THE WESTERN GREAY SQUIRRELS

The western gray squirrel (Sciurus griseus) is an arboreal rodent found along the western coast of the United States and Canada.
In some places, this species has also been known as the silver-gray squirrel, the California gray squirrel, the Oregon gray squirrel, the Columbian gray squirrel and the banner-tail. There are three geographical subspecies: Sciurus griseus griseus (central Washington to the western Sierra Nevada in central California); S. g. nigripes (from south of San Francisco Bay to San Luis Obispo County, California; and S. g. anthonyi, which ranges from San Luis Obispo to northern Baja California).

Description

The western gray squirrel was first described by George Ord in 1818 based on notes taken by Lewis and Clark at The Dalles in Wasco County, Oregon.
Compared with the eastern gray squirrel S. carolinensis or the eastern fox squirrel (which have been introduced into its native range), these squirrels are shy, and will generally run up a tree and give a hoarse chirping call when disturbed. Weights vary from about 0.4 to 1 kilogram (14 to 35 oz), and length (including tail) from 45 to 60 centimetres (18 to 24 in). It is the largest native tree squirrel in the western coastal United States. Western gray squirrels exhibit a form of coloration known as counter shading. The dorsal fur is a silver gunmetal gray, with pure white on the underside; there may be black flecks in the tail. Ears are large but without tufts. The ears turn reddish-brown at the back in the winter. The tail is long and typically very bushy. Tree squirrels undergo a complete head-to-tail molt in the spring and a rump-to-head molt in the fall. Tail hair is replaced only in the spring. Nesting mothers will use their tail hair to line birthing nests. Western gray squirrels eat berries, nuts, a variety of seeds, and the eggs of small birds.

 

 

 Reproduction

Western gray squirrels mate over an extended period ranging from December through June. Young are born after approximate 44 day gestation period. Juveniles emerge from nests between March and mid-August. Litter sizes range from one to five kits which remain in the nest for a longer period than other squirrels. The kits are relatively slow in development, and will not leave the nest for six months or more, another species disadvantage when in competition with other, more-rapidly fledging squirrels. Young gray squirrels have furled tails which will not reach fullness until adulthood. This is a good indicator of age and maturity. Mother squirrels often seem to be overworked with a stressed appearance, complete with bruised and battered nipples. Mating squirrels can be very physical and will bite and injure each other. Females can be quite territorial, and will chase others away and have fairly violent altercations between themselves.

 

 

 Behavior and diet

Western gray squirrels are forest dwellers, and can be found at elevations up to 2,000 m. Time on the ground is spent foraging, but they prefer to travel distances from tree to tree. They are strictly diurnal, and feed mainly on seeds and nuts, particularly pine seeds and acorns, though they will also take berries, fungus and insects. Pine nuts and acorns are considered critical foods because they are very high in oil and moderately high in carbohydrates, which help increase the development of body fat. They feed mostly in trees and on the ground. They generally forage in the morning and late afternoon for acorns, pine nuts, new tree buds, and fruits. When on alert, they will spread their tails lavishly, creating an umbrella effect that shields them and possibly provides cover from overhead predators. They are scatter-hoarders making numerous caches of food when it is abundant, and thus contribute to the seed dispersion of their food trees. Although squirrels show relatively good scent relocation abilities, some food caches are never reclaimed, becoming seedlings in the spring. Though they do not hibernate, they do become less active during the winter. Like many prey animals, they depend on auditory alerts from other squirrels or birds to determine safety. Once an alarm call is transmitted, those present will join in, and the trees become a cacophony of chirping squirrels. Tree squirrels are prey for bobcats, hawks, eagles, mountain lions, coyotes, cat, raccoons and humans.

Habitat and shelter

Squirrel nests are called dreys and can be seen in trees, built from sticks and leaves wrapped with long strands of grass. There are two stick nest types made by the western gray squirrel: the first is a large, round, covered shelter nest for winter use, birthing, and rearing young. The second is more properly termed a "sleeping platform," a base for seasonal or temporary use. Both types are built with sticks and twigs and are lined with leaves, moss, lichens and shredded bark. The birthing nest may be lined with tail hair. The nest may measure 43 to 91 cm (17 to 36 in) by up to 46 cm (18 in) and is usually found in the top third of the tree. Young or traveling squirrels will also "sleep rough" when weather permits, balanced spread-eagled on a tree limb high above the forest floor. This attitude is also adopted for cooling in hot weather, a behavior also observed in raccoons.

 

Habitat loss and competition

 




The western gray squirrel was listed as a threatened species in Washington state in 1993. Populations of the western gray squirrel have not recovered from past reductions. They are threatened with habitat loss, road-kill mortality and disease. Habitat has been lost due to urbanization, catastrophic wild fires, and areas of forest degraded by fire suppression and overgrazing, allowing the invasion of scotch broom. Notoedric mange, a disease caused by mites, becomes epidemic in western gray squirrel populations and is a major source of mortality. Other species of eastern gray squirrels, fox squirrels, California ground squirrels and wild turkeys^{[citation needed]} are expanding and compete with the western gray.
Listed as extirpated in some California areas, the western gray squirrel in southern California is generally found only in the mountains and surrounding foothill communities. Local rehabilitation experts recount the Eastern Fox Squirrels were released in urban regions of Los Angeles throughout the 20th Century. Fox squirrels (Sciurus niger) were introduced to the Los Angeles area in about 1904. Civil War and Spanish–American War veterans residing at the Sawtelle Veteran’s Home on Sepulveda and Wilshire Boulevards brought fox squirrels as pets to this site from their homes in the areas surrounding the Mississippi Valley (possibly Tennessee). Other introductions of fox squirrels to the Los Angeles area may have taken place during more recent times but detailed records are not available. These aggressive cousins drove the more reclusive western grays back into the mountains, where competition was not so strong. This non-native species introduction appears to be the largest threat in the southern California area.

THE AMERICAN RED SQIRRELS

The American red squirrel (Tamiasciurus hudsonicus) is one of three species of tree squirrel currently classified in the genus Tamiasciurus, known as the pine squirrels (the others are the Douglas squirrel, T. douglasii and Mearns's squirrel, T. mearnsi). American red squirrels are also referred to as pine squirrels, North American red squirrels, boomers,^[3] and chickarees. They are medium-sized (200–250 g) diurnal mammals that defend a year-round exclusive territory. The diet of these tree squirrels is specialized on the seeds of conifer cones. As such, they are widely distributed across North America wherever conifers are common, except on the Pacific coast, where they are replaced by Douglas squirrels. Recently, American red squirrels have been expanding their range to include primarily hardwood areas.^[4]

Taxonomy

American red squirrels should not be confused with Eurasian red squirrels (Sciurus vulgaris); since the ranges of these species do not overlap, they are both commonly referred to as "red squirrels" in the areas where they are native. The specific epithet hudsonicus refers to Hudson Bay, Canada, where the species was first catalogued by Erxleben in 1771.^[5] A recent phylogeny suggests the squirrels as a family can be divided into five major lineages. Red squirrels (Tamiasciurus) fall within the clade that includes flying squirrels and other tree squirrels (e.g., Sciurus).^[6] There are 25 recognized subspecies of red squirrels.^[7]

Description

Red squirrels can be easily identified from other North American tree squirrels by their smaller size, territorial behavior and reddish fur with a white venter (underbelly).^[7] Red squirrels are somewhat larger than chipmunks. The Douglas squirrel is morphologically similar to the American red squirrels, but has a rust-colored venter and is restricted to the southwestern coast of British Columbia and in the Pacific Northwest of the United States. These species' ranges do not overlap.

American red squirrel range

Front view, Gatineau Park, Quebec

American red squirrels are widely distributed across the North American continent. Their range includes most of Canada, the southern part of Alaska, coastal British Columbia, and the Rocky Mountains and boreal forests east to the Atlantic coast.^[7][8] American red squirrels are abundant and not of conservation concern throughout much of their range. However, an isolated population of red squirrels in Arizona has experienced considerable declines in population size. In 1987, this portion of the population was listed as an endangered species.^[9]

 

 

 

Behavior

Feeding

Eating nut, in Edmonton, Alberta, 2013

American red squirrels are primarily granivores, but incorporate other food items into their diets opportunistically.^[7] In Yukon, extensive behavioral observations suggest white spruce seeds (Picea glauca) comprise over 50% of a red squirrel's diet,^[10] but squirrels have also been observed eating spruce buds and needles, mushrooms, willow (Salix sp.) leaves, poplar (Populus sp.) buds and catkins, bearberry (Arctostaphylos sp.) flowers and berries, and animal material such as bird eggs or even snowshoe hare leverets (young).^[11] White spruce cones mature in late July and are harvested by red squirrels in August and September. These harvested cones are stored in a central cache and provide energy and nutrients for survival over the winter and reproduction the following spring. The fallen scales from consumed seed cones can collect in piles, called middens, more than a meter across. White spruce exhibits two- to six-year masting cycles, where a year of superabundant cone production (mast year)^[12] is followed by several years in which few cones are produced.^[13] American red squirrel territories may contain one or several middens.
American red squirrels eat a variety of mushroom species, including some that are deadly to humans.^[14] They clip and gather truffles and other fungi and place them amongst the branches of trees to dry them in the sun.^[15][16][17]

 Reproduction

American red squirrels are spontaneous ovulators.^[18][19] Females enter estrus for only one day, but venture from their territory prior to ovulation, and these exploratory forays may serve to advertise their upcoming estrus. On the day of estrus, females are chased by several males in an extended mating chase. Males compete with one another for the opportunity to mate with the estrous female. Estrous females will mate with 4 to 16 males. Gestation has been reported to range from 31 to 35 days.^[20] Females can breed for the first time at one year of age, but some females delay breeding until two years of age or older. Most females produce one litter per year, but in some years reproduction is skipped, while in other years some females breed twice. Litter sizes typically range from one to five, but most litters contain three or four offspring. Offspring are pink and hairless at birth and weigh about 10 g. Offspring grow at approximately 1.8 g/day while nursing, and reach adult body size at 125 days. They first emerge from their natal nests at around 42 days, but continue to nurse until approximately 70 days.
Nests are most commonly constructed of grass in the branches of trees. Nests are also excavated from witches’ broom—abnormally dense vegetative growth resulting from a rust disease – or cavities in the trunks of spruce, poplar, and walnut trees. American red squirrels rarely nest below ground. Each individual squirrel has several nests within its territory, and females with young move them between nests. Some behavior has been reported within human dwellings using insulation as nesting fodder.
A three-year study of a population of red squirrels in southwest Yukon reported female red squirrels showed high levels of multiple-male mating and would even mate with males with similar genetic relatedness. While males mating with multiple females is quite common in the animal kingdom, females that mate with multiple males is rarer. When female red squirrels chose a mate, genetic relatedness did not play a factor. The relatedness of parents had no effect on the neonatal mass and growth rate of their offspring, nor did it affect the survival rate of offspring to one year of age.^[21]

Dispersal and survival

Red squirrel swimming

Juvenile American red squirrels must acquire a territory and midden prior to their first winter to survive. They can acquire a territory by competing for a vacant territory, creating a new territory or by receiving all or part of a territory from their mothers. This somewhat rare (15% of litters) female behavior is referred to as breeding dispersal or bequeathal, and is a form of maternal investment in offspring.^[22] The prevalence of this behavior is related to the abundance of food resources and the age of the mother. In some cases, females will acquire additional middens prior to reproduction, which they later bequeath to their offspring.^[23] Offspring that do not receive a midden from their mother typically settle within 150 m (3 territory diameters) of their natal territory.^[22]
American red squirrels experience severe early mortality (on average only 22% survive to one year of age). The survival probability, however, increases to age three, when it begins to decrease again. Females that survive to one year of age have a life expectancy of 2.3 years and a maximum lifespan of eight years.
American red squirrels are preyed upon by Canadian lynx (Lynx canadensis), bobcat (Lynx rufus), coyote (Canis latrans), great horned owl (Bubo virginianus), northern goshawk (Accipiter gentilis), red-tailed hawk (Buteo jamaicensis), American crow (Corvus brachyrynchos), American marten (Martes americana), red fox (Vulpes vulpes), gray fox (Urocyon cinereoargenteus), wolf (Canis lupus) and weasel (Mustela sp.).^{[citation needed]}

 

Gallery

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RHINOCEROS

Rhinoceros (/raɪˈnɒsərəs/, meaning "nose horn"), often abbreviated to rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to Southern Asia.
Members of the rhinoceros family are characterized by their large size (they are some of the largest remaining megafauna, with all of the species able to reach one tonne or more in weight); as well as by an herbivorous diet; a thick protective skin, 1.5–5 cm thick, formed from layers of collagen positioned in a lattice structure; relatively small brains for mammals this size (400–600 g); and a large horn. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter, if necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths, relying instead on their lips to pluck food.^[1]
Rhinoceros are killed by humans for their horns, which are bought and sold on the black market, and which are used by some cultures for ornamental or traditional medicinal purposes. East Asia, specifically Vietnam, is the largest market for rhino horns. By weight, rhino horns cost as much as gold on the black market. People grind up the horns and then consume them believing the dust has therapeutic properties.^[2] The horns are made of keratin, the same type of protein that makes up hair and fingernails.^[3] Both African species and the Sumatran rhinoceros have two horns, while the Indian and Javan rhinoceros have a single horn.
The IUCN Red List identifies three of the species as critically endangered.

 

 Taxonomy and naming

Rhinocerotidae Ceratotherium simum Diceros bicornis Dicerorhinus sumatrensis Rhinoceros unicornis Rhinoceros sondaicus

Cladogram following a phylogenetic study.[4]

The word rhinoceros is derived through Latin from the Ancient Greek: ῥῑνόκερως, which is composed of ῥῑνο- (rhino-, "nose") and κέρας (keras, "horn"). The plural in English is rhinoceros or rhinoceroses. The collective noun for a group of rhinoceroses is crash or herd. The name has been in use since the 14th century.^[5]
The family Rhinocerotidae consists of only four extant genera: Ceratotherium (White rhinoceros), Dicerorhinus (Sumatran rhinoceros), Diceros (Black rhinoceros) and Rhinoceros (Indian and Javan rhinoceros). The living species fall into three categories. The two African species, the white rhinoceros and the black rhinoceros, belong to the tribe Dicerotini, which originated in the middle Miocene, about 14.2 million years ago. The species diverged during the early Pliocene (about 5 million years ago). The main difference between black and white rhinos is the shape of their mouths – white rhinos have broad flat lips for grazing, whereas black rhinos have long pointed lips for eating foliage. There are two living Rhinocerotini species, the Indian rhinoceros and the Javan rhinoceros, which diverged from one another about 10 million years ago. The Sumatran rhinoceros is the only surviving representative of the most primitive group, the Dicerorhinini, which emerged in the Miocene (about 20 million years ago).^[6]
A subspecific hybrid white rhino (Ceratotherium s. simum × C. s. cottoni) was bred at the Dvůr Králové Zoo (Zoological Garden Dvur Kralove nad Labem) in the Czech Republic in 1977. Interspecific hybridisation of black and white rhinoceros has also been confirmed.^[7]
While the black rhinoceros has 84 chromosomes (diploid number, 2N, per cell), all other rhinoceros species have 82 chromosomes. However, chromosomal polymorphism might lead to varying chromosome counts. For instance, in a study there were three northern white rhinoceroses with 81 chromosomes.^[8]

Characteristics

The five extant species

The white rhinoceros is actually grey

The black rhinoceros has a beak shaped lip and is similar in color to the white rhinoceros

The Indian rhinoceros has a single horn

Smaller in size than the Indian rhinoceros, the Javan rhinoceros also has a single horn

The Sumatran rhinoceros is the smallest of the rhino species

White rhinoceros

Main article: White rhinoceros

There are two subspecies of white rhinoceros: the southern white rhinoceros (Ceratotherium simum simum) and the northern white rhinoceros (Ceratotherium simum cottoni). As of 2013, the southern subspecies has a wild population of 20,405 – making them the most abundant rhino subspecies in the world. However, the northern subspecies was critically endangered, with as few as four individuals in the wild; the possibility of complete extinction in the wild having been noted since June 2008.^[9] Five are known to be held in captivity, one of which resides at the San Diego Zoo Safari Park.^[10] Four born in a zoo in the Czech Republic were transferred to a wildlife refuge in Kenya in December 2009, in an effort to have the animals reproduce and save the subspecies.^[11]
There is no conclusive explanation of the name white rhinoceros. A popular theory that "white" is a distortion of either the Afrikaans word wyd or the Dutch word wijd (or its other possible spellings whyde, weit, etc.,) meaning wide and referring to the rhino's square lips is not supported by linguistic studies.^[12][13]
The white rhino has an immense body and large head, a short neck and broad chest. Females weigh 1,600 kg (4,000 lb) and males 2,400 kg (5,000 lb). the head-and-body length is 3.5–4.6 m (11–15 ft) and a shoulder height of 1.8–2 m (5.9–6.6 ft). On its snout it has two horns. The front horn is larger than the other horn and averages 90 cm (35 in) in length and can reach 150 cm (59 in). The white rhinoceros also has a prominent muscular hump that supports its relatively large head. The colour of this animal can range from yellowish brown to slate grey. Most of its body hair is found on the ear fringes and tail bristles, with the rest distributed rather sparsely over the rest of the body. White rhinos have the distinctive flat broad mouth that is used for grazing.^[12]

 

 Black rhinoceros

Main article: Black rhinoceros

The name black rhinoceros (Diceros bicornis) was chosen to distinguish this species from the white rhinoceros (Ceratotherium simum). This can be confusing, as the two species are not truly distinguishable by color. There are four subspecies of black rhino: South-central (Diceros bicornis minor), the most numerous, which once ranged from central Tanzania south through Zambia, Zimbabwe and Mozambique to northern and eastern South Africa; South-western (Diceros bicornis occidentalis) which are better adapted to the arid and semi-arid savannas of Namibia, southern Angola, western Botswana and western South Africa; East African (Diceros bicornis michaeli), primarily in Tanzania; and West African (Diceros bicornis longipes) which was declared extinct in November 2011.^[14] The native Tswanan name keitloa describes a South African variation of the black rhino in which the posterior horn is equal to or longer than the anterior horn.^[15]
An adult black rhinoceros stands 1.50–1.75 m (59–69 in) high at the shoulder and is 3.5–3.9 m (11–13 ft) in length.^[16] An adult weighs from 850 to 1,600 kg (1,870 to 3,530 lb), exceptionally to 1,800 kg (4,000 lb), with the females being smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm long, exceptionally up to 140 cm. Sometimes, a third smaller horn may develop.^[17] The black rhino is much smaller than the white rhino, and has a pointed mouth, which it uses to grasp leaves and twigs when feeding.
During the latter half of the 20th century, their numbers were severely reduced from an estimated 70,000^[18] in the late 1960s to a record low of 2,410 in 1995. Since then, numbers have been steadily increasing at a continental level with numbers doubling to 4,880 by the end of 2010. Current numbers are however still 90% lower than three generations ago.^[19]

 

 

Indian rhinoceros

Main article: Indian rhinoceros

The Indian rhinoceros, or greater one-horned rhinoceros, (Rhinoceros unicornis) has a single horn 20 to 100 cm long. It is nearly as large as the African white rhino. Its thick, silver-brown skin forms huge folds all over its body. Its upper legs and shoulders are covered in wart-like bumps, and it has very little body hair. Grown males are larger than females in the wild, weighing from 2,500–3,200 kg (5,500–7,100 lb). Shoulder height is 1.75–2.0 m (5.7–6.6 ft). Females weigh about 1,900 kg and are 3–4 m long. The record-sized specimen was approximately 3,800 kg.
Indian rhinos once inhabited many areas ranging from Pakistan to Burma and maybe even parts of China. However, because of human influence, they now only exist in several protected areas of India (in Assam, West Bengal, and a few pairs in Uttar Pradesh) and Nepal, plus a few pairs in Lal Suhanra National Park in Pakistan. It is confined to the tall grasslands and forests in the foothills of the Himalayas. Two-thirds of the world's Indian rhinoceroses are now confined to the Kaziranga National Park situated in the Golaghat district of Assam, India.^[20]

 

 Javan rhinoceros

Main article: Javan rhinoceros

The Javan rhinoceros (Rhinoceros sondaicus) is one of the most endangered large mammals in the world.^[21] According to 2015 estimates, only about 60 remain, in Java (Indonesia), all in the wild. It is also the least known rhino species. Like the closely related, and larger, Indian rhinoceros, the Javan rhino has a single horn. Its hairless, hazy gray skin falls into folds into the shoulder, back, and rump, giving it an armored appearance. Its length reaches 3.1–3.2 m (10–10 ft) including the head, and its height 1.5–1.7 m (4 ft 11 in–5 ft 7 in). Adults are variously reported to weigh 900–1,400 kg^[22] or 1,360–2,000 kg.^[23] Male horns can reach 26 cm in length, while in females they are knobs or altogether absent.^[23] These animals prefer dense lowland rain forest, tall grass and reed beds that are plentiful with large floodplains and mud wallows.
Though once widespread throughout Asia, by the 1930s they were nearly hunted to extinction in Nepal, India, Burma, Peninsular Malaysia, and Sumatra for the supposed medical powers of their horns and blood. As of 2015, only 58-61 individuals remain in Ujung Kulon National Park, Java, Indonesia. The last rhino in Vietnam was reportedly killed in 2011.^[24][25]

 

 

 Sumatran rhinoceros

Main article: Sumatran rhinoceros

The Sumatran rhinoceros (Dicerorhinus sumatrensis) is the smallest extant rhinoceros species, as well as the one with the most hair. It can be found at very high altitudes in Borneo and Sumatra. Due to habitat loss and poaching, their numbers have declined and it has become the most threatened rhinoceros. About 275 Sumatran rhinos are believed to remain. There are three subspecies of Sumatran rhinoceros: the Western Sumatran rhinoceros (Dicerorhinus sumatrensis sumatrensis), Eastern Sumatran rhinoceros (Dicerorhinus sumatrensis harrissoni) and the extinct Northern Sumatran rhinoceros (Dicerorhinus sumatrensis lasiotis).
A mature rhino typically stands about 1.3 m (4 ft 3 in) high at the shoulder, has a length of 2.4–3.2 m (7 ft 10 in–10 ft 6 in) and weighs around 700 kg (1,500 lb), though the largest individuals have been known to weigh as much as 1,000 kilograms. Like the African species, it has two horns; the larger is the front (25–79 cm), with the smaller usually less than 10 cm long. Males have much larger horns than the females. Hair can range from dense (the densest hair in young calves) to sparse. The color of these rhinos is reddish brown. The body is short and has stubby legs. The lip is prehensile.
Sumatran rhinoceros are on the verge of extinction due to loss of habitat and illegal hunting. Once they were spread across South-east Asia, but now they are confined to several parts of Indonesia and Malaysia due to reproductive isolation. There were 320 of D. sumatrensis in 1995, which by 2011 have dwindled to 216. It has been found through DNA comparison that the Sumatran rhinoceros is the most ancient extant rhinoceros, and related to the extinct Woolly Rhinoceros, Coelodonta. In 1994 Alan Rabinowitz publicly denounced that governments, NGOs and other institutions were lacking in attempts to conserve the Sumatran rhinoceros. In order to conserve it, they would have to be relocated from small forests to breeding programs where their breeding success could be monitored. In order to boost reproduction, the Malaysian and Indonesian governments could also agree on exchanging the gametes of the Sumatran and (smaller) Bornean subspecies. There has also been a proposal by the Indonesian and Malaysian governments for a single management unit for these two ancient subspecies.^[26][27]

Evolution

Coelodonta antiquitatis MHNT

The thick dermal armour of the rhinoceros evolved at the same time as shearing tusks^[28]

Rhinocerotoids diverged from other perissodactyls by the early Eocene. Fossils of Hyrachyus eximus found in North America date to this period. This small hornless ancestor resembled a tapir or small horse more than a rhino. Three families, sometimes grouped together as the superfamily Rhinocerotoidea, evolved in the late Eocene, namely the Hyracodontidae, Amynodontidae and Rhinocerotidae.

Hyracodontidae

Main article: Hyracodontidae

Hyracodontidae, also known as 'running rhinos', showed adaptations for speed, and would have looked more like horses than modern rhinos. The smallest hyracodontids were dog-sized; the largest was Indricotherium, believed to be one of the largest land mammals that ever existed. The hornless Indricotherium was almost seven metres high, ten metres long, and weighed as much as 15 tons. Like a giraffe, it ate leaves from trees. The hyracodontids spread across Eurasia from the mid-Eocene to early Miocene.

Amynodontidae

Main article: Amynodontidae

The Amynodontidae, also known as "aquatic rhinos", dispersed across North America and Eurasia, from the late Eocene to early Oligocene. The amynodontids were hippopotamus-like in their ecology and appearance, inhabiting rivers and lakes, and sharing many of the same adaptations to aquatic life as hippos.

Rhinocerotidae

The family of all modern rhinoceros, the Rhinocerotidae, first appeared in the Late Eocene in Eurasia. The earliest members of Rhinocerotidae were small and numerous; at least 26 genera lived in Eurasia and North America until a wave of extinctions in the middle Oligocene wiped out most of the smaller species. However, several independent lineages survived. Menoceras, a pig-sized rhinoceros, had two horns side-by-side. The North American Teleoceras had short legs, a barrel chest and lived until about 5 million years ago. The last rhinos in the Americas became extinct during the Pliocene.
Modern rhinos are thought to have begun dispersal from Asia during the Miocene. Two species survived the most recent period of glaciation and inhabited Europe as recently as 10,000 years ago: the woolly rhinoceros and Elasmotherium. The woolly rhinoceros appeared in China around 1 million years ago and first arrived in Europe around 600,000 years ago. It reappeared 200,000 years ago, alongside the woolly mammoth, and became numerous. Eventually it was hunted to extinction by early humans. Elasmotherium, also known as the giant rhinoceros, survived through the middle Pleistocene: it was two meters tall, five meters long and weighed around five tons, with a single enormous horn, hypsodont teeth and long legs for running.
Of the extant rhinoceros species, the Sumatran rhino is the most archaic, first emerging more than 15 million years ago. The Sumatran rhino was closely related to the woolly rhinoceros, but not to the other modern species. The Indian rhino and Javan rhino are closely related and form a more recent lineage of Asian rhino. The ancestors of early Indian and Javan rhino diverged 2–4 million years ago.^[29]
The origin of the two living African rhinos can be traced to the late Miocene (6 mya) species Ceratotherium neumayri. The lineages containing the living species diverged by the early Pliocene (1.5 mya), when Diceros praecox, the likely ancestor of the black rhinoceros, appears in the fossil record.^[30] The black and white rhinoceros remain so closely related that they can still mate and successfully produce offspring.^[7]

Comparison of sizes between extant and extinct rhinos

Predators, poaching and hunting

Memorial to rhinos killed by poachers near St Lucia Estuary, South Africa

Adult rhinoceros have no real predators in the wild, other than humans. Young rhinos can however fall prey to big cats, crocodiles, wild dogs, and hyenas.
Although rhinos are large and have a reputation for being tough, they are very easily poached; they visit water holes daily and can be easily killed while they drink. As of December 2009, poaching increased globally while efforts to protect the rhino are considered increasingly ineffective. The most serious estimate, that only 3% of poachers are successfully countered, is reported of Zimbabwe, while Nepal has largely avoided the crisis.^[35] Poachers have become more sophisticated. South African officials have called for urgent action against poaching after poachers killed the last female rhino in the Krugersdorp Game Reserve near Johannesburg.^[36] Statistics from South African National Parks show that 333 rhinoceros were killed in South Africa in 2010,^[37] increasing to 668 by 2012,^[38] and over 1,004 in 2013.^[39][40][41] In some cases rhinos are drugged and their horns removed, while in other instances more than the horn is taken.^[42]
The Namibian government and Save the Rhino International have been positive about the benefits that rhino trophy hunting may hold for conservation. Hunting licenses for five Namibian Black rhinos are auctioned annually. Additionally, support for a legal trade of rhino horn to combat poaching has been growing.^[43] Some conservationists and members of the public however oppose or question this practice.^[44]

Horn trade and use

Rhinoceros horns, unlike those of other horned mammals (which have a bony core), only consist of keratin, similar to human hair and nails. Rhinoceros horns are used in traditional medicines of both Europe and Asia, and for dagger handles in Yemen and Oman. Esmond Bradley Martin has reported on the trade for dagger handles in Yemen.^[45]
Contrary to popular belief, the market for rhino horn is not largely driven by practitioners of Traditional Chinese Medicine specifically. Rather, Vietnamese are currently the biggest consumers of rhino horn and Vietnamese demand drives most of the poaching which has shot up to record levels.^{[46][47][48][49][50][51][52][53][54][55][56][57][58][59]} Some wealthy Vietnamese inhale the powdered horn as a status symbol; in Europe and Vietnam, rhino horn is believed by some to have aphrodisiac properties. The "Vietnam CITES Management Authority" has claimed that Hanoi recently experienced a 77% drop in the usage of rhino horn, but National Geographic has challenged these claims, noticing that there was no rise in the numbers of criminals who were apprehended or prosecuted.^[60]
It is a common misconception that rhinoceros horn in powdered form is used as an aphrodisiac or a cure for cancer in Traditional Chinese Medicine as Cornu Rhinoceri Asiatici (犀角, xījiǎo, "rhinoceros horn"); no TCM text in history has ever mentioned such prescriptions.^{[47][47][61][62][63][64][65][66][67][68]} Western media has falsely propagated this idea for a long time^{[69][70][71][72]} and to an extent, that it eventually caught on in Vietnam.^{[48][61][68][73][74][75]} In Traditional Chinese Medicine (TCM), rhino horn is considered an effective medicine sometimes prescribed for fevers and convulsions,^[76] a treatment not supported by evidence-based medicine and has been compared to consuming fingernail clippings in water.^[77] In 1993, China signed the CITES treaty and removed rhinoceros horn from the Chinese medicine pharmacopeia, administered by the Ministry of Health. In 2011, the Register of Chinese Herbal Medicine in the United Kingdom issued a formal statement condemning the use of rhinoceros horn.^[78] A growing number of TCM educators is also speaking out against the practice.^[79] Discussions with TCM practitioners to reduce the use of rhino horn, has met with mixed results, because some still consider it a life-saving medicine of a better quality than its substitutes.^[80]
In March 2013, some researchers suggested that the only way to reduce poaching would be to establish a regulated trade based on humane and renewable harvesting from live rhinos.^[81] The WWF however opposes legalization of the horn trade, as it may increase demand,^[82] while IFAW released a report by EcoLarge, suggesting that more thorough knowledge of economic factors is required in order to justify the pro-trade option.^[83] The South African government has supported the establishment of a legal trade of rhino horn stating that at the 17th Meeting of Conference of the Parties to CITES (CoP17) in 2016 they will apply for a legal trade in Rhino Horn in an attempt to reduce poaching and prevent the extinction of this species.^[43]
To prevent poaching, in certain areas, rhinos have been tranquillized and their horns removed. Armed park rangers, particularly in South Africa, are also working on the front lines to combat poaching, sometimes killing poachers who are caught in the act. A recent spike in rhino killings has made conservationists concerned about the future of the species.^[84] An average sized horn can bring in as much as a quarter of a million dollars in Vietnam and many rhino range states have stockpiles of rhino horn.^[85][86]
In 2011 the Rhino Rescue Project, organized by Ed and Lorinda Hern of the Rhino & Lion Nature Reserve in Krugersdorp South Africa,^[87] began a horn-trade control method consisting of infusing the horns (while on the animal) with a mixture of a pink dye and an acaricide (to kill ticks) which is safe for rhinos but toxic to humans.^[88] After sedating the animal, holes are drilled into the horns, fittings added, and the cavity connected with rubber hoses to a 2-foot-by-4-inch diameter metal container of the liquid mixture which is then pressurized.^[87] The infusion takes less than 20 minutes of the 45 minutes of anesthesia; because of the high pressure exerted on the animals internal organs from their large body weight, they are turned every 7 minutes while sedated. The procedure also includes inserting three RFID identification chips and taking DNA samples.^[88]
Because of the fibrous nature of rhino horn, the pressurized dye infuses the interior of the horn but does not color the surface or affect rhino behavior. The acaricide is expected to cause nausea, stomach-ache and diarrhea, or convulsions for anyone consuming the horn, depending on the quantity, but would not be fatal; the primary deterrent being the knowledge that the treatment has been applied, communicated by signs posted at the refuges. The original idea grew out of research looking into using the horn as a reservoir for one-time tick treatments, and the acaricide is selected to be safe for the rhino, oxpeckers, vultures, and other animals in the preserve's ecosystem.^[88] It was claimed that the dye can not be successfully removed from horns, and would remain visible on x-ray scanners even when the horn is ground to a fine powder.^[88][89]
The UK charity organization Save the Rhino has criticized horn poisoning on moral and practical grounds. The organization questions the assumptions that the infusion technique works as intended, and that even if the poison were effective, whether middlemen in a lucrative, illegal trade would care much about the effect it would have on buyers on another continent.^[90] They also claim that poisoned horns could heighten demand for non-poisoned horns among wealthier buyers or could fuel the belief in magical properties of the horn if people survive the poisoning.^[90] Additionally, rhino horn is increasingly purchased for decorative use, rather than for use in traditional medicine. Save the Rhino questions the feasibility of applying the technique to all African rhinos, since the acaricide would have to be reapplied every 4 years.^[90] It was also reported that one out of 150 rhinos treated did not survive the anesthesia.^[87]
The only remaining Javan rhino in Vietnam was slaughtered in 2011 by Vietnamese poachers in order to obtain its horn.^[91][92][93] Now only Java contains the last Javan rhinos.^[94][95]
Rhino horn from South Africa was acquired by the North Korean diplomat Park Chol-jun.^[96]

Historical representations

Albrecht Dürer created a famous woodcut of a rhinoceros in 1515, based on a written description and brief sketch by an unknown artist of an Indian rhinoceros that had arrived in Lisbon earlier that year. Dürer never saw the animal itself and, as a result, Dürer's Rhinoceros is a somewhat inaccurate depiction.^{[citation needed]}
There are legends about rhinoceroses stamping out fire in Burma, India, and Malaysia. The mythical rhinoceros has a special name in Malay, badak api, wherein badak means rhinoceros, and api means fire. The animal would come when a fire was lit in the forest and stamp it out.^[97] There are no recent confirmations of this phenomenon. However, this legend has been reinforced by the film The Gods Must Be Crazy (1980), wherein an African rhinoceros is shown to be putting out two campfires.^[98]