Riverine Rabbits must be one of the most challenging species we have ever had the privilege of working with. Long, cold midnight hours spent looking for this species as part of a research and monitoring project on Sanbona Wildlife Reserve, in the Klein Karoo, delivered excellent, but very infrequent sightings.
The popular history of the Riverine Rabbit, Bunolagus monticularis, reaches back to the beginning of the twentieth century when it was first collected by a British soldier convalescing at Deelfontein in the Great Karoo. Deelfontein is a village in the Northern Cape, 46 kilometers south of De Aar, and was selected as an ideal location for a large field hospital during the Second South African War (1899 – 1902).
Specimens were found by the British Trooper C.H.B. Grant while he was stationed at Deelfontein. Two specimens were sent to the British Museum of Natural History where Dr. Oldfield Thomas, keeper of the Department of Mammals, recognized it as a new species and described it as being “of an entirely different type to anything hitherto known, either from South Africa or from elsewhere”. The species was originally described as genus Lepus,
due to its hare-like morphology. However, because of significant differences to Lepus, the species nomenclature was changed sometime later to Bunolagus monticularis. The original belief was that the species utilized rocky habitat which would explain the specific name ‘monticularis’, as the dictionary definition of a monticule is a small mountain, hill or mound. Probably because of the similarity of Pronolagus and Bunolagus it must have been assumed that Bunologus would have shared the habitat requirements of rocky and mountainous terrain. This led Captain G.C. Shortridge, the Curator of the Kaffrarian Museum in King William’s Town, who was a prolific collector of zoological material, to take up the search for the species and offered a reward of a pound Sterling for the capture of a specimen, which spawned on of the species common Afrikaans name “pondhaas” (poundhare). Due to the inaccurate habitat description Shortridge was misled for 20 years, searching in mountainous and rocky habitats for the species.
In 1947 the residents of Calvania pointed out to Captain Shortridge that he was looking in the wrong terrain and should concentrate his search on the alluvium fringing dry river beds. Shortridge began searching the Karroid scrub along the seasonal Fish and Rhinoceros Rivers in the surroundings areas and was at once successful, collecting four specimens. This was the first sign that the habitat described by Dr. Thomas was incorrect. Once aware of the incorrect habitat description Shortridge returned in the following year of 1948 and collected more specimens along the Fish River, approximately 100 kilometers south of Calvania, also in the Great Karoo, linking the species to this specific Karoo habitat.
In 1978 a research project was launched by the Mammal Research Institute of the University of Pretoria, and during the initial search for Bunolagus along the Fish and Rhinoceros rivers, the researchers realized that most of Riverine habitat had been ploughed under. Eventually a specimen was collected in the Victoria West district. Due to the alarming decrease of the required habitat, and the lack of any studies on the life history of the Riverine Rabbit, the species was placed on the endangered list and a study of its ecology was initiated.
In 2004 the first records of this species in the Klein Karoo in the Western Cape was documented outside of Touwsrivier, and in 2006 a dead roadkill specimen was found on Sanbona Wildlife Reserve in the Klein Karoo. Subsequently there has been more specimens found in the Robertson district on a wine farm just outside of the town.
On the 5th of December 2013, a research team from Cape Nature was successful in capturing a juvenile Riverine Rabbit on Anysberg Nature Reserve, also in the Klein Karoo – making this the first sighting of Bunolagus monticularis on formally protected land.
In 2014 the Endangered Wildlife Trust (EWT) launched a research study in the Klein Karoo. Currently all conservation efforts for the Riverine Rabbit and its habitat are coordinated by the Riverine Rabbit Working Group (RRWG), a Working Group of the EWT, which is an IUCN member.
The Riverine Rabbit Working Group’s vision is a functional, healthy Karoo ecosystem and suitable socio economic conditions that can support a stable population of Riverine Rabbits along the seasonal river courses of the Karoo region. The group aims to conserve the biodiversity of the Karoo region, to encourage private landowners to participate in conservation stewardship and to promote integrated land management practices that can sustain the Riverine Rabbit, its habitat and many other species while ensuring socio-economic benefits to landowners and communities – the species may thus function as the Flagship Species of the Karoo, and ultimately an indicator of riverine habitat health.
The latest edition of the Red data Book of South African Mammals: A Conservation Assessment lists the Riverine Rabbit as critically endangered, elevating the species from its previous status of endangered. Surveys showed that there existed less than 250 mature individuals. This rapid population decline is due to the loss of between fifty and sixty percent of the habitat in the past 70 years. The decline may have been arrested due to a decrease in cultivation, public awareness and the establishment of conservancies. No subpopulation is estimated to contain more than 50 individuals and the subpopulations are isolated due to anthropogenic (caused directly by human interference) barriers to dispersal. The possibility of extinction is forecast to occur within the next 100 years, and the likelihood thereof is greater than 50 percent.
The major reason for the decline within the population of the Riverine Rabbit is that the habitat has become highly fragmented and transformed. Studies have shown that Riverine Rabbit habitat has been fragmented up to 67 percent in certain areas and that can be taken as representative of the entire distribution. The decrease in habitat quality and quantity is predicted to continue and is exacerbated by the isolation of subpopulations by jackal proof fencing and severe land transformation.
There are a number of diagnostic features of the Riverine Rabbit which makes its identification quite easy. The ears are noticeably long in proportion to their body. There is a very prominent white eye ring and a black stripe running along the sides of the lower jaw along the cheek and tailing out upwards towards the base of the ears. There is creamy rufous tinged fur on the belly, throat and legs, with a prominent dark red patch on the neck. The hind foot is noticeable with its broad club like attributes and the tail distinguishes the River Rabbit from rock-rabbits due to its round and woolly appearance, also with a tinge of rufous and black towards the tip.
Riverine Rabbits are habitat specialists occurring in riverine vegetation on the soft and nutrient rich alluvial soils associated with the seasonal river systems of the Great Karoo. The riverine bush is dense and discontinuous and consists of shrubs 0.5 to 1 meter in height, providing shelter from heat and predators. Soil types are vitally important to the habitat of the species as the species utilises soft and deep silt soils for burrowing and constructing breeding dens. Very little is known of the ecology of the species within the Klein Karoo.
The Riverine Rabbit is a nocturnal species, feeding at night and resting during the day in forms that are scraped out underneath Karoo vegetation. In other hares and rabbit species, light, vegetation and temperature are the major factors that determine the length of the breeding seasons. However, in the semi-arid Karoo system, the unpredictable nature of the rainfall, accompanied by vegetation condition, are the factors that will stimulate reproduction in the Riverine Rabbit. The rabbit is the only digging rabbit to be found on the African continent and utilises the deeps alluvial soils in the river floodplains to construct stable breeding stops. As most of the Karoo is characterized by sparse shrub land that occurs on hard and rocky ground, only the Riverine areas manage to provide the deep alluvial soils to construct the breeding burrows. The burrow is long and broadens from the entrance. When occupied by young the rabbit will plug the entrance to the burrow with soil; and twigs. The females will build a nest inside the breeding chamber out of their belly hair and grass. The breeding season runs from August to May and normally only consists of one, or possibly two young. The young weigh 40 grams at birth and unlike leverets (newborn hares), which are born fully furred with open eyes and independent from their mother after 48 hours from their birth, the kittens (Riverine Rabbit newborn) are altricial. They are born blind, hairless and completely dependent on their mother. The kittens are reared inside the fur and grass lined breeding chamber for fourteen days by their mother before the young are ready to leave the burrow.
They are predominantly browsers, but will eat grasses during the wet growing season when the first green flush is available. Favoured browse is Pteronia ertythrochaeta, Kochia pubescens, Salsola glabrescens and Mesembryanthemaceae, which probably provides most of the Riverine Rabbits water requirements. Two types of droppings are produced. At night when the rabbit is active, hard pellets are deposited, while during the day caprophagy is practiced whereby the droppings are soft and reingested by the rabbit. In this way the Riverine Rabbit will be able to obtain Vitamin B, produced by bacteria in its hind gut as well as minerals such as calcium and phosphorous which are then recycled.
This is probably one of the most difficult species for keen naturalists to search for. Bionerds.co.za spent many EcoExploration hours on our own and with interested parties searching for these elusive rabbits, and in 3 years we had more than 100 sightings, with majority of them during the new moon phase on wind still nights. Currently the best places for possible sightings is Sanbona Wildlife Reserve where you could book luxurious accommodation and have a guide take to the most favourable areas on the reserve to see this rabbits. Anysberg Nature Reserve is also an option, where various accommodation options are available.