Unfamiliar Humans Research Articles

Agenda of Early Life Experience and Its Association with Sensitivity to Human Presence and Familiarity in Wild-Born Orphaned Captive Cheetahs.

It has been argued that domestication explains the ability of domestic animals to use human cues, but similar abilities exist in wild animals repeatedly exposed to humans. Little is known on the importance of the developmental stage of this exposure for developing such abilities. Orphancy and subsequent hand-rearing constitute a quasi-experimental situation for investigating this question. Cheetahs (Acinonyx jubatus) are interesting as they present a two-step development, spending their first two months of life in a den with occasional visits from the mother, and then accompanying their mother outdoors. Mother loss may occur at any of these stages, and the orphaned cheetahs are then taken under human care. We tested the importance of the stage of development on their long-term perception of humans by comparing the reactions of adult wild-born cheetahs, orphaned at "den-age" (Early-Orphaned, 0-2 months) or at a later stage (Late-Orphaned, 2-6 months), to motionless humans (familiar vs. unfamiliar). The results showed that Early-Orphaned, but not Late-Orphaned cheetahs, produced affiliative calls (purrs) towards humans and discriminated familiar and unfamiliar humans. Taken together, these results suggest that the timing in which an emotional bond is created with the primary caregiver (humans in the case of Early-Orphaned cheetahs and the mother in the case of Late-Orphaned cheetahs) is crucial in determining the reaction towards the species of the early caregiver throughout life.

Enhancing stress assessment in sledge reindeer (Rangifer tarandus): a pilot study on infrared thermal imaging and its opportunities for advancement as a welfare assessment tool

Measuring immediate physiological stress responses in animals can be challenging; saliva and blood sampling, while invasive, may also generate confounding stress responses, and equipping animals with heart rate sensors is not always feasible. Nevertheless, emerging technologies offer a non-invasive and contactless method to measure additional body surface temperature changes induced by acute stress, using infrared thermal measurement of the eye caruncle region. Contactless temperature measurement has the potential to assess the emotional state of animals affected by human physical contact. Reindeer, being highly sensitive to touch and naturally avoiding physical contact, exemplify this case. With growing interest in safari tours involving sledging reindeer, there is a need to investigate how these animals are affected by human interactions and how they adapt to daily close contact. In this pilot experiment, we evaluated the efficacy of thermal imaging in measuring medial canthus temperature fluctuations in non-habituated sledging reindeer while being petted by unfamiliar humans. Our findings support the hypothesis that medial canthus temperature significantly decreases during petting and increases once the interaction ceases, aligning with established stress response patterns found in the literature. This pilot experiment underscores the potential of infrared thermal imaging for non-invasively monitoring physiological responses to stress in tamed reindeer. Moreover, it sets the foundation for refining methodologies and experimental designs using infrared thermal imaging in animal welfare research.

Do sheep (Ovis aries) discriminate human emotional odors?

While sheep can detect and discriminate human emotions through visual and vocal cues, their reaction to human body odors remains unknown. The present study aimed to determine whether sheep (Ovis aries) can detect human odors, olfactorily discriminate stressed from non-stressed individuals, and behave accordingly based on the emotional valence of the odors. Axillary secretions from 34 students were collected following an oral examination (stress odor) or a regular class (non-stress odor). Fourteen female and 15 male lambs were then exposed to these odors through a habituation-dishabituation procedure. The habituation stimulus was presented four times for one minute, followed by the dishabituation stimulus presented once for one minute. Behavioral variables included spatiality relative to target odors, approach/withdrawal, ear positioning, sniffing, ingestion, and vocalization. Both female and male lambs more often positioned their ears backwards/forwards, and asymmetrically when exposed to the dishabituation stimulus, but regardless of their stress or non-stress value. They also changed their approach behavior when exposed to the dishabituation stimuli. Lambs displayed some behavioral signs of discrimination between the habituation and dishabituation odors, but regardless of their relation to stress or non-stress of human donors. In sum, this exploratory study suggests that young sheep respond negatively to the odor of unfamiliar humans, without showing any specific emotional contagion related to the stress odor. This exploratory study suggests young ovines can detect human body odor, a further step toward understanding the human-sheep relationship.

The human-animal relationship in zoo-housed mammals: Behavioral and physiological responses to visitor and keeper interactions

Human-animal relationships (HARs) and interactions strongly influence animal welfare. Thus, advocating for positive HAR is essential for maintaining positive physical and mental health. In particular, zoo–housed species not only are exposed daily to unfamiliar humans (visitors) but also need to routinely interact with zookeepers, veterinarians, trainers, and other staff. In contrast to those in livestock and companion animals, HARs in zoos have not been extensively studied, although it is known that negative interactions can elicit stress-related behavioral and physiological responses. The present review aims to address the importance of positive HAR in wildlife species under human care. The main behavioral and physiological responses to interactions with familiar and unfamiliar humans will be discussed for a wide range of species (because HARs can also be influenced by animal-related factors). Moreover, potential alternatives to address and promote positive HAR in zoo-housed animals (e.g., environmental enrichment and positive reinforcement training) will be addressed. The HAR is part of the Five Domains Model of Animal Welfare. Therefore, recognizing that caregivers/medical staff and visitors' presence can affect an animal’s emotional state is important for establishing beneficial relationships for wildlife under human care.

A first exploratory comparison of the behaviour of wolves (Canis lupus) and wolf-dog hybrids in captivity

Extensive introgression of genes from domesticated taxa may be a serious threat for the genomic integrity and adaptability of wild populations. Grey wolves (Canis lupus) are especially vulnerable to this phenomenon, but there are no studies yet assessing the potential behavioural effects of dog-introgression in wolves. In this study, we conducted a first systematic comparison of admixed (N = 11) and non-admixed (N = 14) wolves in captivity, focusing on their reaction to unfamiliar humans and novel objects, and the cohesiveness of their social groups. When exposed to unfamiliar humans in the experimental task, wolves were more vigilant, fearful and aggressive than admixed wolves, and less likely to approach humans, but also more likely to spend time in human proximity. When exposed to novel objects, wolves were more aggressive than admixed wolves, less likely to spend time in object proximity, and more likely to interact with objects, but also less vigilant and as fearful as admixed wolves. Finally, social networks were more cohesive in wolves than in admixed wolves. Although caution is needed when comparing groups of captive individuals with different life experiences, our study suggests that dog admixture may lead to important behavioural changes in wolves, with possible implications for conservation strategies.

Catcalls: exotic cats discriminate the voices of familiar caregivers.

The ability to differentiate familiar from unfamiliar humans has been considered a product of domestication or early experience. Few studies have focused on voice recognition in Felidae despite the fact that this family presents the rare opportunity to compare domesticated species to their wild counterparts and to examine the role of human rearing. We tested whether non-domesticated Felidae species recognized familiar human voices by exposing them to audio playbacks of familiar and unfamiliar humans. In a pilot study, we presented seven cats of five species with playbacks of voices that varied in familiarity and use of the cats' names. In the main study, we presented 24 cats of 10 species with unfamiliar and then familiar voice playbacks using a habituation-dishabituation paradigm. We anticipated that human rearing and use of the cats' names would result in greater attention to the voices, as measured by the latency, intensity, and duration of responses regardless of subject sex and subfamily. Cats responded more quickly and with greater intensity (e.g., full versus partial head turn, both ears moved versus one ear twitching) to the most familiar voice in both studies. They also responded for longer durations to the familiar voice compared to the unfamiliar voices in the main study. Use of the cats' name and rearing history did not significantly impact responding. These findings suggest that close human contact rather than domestication is associated with the ability to discriminate between human voices and that less social species may have socio-cognitive abilities akin to those of more gregarious species. With cats of all species being commonly housed in human care, it is important to know that they differentiate familiar from unfamiliar human voices.

Human social buffer in goats and dogs

The primary goal of this study was to explore the social buffering effect that humans offer to goats and dogs with limited exposure to human socialization, particularly in situations involving interactions with unfamiliar humans. A total of 13 dogs and 14 goats were selected for the study, all of which had limited prior socialization with humans. Each animal was placed in a testing room with unfamiliar humans for 15 min. Three experimenters aimed to establish a comfortable environment, encouraging social interaction by offering food to the animals and assessing the animals’ willingness to accept food and their response to being approached and petted. If both conditions were satisfied, the animals were classified as “social”. If one or none of the conditions were met, the animals were classified as “not social”. Cortisol levels were measured by collecting blood samples before and after the test. Non-parametric tests together with a GzLM showed that the effect of human social buffering in goats was different in comparison to dogs: goats exhibited higher cortisol levels after the test, while dogs did not show a significant change. Further analysis demonstrated that “social” goats had a lower likelihood of experiencing significant changes in cortisol levels than dogs. Thus, once human interactions are accepted, both species could benefit from social buffering. In summary, this study enhances our understanding of how dogs and goats respond to social interactions with humans in the social buffering effect.

Perceptual integration of bodily and facial emotion cues in chimpanzees and humans.

For highly visual species like primates, facial and bodily emotion expressions play a crucial role in emotion perception. However, most research focuses on facial expressions, while the perception of bodily cues is still poorly understood. Using a novel comparative priming eye-tracking design, we examined whether our close primate relatives, the chimpanzees (Pan troglodytes), and humans infer emotions from bodily cues through subsequent perceptual integration with facial expressions. In experiment 1, we primed chimpanzees with videos of bodily movements of unfamiliar conspecifics engaged in social activities of opposite valence (play and fear) against neutral control scenes to examine attentional bias toward succeeding congruent or incongruent facial expressions. In experiment 2, we assessed the same attentional bias in humans yet using stimuli showing unfamiliar humans. In experiment 3, humans watched the chimpanzee stimuli of experiment 1, to examine cross-species emotion perception. Chimpanzees exhibited a persistent fear-related attention bias but did not associate bodily with congruent facial cues. In contrast, humans prioritized conspecifics' congruent facial expressions (matching bodily scenes) over incongruent ones (mismatching). Nevertheless, humans exhibited no congruency effect when viewing chimpanzee stimuli, suggesting difficulty in cross-species emotion perception. These results highlight differences in emotion perception, with humans being greatly affected by fearful and playful bodily cues and chimpanzees being strongly drawn toward fearful expressions, regardless of the preceding bodily priming cue. These data advance our understanding of the evolution of emotion signaling and the presence of distinct perceptual patterns in hominids.

Human-animal interactions and machine-animal interactions in animals under human care: A summary of stakeholder and researcher perceptions and future directions

Abstract Animals under human care are exposed to a potentially large range of both familiar and unfamiliar humans. Human-animal interactions vary across settings, and individuals, with the nature of the interaction being affected by a suite of different intrinsic and extrinsic factors. These interactions can be described as positive, negative or neutral. Across some industries, there has been a move towards the development of technologies to support or replace human interactions with animals. Whilst this has many benefits, there can also be challenges associated with increased technology use. A day-long Animal Welfare Research Network workshop was hosted at Harper Adams University, UK, with the aim of bringing together stakeholders and researchers (n = 38) from the companion, farm and zoo animal fields, to discuss benefits, challenges and limitations of human-animal interactions and machine-animal interactions for animals under human care and create a list of future research priorities. The workshop consisted of four talks from experts within these areas, followed by break-out room discussions. This work is the outcome of that workshop. The key recommendations are that approaches to advancing the scientific discipline of machine-animal interactions in animals under human care should focus on: (1) interdisciplinary collaboration; (2) development of validated methods; (3) incorporation of an animal-centred perspective; (4) a focus on promotion of positive animal welfare states (not just avoidance of negative states); and (5) an exploration of ways that machines can support a reduction in the exposure of animals to negative human-animal interactions to reduce negative, and increase positive, experiences for animals.

Current Knowledge on the Transportation by Road of Cattle, including Unweaned Calves.

Transport conditions have the potential to alter the physiological responses of animals to the psychological or physical stress of transport. Transportation may introduce multiple physical and psychological stressors to unweaned calves and adult cattle, including noise, overcrowding, food and water deprivation, extreme temperatures, commingling with unfamiliar animals, handling by unfamiliar humans, and being placed in a novel environment upon arrival. Apart from these factors, the type of road and even driving skill may affect the welfare of animals. One of the concerns regarding cattle transport is that the handling and marketing of animals prior to a journey may lengthen the period of feed withdrawal. Furthermore, feed withdrawal can impact animal welfare through hunger and metabolic stress. Transportation is also associated with a decrease in animal performance as well as an increase in the incidence of bovine respiratory disease. It is well established that the transportation of cattle is a stressor that causes a quantifiable response; however, excessive stress during transport resulting in physiological or pathological changes can be reduced with best management practices. The objective of this review was to analyse the available scientific literature pertaining to the transport by road of cattle, including unweaned calves.

Using qualitative behavior assessment to investigate the effect of tourist presence on the welfare in captive tigers (Panthera tigris) in three tourism facilities in Thailand.

Numerous facilities around the world offer tourists interactive experiences with captive tigers. Yet, the animal welfare implications of this practice have not been widely studied. This study aimed to investigate whether qualitative behavioral assessment (QBA) could: (i) provide a valid indicator of tiger's emotional state and (ii) be applied to assess whether unfamiliar human presence with hand-raised captive tigers had an impact on the emotional state of those tigers. To investigate this, QBA was applied to video clips of hand-raised captive tigers from three sites (two offering unfamiliar human interaction, Sites A and C, and one retirement site with no direct interactions, Site B) in Thailand. QBA allows inferences to be made about animal emotion on the basis of descriptions of behavioral expression. Analysis, using a free choice profiling methodology, was provided by observers (N = 38) split between three groups; tiger keepers and vets from the Thai venues (n = 12), UK-based animal behavior MSc and vet students (n = 16), and international tiger keepers (n = 10). Tigers (N = 35) were split between Sites A (n = 7), B (n = 18), and C (n = 10) and filmed at three time points; morning (0800-0930 h); midday, (1130-1230 h); and evening, (1630-1830h) totaling 105 clips. Using generalized procrustes analysis, a consensus profile was calculated for each observer group. Two meaningful dimensions of behavioral expression, explaining 75.0% of the variation, were observed across these groups: Dimension 1 (D1: "active"/"interested"/"agitated" to "relaxed"/"calm"/"chilled-out") and Dimension 2 (D2: "bored"/"stressed"/"frustrated" to "relaxed"/"curious"/"interested"). There was clear agreement between the three observer groups in terms of tiger emotional expression along D1. However, agreement was more variable on D2. The behavioral expression on D1 was not significantly affected by site but was significantly affected by an interaction between age and time of day. Time of day also affected scores on D2, with the Thai observer group also showing an effect of site. During the midday period, when unfamiliar humans were present, all tiger age groups showed more positive behavioral expressions on D1 (lower scores: "relaxed"/"calm"/"chilled-out") and more negative behavioral expressions on D2 (higher scores: "bored"/"stressed"/"frustrated"), which could indicate that the presence of unfamiliar humans was a stressor. However, tigers in the retirement Site C also displayed similar behavioral expressions, which could indicate a deeper welfare issue. With further development, QBA could be used as part of a valid tool for long-term measurement of behavioral expression in captive tigers.

Unfamiliar human-induced social buffering effect in kennel-residing Australian Cattle Dogs

The "isolation syndrome" is a term used to describe the stress responses observed in highly social species when they lack social interactions. This syndrome affects various aspects of an individual's welfare, including hormonal, behavioral, and physiological systems. Dogs, known for their social nature, have been used as a model to study the effects of social buffering provided by conspecifics or humans. This study aims to investigate the social buffering effect of humans on dogs and determine if it is solely associated with bonding or socialization. The study selected Australian Cattle Dogs with limited social interactions with humans, ensuring that no direct bonds or human socialization were involved. The dogs were randomly assigned to either an isolation or social condition, and cortisol levels were measured before and after the tests to evaluate stress responses. The results showed that isolation led to a significant increase in cortisol levels, indicating a stress response. However, in the presence of unfamiliar humans, cortisol levels did not increase significantly, suggesting a lack of stress response. This finding suggests that humans can serve as social buffers for dogs, even without prior bonding or socialization. Therefore, dogs without systematic human socialization still benefited from the presence of unfamiliar humans.

The effect of COVID-19 lockdown restrictions on self-directed behaviour, activity budgets, movement patterns, and spatial use in semi-captive African elephants (Loxodonta africana)

Captive African elephants are continuously exposed to tourism, which can lead to chronic stress, and subsequently negatively impact an animals’ health, welfare, and fitness. However, the COVID-19 pandemic led to global closures of animal tourism venues, and thus a sudden and prolonged absence of tourists. We examined the impact of this abrupt, unique scenario on 10 semi-captive African elephants (8 F, 2 M; aged 12-30 yrs) maintained at the Knysna Elephant Park, South Africa, which offers close human-elephant interactions. We monitored rates of self-directed behaviours (SDBs), a novel indicator of anxiety in this species, to observe differences before, during, and after lockdown. SDBs were recorded as they occurred, along with the number of tourists present during sampling. Additionally, we recorded general behaviours to calculate activity budgets, and monitored the elephants’ movement patterns and spatial use. The data examined represented 3 × 2-month periods; Pre (February 2020-March 2020), where tourist pressure was normal, During (March 2020-April 2020), where tourism was non-existent, and Post (November 2020-January 2021), where tourism had returned. Pre was set as the reference category to compare against the normative baseline. Results revealed SDB rates were significantly lower During (p < 0.001), and significantly higher Post (p = 0.033), demonstrating a reduction in anxiety-related behaviour due to the absence of tourists, and that the return of tourists perhaps invoked higher levels of anxiousness than before lockdown implementation. Similarly, both Low (p < 0.001) and High (p < 0.001) numbers of tourists significantly correlated with elevated SDBs, providing evidence that elephants perceived tourist presence alone as stressful. Activity budget analyses revealed a decrease in locomotion (p < 0.001), resting (p < 0.001), and comfort (p = 0.005) During, and an increase in feeding and time spent out of sight (both p < 0.001). Post resulted in an increase in locomotion (p = 0.004) and feeding behaviours (p = 0.007), and a decrease in comfort behaviour (p < 0.001) and time spent out of sight (p = 0.040). Lastly, elephants’ movement patterns varied between lockdown phases, with mean distance travelled (meters) significantly less During (p < 0.001) than Pre and Post. A preference for off-exhibit zones was observed During (p < 0.001) as opposed to Pre and Post. Together, these findings provide further evidence of the stressful effect of tourism, and how the presence of unfamiliar humans and human-animal interactions alters both the behaviour and movement of captive animals.

Long-term effects of early maternal deprivation on goat social behaviour

Early maternal deprivation has been shown to disrupt goat kids’ social behaviour and stress-coping strategy, and has long-term effects in other species like cattle. We studied the long-term effects of early maternal deprivation on 18-month-old goats. Seventeen goats were raised together with their dams (DR kids) and other lactating goats and kids, while 18 goats were separated from their dams three days after birth and artificially reared together (AR kids). Kids of both treatments were weaned around two to three months of age, grouped and raised together until this study 15 months later. Affiliative, playful, and agonistic behaviour was recorded by focal sampling in the home pen, when the focal goat had rejoined the herd after being physically isolated for 3 minutes, and after the focal goat was restrained and manipulated for 3 minutes. Behavioural observations were also conducted after the goats were introduced in groups of four in a herd of 77 unknown, lactating multiparous goats. Avoidance distance tests were performed in the home pen to assess the human-animal relationship. Salivary cortisol was measured before and after physical isolation, and faecal glucocorticoid metabolites were measured before and 24 hours after introduction in the lactating herd. In the home pen, AR goats were involved in less head nudging than DR goats, but other social behaviours or their behavioural and physiological response to the various stressful situations were not affected by their rearing treatment. Upon introduction in a DR lactating herd, most of the agonistic interactions observed were initiated by multiparous goats towards the introduced AR and DR goats alike. AR goats received more threats from the multiparous goats than DR goats, but were involved in less clashing than DR goats. AR goats showed less avoidance of familiar and unfamiliar humans than DR goats. Overall, previously AR and DR goats showed only a few differences in affiliative and agonistic behaviours in their home pen or after being exposed to different stressors 15 months later. Nonetheless, after being introduced into a multiparous goat herd, AR goats were still threatened more often than DR goats, and DR goats clashed more than AR goats, suggesting some persistent differences in their social abilities observed at an early age before and after weaning. As predicted, AR goats remained less fearful of humans than DR goats.

Appeasement function of displacement behaviours? Dogs’ behavioural displays exhibited towards threatening and neutral humans

Appeasement signals are behavioural patterns displaying an animal’s non-aggressive attitude and are hypothesized to reduce the aggressive behaviours in the receiver. In domestic dogs, specific displacement behaviours (i.e., behavioural patterns exhibited without an apparent function related to the ongoing situation), have been suggested to function as appeasement signals. To test this possibility, we assessed whether the occurrence of these behaviours was dependent on a social conflict context, predicting that, if displacement behaviours also function as appeasement signals, they should be more prevalent in a conflict vs. non-conflict context. Fifty-three dogs were exposed to two unfamiliar humans approaching them in either a mildly threatening or neutral way. We categorized the attitude of the dogs towards the strangers as “reactive”, i.e., barking and lunging towards the stimulus, and “non-reactive”, i.e., remaining passive in front of the stimuli. We coded dogs’ displacement activities and modelled their duration or frequency as a function of the interaction between the test condition and the attitude of the dog. Displacement behaviours of “blinking”, “nose licking” and “lip wiping” were associated with a “non-reactive” attitude, independently from the test condition, confirming an association with a non-aggressive intention. “Head turning” was associated with a “non-reactive” attitude in the threatening condition. In conclusion, dogs with a non-aggressive attitude exhibited more putative appeasement signals; however, these were not strictly associated with a conflict-ridden situation, calling for further investigation of their function.

Unfamiliar faces might as well be another species: Evidence from a face matching task with human and monkey faces

ABSTRACT Humans are good at recognizing familiar faces, but are more error-prone at recognizing an unfamiliar person across different images. It has been suggested that familiar and unfamiliar faces are processed qualitatively differently. But are unfamiliar faces at least processed differently from monkey faces? Here we tested 366 volunteers on a face matching test – two images presented side-by-side with participants judging whether the images show the same identity or two different identities – comparing performance with familiar and unfamiliar human faces, and monkey faces. The results showed that performance was most accurate for familiar faces, and was above chance for monkey faces. Although accuracy was higher for unfamiliar humans than monkeys on different identity trials, there was no unfamiliar human advantage over monkeys on same identity trials. The results give new insights into unfamiliar face processing, showing that in some ways unfamiliar faces might as well be another species.

Ecological factors shape quantitative decision-making in coyotes.

Much research has focused on the development and evolution of cognition in the realm of numerical knowledge in human and nonhuman animals but often fails to take into account ecological realities that, over time, may influence and constrain cognitive abilities in real-life decision-making. Cognitive abilities such as enumerating and timing are central to many psychological and ecological models of behavior, yet our knowledge of how these are affected by environmental fluctuations remains incomplete. Our research bridges the gap between basic cognitive research and ecological decision-making. We used coyotes (Canis latrans) as a model animal system to study decision-making about smaller, more proximal food rewards and larger, more distant food rewards; we tested animals across their four reproductive cycle phases to examine effects of ecological factors such as breeding status and environmental risk on quantitative performance. Results show that coyotes, similar to other species, spatially discount food rewards while foraging. The degree to which coyotes were sensitive to the risk of obtaining the larger food reward, however, depended on the season in which they completed the foraging task, the presence of unfamiliar humans (i.e., risk), and the presence of conspecifics. Importantly, our results support that seasonal variations drive many differences in nonhuman animal behavior and cognition (e.g., hibernation, breeding, food resource availability). Further, it may be useful in the future to extend this work to humans because seasons may influence human cognition as well, and this remains unexplored in the realms of enumeration, timing, and spatial thinking.

Cetacean responses to violation of expectation paradigm in a free-swim context.

The investigation of individual responses to unexpected stimuli or outcomes provides insights into basic cognitive processes, such as mental representations, emotional states of surprise, and detections of anomalies. Three experiments using a violation of expectation paradigm were conducted with 12 belugas and 17 bottlenose dolphins in managed care to test two classes of stimuli (humans and objects) in manipulated sequences of familiar and unfamiliar humans (Study 1, trainers and strangers), familiar and unfamiliar objects (Study 2, typical enrichment devices and new objects), and finally objects and humans (Study 3). Gaze durations were assessed for each condition in a given study during free-swim contexts. The results supported previous findings that visual stimuli, regardless of class, were stimulating and intriguing for both belugas and bottlenose dolphins. Belugas were more likely to gaze longer at human and object stimuli and tended to gaze longer at unexpected experiences than control or expected experiences. Bottlenose dolphins showed similar trends except when objects were involved. Individual variability was present for both species with some individuals showing stronger patterns of responses for expected experiences than others. After 2years of intermittent experiments, belugas and bottlenose dolphins in managed care maintained their curiosity about visual stimuli, for which they received no primary reinforcement. Investigating responses to unexpected stimuli with animals in managed care may provide insight into how these animals respond to biologically relevant conditions, such as boat presence, predators, and unfamiliar conspecifics.

Prolonged proximity to humans ensures better performance of semi-captive Asian elephants at discriminating between human individuals by voice

To avoid risks, organisms must recognize threatening heterospecies from non-threatening onesviaacoustic cues from a distance. With land-use change, humans have encroached considerably into natural areas. Therefore, it is beneficial to animals to use acoustic cues to discriminate between different levels of threats posed by humans. Our study aims at testing this discriminatory ability in Asian elephants (Elephas maximus), animals that have been for long history subjected to human interaction. We tested whether eighteen semi-captive elephants could discriminate between voices of their own mahouts (i.e., who take care of the elephants exclusively) and of other mahouts (unfamiliar individuals). The results showed that elephants responded successfully to the commands from their own mahouts, with an average response rate as high as 78.8%. The more years the mahouts had been as their caretakers, the more the elephant showed active responses toward the commands. Female elephants responded to the commands more frequently and faster than males. Also younger elephants responded more frequently and faster than older elephants. We argue that Asian elephants can discriminate between familiar and unfamiliar humans by acoustic cues alone. Proximity with humans may be a factor, as fundamental as domestication, for animals to develop heterospecies discriminatory ability.

Familiarity mediates apes' attentional biases toward human faces.

In zoos, primates experience markedly different interactions with familiar humans, such as the zookeepers who care for them, compared with those with unfamiliar humans, such as the large volume of zoo visitors to whom they are regularly exposed. While the behaviour of zoo-housed primates in the presence of unfamiliar, and to a lesser extent familiar, humans has received considerable attention, if and how they spontaneously distinguish familiar from unfamiliar people, and the cognitive mechanisms underlying the relationships they form with familiar and unfamiliar humans, remain poorly understood. Using a dot-probe paradigm, we assessed whether primates (chimpanzees and gorillas) show an attentional bias toward the faces of familiar humans, with whom the apes presumably had a positive relationship. Contrary to our predictions, all subjects showed a significant attentional bias toward unfamiliar people's faces compared with familiar people's faces when the faces showed a neutral expression, both with and without a surgical face mask on, but no significant attentional bias when the faces showed a surprised expression. These results demonstrate that apes can spontaneously categorize humans based on familiarity and we argue that the attentional biases the apes showed for unfamiliar human faces reflect a novelty effect.