The Kangaroo industry
Failed Rabbit Controls in Australia
The history of the rabbit in Australia demonstrates that people can be really silly. In 1859, a farmer introduced 24 grey rabbits to remind him of home. At the time, the man wrote:
By 1900, the rabbits had reached plague proportions and were causing extreme environmental damage. They ring-barked trees, ate fields to oblivion and caused massive soil erosion by digging burrows.
While the introduction of the rabbit was on the silly side, some of the attempts to control the rabbit have been even more intellectually challenged. One of the early methods was to build a 1,833 km long fence to keep rabbits out of Western Australia. It was quite optimistic thinking to believe that it was ever going to keep out the singular pregnant female that would make it obsolete. Rabbits simply burrowed underneath, went through open gates or the fence was knocked down by camels and the rabbits went over the top. To make matters worse, the fence became a land version of the drift nets of death seen in the oceans. Kangaroos sometimes got their legs caught in the wires and thousands of migrating emus came to the fence and perished.
The next attempt at control was the myxoma virus. When it was first introduced in the 1950s, the virus killed up to 99 per cent of rabbits without infecting any other species. From a perspective of economics, the myxoma virus was a resounding success; estimated to have added billions to Australian agricultural output. From a perspective of native Australian animals; however, the virus was problematic. By temporarily removing rabbits from ecosystems, large numbers of predators, such as quolls, eagles, foxes, cats, and goannas, turned their attentions to small marsupials, such as bilbies, which were hunted into extinction before the predators also saw their numbers decline. Fast breeding myxomatosis immune rabbits subsequently migrated into ecosystems ravaged by myxomatosis. In comparison to what they once had been like, these ecosystems had few competitors for the rabbit, and even less predators. Paradoxically, the final outcome was in the rabbit's interests and biodiversity was actually decreased by trying to eliminate rabbits.
Perhaps the series of catastophes on Macquarie Island best shows of the environmental damage that has been caused by a obsessive desire to kill rabbits without considering that there may be collateral damage. Macquarie Island is a 34km by 5km island halfway between Australia and Antarctica. Cats and rabbits were introduced in 1860s to provide food if sailors were shipwrecked. Overtime, the two species formed a balance with each other.
That balance was interrupted in the 1960s when the myxomatosis virus was introduced to reduce rabbit numbers. Each time a virus outbreak decimated rabbit populations, the cats started hunting native birds. In the 1990s, scientists gained $500,000 in funding to eliminate a population of only around 500 cats that had been on the island for almost a century and a half. When the final cat was removed in 2000, rabbit numbers were somewhere between 4,000 and 20,000. Within 6 years, the population had reached 130,000 and Macquarie Island's vegetation was being eaten to extinction.
(Left. Macquarie Island before the removal of cats. Right, after the removal.)
In 2011, $26,000,000 was spent trying to remedy the disaster. The first stage of the plan involved releasing another virus, the rabbit calicivirus, which had an average kill rate of around 90%. The second stage involved using helicopters to drop 307 tonnes of brodifacoum baits for the rabbits that survived the virus. This was around 3 tonnes of bait for every square kilometre. The third stage involved hunters and dogs searching the island for the next seven years with burrow bombs, and poisons to kill the rabbits that were expected to have survived the virus and baits.
The virus and baits were released in July 2011. By December 2011, hunters had caught a further 13 rabbits that had survived the virus and baits. One of these rabbits was a female that had bred. In February 2012, it was reported in the Australian newspaper that perhaps 10 rabbits were still on the island, but they were difficult to find in the recovering vegetation. Because rabbit eradication attempts have previously failed on most islands, the survival of rabbits was anticipated.
Before the poisoning began, scientists conceded that the collateral damage of their rabbit control programs would include a significant number of the local bird population that either ate the baits or the poisoned bodies of the dead rabbits.
Although the scientists predicted the death of birds, they didn't predict that, upon the elimination (or virtual elimination) of rabbits, Macquarie Island would be overrun with invasive weeds that were previously eaten by the rabbits. Furthermore, they didn’t predict a 90 per cent die back of the native Azorella plant. One scientist explained the die back as a possible result of global warming. Another explained it as a possible side affect of dropping three tonnes of a very nasty chemical on every square kilometre.
On Macquarie island, the scientists choice of poison was brodifacoum. On the mainland, the preferred choice is 1080 poison, a synthetically produced substance that is a replication of a naturally occurring poison found in plant species such as poison bush. Although native animals can eat the foliage, seeds and flowers of the plants with no ill effect, it is deadly on the feral animals that have not evolved alongside it.
1080 is a slightly better control method than a virus and brodifacoum because as well as rabbits being killed, poisons can be made for cats and foxes as well. In this way, both predators and rabbits can be removed. Nevertheless, it is still results in a shock to the ecosystem and only temporarily removes the ferals until more migrate in to take their place. Furthermore, not all native animals have been exposed to poison bush thus 1080 can kill native animals as well.
Contrary to stereotypes, the rabbit isn't a great competitor and is not ideally suited to Australian conditions. Unlike marsupials, it isn't a great conserver of energy, it can't control its breeding to adapt to drought conditions, it isn't able to eat the diversity of food as can competitors like the bilby, and it is not as mobile through potted terrain as are hoping marsupials. On Kangaroo Island, goannas have actually eaten them to extinction.
The rabbit's only real advantage is that it is a fast breeder so can quickly fill voids when the ecosystem is in a state of imbalance or predators are low in numbers. It is just a shame that by trying to help the native animals, or protect lambs on sheep farms, humans are actually helping rabbits. If humans wouldn't interfere, the rabbit would probably go extinct in Australia just as it has gone extinct on Kangaroo Island and is in danger of extinction in many parts of the world. In areas of Australia that aren't subjected to continous fox, cat, and rabbit eradication programs, rabbit numbers are actually very low and do the little harm that the English settler originally envisaged.
Bush fire prevention