 | issue = 1 | pages = 55–62 | year = 1990}}</ref> There is also research suggesting that browsing competition below 2&nbsp;m is intense, and giraffes feed more efficiently (gaining more leaf biomass per bite) higher in the canopy.<ref>{{Cite journal|author= Cameron, E. Z.; du Toit, J. T. | title = Winning by a Neck: Tall Giraffes Avoid Competing with Shorter Browsers| journal = American Naturalist | volume = 169| issue = 1| pages = 130–135| year = 2007| doi = 10.1086/509940 |pmid= 17206591}}</ref><ref>{{Cite journal|author= Woolnough, A. P.; du Toit, J. T. | title = Vertical zonation of browse quality in tree canopies exposed to a size-structured guild of African browsing ungulates| journal = Oecologia | volume = 129| issue = 1| pages = 585–590| year = 2001| doi = 10.1007/s004420100771}}</ref> However, scientists disagree about just how much time giraffes spend feeding at levels unreachable to other browsers.<ref name=sim2010/><ref name=dt1990/><ref name=sexdiff>{{Cite journal|doi= 10.1111/j.1439-0310.1991.tb01190.x |author= Young, T. P.; Isbell, L. A. | title = Sex differences in giraffe feeding ecology: energetic and social constraints| journal = Ethology | volume = 87| issue = 1-2| pages = 79–89| year = 1991 |dio = 10.1007/s004420100771}}</ref> Although giraffes can feed as low as 0.5&nbsp;m and as high as 6&nbsp;m off the ground, it appears that they most often feed between 2 and 4&nbsp;m (7–14&nbsp;ft).<ref name=sexdiff/>


The other main theory, the [[sexual selection]] hypothesis, proposes that the long necks evolved as a secondary [[sexual dimorphism|sexual characteristic]], giving males an advantage in "necking" contests (see below) to establish dominance and obtain access to sexually receptive females.<ref name=sim1996>{{Cite journal|author=Simmons, R. E.; Scheepers, L. | title = Winning by a Neck: Sexual Selection in the Evolution of Giraffe| journal = The American Naturalist| volume = 148| issue = 5| pages = 771–786| year = 1996|url=http://bill.srnr.arizona.edu/classes/182/Giraffe/WinningByANeck.pdf|doi=10.1086/285955}}</ref> In support of this theory, males have proportionally larger necks than females,<ref name=sim2010/><ref name=sim1996/> and males with longer, bigger necks are more successful in dominance displays and courtship behavior.<ref name= "Pratt 1985"/> However, a major criticism of this theory is that it fails to adequately explain why female giraffes also have long necks.<ref>{{Cite journal|author= Mitchell, G.; van Sittert, S. J.; Skinner, J. D. | title = Sexual selection is not the origin of long necks in giraffes.| journal = Journal of Zoology | volume = 278| issue = 4| pages = 281–286| year = 2009| doi=10.1111/j.1469-7998.2009.00573.x}}</ref>
The other main theory, the [[sexual selection]] hypothesis, proposes that the long necks evolved as a secondary [[sexual dimorphism|sexual characteristic]], giving males an advantage in "necking" contests (see below) to establish dominance and obtain access to sexually receptive females.<ref name=sim1996>{{Cite journal|author=Simmons, R. E.; Scheepers, L. | title = Winning by a Neck: Sexual Selection in the Evolution of Giraffe| journal = The American Naturalist| volume = 148| issue = 5| pages = 771–786| year = 1996|url=http://bill.srnr.arizona.edu/classes/182/Giraffe/WinningByANeck.pdf|doi=10.1086/285955}}</ref> In support of this theory, males have proportionally larger necks than females,<ref name=sim2010/><ref name=sim1996/> and males with longer, bigger necks are more successful in dominance displays and courtship behavior.<ref name= "Pratt 1985"/> However, a major criticism of this theory is that it fails to adequately explain why female giraffes also have long necks.<ref>{{Cite journal|author= Mitchell, G.; van Sittert, S. J.; Skinner, J. D. | title = Sexual selection is not the origin of long necks in giraffes.| journal = Journal of Zoology | volume = 278| issue = 4| pages = 281–286| year = 2009| doi=10.1111/j.1469-7998.2009.00573.x}}</ref>

Revision as of 04:52, 2 November 2011

For other uses, see Giraffe (disambiguation).

Giraffe[1]
A giraffe in Mikumi National Park, Tanzania
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Artiodactyla
Family:
Giraffidae
Genus:
Giraffa
Species:
G. camelopardalis
Binomial name
Giraffa camelopardalis
Range map (Rothschild Giraffe, not marked on this map, is found in Uganda and west-central Kenya)

The giraffe (Giraffa camelopardalis) is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant. Its scientific name, which is similar to its archaic English name of camelopard, refers to its irregular patches of color on a light background, which bear a token resemblance to a leopard's spots, and its face, which is similar to that of a camel. The average mass for an adult male giraffe is 1,200 kilograms (2,600 lb) while the average mass for an adult female is 830 kilograms (1,830 lb).[3][4] It is approximately 4.3 meters (14 ft) to 5.2 metres (17 ft) tall, although the tallest male recorded stood almost 6 metres (20 ft).[3][4]

The giraffe is related to other even-toed ungulates, such as deer and cattle, but is placed in a separate family, the Giraffidae, consisting of only the giraffe and its closest extant relative, the okapi. Its range extends from Chad in Central Africa to South Africa. Giraffes usually inhabit savannas, grasslands, or open woodlands. However, when food is scarce they will venture into areas with denser vegetation. They prefer areas with plenty of acacia growth. They will drink large quantities of water when available, which enables them to live for extended periods in arid areas.

Etymology

The name "giraffe" has its earliest known origins in the Arabic word الزرافة al-zirāfah, perhaps from an African name. There were several Middle Eastern spellings such as jarraf, ziraph, and gerfauntz.[5] During the early The Italian form giraffa arose in the 1590's from Arabic.[5] It appears in English from the 16th century through the French girafe.[5] The species name camelopardalis (camelopard) is derived from its Latin name, where it was described as having characteristics of both a camel and a leopard.[6]

Taxonomy and evolution

The giraffe is one of only two living species of the family Giraffidae, along with the okapi. The family was once much more extensive, with over 10 fossil genera described. An early ancestor of the giraffids was a 3 m (9.8 ft) tall antelope-like mammal that roamed Europe and Asia some 30–50 million years ago (mya).[7] Closer ancestors of modern giraffes likely evolved 8 mya in southern central European, arising via the family Palaeomerycidae. Animals of the family Antilocapridae (survived by the pronghorn) and the giraffids arose from the palaeomerycids.[8] The earliest known giraffid was Climacoceras, which still resembled deer, having large antler-like ossicones. It first appeared in the early Miocene epoch. Later examples include the genera Palaeotragus (from which the okapi arose) and Samotherium, which appeared in the early-to-mid-Miocene. They were both tall at the shoulder, and had developed the simple, unbranched ossicones of modern giraffids, but still had relatively short necks.[9] From the late Pliocene onwards, the variety of giraffids drastically declined. The genus Bohlinia entered China and northern India due to climate change. From here, the genus Giraffa arose and included a number of long-necked species. Around 7 mya, Giraffa giraffes entered Africa through Ethiopia.[8] Further climate changes caused the extinction of the Asian giraffes while the African giraffes survived and radiated into several different species,[8] such as Giraffa jumae, which do not survive today.[9] G. camelopardalis arose around 1 mya in East Africa.[8]

The giraffe was one of the many species first described by Linnaeus in 1758. He gave it the binomial name of Cervus camelopardalis in the 10th edition of his Systema Naturae.[10] Brisson erected the genus Giraffa in 1762.[3]

Subspecies

Genetic subdivision in the giraffe based on mitochondrial DNA sequences[11]

Different authorities recognize different numbers of subspecies, differentiated by size, color and pattern variations and range.[1][2][12] Some of these subspecies may prove to be separate species[2] as they appear to be reproductively isolated despite their mobility.[11] The subspecies recognized by most recent authorities are:

  • G. c. camelopardalis,[13] the nominate subspecies, is known as the Nubian Giraffe. Its coat pattern has large, four-sided spots of chestnut brown on an off-white background and no spots on inner sides of the legs or below the hocks. It is found in eastern Sudan and northeastern DR Congo. It has been estimated that fewer than 250 remain in the wild, but little is known about this subspecies and consequently this estimate is labelled with great uncertainty.[14] It is very rare in captivity, although kept at Al Ain Zoo in the United Arab Emirates.[15]
  • G. c. reticulata,[13] known as the Reticulated[13] or Somali Giraffe, has a coat pattern of well defined patches that are usually bright orange-brown in colour.[16] These patches have sharp edges and are separated by bold, bright white lines.[16] It ranges from northeastern Kenya, into southern Ethiopia and Somalia. It has been estimated that fewer than 5.000 remain in the wild,[14] and based on ISIS records it is among the most common in zoos, with more than 450 kept.[17]
  • G. c. angolensis, the Angolan or Smoky Giraffe, has large spots with some notches around the edges, extending down the entire lower leg. It is found in southern Angola, northern Namibia, southwestern Zambia, Botswana and western Zimbabwe. It has been estimated that fewer than 20,000 remain in the wild,[14] and based on ISIS records approximately 20 are kept in zoos.[17]
  • G. c. antiquorum,[13] the Kordofan Giraffe, has smaller, more irregular spots that cover the inner legs. Its distribution includes southern Chad, Central African Republic and northern Cameroon. Populations in Cameroon were formerly included in G. c. peralta instead, but this was incorrect.[18] Fewer than 3,000 are believed to remain in the wild.[14] Considerable confusion has existed over the status of this subspecies and G. c. peralta in zoos. In 2007 it was shown that all "G. c. peralta" in European zoos actually are G. c. antiquorum.[18] Consequently, approximately 65 are kept in zoos based on ISIS records.[17]
  • G. c. tippelskirchi,[13] known as the Maasai Giraffe[13] or Kilimanjaro Giraffe, has jagged-edged, vine-leaf shaped spots of dark brown on a brownish-cream background.[16] It is the darkest coloured subspecies.[16] It occurs in central and southern Kenya and Tanzania. It is estimated that fewer than 40,000 remain in the wild,[14] and based on ISIS records approximately 100 are kept in zoos.[17]
  • G. c. rothschildi,[13] is known variously as the Rothschild Giraffe[13] or Baringo Giraffe or Ugandan Giraffe. Its coats bears deep brown, blotched or rectangular spots with poorly defined cream lines. Its legs are mostly white with no pattern.[16] Its range includes Uganda and west-central Kenya, especially near Lake Baringo. It may also occur in southern Sudan.[19] Fewer than 700 are believed to remain in the wild,[14] and based on ISIS records more than 450 are kept in zoos.[17]
  • G. c. giraffa, the South African Giraffe, has rounded or blotched spots, some with star-like extensions on a light tan background, running down to the hooves. It is found in northern South Africa, southern Botswana, southern Zimbabwe and southwestern Mozambique. It is estimated that fewer than 12,000 remain in the wild,[14] and based on ISIS records approximately 45 are kept in zoos.[17]
  • G. c. thornicrofti,[13] called the Thornicroft Giraffe[13] or Rhodesian Giraffe, has star-shaped or leafy spots extend to the lower leg. It is restricted to the Luangwa Valley in eastern Zambia. Fewer than 1,500 remain in the wild,[14] and based on ISIS records none are kept in zoos.[17]
  • G. c. peralta,[13] commonly known as the West African Giraffe[13] or Nigerian Giraffe, has numerous pale, yellowish red spots. It is endemic to southern Niger. With fewer than 220 individuals remaining in the wild, it is the rarest giraffe subspecies.[14] Giraffes in Cameroon were formerly believed to be this subspecies, but are actually G. c. antiquorum.[18] This has also resulted in some confusion over its status in zoos, but in 2007 it was established that all "G. c. peralta" kept in European zoos actually are G. c. antiquorum.[18]

Formerly, the Kordofan and West African Giraffes were regarded as a single subspecies, but genetic evidence has confirmed that they represent two separate subspecies.[18] Comparably, the Rothschild's Giraffe has been considered a hybrid population,[12] but genetic evidence has confirmed that it is a valid subspecies.[11] By contrast, scientists have proposed four other subspecies — Cape Giraffe (G. c. capensis), Lado Giraffe (G. c. cottoni), Congo Giraffe (G. c. congoensis), and Transvaal Giraffe (G. c. wardi) — but today none of these is widely accepted.[1] One genetic study on Smoky Giraffes suggests that the northern Namib Desert and Etosha National Park populations are distinct subspecies.[20]

Although giraffes of these populations interbreed freely under conditions of captivity, suggesting that they are subspecific populations, genetic testing published in 2007 has been interpreted to show that there may be at least six species of giraffe that are reproductively isolated and not interbreeding, even though no natural obstacles, like mountain ranges or impassable rivers block their mutual access. The study found that the two giraffe populations that live closest to each other— the reticulated giraffe (G. camelopardalis reticulata) of north Kenya, and the Masai giraffe (G. c. tippelskirchi) in south Kenya— separated genetically between 0.13 and 1.62 million years ago, judging from genetic drift in nuclear and mitochondrial DNA.[11]

The implications for conservation of as many as eleven such cryptic species and subspecies were summarised by David Brown for BBC News: "Lumping all giraffes into one species obscures the reality that some kinds of giraffe are on the brink. Some of these populations number only a few hundred individuals and need immediate protection."[21]

Anatomy and morphology

Giraffe skeleton on display by The Museum of Osteology, Oklahoma City, Oklahoma.

Male giraffes are up to 5.5 metres (18 ft) tall at the horn tips, and weigh between 800 and 1,930 kilograms (1,760 and 4,250 lb). Females are between 4 and 4.5 metres (13 and 15 ft) tall and weigh between 550 and 1,180 kilograms (1,210 and 2,600 lb). The coat is made up of brown blotches or patches separated by lighter hair. Each giraffe has a unique coat pattern.[22] Besides camouflage, the patches may serve as thermal windows, being the site of large blood vessels and large sweat glands.[23] The giraffe's fur may serve as a chemical defence, and is full of antibiotics and parasite repellents that give the animal a characteristic scent. Old males are sometimes nicknamed "stink bulls". There are at least eleven main aromatic chemicals in the fur, although indole and 3-methylindole are responsible for most of their smell. Because the males have a stronger odour than the females, it is also suspected that it has a sexual function.[24] Along the animal's neck is a mane which is about 12 centimetres (4.7 in) in adults.[3] The skull of the giraffe is lightened by large sinuses which exist in the upper part.[25]: 70 

Horns

Both sexes have prominent horns, formed from ossified cartilage and covered in skin, also known as ossicones. The appearance of horns is a reliable method of identifying the sex of giraffes, with the females displaying tufts of hair on the top of the horns, whereas males' horns are larger and tend to be bald on top — the hairs worn away due to necking in combat. Males sometimes develop calcium deposits which form bumps on their skull as they age, which can give the appearance of up to three additional horns.[26] The horns are well vascularized and may also have a thermoregulatory function.[23]

Legs, locomotion and posture

Giraffes have front legs which are about 10% longer than their hind legs. With the front legs, the radius and the ulna are articulated by the carpus which, while the equivalent of the human wrist, behaves like a knee.[25]: 70  True knees exist in the hind legs.[25]: 70  The hooves are quite large, being up to 6 inches across in males and up to 4 inches across in females.[25]: 68  The giraffe can reach a sprint speed of up to 60 km/h (37 mph)[27] but cannot sustain a lengthy chase. The apparent inflexibility of its legs give it a stiff gait when walking.[25]: 68  Walking is done with the legs on one side of the body moving together followed by the same being done by the legs on the other side.[25]: 72  When running the giraffe thrusts its front legs into the air and when they touch the ground they push off again.[28]: 15  When the hind legs land together the process begins again.[28]: 15  The giraffe is briefly airborne when running.[28]: 15  A giraffe can jump by pulling its neck back, which puts most of its weight over its hind legs, and then thrust it forward lifting its front legs and pushing off with its hind legs.[28]: 17  When it needs to bend down to drink, the giraffe employs two strategies: it may splay its legs apart or bend its front legs.[22] To lie down, a giraffe kneels on its front legs and then lowers the rest of its body down. To get up, the giraffe thrusts itself on its front "knees" with its neck and then raises its hindquaters and straightens its hind legs.[28]: 17  The giraffe has one of the shortest sleep requirements of any mammal, which averages only 4.5 or 4.6 hours per day.[29] A giraffe may sleep lying down and curled up.[22]

Giraffes are difficult and dangerous prey. They defend themselves with powerful kicks which, when well-placed, can kill a predator.[25]: 68  Most attacks on giraffes occur at watering holes, when the bent-over animals are at their most vulnerable and least attentive. Lions are the only predators which pose a serious threat to an adult giraffe.[22] When hunting giraffes, lions try to knock the lanky animal off its feet and pull it down.[30]

Swimming

Although no definitive study has been publicly conducted, giraffes are assumed to be unable to swim. It has been estimated that the giraffe's proportionally larger limbs have very high rotational inertias and this would make rapid swimming motions strenuous.[31] A swimming giraffe would be forced into a posture where the neck is sub-horizontal and since it has thorax that is pulled downwards by the large fore limbs it would not be able to move the neck and limbs synchronously as a giraffe would be able to do when moving on land. This may further hamper the animal's ability to move its limbs effectively underwater.[31]

A computer simulation conducted by Scientific American suggested that while a giraffe could float, "they would be clumsy and unstable in water".[32] The simulation suggests the giraffe's high density in its limb bones would make it slow and suffer from high drag.[32] Furthermore, the weight of the forelimbs and shoulder would pull the front of the giraffe down, straining its neck.[32]

Neck

An adult male giraffe feeding high up on an acacia.

The giraffe's extreme altitude is a consequence of its extremely elongated neck, which can be over 2 m (7 ft) in length,[33] accounting for nearly half of the giraffe's vertical height. The neck is supported by a shoulder hump made of muscles.[28]: 12  The neck is held up by the ligamentum nuchae.[25]: 72  This allows the neck to spring into its default position after the giraffe lowers it to the ground. The increase in neck length results from the disproportionate elongation of the cervical vertebrae, rather than the addition of more vertebrae. The cervical vertebrae comprise about 45–50% of the giraffe vertebral column, compared to the 30% typical of similar large ungulates, including the giraffe’s closest extant relative, the okapi. This elongation, which occurs in large part after birth,[34] is a 150% increase in vertebrae length over similar sized animals.

In addition to their elongated cervical vertebrae, giraffes have their point of articulation between the cervical and thoracic vertebrae is shifted to lie between T1 and T2, the first and second thoracic vertebrae, rather than between C7 and T1, as in most other ruminants.[33][34] This allows C7 to contribute directly to increased neck length, and has sparked the suggestion that T1 is actually C8, and giraffes have added an extra cervical vertebra.[35] However, this proposition is generally not accepted, as T1 has other morphological features, such as an articulating rib, deemed diagnostic of thoracic vertebrae. Also, the exceptions to the mammalian constraint of seven cervical vertebrae are generally characterized by increased neurological anomalies and maladies, symptoms that have not been observed in giraffes.[33] Because of its long neck, the giraffe inhales a lot of air that is not used for respiration and the windpipe contains a mix of inhaled and exhaled air with corresponding low oxygen levels. As such the giraffe must breath more regularly than expected for an animal of its size and takes more than 20 breaths a minute when resting.[25]: 77 

There are two main hypotheses regarding the evolutionary origin and maintenance of elongation in giraffe necks.[36] The "competing browsers hypothesis" was originally suggested by Charles Darwin and only challenged recently. It suggests that competitive pressure from smaller browsers, such as kudu, steenbok, and impala, drove the elongation of the neck so giraffes could reach nutrients competitors could not. This advantage is real – giraffes can and do feed up to 5 m, while most of their competitors, kudu, can only feed up to about 2 m (7 ft).[37] There is also research suggesting that browsing competition below 2 m is intense, and giraffes feed more efficiently (gaining more leaf biomass per bite) higher in the canopy.[38][39] However, scientists disagree about just how much time giraffes spend feeding at levels unreachable to other browsers.[36][37][40] Although giraffes can feed as low as 0.5 m and as high as 6 m off the ground, it appears that they most often feed between 2 and 4 m (7–14 ft).[40]

The other main theory, the sexual selection hypothesis, proposes that the long necks evolved as a secondary sexual characteristic, giving males an advantage in "necking" contests (see below) to establish dominance and obtain access to sexually receptive females.[41] In support of this theory, males have proportionally larger necks than females,[36][41] and males with longer, bigger necks are more successful in dominance displays and courtship behavior.[42] However, a major criticism of this theory is that it fails to adequately explain why female giraffes also have long necks.[43]

Bending down to drink is more strenuous for a giraffe than for other ungulates.

Circulatory system

Modifications to the giraffe's structure have evolved, particularly to the circulatory system. A giraffe's heart, which can weigh up to 10 kg (22 lb)[25]: 76  and measure about 60 cm (2 ft) long, must generate approximately double the normal blood pressure for an average large mammal to maintain blood flow to the brain.[25]: 76  In the upper neck, a complex pressure-regulation system called the rete mirabile prevents excess blood flow to the brain when the giraffe lowers its head to drink.[25]: 77 

The jugular veins also contain several (most commonly seven) valves to minimise blood flowing back into the head and assist it getting to the inferior vena cava and right atrium in the same situation.[44] Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). In other animals such pressure would force the blood out through the capillary walls; giraffes, however, have a very tight sheath of thick skin over their lower limbs which maintains high extravascular pressure in the same way as a pilot's g-suit.[13]

Lifestyle

Social structure and breeding habits

Giraffes normally gather around a food source.
Male giraffe mounting a female. Only dominant males will be able to mate.

While giraffes are usually found in groups, the composition of these groups is more fluid than in other social ungulates.[45] They are a largely transient species with few strong social bonds and aggregations usually disband every few hours, although calving groups can last weeks to months.[46] For research purposes, a "group" has been defined as "a collection of individuals that are less than a kilometre apart and moving in the same general direction."[42] Giraffe groups can range from over 40 individuals to only a few individuals with the latter being more common.[47] Female giraffes associate in groups of a dozen or so members, occasionally including a few younger males. Calves and sub-adults are rarely alone.[42] Giraffe groups with young tend to feed in more open areas, presumably to provide better visibility to detect predators. This may reduce their feeding efficiency.[40]

Reproduction is broadly polygamous, with a few older males impregnating the fertile females. Male giraffes determine female fertility by tasting the female's urine in order to detect estrus, in a multi-step process known as the Flehmen response.[46][42] Once a estrous female is detected, the male will them attempt to court her.[42] Males prefer younger females, possibly because the latter are more fertile,[46][42] while females prefer older, more dominant males.[46][42] During courtship, dominant males will displace subordinates from the presence of the females, by staring and walking towards them. Thus the female prolongs the courtship process for as long as possible so only the most dominant male remains and copulation will follow.

Although generally quiet and non-vocal, giraffes have been heard to communicate with various sounds. Courting males will emit loud coughs.[22] Females will call their young by whistling or bellowing. Calves will bleat, moo, or make mewing sounds. In addition, giraffes will grunt, snort, hiss, or make strange flute-like sounds.[22] Recent research has provided evidence that the giraffes produce infrasound.[48]

Two young, Maasai Giraffes, Serengeti National Parkm Tanzania. About 1 week old. One in background still has umbilical cord.

Birthing, parental care, and lifespan

Giraffe gestation lasts between 400 and 460 days, after which a single calf is normally born, although twins occasionally occur.[49] The mother gives birth standing up and the embryonic sack usually bursts when the baby falls to the ground. Newborn giraffes are about 1.8 metres (5.9 ft) tall.

Within a few hours of being born, calves can run around and are indistinguishable from a week-old calf; however, for the first two weeks, they spend most of their time lying down, guarded by the mother.[46][50] It has been speculated that their characteristic spotted pattern provides a certain degree of camouflage. Mothers with calves will gather in nursery herds which are usually made up of two or more infants and/or juveniles and their mothers moving or browsing together.[50] Mothers in a group may sometimes leave their calves, in what is known as a "calving pool", with one female while they travel to other areas.[50] Males largely play no role in raising the young.

The young can fall prey to lions, Nile crocodiles, leopards, spotted hyenas, and wild dogs. Mother giraffes will stand over their young and kick at a predator that comes near.[22] Giraffes only defend their own young and form calving herds for selfish reasons.[50] 25-50% of giraffe calves reach adulthood. Maximum lifespan is around 25 years in the wild[13] and 28 years in captivity.[51] In captivity, human-reared giraffes may display stereotypy. Due to a subconscious response to suckle milk from their mother, something which many human-reared giraffes and other captive animals do not experience, giraffes resort instead to excessive tongue use on inanimate objects.[52]

Necking

Male giraffes will engage in necking for various reasons, notably combat and homosexual courtship.

Male giraffes often engage in necking, which has been described as having various functions. One of these is combat. Battles can be fatal, but are more often less severe, generally ending when one giraffe surrenders to the other. The longer the neck, and the heavier the head at the end of the neck, the greater the force a giraffe is able to deliver in a blow. It has also been observed that males that are successful in necking have greater access to estrous females, so the length of the neck may be a product of sexual selection.[53]

After a necking duel, a giraffe can land a powerful blow with his head — occasionally knocking a male opponent to the ground. These fights rarely last more than a few minutes or end in physical harm.

Another function of necking is homosexual, in which two males caress and court each other, leading up to mounting and climax. Such interactions between males are more frequent than heterosexual coupling.[54] In one study, up to 94% of observed mounting incidents took place between two males. The proportion of same sex activities varied between 30 and 75%, and at any given time one in twenty males were engaged in non-combative necking behaviour with another male. Only 1% of same-sex mounting incidents occurred between females.[55]

Diet

Giraffe extending its tongue to feed. Its tongue, lips and palate are tough enough to deal with sharp thorns in trees.

Giraffes browse on the twigs of trees, preferring trees of the genera Acacia, Commiphora and Terminalia, and also eat grass and fruit.[12][56] The tongue, lips and palate are tough, which allows them to feed on trees with sharp thorns. The giraffe's tongue is about 45 centimetres (18 in) long and prehensile, allowing the animal to grasp leaves with it and pull them to the mouth. In Southern Africa, giraffes feed on all acacias, especially Acacia erioloba. A giraffe can eat 65 pounds (29 kg) of leaves and twigs daily, but can survive on just 15 pounds (6.8 kg).[56]

The giraffe requires less food than typical grazing animals, because the foliage it eats has more concentrated nutrition and it has a more efficient digestive system.[12] During the wet season, food is abundant and giraffes disperse widely, but during the dry season they need to congregate around evergreen trees and bushes.[12] The giraffe uses its lower incisor teeth to "cromb" leaves while browsing.[25]: 70  As a ruminant, it first chews its food, then swallows for processing and then visibly regurgitates the semi-digested cud up their necks and back into the mouth, to chew again. This process is usually repeated several times for each mouthful. The giraffe can survive without water for extended periods.[56] Compared with domestic cattle, giraffes have a comparatively short small intestine with a comparatively long large intestine, giving it a small ratio of small:large intestine.[57] When water is available, giraffe may drink at intervals lasting 3 days or less. Giraffes can also get water from green leaves, especially when covered in dew.[22]

Human interactions

Painting of a giraffe taken from Somalia to China during the Ming Dynasty

In art and culture

Ancient Egyptian art depicting Nubians with a giraffe (c. 1358-1350 BCE)

Arab prophets and poets considered the giraffe the "queen of beasts" for what they saw as its delicate features and fragile form.[58] Eastern sultans prized them as special pets.[58] Giraffes were also known to the people of the Mediterranean region during antiquity.[58] Ten of these animals were apparently kept by Pompey at his theater in Rome.[58] During the Middle Ages, giraffes apparently were mostly forgotten by Europeans except in legends from Arab travelers.[58] The Medici giraffe was a giraffe presented to Lorenzo de' Medici in 1486. It caused a great stir on its arrival in Florence,[59] being reputedly the first living giraffe to be seen in Italy since the days of Ancient Rome. Another famous giraffe, called Zarafa, was brought from Africa to Paris in the early 19th century and kept in a menagerie for 18 years.[60] Giraffe is a novel by the author J. M. Ledgard. The work concerns a true incident in which 49 giraffes were slaughtered in the Czech Republic (then Czechoslovakia) in 1975 following the suspected outbreak of disease amongst the group. The novel contains extensive information about the species, including the long history of European fascination with the beast and its captivity in zoos.

Giraffes can be seen in paintings, including the famous painting of a giraffe which was taken from Somalia to China in 1414. The giraffe was placed in a Ming Dynasty zoo.[61] At one point the giraffe was associated with the mythical Qilin, and a derivative of that name (kirin) is still used as the word for giraffe in Japan, Taiwan, and Korea.

Giraffes continue to have a presence in modern popular culture; most notably Toys "R" Us mascot Geoffrey the Giraffe. They also appear as miscellaneous characters in films like The Lion King and Dumbo. They have had more prominent roles with Melman from Madagascar and Longrack from the Transformers universe.

Scientific inspiration

Giraffes have been used as examples for introducing ideas in evolution, especially to illustrate the ideas of Lamarck. Lamarck believed that the giraffe's long neck developed as a result of ancestral giraffe's reaching to browse on the leaves of tall trees.[62] In addition the coat patterns of several subspecies of giraffe have been modelled using reaction-diffusion mechanisms.[63] The giraffe's skin has been studied by scientists developing suits for astronauts and fighter plan pilots.[25]: 76 

Conservation

The last viable population of the West African Giraffe is between Kouré and the Dosso Reserve in Niger.

Overall, the giraffe is regarded as Least Concern from a conservation perspective by the International Union for Conservation of Nature (IUCN), as it still is widespread and occurs in numerous reserves.[2] However, the giraffe has been extirpated from many parts of its former range, including Burkina Faso, Eritrea, Guinea, Malawi, Mauritania and Senegal.[2] It may also have disappeared from Angola, Mali and Nigeria.[2] Two subspecies, the West African Giraffe (G. c. peralta) and the Rothschild Giraffe (G. c. rothschildi), have been classified as endangered[19][64] with wild populations of each of these numbering in the hundreds.[14] Additionally, it has been suggested that the Nubian Giraffe (G. c. camelopardalis) is the most threatened of all giraffes[12] and may number fewer than 250, but little recent information is available and consequently that estimate is labelled with considerable uncertainty.[14]

Giraffes are hunted for their tails, hides and meat.[56] The tails are used as good luck charms, thread and flyswatters.[56] In addition, habitat destruction also hurts the giraffe. In the Sahel trees are cut down for firewood and to make way for livestock. Normally, giraffes are able to cope with livestock since they feed in the trees above their heads. The giraffe is a protected species in most of its range. The total African giraffe population has been estimated to range from 110,000 to 150,000. Kenya (45,000), Tanzania (30,000), and Botswana (12,000), have the largest national populations.[65] More recent estimates suggest fewer than 80,000 remain in total.[14]

See also

References

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