MR MCGREGOR’s only desire was to keep Peter and his pesky playmates off his vegetable patch – and, if he got lucky, to make a pie out of them, according to Beatrix Potter. Meanwhile Elmer Fudd’s fervent wish was to , Bugs.
Popular culture depicts a certain antagonism between human and rabbit, while often emphasising the bunnies’ role as sassy survivors. But having already seen off one huge existential threat in the past century, the viral disease myxomatosis, rabbits now face another horrendous adversary, rabbit haemorrhagic disease virus, or RHDV. At the same time, we have come to realise that rabbits aren’t just fast-breeding agricultural pests, but key to many healthy, functioning ecosystems worldwide. “Rabbits are in a lot of trouble,” says Pip Mountjoy at UK government agency Natural England. “They need our help.”
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The European rabbit, Oryctolagus cuniculus, . It was once widespread across Europe, including the British Isles, before being penned into Iberia by the last ice age. Their global expansion began in the 1st century BC with the Romans, who domesticated rabbits for food and fur and spread them back across their former range.
Some say the Romans reintroduced the rabbit to Britain, others point to the Normans. It was definitely the British who brought them to Australia in 1859 and New Zealand in the 1860s. A small colony established in the US in 1875 to control weeds quickly expanded across North America. The European rabbit is now one of the most widespread species on Earth, living on every continent except Antarctica.
That is partly because rabbits breed like, well, rabbits. Females are reproductively mature at three to four months and have frequent litters of up to six kits. A breeding pair can produce 40 kits a year, and fertile males roam widely (see “Rabbit rules”). In the 19th and early 20th centuries, developments such as the planting of winter fodder crops for livestock and the slaughter of natural predators also boosted populations, making rabbits a serious agricultural pest in many parts.
With shotguns, ferrets, traps and poisons proving to be ineffective, and fences simply burrowed under, thoughts turned to a more dastardly method of control: biological warfare. In the 1950s, through a mixture of accident and intention, myxomatosis was unleashed, almost entirely wiping out rabbit populations, first in Australia and then in Europe (see “Myxomageddon”, page 44).
Only then did we realise how much we missed them. It turns out that rabbits are both a keystone species and an ecosystem engineer crucial to maintaining entire sensitive food webs and habitats. On the island of Skokholm off Pembrokeshire, UK, for example, scene of an early myxomatosis trial, rabbit burrows provide nesting sites for puffins and shearwaters. Many airborne and land-based predators rely on rabbits for food, while their relentless grazing and burrowing maintains semi-open “mosaic” habitats rich in wildlife. One example is the , UK, a Special Area of Conservation that features the country’s only active, constantly moving inland sand dunes and rare wildlife, including the , a plant found nowhere else in the world.
Following rabbits’ near-elimination in the UK, some farmers rejoiced at increased crop yields. But plant communities became less diverse and rabbit-eaters, such as buzzards, stoats and peregrines, suffered heavy losses. In 1979, the large blue butterfly went locally extinct in the country, its caterpillars starved by a lack of the red ants that once thrived in rabbit-grazed grasslands and fed them. Similar shifts were seen in Australian wildlife, with .
It might seem counter-intuitive that an introduced species can also be a keystone species, says , UK, who has been studying Britain’s rabbits for half a century. But many landscapes in places like the UK are intensively managed, so what is “natural” is debatable. In areas like the Breckland, rabbits have taken over from native herbivores that are no longer present, such as wild boar, says Mountjoy.
The new threat of RHDV was identified in China in 1984. It kills 80 to 90 per cent of its victims like a bunny-boiling Ebola. Victims bleed from the mouth and nose, convulse, fall into a coma and die. The first wave of the disease spread rapidly into Europe. Spain recorded its first case in 1988. Soon more than 60 per cent of Iberia’s wild rabbits succumbed, pushing their natural predators, the Iberian lynx and the Spanish imperial eagle, closer to extinction.
A new wave of a related disease, RHDV2, struck in 2010 and caused further “massive declines”, says Miguel Delibes-Mateos at the Institute for Advanced Social Studies in Cόrdoba, Spain. Between 2012 and 2014, the rabbit population in the Doñana National Park in Andalucía, Spain, once a rabbit stronghold, fell by more than 80 per cent. Across Iberia, declines of 60 to 70 per cent have been closely mirrored by falls in lynx and eagles. The UK Breeding Bird Survey, which also records mammals, shows a 64 per cent decline in .
The origin of the RHDVs remains unknown, says Kevin Dalton at the University of Oviedo, Spain. Like myxomatosis, they might have jumped species, or they could have arisen from recombination events, where two viruses mash up their genomes. But their effects have been enough for the International Union for Conservation of Nature to . As recently as 1996, it was in the “least concern” category.
Conservation efforts so far have largely failed, in part because many people still consider rabbits a common pest and fair game. “Why would a species that you kill 6 million of a year by hunting need conservation?”, says Carlos Rouco at the University of Cόrdoba. Around , but more than 90 per cent die from predation, disease and stress.
There are some glimmers of hope. In some areas of Spain, 60 per cent of rabbits now have antibodies to RHDV2. And . There are two subspecies – Oryctolagus cuniculus cuniculus and O. c. algirus, which diverged around 2 million years ago – that each occupy their own halves of the Iberian peninsula, divided by a diagonal line running north-west to south-east. They coexist along the border, but don’t interbreed; Delibes-Mateos has proposed that they should be recognised as separate species. The big declines are in the O. c. algirus zone to the south, which is also where the lynx and eagles live. To the north, O. c. cuniculus is stable or even increasing. Exactly why isn’t known, says Delibes-Mateos, but finding out could be a route to stabilising populations in the south.
One way to help colonies seems to be to increase their size, perhaps because rabbits then have more exposure to the virus as kits and develop immunity. In Breckland, Bell has found that piles of brush placed strategically within 40 metres of an occupied warren provide enough cover for rabbits to expand their earthworks. In a , more than 40 per cent of her brush piles ended up with a warren underneath and more than 90 per cent showed signs of rabbit activity. This simple, low-tech but effective intervention could be used in any rabbit-dependent habitat, she says. Rouco and Delibes-Mateos suggest something similar could make previously unsuccessful restocking efforts more effective.
Other interventions would be more general habitat restoration, although there is little money around for that, and to stop keeping domestic rabbits in close proximity to wild ones. Otherwise, however, it seems we have little choice but to let evolution run its course and hope the virus becomes less deadly. Some point out that the current huge drops in rabbit numbers are measured against the 1950s, when populations were possibly artificially inflated. Overall, it is clear rabbits are in a hole, says Rouco – but then again, they have bounced back before. “I’m 95 per cent confident they won’t go extinct,” he says. Here’s hopping.
Myxomageddon
The devastating lethality of myxomatosis on the European rabbit was first noted in 1896, when bacteriologist Giuseppe Sanarelli at the Uruguayan Institute of Hygiene in Montevideo watched in horror as almost his entire colony of imported experimental rabbits succumbed to an unknown disease. Necropsies revealed the cause of death as tumours in multiple organs, hence the name: a myxoma is a type of connective tissue tumour.
Sanarelli thought mosquitoes were implicated because rabbits kept indoors didn’t catch the disease. After failing to find a bacterial cause, he also surmised it must be viral. He was right: myxomatosis is caused by a poxvirus carried by mosquitoes and other biting insects that normally infects South American cottontail rabbits benignly.
In the early 1930s, the Australian Council for Scientific and Industrial Research (later CSIRO) hit on the idea of using myxomatosis for biological control. In 1934, former employee Charles Martin, by then in semi-retirement at the University of Cambridge, UK, , and wiped out the lot. Field trials followed on Skokholm, an island off the coast of Pembrokeshire, UK, that had become overrun with rabbits, as well as in Australia, but they flopped.
In 1950, however, CSIRO released infected rabbits into the Murray valley in south-east Australia. These died without significantly spreading the disease: myxomatosis can be caught though close rabbit-to-rabbit contact, but ill rabbits tend to socially isolate.
Later that year, however, myxomatosis suddenly erupted, spreading fast and with almost total lethality in the rabbit populations it encountered. The turnaround was put down to the Australian summer of 1950 to 1951 being very wet, meaning myxomatosis-carrying mosquitoes bred in areas normally too dry for them. When the outbreak fizzled out in 1951, it was because almost all of south-eastern Australia’s estimated 100 million rabbits had already kicked the bucket.
It was a similar story with a European outbreak that began when French bacteriologist and landowner Paul-Fόlix Armand-Delille deliberately and illegally released two rabbits he had infected onto his estate in France in 1952. The disease rapidly spread across western Europe and into the British Isles. There is a widespread belief that the disease was deliberately introduced into the UK, but it appears it wasn’t: according to a , Fisheries and Food, it was much discussed, but never approved. The first case, recorded in Kent in 1953, probably hopped across the channel naturally. Deliberate spread of myxomatosis was criminalised in the UK in 1954, but this was too late: more than 99 per cent of rabbits that encountered the disease in the UK died, a carnage they are still recovering from (see main story).
Rabbit rules
Rabbit society is “really complex”, says Diana Bell at the University of East Anglia in the UK. They live in groups of up to 20 individuals, which cooperate to defend their territory, but fight like rabbits in a sack for dominance over it. The prize for being alpha female is control of the group’s breeding rights; for alpha males, it is access to females.
Once weaned, male offspring leavethe warren to spread their wild oats. Females stay put in the territory, forming a matriarchal society of mothers, daughters, sisters, grandmothers and aunts led by the dominant female. She rules the warren with a rod of iron, often killing her subordinates’ kits by dragging them into the open to be picked off by predators.
But the top job is often up for grabs: while wild rabbits can live to nine, . “In Spain, they have more than 30 predators,” says Carlos Rouco at the University of Cόrdoba. Corre, conejo, corre!
