Collective close calling mediates group cohesion in foraging meerkats via spatially determined differences in call rates

During group movements, many socially living and group-foraging animals produce contact calls. Contact calls typically function to coordinate and maintain cohesion among group members by providing receivers with information on the callers' location or movement-related motivation. Previous work suggests that meerkats, Suricata suricatta, also produce short-range contact calls, so-called ‘close calls’, while foraging to maintain group cohesion. Yet, the underlying mechanism of how meerkats coordinate cohesion via close calling is unclear. Using a combination of field observations and playback experiments we here show that foraging meerkats adjusted the call rates of their continuously produced close calls depending on their spatial position to group members. Specifically, meerkats called at higher rates when foraging at a closer distance to and when surrounded by conspecifics; however, the number of calling individuals or their call rates did not affect a subject's close call rate. Overall, close call playbacks elicited a call response in receivers and attracted them to the sound source. Our results suggest that differences in individual close call rates are determined by a meerkat's proximity to other group members, being assessed through their vocal interactions. We discuss how local differences in individual call rates may extrapolate to the group level, where emerging ‘vocal hotspots’ indicate areas of high individual density, in turn attracting and potentially guiding group members' movements. Hence, the described pattern illustrates a so far undocumented call mechanism where local differences in the call rates of continuously produced close calls can generate a group level pattern that mediates the cohesion of progressively moving animal groups

Social organization of a solitary carnivore: spatial behaviour, interactions and relatedness in the slender mongoose

The majority of carnivore species are described as solitary, but little is known about their social organization and interactions with conspecifics. We investigated the spatial organization and social interactions as well as relatedness of slender mongooses (Galerella sanguinea) living in the southern Kalahari. This is a little studied small carnivore previously described as solitary with anecdotal evidence for male associations. In our study population, mongooses arranged in spatial groups consisting of one to three males and up to four females. Male ranges, based on sleeping sites, were large and overlapping, encompassing the smaller and more exclusive female ranges. Spatial groups could be distinguished by their behaviour, communal denning and home range. Within spatial groups animals communally denned in up to 33% of nights, mainly during winter months, presumably to gain thermoregulatory benefits. Associations of related males gained reproductive benefits likely through increased territorial and female defence. Our study supports slender mongooses to be better described as solitary foragers living in a complex system of spatial groups with amicable social interactions between specific individuals. We suggest that the recognition of underlying ‘hidden' complexities in these apparently ‘solitary' organizations needs to be accounted for when investigating group living and social behaviour

Call concatenation in wild meerkats

Repertoire size, frequently determined by the number of discrete call types, has been used to assess vocal complexity in animals. However, species can also increase their communicative complexity by using graded signals or by combining individual calls. Animal call sequences can be divided into two main categories, each subdivided into two classes: repetitions, with either an unlimited or finite number of iterations of the same call type, and mixed call combinations, composed of two or more graded or discrete call types. Social contexts involve a wide range of behaviours and, unlike predation contexts, can be associated with both positive and negative emotions. Therefore, interactions linked to social contexts may place additional demands on an animal's communicative system and lead to the use of call combinations. We systematically documented call combinations produced by wild meerkats, Suricata suricatta, a highly social carnivore, in social contexts in their natural habitat. We observed 12 distinct call combinations belonging to all four classes of combination, produced in all the observed behavioural contexts. Four combinations were each produced in a specific context whereas the remaining eight were produced in several contexts, albeit in different proportions. The broad use of combinations suggests that they represent a non-negligible part of meerkat social communication and that they can be used in flexible ways across various behavioural contexts. Comparison with combinations produced in predation contexts indicated that social call combinations are more varied in number of classes and structural complexity than the former, perhaps due to the greater variety of social contexts. However, in meerkats, combinations of functionally referential calls have been documented in predation but not social contexts, suggesting that both social and predation pressures may play a role in the evolution of combinatoriality in animal communication

Vocalization-associated respiration patterns: thermography-based monitoring and detection of preparation for calling

Vocal emission requires coordination with the respiratory system. Monitoring the increase in laryngeal pressure, which is needed for vocal production, allows detection of transitions from quiet respiration to vocalization-supporting respiration. Characterization of these transitions could be used to identify preparation for vocal emission and to examine the probability of it manifesting into an actual vocal production event. Specifically, overlaying the subject's respiration with conspecific calls can highlight events of call initiation and suppression, as a means of signalling coordination and avoiding jamming. Here, we present a thermal imaging-based methodology for synchronized respiration and vocalization monitoring of free-ranging meerkats. The sensitivity of this methodology is sufficient for detecting transient changes in the subject's respiration associated with the exertion of vocal production. The differences in respiration are apparent not only during the vocal output, but also prior to it, marking the potential time frame of the respiratory preparation for calling. A correlation between conspecific calls with elongation of the focal subject's respiration cycles could be related to fluctuations in attention levels or in the motivation to reply. This framework can be used for examining the capability for enhanced respiration control in animals during modulated and complex vocal sequences, detecting ‘failed’ vocalization attempts and investigating the role of respiration cues in the regulation of vocal interactions

Decline and fall: The causes of group failure in cooperatively breeding meerkats.

Funder: MAVA FoundationFunder: Universität ZürichIn many social vertebrates, variation in group persistence exerts an important effect on individual fitness and population demography. However, few studies have been able to investigate the failure of groups or the causes of the variation in their longevity. We use data from a long-term study of cooperatively breeding meerkats, Suricata suricatta, to investigate the different causes of group failure and the factors that drive these processes. Many newly formed groups failed within a year of formation, and smaller groups were more likely to fail. Groups that bred successfully and increased their size could persist for several years, even decades. Long-lived groups principally failed in association with the development of clinical tuberculosis, Mycobacterium suricattae, a disease that can spread throughout the group and be fatal for group members. Clinical tuberculosis was more likely to occur in groups that had smaller group sizes and that had experienced immigration

Effect of group size and experience on the ontogeny of sentinel calling behaviour in meerkats

Increased vulnerability to predation results in young individuals of many species experiencing higher predation pressure than adults. Consequently, the production of antipredator-related calls by young can differ from that of the same vocalizations given by adults. Sentinel behaviour is a coordinated vigilance behaviour, where one individual climbs on an elevated position and scans the surroundings for predators, while the rest of the group is mainly foraging. Meerkat, Suricata suricatta, sentinels produce six distinct sentinel call types, which inform other group members about the perceived predation risk, resulting in the adjustment of personal vigilance behaviour in foraging group members. Here, we investigated the onset of sentinel behaviour and the ontogeny of the different sentinel call types as well as the development of individual vocal signatures in meerkats. We found that meerkats started acting as a sentinel around 200 days of age, but this was highly dependent on group size, with individuals from smaller groups exhibiting sentinel behaviour earlier than individuals from larger groups. All six sentinel call types were already present in the repertoire upon first emergence of the behaviour; however, call rates of ‘all-clear’ calls increased while ‘warning’ calls decreased with increasing experience as sentinel. Analysis of one of the most frequent sentinel calls, the double note calls, indicated that fundamental frequency, mean amplitude, duration and entropy differed consistently between individuals, but we found no effect of age. Rather, our results provide evidence that individual signatures in this call type were already developed when young meerkats first started to act as sentinel and changed little with age. To conclude, we showed little ontogenetic change in overall sentinel behaviour as well as in its vocal coordination, indicating potentially high selection pressures on antipredator behaviours, such as the sentinel system, resulting in consistent behavioural responses upon first emergence.The long-term field site KMP was financed by the Universities of Cambridge and Zurich, and the MAVA foundation. This article has relied on records of individual identities and/or life histories maintained by the KMP, which has been supported financially by the European Research Council and the University of Zurich.http://www.elsevier.com/locate/anbehavhj2022Mammal Research Institut

Flexible alarm calling in meerkats: the role of the social environment and predation urgency

Flexible vocal production has been demonstrated in several vertebrate species, with much work focusing on the role of the social "audience” in explaining variation in call production. It is, however, likely that the decision to call is an emergent property of both external and internal factors, and the extent to which these factors are integrated has been little investigated. We addressed this question by examining the production of alarm calls in wild male meerkats (Suricata suricatta) in different social environments and different predator-encounter contexts. Males searching for reproductive opportunities (rovers) were followed 1) in their home group and when prospecting either 2) solitarily or 3) in a coalition with other males. Results showed that conspecific presence influenced the production of flee-alarm and recruitment calls. Solitary rovers were less likely to produce flee-alarm calls compared with when they are with conspecifics, whether coalitionary rovers or the rover's home group. Experimentally elicited recruitment calls were also produced less when males were solitary than when in their home group. Bark vocalizations, emitted when meerkats were safe, were always produced irrespective of conspecific presence, indicating that these calls function to address predators. The probability of producing flee alarms also increased with the urgency of the predation event. Our results indicate that variation in alarm call production depends on whom the call is addressed to and also on the motivational state of the caller. We argue that neglecting to integrate internal and external factors when elucidating mechanisms underlying vocal production can potentially lead to misguided, parsimonious conclusions regarding vocal flexibility in animal

Diurnal oscillations in gut bacterial load and composition eclipse seasonal and lifetime dynamics in wild meerkats.

Circadian rhythms in gut microbiota composition are crucial for metabolic function, yet the extent to which they govern microbial dynamics compared to seasonal and lifetime processes remains unknown. Here, we investigate gut bacterial dynamics in wild meerkats (Suricata suricatta) over a 20-year period to compare diurnal, seasonal, and lifetime processes in concert, applying ratios of absolute abundance. We found that diurnal oscillations in bacterial load and composition eclipsed seasonal and lifetime dynamics. Diurnal oscillations were characterised by a peak in Clostridium abundance at dawn, were associated with temperature-constrained foraging schedules, and did not decay with age. Some genera exhibited seasonal fluctuations, whilst others developed with age, although we found little support for microbial senescence in very old meerkats. Strong microbial circadian rhythms in this species may reflect the extreme daily temperature fluctuations typical of arid-zone climates. Our findings demonstrate that accounting for circadian rhythms is essential for future gut microbiome research

Signalling adjustments to direct and indirect environmental effects on signal perception in meerkats.

The efficiency of communication between animals is determined by the perception range of signals. With changes in the environment, signal transmission between a sender and a receiver can be influenced both directly, where the signal's propagation quality itself is affected, and indirectly where the senders or receivers' behaviour is impaired, impacting for example the distance between them. Here we investigated how meerkats (Suricata suricatta) in the Kalahari Desert adjust to these challenges in the context of maintaining group cohesion through contact calls. We found that meerkats changed their calling rate when signal transmission was affected indirectly due to increased dispersion of group members as during a drought, but not under typical wet conditions, when signal transmission was directly affected due to higher vegetation density. Instead under these wetter conditions, meerkats remained within proximity to each other. Overall, both direct and indirect environmental effects on signal perception resulted in an increased probability of groups splitting. In conclusion, we provide evidence that social animals can flexibly adjust their vocal coordination behaviour to cope with direct and indirect effects of the environment on signal perception, but these adjustments have limitations