Culling is an established means of controlling animal populations in wildlife management, although sometimes met with controversy. In recent years studies have shown that the impact of culling on cognitively advanced mammalian communities that have highly complex social structures can result in long-term effects on the behaviour of survivors. Until the early 1990’s elephant culling was administered in South Africa’s largest game reserve, Kruger National Park, targeting adult members of the herds and relocating the younger members. Karen McComb and Graeme Shannon from the University of Sussex, UK, and colleagues studied a population of elephants founded from the young orphans of culls at Kruger National Park, and compared their behavior to that of elephants from a relatively undisturbed population. In their study published in Frontiers in Zoology, they investigated the social impact of culling on key decision-making abilities in members of these populations. Here McComb and Shannon explain more about the complex nature of elephant social structures and the implications of their findings.
How are elephant societies organised and how is social dominance determined?
Elephants live in complex fission-fusion societies, which involve the stable core units of related females and their young (family units) interacting, joining and separating from other social groups over time. Because of this fluidity, females come into contact with hundreds of others in the population as they move and feed. Relatedness plays a part here, with social groups more likely to associate with each other if the oldest females are genetic relatives. Another key aspect of elephant society is the dominance hierarchy, which is primarily determined by age, with older and larger females being more dominant than younger individuals both within the family group and also during inter-group encounters.
In what ways do African elephants recognise each other, and communicate dominance both within and between social groups?
Elephants use a range of different information to discern the identity of other social groups, including vocal communication and olfactory cues. These discriminatory abilities enable elephants to distinguish strangers that may present a genuine social threat from more familiar associates. Furthermore, such cues can be detected before the groups come into direct contact, providing a means for families to avoid each other and prevent conflict. Social dominance is based on size and age which, as we demonstrated in the paper, can be accurately discerned by elephants in our natural undisturbed population using key vocal characteristics such as pitch and resonance frequencies in calls. The social dominance hierarchy of closely associated individuals and family group members is likely established and learnt through experience from a young age. These dominance relationships are frequently reinforced by older and larger individuals leading decision-making and gaining primary access to key resources (e.g. water, shade).
Your study uses playback experiments to analyse the effect of human disturbances on the social structure of elephants. Can you explain what playback techniques are and how these were utilised in your study?
Playback experiments involve broadcasting high quality recordings of animal vocalisations in naturalistic situations and monitoring the response of listeners. This provides a very powerful tool for getting inside animal minds, allowing us to investigate decision-making and cognitive abilities in the wild as we did here. Playing specific calls back under controlled experimental conditions to known individual animals or social groups enables us to accurately document their behavioural responses to a range of social or ecological threat situations.
In this study, we used recordings of elephant contact calls from our study populations in Kenya and South Africa. Contact calls are vocalisations that adult females use to advertise their location to widely spaced social companions. In the first experiment, we used these recorded calls to compare social knowledge directly in the two populations on the basis of subjects’ reactions to callers from three distinct social categories (high and low association index callers within the same population, constituting familiar versus unfamiliar associates, and alien callers from a separate population). The second experiment contrasted the responses of family groups in both populations to callers where age-related acoustic cues in our re-synthesised calls accurately simulated unknown individuals on an increasing scale of social dominance.
What did your study reveal in terms of how human disturbances, such as culling and translocations, affect the social structure of surviving elephant populations?
The findings of our study demonstrated that the Pilanesberg elephants, which experienced a profoundly traumatic experience decades previously (i.e. culling) – followed by the loss of older social role models – had impaired decision-making abilities in realms that are central to social functioning in such a long-lived and cognitively advanced species. These elephants were unable to correctly assess key social information on the identity or dominance of callers (simulated using our playback experiments), whilst family groups in our natural and undisturbed Amboseli population exhibited well-developed social discrimination skills in these respects.
These results highlight for the first time how traumatic experiences have the potential to disrupt the cognitive abilities and social functioning of elephants in the long-term, with direct implications for population integrity. Furthermore, they provide key insights into the likely impacts of trauma on other long-lived social species including primates and cetaceans both in the wild and captivity. Indeed, our study was published shortly after the documentary ‘Blackfish’ was first released in the USA, a powerful film that explores the impacts of captivity on killer whales, another highly social and intelligent species, with strong parallels to the findings on elephants.
In the short term, it is likely that traumatic experiences (e.g. culling, poaching) result in survivors experiencing extremely high stress, which can lead to the expression of aberrant behaviours such as hyper-aggression, persistent fear and calf abandonment. Beyond this, the survivors then have to grow up in populations where older role models are absent.
Your study showed that elephants who suffer disturbances such as culling and translocation have poorer social skills. What do you think is the main cause of this deficit?
It is difficult for us to tease apart the relative contributions of direct traumatic impacts on neurological function and the loss of key social knowledge through the absence of older and more experienced individuals to act as role models. However, it is highly probable that both of these factors have significant impacts on survivors of extreme trauma, and that the specific contribution varies between individuals and populations. For example, whilst the Pilanesberg family groups demonstrated compromised social knowledge, they did not exhibit other widely documented behaviours associated with trauma, including hyper-aggression, persistent fear and calf abandonment. This has been observed in a number of other elephant populations in South Africa that were populated with individuals translocated following culling events.
What are the biggest threats to African elephant populations?
The greatest current threat to elephants is poaching for ivory. Since 2008 the demand and cost of ivory has risen dramatically, resulting in a surge of elephant killing across the continent that does not only threaten to drive populations towards extinction, but also severely impacts the social functioning of the survivors. The loss of available habitat and increased conflict with human populations also presents a severe threat to the long-term persistence of elephants in Africa.
What do you think are the most important tactics for elephant conservation?
Elephant conversation requires a multi-faceted approach, which includes direct action to prevent the illegal killing of elephants, whilst at the same time educating potential consumers of ivory on the impacts of this wide-scale slaughter that could ultimately result in the extinction of elephants. Resources are also required to ensure the long-term persistence of elephant populations by both protecting elephant habitat and providing solutions to human-elephant conflict. Our research demonstrated the importance of not only maintaining numbers, but also population integrity, by ensuring that the complex society within which elephants live naturally – the social fabric of their lives – is adequately protected.