HIPPOS in South Africa, cats in Australia, deer in the US, badgers in the UK. Across the world, governments are announcing plans to cut back the numbers of some of our most-loved animals. The latest is a Siberian reindeer 鈥� which could spread anthrax 鈥� just before Christmas.
Such mass slaughter invariably sparks fierce debate between politicians, conservationists, farmers and animal-rights activists. Is it reasonable to kill animals if they threaten other species or are under threat themselves?
There are three circumstances that justify lethal wildlife control, says Bidda Jones of animal welfare group RSPCA Australia. The first is if culling will save animals from an even worse fate. For example, South Africa announced last month that it would kill some from suffering food shortages while the country endures a severe drought.
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Culling can also be necessary if other animals are harmed by a species out of control. Feral cats are culled in Australia to protect native wildlife. Kangaroos are also lethally controlled when their numbers balloon, to prevent them from .
Finally, animals that threaten livestock or human safety may need to be eliminated. In the US, overabundant deer are culled to prevent car collisions and Lyme disease transmission to humans. In the UK, badgers have been culled to slow the spread of bovine tuberculosis among cattle. And Norway has recently approved a plan to cull two-thirds of its native wolf population to reduce attacks on sheep.
The ethical debate becomes murky when a decision must be made about which animals warrant greater protection, says Jones. 鈥淧eople have different values,鈥� she says. Farmers value their livestock, conservationists often seek to protect overall biodiversity, which may require culling certain species, whereas many animal-rights groups believe that all killings are unjustified.
Popular animals tend to attract the most vocal support, says Katherine Moseby at the University of Adelaide, Australia. The public backlash last year when the Australian government announced a plan to kill is one example. 鈥淧eople love what they know 鈥� they have cats as pets and spend a lot of time around them and understand them,鈥� she says. 鈥淏ut they鈥檙e not the ones out there seeing our native wildlife being slaughtered by cats every day.鈥�
Culling methods vary, from shooting in the head 鈥� seen as the most humane way because of its immediacy 鈥� to poison, traps and even specific viruses, but does the general principle actually work?
Killing overabundant species seems like a logical strategy to reduce their impact, but it often backfires, says , an ecologist at the University of Tasmania, Australia. 鈥淚n many cases, removing some animals actually increases the survival and reproduction of the ones that remain, and provides opportunities for new animals to move in,鈥� he says.
Isn鈥檛 it ironic?
This was recently demonstrated in Tasmania, when culling a third of the feral cats at four study sites led to population increases of between 75 and 211 per cent. Remote cameras showed that as dominant cats were removed, more cats crept in from outside. Equally, a small-scale culling of ferrets on Rathlin Island in the UK ended up doubling the population because the remaining ones had more resources, which encouraged additional breeding.
Killing predators to protect livestock can also have counterintuitive effects. A recent US study found that the more wolves were culled, the more and cattle there were the following year. Attacks on Australian cattle have also been shown to be higher after dingoes are baited. 鈥淭he wolves or dingoes that move in are typically solitary young males. They often have a higher propensity to attack livestock than the family groups that would be there if you just left them alone,鈥� says Johnson.
The in 2013 in the UK is on similarly shaky ground, with no clear evidence yet that it is reducing bovine tuberculosis cases. 鈥淥ften these things are done unthinkingly,鈥� says Johnson. 鈥淭here鈥檚 very rarely a proper evaluation of whether it will work and justify the cost.鈥�
Lethal wildlife control can be effective if it is widespread or conducted on islands, so that culled animals are not replaced by more from outside the region, says Johnson. For example, Australia recently successfully by shooting them from helicopters, targeting their entire 1.3-million-square-kilometre range. This large-scale approach prevented the camel population from rebounding, but was costly and labour-intensive.
Is there a better way? Non-lethal solutions for managing wildlife are cheaper, more ethical and more effective, says Johnson. Instead of trying to minimise animal numbers, these approaches often focus on minimising their impacts.
One example of this strategy is to plant more native grasses to make it harder for feral cats to catch small mammals that hide in them. In sparse, open landscapes that have been degraded by grazing and fire, 70 per cent of feral cat hunts are successful. But in thick, grass-covered areas, only 17 per cent of hunts succeed.
鈥淭he more the wolves were culled, the more attacks on sheep and cattle there were the following year鈥�
Farmers have found that stationing guard dogs deters predators from attacking livestock. In a , cheetah attacks on sheep, goats and cattle stopped in 91 per cent of places with guard dogs.
鈥淭hese sorts of indirect measures 鈥� increasing vegetation cover, improving land conditions and so on 鈥� can be implemented fairly easily,鈥� says Moseby. 鈥淚 think culling has to stay in there as an option but we need to look at the broader picture.鈥�
Some have suggested more unusual ways to keep numbers down. Small studies have demonstrated that contraceptive implants can reduce the reproductive rate of kangaroos, but the approach is expensive and unsuitable for animals that are difficult to trap or that spread over large areas.
Genetic engineering techniques such as CRISPR could be used to alter sex-determining genes in invasive species so that all offspring are male and sterile. This has been demonstrated in lab mosquitoes, but hasn鈥檛 yet been tested in the wild. 鈥淭here are obviously massive questions about whether it would be ethical and what would happen if it got into areas where animals were native,鈥� says Moseby.
Sophisticated non-lethal control strategies may help to appease our guilt over killing animals, but we still don鈥檛 know if they will be effective or about their potential downsides.
In the meantime, it is important to ensure that the control methods we use are scientific and thoroughly evaluated. Killing wildlife is often seen as a quick fix, but it won鈥檛 work, or it might backfire, if it is not done in the right way. Evidence-based non-lethal approaches such as landscape modification also need to become integral parts of wildlife management plans. Not only will this help us manage wildlife, it will also help us sleep at night.
Letting nature take its course
Now that we鈥檝e wreaked havoc on native ecosystems by introducing foreign animals, there is a sense of obligation to clean up the mess. But what if we didn鈥檛 try to remove the invaders?
Some ecologists believe that restoring ecosystems to their past glory is impractical. Writing in Nature, a group of ecologists recently argued that we should 鈥渆mbrace the fact of 鈥榥ovel ecosystems鈥� and incorporate many alien species into management plans鈥�. If a hands-off approach was adopted, some native species could evolve defence mechanisms that allow them to coexist with invasive animals. For example, some native Australian snakes have evolved smaller jaws since the introduction of poisonous cane toads in the 1930s that reduce their ability to eat large toads containing lethal doses of toxin.
However, these are likely to be rare cases, says George Wilson at the Australian National University. Almost 90 birds, 45 mammals and 10 reptiles have already been driven to extinction by invasive predators, and the list of threatened species continues to grow, he says. 鈥淭he idea that you could just let nature run its course is absolute nonsense 鈥� it鈥檚 ecological cuckoo-land.鈥�
This article appeared in print under the headline 鈥淭o kill or not to kill?鈥�
