The riverine rabbit (Bunolagus monticularis), also known as the bushman rabbit or bushman hare, is a species of rabbit that lives among patches of thick vegetation in the Karoo of South Africa's Western and Northern Cape provinces. It is the only member of the genus Bunolagus. It is classified a critically endangered species by the International 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 the hares, 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 is nocturnal and herbivorous, and its diet consists of grasses, flowers and leaves, most of which are dicotyledons. The riverine rabbit digs burrows in the soft alluvial soils of its habitat near seasonal rivers for protection 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 are polygamous, 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.
Taxonomy and evolution The riverine rabbit's scientific name is Bunolagus monticularis. It was first described from two specimens by the British zoologist Oldfield Thomas in 1903 as Lepus monticularis, with Lepus being the genus of the hares. The type specimen, a female of the species, was collected by Claude H. B. Grant in Deelfontein, Cape Colony, South Africa and sent to the Natural History Museum, London (then the National Museum) by Arthur Sloggett, where it still resides today. It was then known as the "Kopje Hare of Deelfontein". The specific name monticularis is derived from the Latin monticulus, meaning 'little mountain' and referring to the kopjes (diminutive word for 'mountain', kop, in Afrikaans) where it was found. It was separated into its own genus Bunolagus in 1929, due to the distinguishing characteristics of its thick, short limbs, uniformly coloured, cylindrical tail, and some aspects of the skull. 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 later genetic analysis, confirmed its placement in a monotypic genus. Other common names of Bunolagus monticularis include bushman hare and bushman rabbit. Afrikaans common names include boshaas and vleihaas, referring to its moist and dense habitat; bos means 'forest' or 'thicket', vlei means 'swamp', and haas means 'hare'. Other Afrikaans common names are pondhaas, 'pound hare', referring to the fact that specimens were once sought for a pound sterling each by the curator of the Kaffrarian Museum, mammalogist Guy C. Shortridge. It is also known as the doekvoetjie, 'cloth foot', referring to the rabbit's furred hind feet, and oewerkonyn, 'shore rabbit'. Bunolagus monticularis is most closely related to the European rabbit, the hispid hare, and the Amami rabbit. The following cladogram is based on work done by Matthee and colleagues in 2004 and clarifications from Abrantes and colleagues in 2011, and is based on nuclear and mitochondrial gene analysis:
There are no confirmed fossils of Bunolagus. It was thought to date back to the middle Pleistocene, 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 of Lepus. No subspecies are recognized, but there are significant genetic differences between isolated populations above and below the Great Escarpment.
Characteristics
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. 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, are rufous in colour. 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. The ears measure 11–12 centimetres (4.3–4.7 in) and are rounded at the tips. Females are slightly larger than males. Its dental formula is 2.0.3.31.0.2.3 × 2 = 28—two pairs of upper and one pair of lower incisors, no canines, three upper and two lower premolars on each side, and three upper and lower molars on either side of the jaw—as is the case with all leporids. The riverine rabbit appears similar to hares (lagomorphs in the genus Lepus). It most closely resembles the Cape hare (Lepus capensis) in its morphology, but not in its fur patterns. The skulls 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 the premolar teeth. The bulla, a bone structure enclosing the base of the ear, is much larger than that of most other rabbits; the volcano rabbit (Romerolagus) and pygmy rabbit (Brachylagus) have similarly large bullae, but smaller pinnae (the externally visible part of the ear). It is sometimes compared to the red rock hares, some of which overlap it in distribution; in its first description, it was noted as being about the same size as the Natal red rock hare (Pronolagus crassicaudatus), though it has been later described as smaller than all red rock hares besides Smith's red rock hare (P. rupestris).
Habitat and distribution
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