Selective harvest, such as poaching, impacts group-living animals directly through mortality of individuals with desirable traits, and indirectly by altering the structure of their social networks. Understanding the relationship between disturbance-induced, structural network changes and group performance in wild animals remains an outstanding problem. To address this problem, we evaluated the immediate effect of disturbance on group sociality in African savanna elephants—an example, group-living species threatened by poaching. Drawing on static association data from ten free-ranging groups, we constructed one empirically based, population-wide network and 100 virtual networks; performed a series of experiments ‘poaching’ the oldest, socially central or random individuals; and quantified the immediate change in the theoretical indices of network connectivity and efficiency of social diffusion. Although the social networks never broke down, targeted elimination of the socially central conspecifics, regardless of age, decreased network connectivity and efficiency. These findings hint at the need to further study resilience by modeling network reorganization and interaction-mediated socioecological learning, empirical data permitting. The main contribution of our work is in quantifying connectivity together with global efficiency in multiple social networks that feature the sociodemographic diversity likely found in wild elephant populations. The basic design of our simulation makes it adaptable for hypothesis testing about the consequences of anthropogenic disturbance or lethal management on social interactions in a variety of group-living species with limited, real-world data.
Driven by reproductive motives, male African elephants (Loxodonta africana) in musth often expand their home ranges to locate estrous females. This extended range, coupled with heightened aggression often observed in musth males, can be particularly problematic in regions where human-modified landscapes and elephant territories increasingly overlap. Several mitigation tools have been tested to resolve a wide range of human–elephant conflicts with varying degrees of success due to geographical disparities and habituation. We present findings on the potential application of estrous call playbacks in manipulating the behavior and movement of male elephants non-invasively, particularly mature musth adults and younger post-dispersal males, in Etosha National Park. Estrous vocalizations were presented across 26 experimental trials to mature musth adults (n = 5), mature non-musth adults (n = 6), and non-musth males belonging to younger, post-dispersal age classes (n = 8), with behavioral responses scored on a gradient scale from 0–1. Both mature musth adults and younger non-musth elephants were significantly more likely to respond with the highest intensity by approaching the acoustic source compared to mature non-musth adults that avoided the call. However, younger males tested in the presence of an older, higher-ranking male tended to react with a lower intensity than those tested alone. This result likely demonstrates the influence of social hierarchy and associations on male elephant behavior. We also observed a significant increase in physiological response, measured by defecation rate, across all male groups in response to the estrous call playbacks. Our findings suggest that using estrous calls as acoustic deterrents may effectively and non-invasively aid in reducing tension at the human–elephant interface, depending on the age, social context, and reproductive status of the male elephant.
Poaching of mature and socially influential African savanna elephants for their prominent tusks alters the structure of their social networks. To learn if targeted poaching affects the functioning (i.e., connectedness and efficiency) of elephant associations, we simulated network formation and disturbance via poaching experiments in one wild and 100 virtual populations. To simulate virtual networks, we built a non-spatial, individual-based model guided by empirical association trends. After poaching of 1) the most mature or socially central individuals or 2) individuals selected at random, we evaluated network connectedness and efficiency. The networks never broke down, suggesting their robustness. Unlike in age-specific deletions, eliminating individuals with the highest topological centrality led to a decrease in network connectedness and efficiency. The simulated networks, although structurally stable, became less functionally resilient when subject to poaching-like stress. Our work may offer new insights into elephant behavior vis-a-vis anthropogenic pressure, and inform conservation efforts focused on translocation of social species or trophy hunting practices.
For social mammals, phenotypic factors, such as age and reproductive state, and environmental factors, such as competition and requirements for offspring, shape individual resource needs and cause animals to display behavioural patterns most useful in resource acquisition. Female mammals trade off investment in growth and survival against complex and resource-intensive reproductive challenges; thus, they alter behaviours according to changing priorities. To maximize net gain females increase resource intake or limit its expenditure. Behaviours that involve resource acquisition, such as foraging, are potentially rewarding, yet lead to competition, especially in group-living species; whereas behaviours that do not provide resources, such as resting or grooming, encourage sharing and buffer competition. In cooperative species with linear dominance hierarchies such as female African elephants (Loxodonta africana africana), rank is often determined by age and size, which are highly correlated. When compared with younger, competitively disadvantaged individuals, higher ranked animals attain greater access to resources, but other phenotypic and environmental factors may influence their needs. Hence, we examined how lactational status and sex of the nursing offspring influenced time spent on resource acquisition, and we assessed how these factors affect rates of aggression related to age. We conducted the study at Addo Elephant National Park in South Africa from June to December 2010, using 20 min focal animal sampling on reproductively mature females (). Adult females () exhibited aggression more frequently and socialized in a non-aggressive manner less frequently than subadult females (). Lactating females () spent more time foraging, displayed aggression more frequently, socialized in a non-aggressive manner less frequently, and exhibited chemosensory behaviours less frequently than non-lactating conspecifics (). Mothers of female calves () spent more time foraging than mothers of male calves (). The latter spent more time nursing and resting. We show how behavioural patterns, permitted or limited by age (correlated with size and rank) and reproductive condition, pertain to resource needs in female elephants, in contexts not directly related to survival or starvation avoidance. We discuss our findings in the context of female social relationships, for a long-lived, cooperative species.
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