Conservation is all about decision-making. It is also a crisis discipline. I recently saw a meme describing conservation as the world’s hardest game of ‘Would you Rather?’ and this made me laugh, because it’s true. A lot of time, there is no clear path to success, no right or wrong. There are almost always trade-offs, compromises, and hard pills to swallow.

Culling is a typical example of a trade-off. Culling is the selective killing of members of an animal population in order to reduce the overall population size. It is considered controversial because it means that someone, somewhere decides who lives and who dies, and because it seemly contradicts the aims of conservation. The notion of conserving wildlife and biodiversity on the face of it suggests conserving all wildlife. Therefore, the idea of killing even one animal and calling it conservation, seems like a direct contradiction.

So, can you ever kill animals and call on conservation?

There are many examples where culling is required for the greater good. There are three main circumstances under which culling is used as a form of conservation management:

1. Population control
2. To remove invasive species
3. Controlling disease among a population

1. Population Control

Sometimes population control is necessary for conserving biodiversity as a whole. The majority of terrestrial natural spaces, including national parks, are finite spaces. This is largely due to human encroachment, to prevent conflict with humans, and to protect the biodiversity within the space. Therefore, if certain species populations get too big, culling is used to reduce their size.

A finite space, say a national park, will have a carrying capacity for various species. Carrying capacity means the maximum population size of a species or group of species the environment can sustain given the resources available. For example, National Park A may have a carrying capacity of 40 elephants and 100 smaller browsers, whereas National Park B may have a carrying capacity of 20 elephants with 170 smaller browsers.

Anything above these levels and there would not be enough browse to sustain the populations of elephants and smaller browsers. Equally, too far below these levels could mean that the woody vegetation cover would increase which could be problematic for other species, such as grazers or those who rely on grassland. Maintaining ecosystem equilibrium is an essential part of conservation management, and thus understanding the area’s carrying capacity is incredibly important. Finite spaces mean finite resources.

There are of course, several possibilities to consider if you decide you need to reduce the size of a particular population. Let’s take deer as our example: You run a national park and the deer population in your park has increased above carrying capacity and you need to reduce it. Deer are grazers and having large populations of grazers can be detrimental as when grass becomes over-grazed it can lead to soil erosion, which can cause flooding of rivers. Equally, if there are too many grazers, the grass won’t keep up and eventually, you could run out of food to sustain your deer population.

The options you have include culling, translocations, sterilisation, and biocontrol.

Translocations are a good option if there is another national park who is below carrying capacity of deer and would take some of yours. Equally translocations are an important tool to improve genetic diversity within your population. However, this is expensive and if everywhere is at carrying capacity or above, you have nowhere to go.

Sterilising your population to prevent it increasing solves the problem going forward, but it is also expensive and in certain species it is not a reliable method of population control. Furthermore, if you are already too far above carrying capacity, then sterilisation alone does not solve your problem.

Biocontrol is where your head turns next. Biocontrol means introducing a biological agent to control the population using natural processes.

Yellowstone National Park famously reintroduced wolves to control the deer populations there and re-establish an ‘ecology of fear’. The deer population numbers not only dropped with the wolves’ present, but the deer also moved around more and relieved grazing pressure on the vulnerable floodplain. To  control your deer population, you could bring in wolves or other predators. However, as you might imagine, introducing a top predator into any environment is not as simple as just finding a wolf, shipping it over, and releasing it on your land (not that any phase of that would be simple either). There would be huge amounts of red tape, and you would need cooperation and support from local people to introduce wolves nearby, particularly farmers.

So, you are left with culling: killing individuals to reduce the overall population size. Although this sounds harsh, it is cheaper and easier than the other options. Sometimes culling can be used in unison with sterilisation, meaning less animals need to be culled. Although introducing wolves may sound like the optimal solution for the environment, allowing nature to correct itself (or correct our mistakes), there are so many added complications. Culling is simple and effective.

2. Invasive species

Invasive species are species that have been introduced to a new area (either on purpose or accidently) but are now causing damage or having a negative impact on indigenous (native) species. Not all introduced species are invasive, only those that cause harm. Culling is widely used to remove invasive Indo-Pacific lionfish, Pterois volitans and P. miles in the Caribbean. Again, the use of biocontrol is often favoured and sometimes incredibly successful and effective. I think most conservationists would prefer the use of biocontrol to culling, but sometimes culling is all we are left with.

There is always an ethical dilemma related to culling: is it okay to kill living creatures? But when it comes to invasive species, this dilemma is nuanced by how that species came to be invasive. If we introduced the species to a new area ourselves, either accidentally or deliberately, are we justified in removing it in such a way? Equally, if the species has been long established in its new home, even if it is causing harm to the other residents, what are the ethics of removing them?

Interestingly, most people probably feel more comfortable culling invasive species than culling for population control of native species, because we can more clearly see the problem and the harm invasive species are doing. We can treat invasive species as the “bad guys” and thus, sleep safely in the knowledge that our culling programme will save the day. We often don’t dwell on the fact that human activities are the biggest cause of the spread of invasive species.

3. Disease

Culling has been used to control the spread of disease in the past, both within populations and to prevent cross-species contamination, including from wildlife to humans and domestic animals. In southern Africa during the 20th century, wildlife-free corridors were created through culling about 660,000 animals across 36 species (including elephants and black rhino) in order to protect cattle farms from the spread of trypanosomiasis. Culling red foxes  during the 1960s was more effective than oral immunisations at controlling rabies in Europe.

However, unlike in the cases of population control and controlling invasive species, the use of culling to control disease is often ineffective. Badgers in the UK are culled in an attempt to limit or prevent the spread of bovine TB which impacts the farming community. However, there is no evidence this cull is working, and no scientific conclusions can be drawn from the cull pilots. In fact, scientists concluded after an 8-year-long study by saying ‘badger culling  can make no meaningful contribution to cattle TB control in Britain.’

Making decisions without evidence could have detrimental impacts on the ecosystems badgers inhabit, as well as the badger populations themselves. The badger cull is strongly opposed by scientists and other conservationists (myself included), the British Veterinary Association, and the vast majority of the British public.

Conclusions

Overall, there is a place for culling within conservation when used correctly. When populations of certain species exceed the carrying capacity of a reserve or national park, then that population needs to be reduced to allow the ecosystem to function and other species to thrive. The same goes for invasive species. If culling is the only available option, then that is what is needed. It is a shame that often these decisions come down to money. When it comes to controlling disease, culling is often less effective than other measures, and implementing an ill-thought-out culling programme can have catastrophic consequences.