Marta B. Manser

Costs of cooperative behaviour in suricates (Suricata suricatta)

Functional interpretations of helping behaviour suggest that it has evolved because helpers increase their direct or indirect fitness by helping. However, recent critiques have suggested that helping may be an unselected extension of normal parental behaviour, pointing to evidence that all mature individuals commonly respond to begging young (whether they are parents, relatives or non–relatives) as well as to the lack of evidence that cooperative activities have appreciable costs to helpers. Here we provide an example of one form of cooperative behaviour that is seldom performed by parents and has substantial energetic costs to helpers. In the cooperative mongoose, Suricata suricatta, non–breeding adults commonly babysit young pups at the natal burrow for a day at a time, foregoing feeding for 24 hours. Parents rarely contribute to babysitting, and babysitting has substantial energetic costs to helpers. Members of small groups compensate for the reduced number of participants by babysitting more frequently, and neither the proportion of time that babysitters are present nor the survival of litters vary with group size.

Suricate alarm calls signal predator class and urgency.

Human speech encodes both referential and affective information, but evidence for a similar phenomenon in animal vocalizations has been lacking. Recent work on suricates, an African mongoose, shows that animal alarm calls simultaneously encode information about both predator type and the signalers perception of urgency.

The information that receivers extract from alarm calls in suricates

Field observations and acoustic analyses have shown that suricate (Suricata suricatta) alarm calls vary in their acoustic structure depending on predator type. In this study, we tested whether receivers respond appropriately when hearing a call in the absence of a predator. Although the only way for suricates to escape from predators is to retreat to boltholes, responses to playbacks could be divided into distinct categories. The subjects responded differently to alarm calls given in response to aerial or terrestrial predators and to recruitment calls emitted in response to snakes and deposits on the ground. Suricates also showed rather distinct responses to low, medium and high urgency aerial calls. Differences in the responses were less obvious for different levels of urgency in the terrestrial and recruitment calls. Suricate receivers thus gain information about both the predator type and level of urgency from the acoustic structures of their calls.

Latrine distribution and patterns of use by wild meerkats: implications for territory and mate defence

Many carnivores defend territories and deposit faeces and other scent marks at specific latrine sites. The role of latrines in territory defence is well established, but evidence suggests at least a subsidiary role in mate defence. We investigated latrine function in cooperative meerkats, Suricata suricatta. By analysing the spatial and temporal distribution of latrines we found patterns that might facilitate information transmission to a range of potential intruders. Each group of meerkats usually shared one latrine with each known neighbouring group, which probably allowed efficient intergroup monitoring of surrounding land tenure. The remaining latrines were primarily concentrated in territorial core regions. As transient groups and prospecting males enter territories unpredictably, this distribution may maximize the likelihood of latrine discovery. In large meerkat territories, the chance of intruders missing widely spaced boundary scent marks is high, and a core-marking strategy may therefore be more effective. Latrines were positioned close to refuge sites, which may further increase the likelihood of intercepting intruders, as prospectors are known to visit these sites regularly during intrusions. Although latrine use did not increase during periods when resident females were sexually receptive, it was significantly more likely during the peak breeding period in general, and occurred at significantly greater rates during observation periods when prospecting males were encountered. As prospectors threaten resident male reproductive success, these results highlight the potential importance of latrines in mate defence.

Acoustic sequences in non-human animals: a tutorial review and prospectus

Animal acoustic communication often takes the form of complex sequences, made up of multiple distinct acoustic units. Apart from the well‐known example of birdsong, other animals such as insects, amphibians, and mammals (including bats, rodents, primates, and cetaceans) also generate complex acoustic sequences. Occasionally, such as with birdsong, the adaptive role of these sequences seems clear (e.g. mate attraction and territorial defence). More often however, researchers have only begun to characterise – let alone understand – the significance and meaning of acoustic sequences. Hypotheses abound, but there is little agreement as to how sequences should be defined and analysed. Our review aims to outline suitable methods for testing these hypotheses, and to describe the major limitations to our current and near‐future knowledge on questions of acoustic sequences. This review and prospectus is the result of a collaborative effort between 43 scientists from the fields of animal behaviour, ecology and evolution, signal processing, machine learning, quantitative linguistics, and information theory, who gathered for a 2013 workshop entitled, ‘Analysing vocal sequences in animals’. Our goal is to present not just a review of the state of the art, but to propose a methodological framework that summarises what we suggest are the best practices for research in this field, across taxa and across disciplines. We also provide a tutorial‐style introduction to some of the most promising algorithmic approaches for analysing sequences. We divide our review into three sections: identifying the distinct units of an acoustic sequence, describing the different ways that information can be contained within a sequence, and analysing the structure of that sequence. Each of these sections is further subdivided to address the key questions and approaches in that area. We propose a uniform, systematic, and comprehensive approach to studying sequences, with the goal of clarifying research terms used in different fields, and facilitating collaboration and comparative studies. Allowing greater interdisciplinary collaboration will facilitate the investigation of many important questions in the evolution of communication and sociality.

Cortisol levels are positively associated with pup-feeding rates in male meerkats

In societies of cooperative vertebrates, individual differences in contributions to offspring care are commonly substantial. Recent attempts to explain the causes of this variation have focused on correlations between contributions to care and the protein hormone prolactin, or the steroid hormone testosterone. However, such studies have seldom considered the importance of other hormones or controlled for non-hormonal factors that are correlative with both individual hormone levels and contributions to care. Using multivariate statistics, we show that hormone levels explain significant variation in contributions to pup-feeding by male meerkats, even after controlling for non-hormonal effects. However, long-term contributions to pup provisioning were significantly and positively correlated with plasma levels of cortisol rather than prolactin, while plasma levels of testosterone were not related to individual patterns of pup-feeding. Furthermore, a playback experiment that used pup begging calls to increase the feeding rates of male helpers gave rise to parallel increases in plasma cortisol levels, whilst prolactin and testosterone levels remained unchanged. Our findings confirm that hormones can explain significant amounts of variation in contributions to offspring feeding, and that cortisol, not prolactin, is the hormone most strongly associated with pup-feeding in cooperative male meerkats.

The irrelevance of individual discrimination in meerkat alarm calls

Individual discrimination is an important element in the evolution of social behaviour and is particularly important in social living species which show intense intragroup interactions. Numerous previous studies, particularly with nonhuman primates, ground squirrels and marmots, demonstrate the widespread ability of various species to signal and perceive individual identity from vocalizations. The function of individually different alarm calls is thought to assist in the detection of unreliable individuals. This would allow individuals to optimize the benefits of antipredator behaviour by self-assessing the relative predation risk, and responding selectively to reliable callers. In this study we investigated whether meerkats, Suricata suricatta, a social mongoose, discriminated among alarm callers individually, and adjusted their response accordingly. Several parameters of the acoustic structure of meerkat alarm calls were measured and analysed with multivariate statistics. Within groups, the 10-fold cross-validation of a multinomial regression yielded, on average, 90% correct assignment. This strongly suggests that meerkats have individually distinct alarm calls. With a habituation–dishabituation playback experiment, we then tested whether meerkats use this information to discriminate between individual callers. Receivers did not distinguish between different individuals in the playback experiments. In meerkats, unreliable callers appear to be uncommon, and the cost of being predated might exceed the costs of responding to an unreliable caller, thus rendering a reliability-based discrimination mechanism unnecessary. Although meerkat alarm calls contain information on individual identity, this information does not appear to be important to the receivers in this context.

Moving calls: a vocal mechanism underlying quorum decisions in cohesive groups

Members of social groups need to coordinate their behaviour when choosing between alternative activities. Consensus decisions enable group members to maintain group cohesion and one way to reach consensus is to rely on quorums. A quorum response is where the probability of an activity change sharply increases with the number of individuals supporting the new activity. Here, we investigated how meerkats (Suricata suricatta) use vocalizations in the context of movement decisions. Moving calls emitted by meerkats increased the speed of the group, with a sharp increase in the probability of changing foraging patch when the number of group members joining the chorus increased from two up to three. These calls had no apparent effect on the groups movement direction. When dominant individuals were involved in the chorus, the groups reaction was not stronger than when only subordinates called. Groups only increased speed in response to playbacks of moving calls from one individual when other group members emitted moving calls as well. The voting mechanism linked to a quorum probably allows meerkat groups to change foraging patches cohesively with increased speed. Such vocal coordination may reflect an aggregation rule linking individual assessment of foraging patch quality to group travel route.

Language evolution: syntax before phonology?

Phonology and syntax represent two layers of sound combination central to languages expressive power. Comparative animal studies represent one approach to understand the origins of these combinatorial layers. Traditionally, phonology, where meaningless sounds form words, has been considered a simpler combination than syntax, and thus should be more common in animals. A linguistically informed review of animal call sequences demonstrates that phonology in animal vocal systems is rare, whereas syntax is more widespread. In the light of this and the absence of phonology in some languages, we hypothesize that syntax, present in all languages, evolved before phonology.

The audience effect in a facultatively social mammal, the yellow mongoose, Cynictis penicillata

The audience effect has been shown in numerous group-living vertebrates but whether it is present in facultatively social species is unknown. We investigated the antipredator responses of the yellow mongoose, a mammal that dens in groups but primarily forages alone. To examine the effect that the social environment has on their communication, we performed a combination of field observations and experiments with live and model predators on a habituated population of mongooses. Social context affected both the communicative and the flight behaviour of yellow mongooses. Alarm vocalizations were used almost exclusively when individuals were in a group rather than solitary. The visual alarm signal, a raised tail, was predominantly used by solitary individuals when predators were outside attack range. This study apparently is the first to show an audience effect in a facultatively social mammal, suggesting that even rare social interactions lead to the ability to respond flexibly to predators depending on the presence or absence of conspecifics.