A Plague of Rabbits

In Australia, rabbits are a curse.  The long-eared infestation started in 1859 when Thomas Austin, an estate owner, imported a mixture of wild and domestic rabbits from Europe to release on his large farm.  He hoped to recreate the hunting conditions of England where he had enjoyed shooting rabbits when younger.  He is famously quoted as saying  “The introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting.”

Rabbits in the Arid Australian Countryside

Thus began the greatest population explosion of mammals known in human history.  Within a decade, rabbits had overrun Southern Australia. Two million of the animals were harvested annually with no effect whatsoever on the larger population.  A combination of mild winters, no predators, and light scrub vegetation allowed the creatures to breed year round and increase their numbers exponentially with no natural resistance. They ate away whole ecosystems of scrub vegetation and outcompeted the little marsupial herbivores that lived there into extinction.  By gnawing down saplings they killed entire forests within the lifespan of the trees therein.  By digging warrens and denuding the vegetation they caused widespread erosion.  It was an ecological disaster of the first order–a mass extinction caused by bunnies(!)–and only humans were there to fight the fleet-footed enemy.

Australians responded gradually at first and then with increased alacrity and fury.  Shooting and trapping gave way to mass poisonings, ploughing, blasting, and fumigation. Tens of thousands of miles of rabbit proof fence were strung across the continent.  Wicked old world predators like rabbits and foxes were imported to stem the flood of rabbits (and naturally the predators first concentrated on eliminating remaining species of Marsupials).

Rabbits around a waterhole on Wardang Island (1930s)

Australians have gradually learned to make use of the rabbits.  In times of distress, depression, or famine they have provided a ready source of food for humans and farm animals (ground up rabbits were once a major source of chicken food for example).  The fur from so many rabbits created a fur industry and a felt industry.  But make no mistake, the Australians still hate the invasive creatures.   The twentieth century has seen a new campaign of biological war against the rabbits.  In the 1950s an introduced strain of Myxoma virus wiped out an estimated half a billion rabbits.  Then in the early 1990s a calicivirus escaped a secure biological research facility (where scientists were engineering the disease to kill rabbits) and quickly spread through wild and domestic populations.   Yet despite all of the measures taken to kill the creatures they have endured and thrived.  Rabbits are still there, still causing havoc.  It is one of the more vivid lessons in human history about the difficulties of controlling ecosystems.

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Flux

Yesterday’s post—which featured a gory painting of medieval deer hunting—makes one feel sorry for the poor beleaguered deer, which are surely among the most beautiful and graceful of all animals.  And those painted deer were being pursued by crossbow hunters—imagine how much worse things would be with high-powered rifles.  Well actually you don’t have to imagine–here in North America, the dominant cervid, the magnificent white-tailed deer (Odocoileus virginianus) was severely overhunted in the 1800’s as hunters shot wild deer and sold the venison at the market.  Deer populations crashed down below 400,000.  Entire regions of the country lost the white-tailed deer completely.  The sacred animal of Artemis was in deep trouble across the United States.

Deer hunting in 1916

To rectify this situation, the Lacy Act, the first federal wildlife law, was passed in 1900.  The law banned the interstate trafficking of venison (along with other wild game).  Then the Great Depression and the Second World War came along and everything changed again.  During the Depression, rural landholders were forced to move into cities to make a living and land which had been under the plough began to grow back into forest.  When World War II broke out a generation of hunters went abroad to shoot at the Axis instead of whitetails.  After the war, in the 1950s, a clever biologist named Crockford invented a dart-gun system for capturing white-tailed deer and releasing them into habitats where they had died out. So deer made a comeback but their predators did not.  Wolves, grizzlies, cougars, jaguars, alligators, and lynxes were relegated to the deep forest and swamp of protected national parks.

So by the end of the twentieth century, white-tailed deer populations were spiking out of control (heading to well above 30 million) and this in turn had a terrible effect on the forests.  When a forest is partially or wholly timbered (or when it is denuded by some natural means such as a tornado) there is a succession of plant growth which after decades leads back to a mature hardwood forest.  The first plants to grow back are meadow plants–short-lived annual herbs and meter-tall woody plants. Over the course of years these weeds give way to hardwood seedlings like oak and maple which can tolerate the shade created by the provisional meadow growth.  However, in areas overpopulated by deer, the woody meadow plants are nipped up by starving deer and other tree seedlings which can out-compete the great forest trees for nutrient gathering (but which are not shade-tolerant to survive the meadow plants) then flourish.  Beeches, wild cherries, or exotic invaders grow up and the trees of the great forest take lifetimes to supplant them (if they do at all).  In the meantime the overpopulated deer begin to starve and suffer diseases even as they damage the forests.  A strange truth of ecosystems is that predators are nearly as necessary as their prey—even hardy generalists like the white-tailed deer which can live almost anywhere need population controls for their own good (as well as that of the forest).  Perhaps the ancient Greeks were wise to decide that their goddess of the wilderness was both a hunter and a protector of animals and trees.

The white-tailed deer (Odocoileus virginianus)

Biologists, foresters, rangers, and sportsmen are all trying to unscramble the secrets to ecosystem equilibrium, but there might not be any real long-term balance.  The tropical swamps and forests of the Eocene gave way to the temperate woodlands of the Oligocene (where the first tiny deer developed in Europe) which in turn led to the savannahs of the Miocene which allowed artiodactyl grazers to radiate out across the world.  But it is hard to think in such big terms and it is uncomfortable to think about what will come next.  Something within me longs for homeostasis—for the right number of lovely deer beneath the tall native oaks and tulip poplars forever and ever.