| Riverine rabbit Temporal range: middle Pleistocene, 0.4 million years ago | |
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| Bunolagus monticularis inWestern Cape, South Africa | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Lagomorpha |
| Family: | Leporidae |
| Genus: | Bunolagus Thomas, 1929 |
| Species: | B. monticularis |
| Binomial name | |
| Bunolagus monticularis (Thomas, 1903) | |
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| Historic distribution of the Riverine rabbit as described by the IUCN in 2019 Extant (resident) | |
Theriverine rabbit (Bunolagus monticularis), also known as thebushman rabbit orbushman hare, is aspecies ofrabbit that lives among patches of thick vegetation in theKaroo ofSouth Africa'sWestern andNorthern Cape provinces. It is theonly member of thegenusBunolagus. It is classified acritically endangered species by theInternational Union for Conservation of Nature (IUCN); the most recent estimates of the species' population range from 157 to 207 mature individuals, and 224 to 380 total.
First identified in 1903 as a member of thehares, the riverine rabbit is a medium-sized rabbit, about 33.7 to 47.0 centimetres (13.3 to 18.5 in) long. Its fur has a unique dark brown stripe from the edge of its mouth to the base of its ears, and a white to grey ring around each eye. It isnocturnal andherbivorous, and its diet consists of grasses, flowers and leaves, most of which aredicotyledons. The riverine rabbit digsburrows in the softalluvial soils of its habitat near seasonal rivers forprotection from the heat and for females to nest and protect the young. It is the only African rabbit known to dig its own burrows. Riverine rabbits arepolygamous, and live alone throughout the year.
Unlike most rabbits, female riverine rabbits produce only one to two young per year. This contributes to its status as critically endangered, along with habitat loss from agricultural development, soil erosion, and predators.Human impacts on the environment have a significant impact on the species' continued survivability. Currently, there are conservation plans being enacted to stabilise its population and protect its habitat.
The riverine rabbit'sscientific name isBunolagus monticularis.[2] It was first described from two specimens by the British zoologistOldfield Thomas in 1903 asLepus monticularis, withLepus being the genus of thehares. Thetype specimen, a female of the species, was collected byClaude H. B. Grant inDeelfontein, Cape Colony, South Africa and sent to theNatural History Museum, London (then the National Museum) byArthur Sloggett,[3] where it still resides today.[4] It was then known as the "Kopje Hare of Deelfontein".[5] Thespecific namemonticularis is derived from theLatinmonticulus, meaning'little mountain' and referring to thekopjes (diminutive word for'mountain',kop, inAfrikaans) where it was found.[3] It was separated into its own genusBunolagus in 1929,[6] due to the distinguishing characteristics of its thick, short limbs, uniformly coloured, cylindrical tail, and some aspects of the skull.[5] However, the external resemblance of the riverine rabbit to several other rabbits and its hare-like cranium led to confusion among taxonomists for several decades. Analysis of the species'karyotype in 1983, as well as latergenetic analysis, confirmed its placement in amonotypic genus.[7][8]
Othercommon names ofBunolagus monticularis include bushman hare and bushman rabbit.[1] Afrikaans common names includeboshaas andvleihaas, referring to its moist and dense habitat;bos means'forest' or'thicket',vlei means'swamp', andhaas means'hare'.[9] Other Afrikaans common names arepondhaas,'pound hare', referring to the fact that specimens were once sought for apound sterling each by the curator of theKaffrarian Museum, mammalogistGuy C. Shortridge.[10] It is also known as thedoekvoetjie,'cloth foot', referring to the rabbit's furred hind feet,[9] andoewerkonyn,'shore rabbit'.[6]
Bunolagus monticularis is most closely related to theEuropean rabbit, thehispid hare, and theAmami rabbit.[9] The followingcladogram is based on work done by Matthee and colleagues in 2004 and clarifications from Abrantes and colleagues in 2011, and is based onnuclear andmitochondrial gene analysis:[11]
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There are no confirmedfossils ofBunolagus. It was thought to date back to the middlePleistocene,0.4 million years ago in South Africa. Its distribution has likely always been very restricted. One fossil record of the genus was described in 1983, but as of 2007, the associated fossils have been reconsidered as small specimens ofLepus.[12] Nosubspecies are recognized,[13] but there are significant genetic differences between isolated populations above and below theGreat Escarpment.[6][14]
The riverine rabbit has an adult head and body length of 33.7 to 47.0 centimetres (13.3 to 18.5 in), and typically has a dark brown stripe running from the lower jaw over the cheek and upwards towards the base of the ears, and a white ring around each eye.[6] The nuchal patch (the section of fur on the nape of the neck to the base of the ears), as well as the limbs and lower flanks, arerufous in colour.[15] The underside and throat are cream-coloured. Their tails are pale brown with a tinge of black toward the tip and their limbs are short and heavily furred, with the hind foot measuring 9–12 centimetres (3.5–4.7 in). Its coat is soft and silky, more so than that of hares, and is of a reddish-brown to black shade.[6] The ears measure 11–12 centimetres (4.3–4.7 in)[16] and are rounded at the tips.[15] Females are slightly larger than males.[17] Itsdental formula is2.0.3.31.0.2.3 × 2 = 28—two pairs of upper and one pair of lowerincisors, nocanines, three upper and two lower premolars on each side, and three upper and lowermolars on either side of the jaw—as is the case with allleporids.[18]
The riverine rabbit appears similar tohares (lagomorphs in the genusLepus). It most closely resembles theCape hare (Lepus capensis) in itsmorphology, but not in its fur patterns. Theskulls of hares and the riverine rabbit are similar, with the main difference being that the riverine rabbit's is smaller and lacks an opening (foramen) near thepremolar teeth.[6] Thebulla, a bone structure enclosing the base of the ear, is much larger than that of most other rabbits; thevolcano rabbit (Romerolagus) andpygmy rabbit (Brachylagus) have similarly large bullae, but smallerpinnae (the externally visible part of the ear).[19] It is sometimes compared to thered rock hares, some of which overlap it indistribution;[20][1] in its first description, it was noted as being about the same size as theNatal red rock hare (Pronolagus crassicaudatus),[3] though it has been later described as smaller than all red rock hares besidesSmith's red rock hare (P. rupestris).[21]
The riverine rabbit lives in riverine vegetation onalluvial soils adjacent to seasonal rivers.[22] It prefers areas of dense vegetation in river basins and shrubland. The soft alluvial soils of the river basins allow it to create burrows and dens for protection, breeding young, andthermoregulation; it is the only African rabbit known to construct its own burrows.[6] The riverine rabbit requires particular vegetation and soil to construct its burrows,[1] and is sensitive to changes in habitat; thus, it is considered anindicator species within itsdistribution.[23] Plants in the familyAmaranthaceae, those in the genusLycium, andSalsola glabrescens dominate the rabbit's habitat.[16]
The riverine rabbit has adisjunct distribution and historically[12] occurred in two restricted regions in theKaroo, with the most populated regions being the Upper Karoo andBushmanland Vloere (salt pan[24]) areas.[6] Nine distinct populations occur within the species' northern habitat on elevated ground north of the Great Escarpment, and two[14] or three southern populations, which have only been known since 2004, occupy the regions surrounding theBreede,Gourits andOlifants River systems. None of these subpopulations contain more than 50 individuals. Historically, there were five additional subpopulations in localities near the tributaries of and alongside the Vis and Renoster rivers, but it is now considered locally extinct in these regions.[1]
Riverine rabbits are solitary and nocturnal. They feed on grasses, as well as the flowers and leaves ofdicotyledons. During the day, they rest in forms (hollow excavations scraped in the soil under shrubs).[25] The riverine rabbit ispolygamous, and it lives and browses for food alone.[16] The size and overlap ofhome ranges varies based on sex: the males' home ranges overlap slightly with those of various females, with males having an average home range size roughly 60% larger than females (20.9 hectares (52 acres) compared to 12.9 hectares (32 acres)).[26] This home range size is the largest of all rabbits, though it is smaller than those of most hares.[27] The breeding season takes place between August and May, wherein females will make a grass- and fur-lined nest in a burrow, blocking the entrance with soil and twigs to keep out predators. The average length of a generation is two years; in captivity, individuals have been recorded as living up to five years.[26]
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The riverine rabbit mainly feeds throughbrowsing.[25] When grasses are available during the wet season, they are the rabbit's preferred food, but most of the time its diet is restricted to the flowers and leaves ofdicotyledons in the Karoo. These include species in the familiesAsteraceae,Amaranthaceae, andAizoaceae,[28] particularly salt-loving plants such asSalsola andLycium that grow along seasonal rivers in the desert. According to one study, the diet comprises 11.2%Lycium and 34.8% Amaranthaceae.[16] Aside from their conventional food intake, they also consume soft droppings that come directly from the anus in the process known ascecotrophy.[25]
Populations in the more northern areas of thespecies' distribution are more strongly associated with vegetation that grows narrowly along seasonal rivers; those in the southern parts of its distribution are not as closely tied to this type of vegetation and have been observed feeding on newly grown plants infallow land.[6]
The riverine rabbit has a polygamous mating system, wherein males will mate with multiple females. Based on limited observations, the breeding season takes place from August through May, and gestation takes 35 to 36 days. It bears its young underground for protection, relying on soft soil in theflood plains of its habitat to construct its breeding burrows. These burrows are lined with fur and grass, and the entrance is closed off with dirt and twigs forcamouflage from predators. This burrow is 20–30 centimetres (7.9–11.8 in) long, and the nesting chamber within is 12–17 centimetres (4.7–6.7 in) wide.[16] The young are reared in the nesting chamber for the first 2 weeks after birth.[25] The riverine rabbit has 44diploid chromosomes,[6] as do several closely related rabbits, theEuropean rabbit (Oryctolagus cuniculus)[29] andhispid hare (Caprolagus hispidus).[30]
The young that the rabbit produces, one to two kits per litter, arealtricial—born bald, blind, and helpless. Each kit weighs from 40 to 50 grams (0.088 to 0.110 pounds). The helpless young stay with the mother until they are capable of living on their own.[6]
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The riverine rabbit is hunted byVerreaux's eagles,[31]African wildcats,[25] andcaracals.[16]
The riverine rabbit is considered to be in extreme danger of extinction. From 1947 to 1979, it was thought to be extinct, having not been recorded by scientists at all in the intervening years.[10] In 1981, it was first labelled as an endangered species. TheInternational Union for Conservation of Nature (IUCN) classified it ascritically endangered in 2002.[9] The National Red List of South Africa maintained by theSouth African National Biodiversity Institute (SANBI) uses this same classification. Both organizations maintain this position as of their most recent evaluations from 2016.[26] In 2016, the species was estimated to have a population of 157 to 207 mature rabbits[23] and up to 380 overall, which continues to decline. This species' population is divided into several isolated groups, about 12 in total, all with less than 50 rabbits in each. These isolated populations are separated byjackal-proof fencing that surrounds extensivelivestock farms.[1] A 1990 study put forth that the remaining habitat was only able to support 1,435 rabbits,[32] and in 2019, it was estimated that the species occupied a region spanning 2,943 square kilometres (1,136 sq mi) in total.[1] Later studies in 2020 and 2022 put forth that there may be more subpopulations than originally thought, and that the extent of species' endangerment could be exaggerated.[14]
The decline in the riverine rabbit population is largely due to the alteration of its historically limited[12] habitat. Over half of the rabbit's range has been rendered unable to support the species due to agricultural development since 1970. From the early 20th century up until 2008, over two-thirds of its habitat had been lost. Removal of the natural vegetation along the rivers and streams causesloss of alluvial soils and prevents rabbits from constructing stable breeding burrows.Overgrazing of domestic herbivores also causes degradation andhabitat fragmentation.[1] Commercial agricultural development has contributed significantly tohabitat loss, with much of the rabbit's former habitat rendered inhabitable or closed off.[1] The remaining land left to support the species is being damaged byclimate change andlogging.[14] Removal and exploitation of trees limits the rabbit's opportunities for shelter from heat and predators. Structures on rivers likedams isolate subpopulations from each other, discouraging population regeneration.[9] Relatively recent threats to the riverine rabbit arefracking andwind farm developments in theNama Karoo, the former of which could alter the region'shydrology, and both of which will further fragment the available habitat.[6]
In addition to being threatened through loss of habitat, the riverine rabbit may also be susceptible tomyxomatosis, as it shares genes that are affected by theMyxoma virus with the European rabbit, which is significantly impacted by the resultant disease. If the riverine rabbit species were to be exposed to the virus, its numbers could be reduced drastically.[6] The species is also suspected to be hunted forbushmeat or accidentally trapped[33] by farm workers and forsport,[26] though its preference for dense vegetation may thwart hunting efforts that use dogs.[34]
Relative to other similar species, known information about key aspects of the riverine rabbit, such as behaviour and diet, is deficient. Conservation efforts are better informed by researching this species and involving local communities, particularly farmers.[9] Plans to protect the remaining populations have been criticized, with experts claiming that a large part of the remaining land that can support the rabbit is outside the area being preserved for it.[32] Additionally, studies are susceptible tosampling bias, and failure to account for climactic and biological variables can lead to error, which can impact conservation recommendations.[23] Efforts have been made to form agreements with and educate landowners to ensure that certain measures are taken to help and reduce harm to rabbit populations,[9] though as of 2018 few private reserves orprotected areas overlapped regions where the riverine rabbit is present.[6] A 2016 assessment by SANBI noted that there were increased sightings of the species within its extent of occurrence, and thatcamera traps and further observations were needed to confirm the spread of subpopulations in regions south and eastward of the rabbit's native range.[26]
The IUCN recommends further conservation measures in addition to those already planned and advised by SANBI. They recommend capturing the animal as to safely allow it to reproduce without danger of predators or starvation. They also recommend different methods of managing the habitat and the population in the wild.[1] Conservation of the rabbit's habitat and maintaining interconnection between populations is important to the conservation of the species, as its complex genetic structure makes breeding with groups outside of the species difficult, if not impossible.[6][14] An early breeding colony was established at theDe Wildt Cheetah and Wildlife Centre nearPretoria[35] in the late 20th century due to the species' rarity and the centre's historic success in breeding thecheetah andwild dog, though efforts in the early 1990s were met with failure due to poor planning and low genetic diversity.[10] Monitoring of rabbit populations to evaluate effectiveness of current and potential conservation actions has been carried out in part by theEndangered Wildlife Trust.[33] One location being monitored is Sanbona Wildlife Reserve, a protected wilderness area with a successful breeding population where the species is being researched,[31] though efforts to improve population numbers in the wild are favored over captive breeding options according to SANBI.[26] The species' extent as of 2024 is being evaluated through analysis of droppings across the Karoo region.[36]
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