The presence of an avian co-forager reduces vigilance in a cooperative mammal

Many animals participate in biological markets, with strong evidence existing for immediate cooperative trades. In particular, grooming is often exchanged for itself or other commodities, such as coalitionary support or access to food and mates. More contentious is the possibility that nonhuman animals can rely on memories of recent events, providing contingent cooperation even when there is a temporal delay between two cooperative acts. Here we provide experimental evidence of delayed cross-commodity grooming exchange in wild dwarf mongooses (Helogale parvula). First, we use natural observations and social-network analyses to demonstrate a positive link between grooming and sentinel behavior (acting as a raised guard). Group members who contributed more to sentinel behavior received more grooming and had a better social-network position. We then used a field-based playback experiment to test a causal link between contributions to sentinel behavior and grooming received later in the day. During 3-h trial sessions, the perceived sentinel contributions of a focal individual were either up-regulated (playback of its surveillance calls, which are given naturally during sentinel bouts) or unmanipulated (playback of its foraging close calls as a control). On returning to the sleeping refuge at the end of the day, focal individuals received more grooming following surveillance-call playback than control-call playback and more grooming than a matched individual whose sentinel contributions were not up-regulated. We believe our study therefore provides experimental evidence of delayed contingent cooperation in a wild nonprimate species.

In many social species, group members form strong social bonds. Such strong bonds are well-known to generate long-term fitness benefits, but they are also expected to influence short-term behavioural decisions. Here, we use field observations and an experimental manipulation to investigate whether variation in social-bond strength (as determined from grooming interactions) influences nearest-neighbour choices while foraging in wild dwarf mongooses (Helogale parvula). Preferred grooming partnerships (PGPs), representing particularly strong bonds, were found predominately between male–female dyads but among a range of dominance-status dyads. When searching for food, dwarf mongooses with PGPs were more likely than expected by chance to forage close to a preferred grooming partner. Foraging near a strongly bonded groupmate might reduce the predation risk or increase foraging opportunities and the transfer of social information. In addition, there could be stress-reducing benefits, although our field experiment provided no evidence that nearest-neighbour preferences for strongly bonded groupmates were additionally favoured, or indeed disrupted, in the aftermath of a short-term stressful event. Investigating the potential influence of strong social bonds on short-term behavioural decisions with potential fitness consequences is important for our understanding of social interactions and cooperation. Enduring, close social bonds between individuals provide considerable long-term health and fitness benefits, but are also expected to influence short-term behavioural decisions. We investigated whether social-bond strength (as determined from grooming interactions) influenced foraging decisions in cooperatively breeding dwarf mongoose groups. We found particularly strong social bonds in the form of preferred grooming partnerships in a subset of male–female dyads. Dwarf mongoose foraging decisions were affected by the strength of their social relationships with groupmates: individuals with preferred grooming partners preferred to have these individuals as their nearest neighbours when searching for food. We used a field-based experimental manipulation to investigate whether stressful events impact nearest-neighbour choices, but found no evidence that preferences to forage near strongly bonded groupmates were disrupted or more additionally favoured in the aftermath of a stressful event. Our current work extends understanding of how social bonds can potentially influence within-group behaviour.

Robbing rivals: interference foraging competition reflects female reproductive competition in a cooperative mammal

In many species, within-group conflict leads to immediate avoidance of potential aggressors or increases in affiliation, but no studies have investigated delayed post-conflict management behaviour. Here, we experimentally test that possibility using a wild but habituated population of dwarf mongooses (Helogale parvula). First, we used natural and playback-simulated foraging displacements to demonstrate that bystanders take notice of the vocalisations produced during such within-group conflict events but that they do not engage in any immediate post-conflict affiliative behaviour with the protagonists or other bystanders. We then used another playback experiment to assess delayed effects of within-group conflict on grooming interactions: we examined affiliative behaviour at the evening sleeping burrow, 30-60 min after the most recent simulated foraging displacement. Overall, fewer individuals groomed on evenings following an afternoon of simulated conflict, but those that did groomed more than on control evenings. Subordinate bystanders groomed with the simulated aggressor significantly less, and groomed more with one another, on conflict compared to control evenings. Our study provides experimental evidence that dwarf mongooses acoustically obtain information about within-group contests (including protagonist identity), retain that information, and use it to inform conflict-management decisions with a temporal delay.

Social animals that live in groups often have disagreements over access to mates and food. Even fleeting in-group disputes can be costly, disrupting relationships, wasting time and energy, or causing injury if aggression escalates. So, much like humans, many social animals, including primates, birds and dogs, have evolved conflict management strategies to prevent and resolve in-group disagreements. In the immediate aftermath of a conflict, this usually involves changes in the interactions between those involved in the disagreement, or between bystander groupmates and either the victim or aggressor. Less is known about whether social animals can recall past disputes and if they can use conflict management strategies some time after a quarrel has occurred. That is, do aggressive interactions between groupmates influence later social decisions of bystanders in the group? To investigate, Morris-Drake et al. studied groups of wild dwarf mongooses (Helogale parvula) that have become accustomed to living alongside humans in Limpopo Province, South Africa. Dwarf mongooses live in groups of up to 30 individuals, with one dominant breeding pair and lower-ranked helpers. When disagreements arise over food, an aggressor growls deeply and hip-slams the victim away from their foraging patch, stealing the victim’s prey in the process. Victims often produce high-pitched squeals in retreat. Using recordings of these calls, Morris-Drake et al. devised a field experiment to investigate how mongooses responded to nearby conflicts between other group members. Recordings simulating a conflict over food were played to groups of foraging mongooses over the course of an afternoon, so that group members effectively heard what sounded like repeated squabbles between two out-of-sight individuals. Similar to natural conflicts, the mongooses did not engage in any obvious conflict management behaviour immediately after hearing these disputes. But when the group returned to their sleeping burrow that evening, subordinate group members shunned the perceived aggressors from grooming, a key social activity. This work provides evidence that dwarf mongooses keep tabs on conflicts that occur between groupmates. It shows these animals can extract information about conflicts from vocal cues alone and that bystanders use this information when making later social decisions impacting group dynamics. It also adds to growing evidence from baboons, monkeys and chimpanzees that social animals can remember past events and take these into account when interacting with groupmates.

In many species, within-group conflict leads to immediate avoidance of potential aggressors or increases in affiliation, but no studies have investigated delayed post-conflict management behaviour. Here, we experimentally test that possibility using a wild but habituated population of dwarf mongooses (Helogale parvula). First, we used natural and playback-simulated foraging displacements to demonstrate that bystanders take notice of the vocalisations produced during such within-group conflict events but that they do not engage in any immediate post-conflict affiliative behaviour with the protagonists or other bystanders. We then used another playback experiment to assess delayed effects of within-group conflict on grooming interactions: we examined affiliative behaviour at the evening sleeping burrow, 30–60 min after the most recent simulated foraging displacement. Overall, fewer individuals groomed on evenings following an afternoon of simulated conflict, but those that did groomed more than on control evenings. Subordinate bystanders groomed with the simulated aggressor significantly less, and groomed more with one another, on conflict compared to control evenings. Our study provides experimental evidence that dwarf mongooses acoustically obtain information about within-group contests (including protagonist identity), retain that information, and use it to inform conflict-management decisions with a temporal delay.

Handstand scent marking: height matters to dwarf mongooses

ABSTRACTHigh temperatures associated with climate change can have adverse effects on wildlife, but behavioural plasticity may buffer such negative effects. Using long‐term data from wild dwarf mongooses (Helogale parvula), we investigated the impact of high temperatures on daily activity patterns, movement and body mass. On hot days (≥ 35°C) compared with matched cooler ones (≤ 33°C), groups emerged from their overnight sleeping burrow and commenced foraging earlier in the morning and arrived at their overnight sleeping burrow later in the evening. However, there was no evidence that the time spent above ground at the burrow, the proportion of time inactive or the distance moved when foraging were altered on hot days. Consequently, the negative effects of high temperatures were not fully mitigated, as both adults and pups gained less body mass on hot days compared with cooler days. This loss was not compensated fully in the day after a hot day, and evening body mass of adults decreased with an increasing number of consecutive hot days. Together, these results suggest that there are potentially escalating consequences of hot weather for wildlife, especially those species that exhibit limited behavioural plasticity, in an ever‐warming world.

Many species produce alarm calls in response to predator threats. Whilst these can be general alert calls, some are urgency-based, indicating perceived threat level, some are predator-specific, indicating the predator type present, and some encode information about both urgency level and predator type. Predator-specific calls given to a narrow range of stimuli and which elicit a specific, adaptive, response from the receiver are termed functionally referential. Differing escape strategies, habitat structural complexity and sociality may favor the evolution of functionally referential calls. A study of one captive group of dwarf 3 mongooses (Helogale parvula) suggested their alarm calls could transmit information about species, distance and elevation of predators. Using recordings of natural predator encounters, predator presentations and audio playbacks, we investigated the alarm-call system in seven wild dwarf mongoose groups. We recorded 11 different alarm-call types given to nine stimulus categories. Of the five commonly emitted alarm-call types, three appeared to be non-specific and two predator-specific, given to aerial and terrestrial predators respectively. The remaining six call types were rarely produced. Furthermore, aerial alarms were given to a narrower range of stimuli than their terrestrial alarm calls, which were given to both visible terrestrial predators and secondary cues of predators. Unlike other mongoose species, dwarf mongoose seem to use the same alarm-call type for both physically present terrestrial predators and secondary cues of their presence. We argue that detailed knowledge of species’ alarm-call systems under natural conditions can shed light on the evolutionary emergence of different types of alarm calls.

and SummaryInvalid care has already been recorded for a group of captive dwarf mongooses and incorporated huddling round the sick animal, grooming it and giving it preferential access to food. The behavioural responses of a wild group towards an injured group member were essentially the same as described above. In addition, the group members restricted their foraging both spatially and temporally until the injured animal could accompany them normally. Invalid care in this species may be related to the importance of the presence of a large number of adults in the group, groups with few adults having less success in raising their young than larger groups and being especially vulnerable to terrestrial predator attack.

Feeding birds must balance food gathering against predation risk. Group foraging is generally considered as a strategy for optimizing this trade-off. Previous modelling studies assumed that group sizes were static and that all group members are informed of an imminent predator attack if one of them detects it. These models implicitly assumed that birds could estimate group size, and adopt a fixed rate of anti-predator vigilance scanning. Recent empirical results suggest that group sizes are generally dynamic rather than static and the group members are often unaware of another's detection of imminent attack. It has also been observed that vigilance rates are not static but change after the arrival or departure of another. Here, we present a model which allows feeding-group size (and individuals' vigilance rates) to vary dynamically, and investigate the implications which this has for the optimum trade-off between foraging and avoiding predation. We find that newly arrived birds should generally be the most vigilant and that vigilance rates should decrease after the arrival of another into the feeding group but increase after a departure. Vigilance rates should increase as the cost of predator attack increases or if the reward rate from foraging decreases. Vigilance should increase if predator attacks are more common but decrease if predators require a longer time undetected to approach the feeding group. In common with many experimental studies, we observe that vigilance rates decrease as the average number of birds feeding together increases. Hence, the main conclusion of previous works (that foraging in groups is an effective strategy for balancing the conflicting pressures of foraging and avoiding predation) is obtained by our model, despite relaxing several previously used assumptions. Finally, we discuss some of the open questions related to group vigilance and how extensions to our modelling framework might be used to address these.

Feeding birds must balance food gathering against predation risk. Group foraging is generally considered as a strategy for optimizing this trade-off. Previous modelling studies assumed that group sizes were static and that all group members are informed of an imminent predator attack if one of them detects it. These models implicitly assumed that birds could estimate group size, and adopt a fixed rate of anti-predator vigilance scanning. Recent empirical results suggest that group sizes are generally dynamic rather than static and the group members are often unaware of another's detection of imminent attack. It has also been observed that vigilance rates are not static but change after the arrival or departure of another. Here, we present a model which allows feeding-group size (and individuals' vigilance rates) to vary dynamically, and investigate the implications which this has for the optimum trade-off between foraging and avoiding predation. We find that newly arrived birds should generally be the most vigilant and that vigilance rates should decrease after the arrival of another into the feeding group but increase after a departure. Vigilance rates should increase as the cost of predator attack increases or if the reward rate from foraging decreases. Vigilance should increase if predator attacks are more common but decrease if predators require a longer time undetected to approach the feeding group. In common with many experimental studies, we observe that vigilance rates decrease as the average number of birds feeding together increases. Hence, the main conclusion of previous works (that foraging in groups is an effective strategy for balancing the conflicting pressures of foraging and avoiding predation) is obtained by our model, despite relaxing several previously used assumptions. Finally, we discuss some of the open questions related to group vigilance and how extensions to our modelling framework might be used to address these.

In social species, individuals maximize the benefits of group living by remaining cohesive and coordinating their actions. Communication is key to collective action, including ensuring that group members move together; individuals often produce signals when attempting to lead a group to a new area. However, the function of these signals, and how responses to them are affected by intrinsic characteristics of the caller and extrinsic factors, has rarely been experimentally tested. We conducted a series of field-based playback experiments with habituated wild dwarf mongooses, Helogale parvula , a cooperatively breeding and territorial species, to investigate follower responses to movement calls. In our first experiment, we found that focal individuals were more likely to respond to playback of ‘movement calls’ than control ‘close calls’, indicating movement calls function as recruitment signals. In a second experiment, we found that focal individuals responded similarly to the movement calls of dominant and subordinate groupmates, suggesting that dominance status (an intrinsic factor) does not influence receiver responses. In a final experiment, we found that individuals responded to the simulated presence of a rival group, but that this outgroup conflict (an extrinsic factor) did not affect responses to movement calls compared to a control situation. This may be because attention is instead focused on the potential presence of an imminent threat. By using playbacks to isolate the acoustic signal from physical movement cues, our results provide experimental evidence of how movement calls help leaders to attract followers and thus adds to our understanding of recruitment signals more generally. • We used playback experiments to study responses to dwarf mongoose movement calls. • Movement calls elicited a movement response in focal subordinate group members. • Receivers responded equally to calls of dominant and subordinate groupmates. • A simulated rival group threat did not affect responses to movement calls.

Calling for help: dwarf mongoose recruitment calls inform receivers about context and elicit disparate responses

Aggression, Reproduction, and Androgens in Wild Dwarf Mongooses: A Test of the Challenge Hypothesis