Initial findings on visual acuity thresholds in an African elephant (Loxodonta africana)

Multimodal communication and audience directedness in the greeting behaviour of semi-captive African savannah elephants

Many species communicate by combining signals into multimodal combinations. Elephants live in multi-level societies where individuals regularly separate and reunite. Upon reunion, elephants often engage in elaborate greeting rituals, where they use vocalisations and body acts produced with different body parts and of various sensory modalities (e.g., audible, tactile). However, whether these body acts represent communicative gestures and whether elephants combine vocalisations and gestures during greeting is still unknown. Here we use separation-reunion events to explore the greeting behaviour of semi-captive elephants (Loxodonta africana). We investigate whether elephants use silent-visual, audible, and tactile gestures directing them at their audience based on their state of visual attention and how they combine these gestures with vocalisations during greeting. We show that elephants select gesture modality appropriately according to their audience's visual attention, suggesting evidence of first-order intentional communicative use. We further show that elephants integrate vocalisations and gestures into different combinations and orders. The most frequent combination consists of rumble vocalisations with ear-flapping gestures, used most often between females. By showing that a species evolutionarily distant to our own primate lineage shows sensitivity to their audience's visual attention in their gesturing and combines gestures with vocalisations, our study advances our understanding of the emergence of first-order intentionality and multimodal communication across taxa.

Review of sensory modalities of sirenians and the other extant Paenungulata clade

Extant members of Paenungulata (sirenians, proboscideans, and hyracoideans) form a monophyletic clade which originated in Africa. While paenungulates are all herbivorous, they differ greatly in size, life history, and habitat. Therefore, we would expect both phylogenetically related similarities and ecologically driven differences in their use and specializations of sensory systems, especially in adaptations in sirenians related to their fully aquatic habitat. Here we review what is known about the sensory modalities of this clade in an attempt to better elucidate their sensory adaptations. Manatees have a higher frequency range for hearing than elephants, who have the best low-frequency hearing range known to mammals, while the hearing range of hyraxes is unknown. All paenungulates have vibrissae assisting in tactile abilities such as feeding and navigating the environment and share relatively small eyes and dichromatic vision. Taste buds are present in varying quantities in all three orders. While the olfactory abilities of manatees and hyraxes are unknown, elephants have an excellent sense of smell which is reflected by having the relatively largest cranial nerve related to olfaction among the three lineages. Manatees have the relatively largest trigeminal nerve-the nerve responsible for, among other things, mystacial vibrissae-while hyraxes have the relatively largest optic nerve (and therefore, presumably, the best vision) among the Paenungulata. All three orders have diverged significantly; however, they still retain some anatomical and physiological adaptations in common with regard to sensory abilities.

Acoustic structure of forest elephant rumbles: a test of the ambiguity reduction hypothesis

Quantitative assessments of the structure of vocalizations are a fundamental prerequisite to understand a species' vocal communication system and, more broadly, the selective pressures shaping vocal repertoires. For example, to reduce ambiguity in signal interpretation in the absence of auxiliary visual cues, species in densely vegetated habitats should exhibit more discrete vocal signals than species in open habitats. To test this "ambiguity reduction hypothesis", we conducted the first quantitative assessment of the rumble vocalizations of the forest elephant. Based on 686 forest elephant rumbles recorded with autonomous acoustic recording units at four sites across Central Africa, we used model-based cluster analyses paired with subsequent evaluation of cluster-discreteness and discriminant function analyses to quantify the structure of rumbles based on 23 source- and filter-related acoustic parameters. Model-based cluster analyses suggest that rumbles can be classified into five to eight types. Similar to previous findings in savannah elephants and contrary to the ambiguity reduction hypothesis, average silhouette coefficients below 0.34 indicated that these rumble types were highly intergraded. However, discriminant function analyses predicted rumble types with at least 75% accuracy whereby the location of the minimum fundamental frequency, middle slope and peak frequency contributed most to separation between types. In line with an increasing number of studies highlighting that a distinction between discrete and graded repertoires may have little biological significance, we propose that ambiguity reduction may take place through the evolution of perceptual and cognitive mechanisms, rather than acting on vocal production.

Elephants know when their bodies are obstacles to success in a novel transfer task

The capacity to recognise oneself as separate from other individuals and objects is difficult to investigate in non-human animals. The hallmark empirical assessment, the mirror self-recognition test, focuses on an animal's ability to recognise itself in a mirror and success has thus far been demonstrated in only a small number of species with a keen interest in their own visual reflection. Adapting a recent study done with children, we designed a new body-awareness paradigm for testing an animal's understanding of its place in its environment. In this task, Asian elephants (Elephas maximus) were required to step onto a mat and pick up a stick attached to it by rope, and then pass the stick forward to an experimenter. In order to do the latter, the elephants had to see their body as an obstacle to success and first remove their weight from the mat before attempting to transfer the stick. The elephants got off the mat in the test significantly more often than in controls, where getting off the mat was unnecessary. This task helps level the playing field for non-visual species tested on cognition tasks and may help better define the continuum on which body- and self-awareness lie.

Sea lions' (Zalophus californianus) use of human pointing gestures as referential cues

This experiment investigated the ability of four human-socialized sea lions to exploit human communicative gestures in three different object-choice tasks based on directional cues emitted by their caretakers. In Study 1, three of the tested subjects were able to generalize their choice of the pointed target to variations of the basic pointing gestures (i.e., cross-body point, elbow point, foot point, and gaze only), from the very first trials. Study 2 showed that the subjects could follow the pointing gestures geometrically and select the correct target among four possible targets, two on each side of the informant. In Study 3, we tested the robustness of their tendency to follow a pointing gesture by hiding targets behind barriers. One subject was able to follow pointing gestures towards targets not visible at the moment of their decision without any training, despite the presence of another visible and directly accessible one. Taken together, these results suggest that sea lions were able to use the referential property of the human pointing gesture, because they were able to rely on extrapolating precise linear vectors along different pointing body parts in order to identify a precise object rather than merely a general direction. These findings support previous arguments that some non-domesticated species might have as great an ability to respond appropriately to pointing gestures as domesticated dogs. The potential roles of human-socialization and specific features of wild sea lions ecology are discussed.

African elephants (Loxodonta africana) recognize visual attention from face and body orientation

How do animals determine when others are able and disposed to receive their communicative signals? In particular, it is futile to make a silent gesture when the intended audience cannot see it. Some non-human primates use the head and body orientation of their audience to infer visual attentiveness when signalling, but whether species relying less on visual information use such cues when producing visual signals is unknown. Here, we test whether African elephants (Loxodonta africana) are sensitive to the visual perspective of a human experimenter. We examined whether the frequency of gestures of head and trunk, produced to request food, was influenced by indications of an experimenter's visual attention. Elephants signalled significantly more towards the experimenter when her face was oriented towards them, except when her body faced away from them. These results suggest that elephants understand the importance of visual attention for effective communication.