Riverine Rabbit

MammalSouth Africa

Sep 19

Bunolagus monticularis

The riverine rabbit is among the rarest rabbit species in the world. Considered 'critically endangered', only around 250 individuals survive in a few areas of the Karoo Desert in South Africa — where they typically live along seasonal rivers.

The riverine rabbit looks pretty generic, with no obvious features to differentiate it from the other 60 or so species of rabbit and hare.¹ Its fur is reddish-grey, darker on its rump, and silky soft. Its tail is stubby and fluffy, as are its little legs. Its leporine ears protrude high from its head. It wouldn't look out of place foraging in a European forest or bounding across the American prairie. But appearances, in this case, are deceiving, for the riverine rabbit is among the rarest of the Leporidae (rabbits and hares), among the rarest mammals even, and a species in imminent danger of extinction.

The Land of Thirst and Flood

The riverine rabbit is endemic to South Africa, found only in the central and southern regions of the Karoo Desert. The Karoo spans some one-third of South Africa; a land of dwarfish succulents, scrubby shrubs, and buried geophytes ² — each plant growing several feet apart. Sunlight sears and desiccates the soil and the entire region is devoid of any permanent surface water. The desert's name comes from the Khoisan word meaning “land of thirst.”

This seems an odd home for a so-called "riverine" rabbit. But while it may live in a desert, the rabbit is inextricably linked to river habitats — it's just that, for much of the year, those habitats consist only of dry riverbeds. Like the hardy desert vegetation, this rabbit is adapted to an austere and arid environment. To avoid the baking heat, it sleeps the day away in its cool subterranean shelter — it's the only native rabbit in Africa known to dig burrows and it's dependent on the deep, soft alluvial soils to do so. ³

Only when night falls does it emerge from its burrow to browse on the meagre desert fare; nibbling on salt-loving box-thorn plants, buchus, and ink bushes. To get the full benefits of this sparse diet, the rabbit recycles its meals through its system; it eats its own poop. After foraging on foliage at night, and a bit of processing, it dispenses those nutrients in a new form, like all-natural M&M's, which it snacks on in its burrow during the day. Apparently — and this is a very fun fact — its nighttime poop is somewhat dry, while its daytime poop is wetter and richer in B vitamins, making for a tastier and more nutritious snack.

After months of dust and dehydration in the Karoo Desert, the onset of the wet season is often abrupt and intense, arriving in the form of dramatic storms. The driving rains revitalise the rabbit's riparian home ⁴; reviving the parched riverways, spawning seasonal streams, and spurring the ephemeral desert plants into lively rainbow blooms. These brief spectacles of moisture and renewal — typically occurring in Autumn and Summer — create the cyclical rivers beside which the riverine rabbit lives. They cause the banks to grow with dense patches of riverine bushes on which the rabbit feasts and create the soft soils in which it constructs its burrow — enabling the riverine rabbit to survive the austere desert during the rest of the year.

The Rare Riverine Rabbit

The riverine rabbit was discovered as a species in 1902 and, soon after, its survival became jeopardized. The curator of the Kaffrarian Museum in King William’s Town, a man named Captain G.C. Shortridge, put out an offer of one pound for every rabbit delivered to him. As such, the rabbit became known as the ‘pondhaas’, for its monetary value.

In addition to this direct prosecution, humans were stripping the rabbit of its already limited habitat. The flood plains on which the rabbit lives — usually just 100 to 200 metres (330 - 650 ft) wide — are formed as rivers overflow and deposit silt onto their banks. Not only does the silt's composition allow for the construction of stable burrows, but it also encourages the growth of vegetation that the rabbit needs to eat; creating a place more fertile than any other in the Karoo Desert. This fact didn't go unnoticed by people, who began to plough and cultivate these flood plains for their own crops. And where human crops grew, rabbits weren't welcome. Around 50–80% of the riverine rabbit's habitat has been lost to farmland.

With nowhere to burrow, the riverine rabbit has nowhere to raise its young. A female gives birth in a subterranean chamber lined with grasses and fur, where she can watch over her young, safe from predators above such as keen-eyed raptors. The saying "breeding like rabbits" isn't applicable to the riverine rabbit. Each year, the female gives birth to only a single hairless, blind, and helpless kit — an unusually low breeding rate for a rabbit. And this doesn't appear to be compensated by an increased lifespan, as the riverine rabbit seldom lives much longer than four years in the wild.

And the rabbit's longevity only dwindles. It's not only the young kits that must be wary of predators; the black eagle (a.k.a. Verreaux's eagle), with its over two-metre (6.6 ft) wingspan, can easily snatch an exposed adult rabbit in its talons.⁵ Typically, the riverine rabbit avoids such diurnal hunters by hiding in its burrow during the day, but if it is caught in the open, it's capable of impressive feats of agility; jumping more than a metre (3.3 ft) into the air and bounding over bushes, until it finds a sheltered place — usually a scrape in the ground beneath some foliage — where it can hide. But with the introduction and proliferation of livestock, much of the riverine vegetation is grazed down to twigs that offer scant cover from the eyes of an eagle. The rabbit has lost its shelter both below and above the ground.

Hunting pressure from humans continues — even though there is no longer an explicit bounty on the riverine rabbit's head. Our companions, domestic dogs, kill their fair share and this rare rabbit also ends up as roadkill. Rabbits are also indirectly killed when they try to venture onto the farmlands that were once their homes. Traps, set up by farmers to catch pests, sometimes snag and kill riverine rabbits instead. It's estimated that, over the past 70 years, the riverine rabbit population has declined by some 60%, if not more.

Farmer's Friend

In stories, the farmer and the rabbit are often portrayed as adversaries; the rabbit tries to eat the farmer's crops and the farmer tries to thwart it. In reality, the rabbit does a lot of good for the farmer — enough to compensate for a few pilfered carrots.

The riverine rabbit serves as an unwitting caretaker of the soil. As it munches on vegetation, it encourages the plants to regenerate and take root deeper into the ground, preventing the soil from being swept away in floods. Not only do these plants bind the soil, but they also filter rainwater into groundwater, which is then collected by farmers and used to water their livestock. Only through the rabbit's feeding habits is the soil, and the riverine vegetation, properly maintained.

The Future of the Riverine Rabbit

With so many factors to consider — hunting, habitat destruction, a changing climate — the future of any endangered species can often be summed up in one unsatisfying word; uncertain. The case of the riverine rabbit is only made more so by our lack of knowledge. The first step to conserving a species is knowing about it; what kind of habitat it needs, what kind of diet, its activity and breeding patterns, etc. The more we know about a species, the more effective our conservation actions will be. As an example, when choosing which area to use as a protected reserve, if we know everything the species needs to successfully survive and proliferate, we know how to make the most optimal decision.

While the riverine rabbit has long been associated with the Karoo Desert's seasonal rivers, it has begun popping up in habitats far removed from flat flood plains — its specific name, monticularis, even means "mountainous", eluding to one of the alternative types of habitats this rabbit has been found in. One of the main conservation goals ⁶, laid out by organisations like the IUCN, is to build up our knowledge of the riverine rabbit. This charge has been taken up by the Endangered Wildlife Trust (EWT), who've set up over a hundred camera traps to not only gain insight into the secretive lives of these rare rabbits, but potentially discover if populations of riverine rabbits are hiding out in non-riverine habitats.

The riverine rabbit's range map (see below) is split into two disparate chunks of area; a smaller one closer to Cape Town and a larger one further northeast — the latter is amusingly shaped like a deformed rabbit. Depending on new data, these ranges are likely to change. And, depending on how effectively we can enact conservation actions, the ranges may shrink or grow. At the moment, there are estimated to be around 250 riverine rabbits left in the wild and the species is 'critically endangered'. Maybe we'll discover more riverine rabbits hiding somewhere we don't expect, but we can't count on chance when an entire species is at stake.

¹ Within the rabbit and hare family (Leporidae) the riverine rabbit is the sole species in the genus Bunolagus. Apparently, the riverine rabbit isn't closely related to other South African lagomorphs (such as the scrub and cape hares) — its closest relatives are actually a disparate bunch from overseas; the European rabbit, the Hispid hare from India, and the Amami rabbit from Japan.

² Geophytes are plants characterised by their underground storage organs (bulbs, tubers, or rhizomes) which hold water and nutrients. Some familiar examples are onions, carrots, ginger, and potatoes.

³ Alluvial soil, or alluvium, is the stuff left behind by rivers; such as sand, silt, loose clay, or gravel deposited in a riverbed.

⁴ A riparian habitat is one that straddles land and a river or stream, i.e. a river bank.

⁵ To hare and hyrax throughout Africa, Verreaux's eagle is a colossal, nightmarish shadow. It soars over hills and mountains on black wings, stretching to a span of 2.3 metres (7.5 ft). In South Africa, it's commonly just called the black eagle, but it shouldn't be confused with its smaller cousin from tropical Asia. Verreaux's eagle's main prey are hyraxes; stout herbivorous mammals unique to Africa. But where hyraxes are few, the eagle embarks on a diverse killing spree. It hunts hares and rabbits, meerkats and other mongooses, squirrels, cane rats, and other rodents, monkeys and bush babies, and even small lambs and antelope. Birds aren't safe either, with the eagle's kill list extending to crows, pigeons, chickens, herons, swifts, bustards, and sparrow-hawks. Tortoise shells too have been found in the eagle's nest. One study recorded over 100 prey species.

⁶ Along with additional studies on the riverine rabbit, another major conservation goal is teaching local farmers and the broader public what we do know about the species. You can read more about the conservation efforts here: Endangered Wildlife Trust , Sanbona Nature and Wildlife Reserve , Cape Nature, and Edge of Existence.

**Where Does It Live?**

⛰️ Typically near seasonal rivers, but possibly in other habitats too.
📍 The central and southern regions of the Karoo Desert in South Africa.

‘Critically Endangered’ as of 31 May, 2016.

IUCN

Size // Medium
Length // 34 - 47 cm (13 - 18.5 in)
Weight // 1 - 1.5 kg (2.2 - 3.3 lbs)
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: Around 4 years
Diet: Herbivore
Favourite Food: Leaves, flower petals, and grasses 🌱
Class: Mammalia
Order: Lagomorpha
Family: Leporidae
Genus: Bunolagus
Species: B. monticularis

The riverine rabbit sleeps the day away in its burrow; avoiding the daytime heat and diurnal predators. It comes out at night to browse on leaves, grasses, and flower petals.
To get the most from its sparse diet, the riverine rabbit recycles its meals by eating its own poop. It snacks on its own pellets during the day — apparently, its daytime poop is wetter and more rich in B vitamins than its nighttime poop.
In the Karoo Desert, wet seasons typically occur in Autumn and Summer; often coming in the form of sudden storms. During this time, the seasonal rivers, beside which this rabbit lives, flow with water and flood. This changes the composition of the soil and allows for a relative abundance of vegetation to grow.
The riverine rabbit relies on these alluvial soils, deposited by seasonal rivers, for constructing stable burrows, as well as the riverine plants for its food.
A mother riverine rabbit raises her young in her burrow. She typically only has one kit per year — an unusually low birth rate for a rabbit. The kit is born hairless, blind, and reliant on its mother.
Because its natural habitat is relatively fertile, the riverine rabbit has lost between 50–80% of it to farmland and overgrazing by livestock has removed much of the riverine vegetation the rabbit relies on.
Ironically, the riverine rabbit actually benefits farmers. Its eating habits promote the growth of riverine vegetation. The roots of these plants bind the soil and prevent it from being washed away during floods, and they also filter rain water into groundwater, which the farmers extract to water their livestock.
Although it usually avoids predators by residing in its burrow during the day, if caught in the open, the riverine rabbit is capable of bounding more than a metre (3.3 ft) into the air as it dashes away. It will then find a spot beneath some foliage to hide.
Habitat loss has deprived this rabbit of soil for digging its burrow — leaving it with nowhere to raise its young — and overgrazing has stripped the foliage in which it could hide.
Not long after its discovery in 1902, the riverine rabbit had a bounty set on its head. The curator of the Kaffrarian Museum in King William’s Town put out an offer of one pound for every rabbit delivered to him — as a result, the rabbit became known as the 'pondhaas'.
It's estimated that, over the past 70 years, the riverine rabbit population has declined by some 60%, if not more.
The riverine rabbit is the only species in its genus (Bunolagus). Its closest relatives aren't other South African rabbits and hares, but a distant bunch including species like the Hispid hare from India and the Amami rabbit from Japan.
Recent conservation efforts have discovered the riverine rabbit far from riverine habitats — captured on specially set camera traps in areas such as mountainous regions.