Source: http://www.biology-blog.com/
Culling is a term that most of us have heard, probably in connection with management of elephants in the Kruger National Park, or perhaps even badgers in the United Kingdom. This management practice has been the subject of a great deal of heated debate during the course of the last few decades because central to culling is the decision by humans to end the lives of animals. Managers claim that this is done in an attempt to improve the management of an area or population or both, but this is refuted by those who are opposed to culling. More recently the culling debate has erupted in our own back yard (Table Mountain), and it has been used in the media as a catch phrase to elevate the profile of the baboon management debate in the Western Cape.
Indiscriminate use of the term ‘culling’ in local newspapers has led to the misconception by the public that there is a culling protocol for the Peninsula baboons. This is exemplified by a resident of Cape Town suggesting that all of the baboons on the Peninsula have been culled after he drove to Cape Point and then walked through the Tokai plantation without seeing a single baboon. BRU is thus posting this latest blog in an attempt to stimulate informed debate on culling as a management tool and to inform the public on whether the media and members of the public are correct in suggesting that the Peninsula baboons are subject to a culling protocol.
We all live in homes, consume municipal water from dams, drive cars on roads and consume plant and/or animal products that are grown on farms. We have all therefore directly and indirectly contributed to the loss of natural land which is the ultimate cause of humans having to ‘manage’ wildlife populations that have been squeezed into ever smaller areas. We should all shoulder some of the blame for these losses and consequently need to debate sensibly, issues such as culling.
The big picture of culling
What is culling?
With respect to wildlife management, culling is defined as the practice of killing a significant proportion of an animal population in order to reduce the population size or control its growth rate. This practice differs from so-called ‘problem animal control’, which involves the killing of specific individuals to prevent them from causing further damage to infrastructure or causing harm to humans.
When is culling used as a management tool?
Managers use culling as a tool in a variety of situations, including ‘overpopulation’, unusual and problematic population age-sex structure, and when animals take up residence in an area that is undesirable for some reason (e.g., they are non-native to an area). It is essential to understand that culling typically reflects the need to manage a population that has already been adversely impacted by humans. The moment we confined animals to a reserve, prevented populations from engaging in large scale migrations, or removed key components of an ecosystem (e.g., top predators), so we evoked the need for further human intervention to manage ‘impacted’ populations.
Culling to reduce population numbers or change population structure
Strictly speaking, the term ‘overpopulation’ refers to the situation in which animals have exceeded their ‘carrying capacity’ in a given habitat. According to one scientific definition, a population has reached its carrying capacity when it stops growing (as a result of growth-limiting environmental factors). Wildlife managers may not be allowed to let this happen however, as large animals, such as elephants, may have profound structural effects on the landscape they occupy and share with other animals. When elephant numbers are too high within a confined area then elephants may impact negatively on entire ecosystems and indirectly result in the death of other animals. In this case, managers might employ sex- and age neutral culling in attempts to reduce the total numbers of individuals in the population and thus the number of individuals in the population that are breeding.
Unusual population age-sex structures may arise through translocation of animals of a specific sex and age-class, through culling schemes which have not been properly planned, or through deaths resulting from a pathogen that targets animals of a particular sex and age-class. If this occurs, and the condition persists, managers may see abnormal population growth and/or behavioural abnormalities in the population (see article). When this occurs, managers may cull the population selectively in order to restore a typical sex- and age-class structure in the population.
Culling to change patterns of habitat and space use
Examples of animals taking up residence in areas that are not desirable include carnivores that move on to agricultural land (where they may or may not hunt livestock), animals that inadvertently cause some sort of conflict (by moving onto roads for example) and animals that act as vectors of disease moving into agricultural and/or urban environments. When this occurs, managers may cull animals in those areas on a large scale. This may be done in order to reduce the chance of conflict between humans and animals (fewer animals results in lower probability of the problematic behaviour being witnessed). The area-selective culling may also indirectly reduce the numbers of animals present by frightening those that are still alive, away from the area in question (so-called ‘disturbance culling’).
Has culling proven to be successful as a management tool internationally?
There are numerous situations where culling has been applied. In every situation, there are those vehemently opposed to its use, and those strongly in favour of it. Thus, any culling programme must make a thorough assessment of the animal population in question and identify 1: a proximate problem (i.e. too many males, females, adults etc.) and 2: an ultimate problem (i.e. loss of vegetation, human-wildlife conflict etc.). Once the culling has been administered, an assessment must be made to determine whether the proximate and ultimate problems were solved. This is the only way in which the efficacy of culling as a management tool can be determined.
Source: http://www.flickr.com/photos/wabanafcr
Overpopulated white-tailed deer frequently feed in suburban gardens in the United States (proximate problem). When crossing roads, particularly at night, these deer can be a hazard. Annually, more than 1 million vehicle collisions are attributed to deer (ultimate problem). This translates to over 200 human deaths per year. In an effort to reduce these collisions, deer populations have been culled (by sharpshooting) and reduced to between 50% and 75% of their original numbers. Quantification of culling, deer numbers and deer-vehicle collisions, showed that culling was effective in significantly reducing deer-vehicle collisions by between 50% and 80%.
The spread and maintenance of tuberculosis in British cattle has been linked to badgers; animals susceptible to tuberculosis, and capable of transmitting it to cattle. In an effort to reduce the impact of badgers in the transmission of TB, culling was used to reduce their numbers. ‘Reactive culling’ (where badgers were culled in response to TB outbreaks in cattle) was actually shown to increase the incidence of TB in the local cattle. Researchers suggested that as the badger population was being reduced, so remaining badgers were moving more and encountering more cattle (and passing TB onto them). This culling therefore, only reduced badger numbers and did not reduce the spread of TB (ultimate problem).
Has culling been implemented as a management tool in South Africa?
In a local context, elephant management in Kruger National Park (KNP) has become synonymous with culling. The decision to cull elephants in KNP was made in 1967 in response to a growing elephant population. This population previously undertook migratory movements into Mozambique and further north. Fencing of KNP stopped this movement and the now-stationary population started to grow. More elephants meant more competition between elephants, more competition among elephants and other herbivores and more human-wildlife conflict as pressured elephants started breaking through the fence and into neighbouring farms. In the three decades following this, nearly 15000 elephant were culled. While culling managed to reduce elephant numbers (proximate solution), its impact on ultimate goals (conserving other large herbivores & reducing human-elephant conflict) was never quantified properly. In fact, the recommended population size of elephants in Kruger (approximately 7000 elephants) was never based on any ecosystem index. This means that the success or lack thereof of elephant culling in Kruger National Park was never quantified for most of its implementation. This example stresses the importance of identifying and measuring the ultimate targets of culling. Culling for the sake of culling has no management value.
Closer to home: Peninsula baboons and culling
What is the ‘new protocol’ for Peninsula baboon management?
The ‘new protocol’ is in fact not new at all, but is rather a revision of a protocol that was set out ten years ago (see “Getting smart on Bart”). The protocol provides management recommendations for males that disperse into urban areas and males that are repeat raiders, leaving their troops and foraging within the urban edge on human-derived food items. The Peninsula population is closed and there are no predators, thus there is only a finite number of management options that can be considered at present. One of these options is that males that are assisted in dispersing to new troops but fail to integrate and revert to raiding urban areas may, after three captures and relocations, be euthanized.
Are the Peninsula baboons being culled?
No. There is no culling protocol for the Peninsula baboons.
Is BRU masterminding a plan to cull baboons in the Peninsula?
No. Despite some crackpot suggestions by members of the public BRU has no authority to enact any management protocols. All BRU can do is provide the authorities with data that they may then use to inform their management decisions. At the City of Cape Towns “Baboon Expert Workshop” BRU was asked by the City of Cape Town organisers to present management options for the Peninsula population. The city requested specifically that BRU include the option of culling. To this end we stated that any closed population of wildlife that increased in numbers whilst losing space would ultimately face unprecedented levels of conflict and that culling was a management option considered by conservation authorities. Sterilisation is another tool used in the management of wildlife populations that are effectively fenced and thus have finite habitat. BRU strongly recommended alternatives to both culling and sterilisation which are extremely invasive and interfere with natural processes. These included:
1) reducing access to human-derived food sources which have been shown to increase the fertility of females relative to naturally foraging baboons
2) removal of alien vegetation which, because of higher above-ground biomass (relative to fynbos), increases the growth rates of troops relative to naturally foraging baboons
3) protection of the space that the extant troops are currently using. This, which forms part of Tali Hoffman’s PhD, was identified as the single most important step towards achieving the fundamental goal of a sustainable Cape Peninsula baboon population.
Source: http://www.gonomad.com/
Post script
Managers of the Cape Peninsula baboon population are in an invidious position. The more effective they are in reducing human-baboon conflict the more baboons will survive which means that the population will increase despite the ongoing attrition of natural land. Key to this issue is the simple fact that there are no natural predators of baboons on the Peninsula and thus if human conflict was completely eradicated, baboons would eventually become too numerous for the space left over. The question that we all have to grapple with, given we are all part of the problem, is what is the best management practice for the challenge of a population that may (with reduced conflict) exceed the space and food limitations of the Cape Peninsula island?
Further reading
DeNicola, A.J. & Williams, S.C. 2008. Sharpshooting suburban white-tailed deer reduces deer-vehicle collisions. Human-Wildlife Conflicts 2(1), 28-33.
Donnelly, C.A., Woodroffe, R., Cox, D.R., Bourne, J., Gettinby, G., Le Fevre, A.M., McInerney, J.P. and Morrison, W.I. Impact of localized badger culling on tuberculosis incidence in British cattle. Nature 426, 834-837.
Scholes, R.J. & Mennell, K.G. (eds) 2008. Elephant management: A scientific assessment for South Africa. Wits University Press, Johannesburg.
Van Aarde, R.J. and Jackson, T.P. 2007. Megaparks for metapopulations: Addressing the causes of locally high elephant numbers in southern Africa. Biological Conservation 134, 289-297.
