Shermin de Silva

An Asian elephant imitates human speech.

Summary Vocal imitation has convergently evolved in many species, allowing learning and cultural transmission of complex, conspecific sounds, as in birdsong [1, 2]. Scattered instances also exist of vocal imitation across species, including mockingbirds imitating other species or parrots and mynahs producing human speech [3, 4]. Here, we document a male Asian elephant (Elephas maximus) that imitates human speech, matching Korean formants and fundamental frequency in such detail that Korean native speakers can readily understand and transcribe the imitations. To create these very accurate imitations of speech formant frequencies, this elephant (named Koshik) places his trunk inside his mouth, modulating the shape of the vocal tract during controlled phonation. This represents a wholly novel method of vocal production and formant control in this or any other species. One hypothesized role for vocal imitation is to facilitate vocal recognition by heightening the similarity between related or socially affiliated individuals [1, 2]. The social circumstances under which Koshik’s speech imitations developed suggest that one function of vocal learning might be to cement social bonds and, in unusual cases, social bonds across species.

A Comparison of Social Organization in Asian Elephants and African Savannah Elephants

Asian and African elephant species have diverged by ca. 6 million years, but as large, generalist herbivores they occupy similar niches in their respective environments. Although the multilevel, hierarchical nature of African savannah elephant societies is well established, it has been unclear whether Asian elephants behave similarly. Here we quantitatively compare the structure of both species’ societies using association data collected using the same protocol over similar time periods. Sociality in both species demonstrates well-defined structure, but in contrast to the African elephants of Samburu the Uda Walawe Asian elephants are found in smaller groups, do not maintain coherent core groups, demonstrate markedly less social connectivity at the population level, and are socially less influenced by seasonal differences in ecological conditions. The Uda Walawe Asian elephants, however, do maintain a complex, well-networked society consisting of ≥2 differentiated types of associates we term ephemeral and long-term affiliates. These findings imply we must broaden our recognition of multilevel social organization to encompass societies that fall along a gradient of nestedness, and not merely those that exhibit hierarchical nesting. This in turn suggests that multilevel structures may be more diverse and widespread than generally thought, and that phylogenetic comparisons within species-rich clades, such as that of primates, using the methods presented can provide fresh insights into their socioecological basis.

Demographic Variables for Wild Asian Elephants Using Longitudinal Observations

Detailed demographic data on wild Asian elephants have been difficult to collect due to habitat characteristics of much of the species’ remaining range. Such data, however, are critical for understanding and modeling population processes in this endangered species. We present data from six years of an ongoing study of Asian elephants (Elephas maximus) in Uda Walawe National Park, Sri Lanka. This relatively undisturbed population numbering over one thousand elephants is individually monitored, providing cohort-based information on mortality and reproduction. Reproduction was seasonal, such that most births occurred during the long inter-monsoon dry season and peaked in May. During the study, the average age at first reproduction was 13.4 years and the 50th percentile inter-birth interval was approximately 6 years. Birth sex ratios did not deviate significantly from parity. Fecundity was relatively stable throughout the observed reproductive life of an individual (ages 11–60), averaging between 0.13–0.17 female offspring per individual per year. Mortalities and injuries based on carcasses and disappearances showed that males were significantly more likely than females to be killed or injured through anthropogenic activity. Overall, however, most observed injuries did not appear to be fatal. This population exhibits higher fecundity and density relative to published estimates on other Asian elephant populations, possibly enhanced by present range constriction. Understanding the factors responsible for these demographic dynamics can shed insight on the future needs of this elephant population, with probable parallels to other populations in similar settings.

Fission–fusion processes weaken dominance networks of female Asian elephants in a productive habitat

Dominance hierarchies are expected to form in response to socioecological pressures and competitive regimes. We assess dominance relationships among free-ranging female Asian elephants (Elephas maximus) and compare them with those of African savannah elephants (Loxodonta africana), which are known to exhibit age-based dominance hierarchies. Both species are generalist herbivores, however, the Asian population occupies a more productive and climatically stable environment relative to that of the African savannah population. We expected this would lower competition relative to the African taxon, relaxing the need for hierarchy. We tested whether 1) observed dominance interactions among individuals were transitive, 2) outcomes were structured either by age or by social unit according to 4 independent ranking methods, and 3) hierarchy steepness among classes was significant using David’s score. Elephas maximus displayed less than a third the number of dominance interactions as observed in L. africana, with statistically insignificant transitivity among individuals. There was weak but significant order as well as steepness among age-classes but no clear order among social units. Loxodonta africana showed significant transitivity among individuals, with significant order and steepness among age-classes and social units. Elephas maximus had a greater proportion of age-reversed dominance outcomes than L. africana. When dominance hierarchies are weak and nonlinear, signals of dominance may have other functions, such as maintaining social exclusivity. We propose that resource dynamics reinforce differences via influence on fission–fusion processes, which we term “ecological release.” We discuss implications of these findings for conservation and management when animals are spatially constrained.

Controlling for behavioural state reveals social dynamics among male African elephants, Loxodonta africana

The drivers of social affiliation may vary over time as individuals change their goals with respect to changing environments or physical condition. Studies of companion preference rarely consider shifts in motivational state, despite the potential importance of such shifts in structuring association and population processes. Ignoring state dependence in social behaviour may weaken the ability to recognize social properties and identify their underlying drivers. Modifying established approaches, we apply a state-specific analysis to investigate social properties in male African elephants, which are thought to be weakly social. Specifically, we delineate associations during distinct sexually active and inactive periods and quantify common social metrics (network size, density, betweenness and the number and age of preferred companions) to examine how sexual states may relate to male elephant social relationships. We found that state-dependent association index values were higher and quantitative definitions of preferred companions were more conservative than those derived when sexual state was not taken into account. Preferred companions tended to be closer in age among sexually inactive dyads relative to sexually active dyads, indicating that bulls seek out age-mates when sexually inactive. Networks were larger and denser when sexually inactive. By accounting for dynamic behaviour in social systems, this study demonstrates that male African elephants show more social preference than had been previously thought.

African and Asian Elephant Vocal Communication: A Cross-Species Comparison

Although living in substantially different habitats, African (Loxodonta sp.) and Asian (Elephas maximus) elephants are extremely social and intra-specific communication is therefore highly developed in these species. In particular, elephants are very vocal and acoustic signals play an integral part within the society of African and Asian elephants. In this chapter, we provide a cross-species comparison of the African savannah elephant (L. africana) and Asian elephant vocal communication systems, discussing the acoustic structure of various call types, examples of vocal imitation and sound production mechanisms. We aim to explore what the similarities and differences in the communication system of the two species could reveal about call functions, and the ecological conditions that have shaped these communication systems. In light of this, we suggest future comparative investigations of African and Asian elephants that may provide deeper insights into the evolutionary and cognitive bases of the complex signalling mechanisms.