Cross-species discrimination of vocal expression of emotional valence by Equidae and Suidae.

BACKGROUND: Discrimination and perception of emotion expression regulate interactions between conspecifics and can lead to emotional contagion (state matching between producer and receiver) or to more complex forms of empathy (e.g., sympathetic concern). Empathy processes are enhanced by familiarity and physical similarity between partners. Since heterospecifics can also be familiar with each other to some extent, discrimination/perception of emotions and, as a result, emotional contagion could also occur between species. RESULTS: Here, we investigated if four species belonging to two ungulate Families, Equidae (domestic and Przewalski's horses) and Suidae (pigs and wild boars), can discriminate between vocalizations of opposite emotional valence (positive or negative), produced not only by conspecifics, but also closely related heterospecifics and humans. To this aim, we played back to individuals of these four species, which were all habituated to humans, vocalizations from a unique set of recordings for which the valence associated with vocal production was known. We found that domestic and Przewalski's horses, as well as pigs, but not wild boars, reacted more strongly when the first vocalization played was negative compared to positive, regardless of the species broadcasted. CONCLUSIONS: Domestic horses, Przewalski's horses and pigs thus seem to discriminate between positive and negative vocalizations produced not only by conspecifics, but also by heterospecifics, including humans. In addition, we found an absence of difference between the strength of reaction of the four species to the calls of conspecifics and closely related heterospecifics, which could be related to similarities in the general structure of their vocalization. Overall, our results suggest that phylogeny and domestication have played a role in cross-species discrimination/perception of emotions.

Exclusion by donkey's ears: Donkeys (Equus asinus) use acoustic information to find hidden food in a two-way object-choice task.

Once believed uniquely human, the capacity to reason is now investigated in a wide range of species. One component of this ability, inference by exclusion, has been traditionally explored through the cups task, where 2 containers are presented but only 1 covers a food reward (if Cup A is empty, then choose Cup B). Often based on low-level cognitive mechanisms (learning), performance on this task can also reflect reasoning processes in some individuals. Limited taxonomic investigation, however, has hindered our understanding of the factors that contribute to the evolution of reasoning in animals. Using the cups task, we first investigated the ability of 14 semiwild donkeys to locate a food reward by using visual or acoustic cues alone (pretest phase). Although all subjects failed the task when provided with visual cues, 7 donkeys succeeded in the acoustic modality. We thus tested the capacity of donkeys to make choices by exclusion in the acoustic modality (test phase). Three conditions were presented, where subjects received information about either both containers (full information condition), solely the empty container (exclusion condition), or no information (control condition). Most subjects chose the correct container in the full information condition, whereas they chose randomly in the control condition. Except for 1 individual, donkeys improved their performance across trials in the exclusion condition. Our study contributes to the very small body of literature on exclusion based on acoustic cues in animals and paves the way to further experiments on the cognitive processes underlying exclusion performance in donkeys. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Need or opportunity? A study of innovations in equids.

Debate persists over whether animals develop innovative solutions primarily in response to needs or conversely whether they innovate more when basic needs are covered and opportunity to develop novel behaviour is offered. We sourced 746 cases of "unusual" behaviour in equids by contacting equid owners and caretakers directly and via a website (https://innovative-behaviour.org), and by searching the internet platforms YouTube and Facebook for videos. The study investigated whether differences in need or opportunity for innovation were reflected in the numbers of different types of innovations and in the frequencies of repeating a once-innovative behaviour (i) with respect to the equids' sex, age, and breed type, (ii) across behavioural categories, and whether (iii) they were affected by the equids' management (single vs group housing, access to roughage feed, access to pasture, and social contact). We found that the numbers of different types of innovation and the frequency of displaying specific innovations were not affected by individual characteristics (sex, age, breed or equid species). Few types of innovation in escape and foraging contexts were observed, whilst the comfort, play, and social contexts elicited the greatest variety of innovations. We also found higher numbers of different types of innovations in horses kept in groups rather than in individual housing, and with unlimited rather than with restricted access to pasture and roughage. Equids in permanent social contact performed high rates of once-innovative behaviour. We suggest that equids produce goal-directed innovations and repeat the behaviour at high frequency in response to urgent needs for food and free movement or when kept in conditions with social conflict. However, equids devise the greatest variety of innovations when opportunity to play and to develop comfort behaviour arises and when kept in good conditions.

Seminal Plasma, Sperm Concentration, and Sperm-PMN Interaction in the Donkey: An In Vitro Model to Study Endometrial Inflammation at Post-Insemination.

In the donkey, artificial insemination (AI) with frozen-thawed semen is associated with low fertility rates, which could be partially augmented through adding seminal plasma (SP) and increasing sperm concentration. On the other hand, post-AI endometrial inflammation in the jenny is significantly higher than in the mare. While previous studies analyzed this response through recovering Polymorphonuclear Neutrophils (PMN) from uterine washings, successive lavages can detrimentally impact the endometrium, leading to fertility issues. For this reason, the first set of experiments in this work intended to set an in vitro model through harvesting PMN from the peripheral blood of jennies. Thereafter, how PMN, which require a triggering agent like formyl-methionyl-leucyl-phenylalanine (FMLP) to be activated, are affected by donkey semen was interrogated. Finally, we tested how four concentrations of spermatozoa (100 × 106, 200 × 106, 500 × 106 and 1000 × 106 spermatozoa/mL) affected their interaction with PMN. We observed that semen, which consists of sperm and SP, is able to activate PMN. Whereas there was a reduced percentage of spermatozoa phagocytosed by PMN, most remained attached on the PMN surface or into a surrounding halo. Spermatozoa not attached to PMN were viable, and most of those bound to PMN were also viable and showed high tail beating. Finally, only sperm concentrations higher than 500 × 106 spermatozoa/mL showed free sperm cells after 3 h of incubation, and percentages of spermatozoa not attached to PMN were higher at 3 h than at 1 h, exhibiting high motility. We can thus conclude that semen activates PMN in the donkey, and that the percentage of spermatozoa phagocytosed by PMN is low. Furthermore, because percentages of spermatozoa not attached to PMN were higher after 3 h than after 1 h of incubation, we suggest that PMN-sperm interaction plays an instrumental role in the reproductive strategy of the donkey.

Evolutionary constraints on equid domestication: Comparison of flight initiation distances of wild horses (Equus caballus ferus) and plains zebras (Equus quagga).

Habituation to humans was an essential component of horse (Equus caballus ferus) domestication, with the nondomestication of zebras (Equus quagga) possibly reflecting an adaptive constraint on habituation. We present the human hunting hypothesis, arguing that ancestral humans hunted African animals, including zebras, long enough to promote a persistent wariness of humans, whereas a briefer period of hunting horses in Central Asia influenced by glacial cycles was unlikely to produce an equally persistent wariness. An alternative habituation to humans hypothesis, prompted by field observations, posits that zebras can habituate well to nonthreatening humans given sufficient exposure. If so, other factors must account for zebra nondomestication. To examine these hypotheses, we compared the flight initiation distances (FIDs) of wild horses in the United States and plains zebras in Africa to a human approaching on foot (N = 87). We compared the flight behavior of both species at sites with low and high exposure to humans (mean humans/acre = .004 and .209, respectively). Analyses revealed a significant interaction (p = .0001) between equid species and level of human exposure. The mean FIDs of horses (146 m) and zebras (105 m) with low human exposure did not differ appreciably (p = .412), but these distances were substantially longer (p < .0001) than those of horses (17 m) and zebras (37 m) with high human exposure that did differ significantly (p < .0001). The finding that plains zebras habituate less completely to humans than horses do might reflect an adaptive response to historical hunting and partly explain their resistance to domestication.

Behavioural repertoire of working donkeys and consistency of behaviour over time, as a preliminary step towards identifying pain-related behaviours.

BACKGROUND: The donkey has a reputation for stoicism and its behavioural repertoire in clinical contexts is under-reported. Lack of understanding of the norms of donkey behaviour and how it may vary over time can compromise use of behavioural measures as indicators of pain or emotional state. The objective of this study was to find out whether the behaviour of working donkeys was influenced by gender, the time of day or differed between days with a view to assessing how robust these measures are for inclusion in a working donkey ethogram. METHODOLOGY/PRINCIPAL FINDINGS: Frequency and consistency of postural and event behaviours were measured in 21 adult working donkeys (12 females; 9 males). Instantaneous (scan) and focal sampling were used to measure maintenance, lying, ingestive and investigative behaviours at hourly intervals for ten sessions on each of two consecutive days. High head carriage and biting were seen more frequently in male donkeys than females (P<0.001). Level head carriage, licking/chewing and head-shaking were observed more frequently in female donkeys (P<0.001). Tail position, ear orientation, foot stamping, rolling/lying and head-shaking behaviours were affected by time of day (P<0.001). However, only two variations in ear orientation were found to be significantly different over the two days of observations (P<0.001). Tail swishing, head shaking, foot stamping, and ears held sideways and downwards were significantly correlated (P<0.001) and are assumed to be behaviours to discourage flies. CONCLUSIONS/SIGNIFICANCE: All donkeys expressed an extensive behavioural repertoire, although some differences in behaviour were evident between genders. While most behaviours were consistent over time, some behaviours were influenced by time of day. Few behaviours differed between the two test days. The findings can be used to inform the development of a robust, evidence-based ethogram for working donkeys.

Spatial cognition and perseveration by horses, donkeys and mules in a simple A-not-B detour task.

We investigated perseveration and detour behaviour in 36 equids (Equus caballus, E. asinus, E. caballus × E. asinus) and compared these data to those of a previous study on domestic dogs (Canis familiaris). The animals were required to make a detour through a gap at one end of a straight barrier in order to reach a visible target. After one, two, three or four repeats (A trials), the gap was moved to the opposite end of the barrier (B trials). We recorded initial deviations from the correct solution path and the latency to crossing the barrier. In the A trials, mules crossed the barrier significantly faster than their parental species, the horses and donkeys. In the B trials, following the change of gap location, all species showed a reduction in performance. Both dogs and horses exhibited significant spatial perseveration, going initially to the previous gap location. Donkeys and mules, however, performed at chance level. Our results suggest that hybrid vigour in mules extends to spatial abilities.

Lion, ungulate, and visitor reactions to playbacks of lion roars at Zoo Atlanta.

Felids in captivity are often inactive and elusive in zoos, leading to a frustrating visitor experience. Eight roars were recorded from an adult male lion and played back over speakers as auditory enrichment to benefit the lions while simultaneously enhancing the zoo visitor experience. In addition, ungulates in an adjacent exhibit were observed to ensure that the novel location and increased frequency of roars did not lead to a stress or fear response. The male lion in this study roared more in the playback phase than in the baseline phases while not increasing any behaviors that would indicate compromised welfare. In addition, zoo visitors remained at the lion exhibit longer during playback. The nearby ungulates never exhibited any reactions stronger than orienting to playbacks, identical to their reactions to live roars. Therefore, naturalistic playbacks of lion roars are a potential form of auditory enrichment that leads to more instances of live lion roars and enhances the visitor experience without increasing the stress levels of nearby ungulates or the lion themselves, who might interpret the roar as that of an intruder.

Mules in Herodotus: the destiny of half-breeds.

In his Histories, Herodotus uses the mule as a symbol of both potential advantages and risks of intermarriage and reproduction between different ethnic groups. Both literal mules and the children of mixed marriages are symbols of revolutions and new dynasties. These revolutions are often marked by an attempt to blend or conglomerate distinct cultural nomoi, or customs. Herodotus' stories about ethnically mixed leaders and their effects upon their societies serve as both encouragement and warning to governments like Athens and the Persian Empire.

Comparing responses of four ungulate species to playbacks of baboon alarm calls.

A growing body of evidence suggests that a wide range of animals can recognize and respond appropriately to calls produced by other species. Social learning has been implicated as a possible mechanism by which heterospecific call recognition might develop. To examine whether familiarity and/or shared vulnerability with the calling species might influence the ability of sympatric species to distinguish heterospecific alarm calls, we tested whether four ungulate species (impala: Aepyceros melampus; tsessebe: Damaliscus lunatus; zebra: Equus burchelli; wildebeest: Connochaetes taurinus) could distinguish baboon (Papio hamadryas ursinus) alarm calls from other loud baboon calls produced during intra-specific aggressive interactions ('contest' calls). Overall, subjects' responses were stronger following playback of alarm calls than contest calls. Of the species tested, impala showed the strongest responses and the greatest difference in composite response scores, suggesting they were best able to differentiate call types. Compared with the other ungulate species, impala are the most frequent associates of baboons. Moreover, like baboons, they are susceptible to both lion and leopard attacks, whereas leopards rarely take the larger ungulates. Although it seems possible that high rates of association and/or shared vulnerability may influence impala's greater ability to distinguish among baboon call types, our results point to a stronger influence of familiarity. Ours is the first study to compare such abilities among several community members with variable natural histories, and we discuss future experiments that would more systematically examine development of these skills in young ungulates.

Environmental and demographic risk factors for poor welfare in working horses, donkeys and mules in developing countries.

Over 85% of equids live in developing countries, where they are usually used for work. We aimed to identify environmental factors associated with potential welfare problems in working equids, helping target welfare interventions towards the most vulnerable animals. Over 5 years, non-invasive behavioural and physical data were collected from 5481 donkeys, 4504 horses, and 858 mules across nine developing countries. Hoof and limb problems were over 90% prevalent, and 85% of equids were thin. Older, thinner animals had the most problems, and species differences in susceptibility were found. Equids used to transport people by cart, to carry goods by pack, or to work in bricks kilns had more problems than other equids. Rural equids had more problems than urban ones, but urban equids had more lesions, and were more aggressive towards observers. Equids were significantly thinner when climates were warmer. These results should aid the development and targeting of specific welfare interventions.

Mule cognition: a case of hybrid vigour?

This study compares the behaviour of the mule (Equus asinus x Equus caballus) with that of its parent species to assess the effects of hybridization on cognition. Six mules, six ponies (E. caballus) and six donkeys (E. asinus) were given a two choice visual discrimination learning task. Each session consisted of 12 trials and pass level was reached when subjects chose the correct stimulus for at least 9 out of the 12 trials in three consecutive sessions. A record was made of how many pairs each subject learnt over 25 sessions. The mules' performance was significantly better than that of either of the parent species (Kruskal-Wallis: H(x) = 8.11, P = 0.017). They were also the only group to learn enough pairs to be able to show a successive reduction in the number of sessions required to reach criterion level. This study provides the first empirical evidence that the improved characteristics of mules may be extended from physical attributes to cognitive function.