Fission–fusion dynamics in wild giraffes may be driven by kinship, spatial overlap and individual social preferences

The ontogeny of social networks in wild great tits (Parus major)

Sociality impacts many biological processes and can be tightly linked to an individual's fitness. To maximize the advantages of group living, many social animals prefer to associate with individuals that provide the most benefits, such as kin, familiar individuals, or those of similar phenotypes. Such social strategies are not necessarily stable over time but can vary with changing selection pressures. In particular, young individuals transitioning to independence should continuously adjust their social behavior in light of developmental changes. However, social strategies exhibited during adolescence in animals are understudied, and the factors underlying social network formation during ontogeny remain elusive. Here, we tracked associations of wild great tits (Parus major) during the transition to independence and across their first year of life. Both spatial and social factors predicted dyadic associations. During the transition to independence in spring, fledglings initially preferred to associate with siblings and peers over non-parent adults. We found no evidence for preferred associations among juveniles of similar age or fledge weight during that time but weak evidence for some potential inheritance of the parental social network. By autumn, after juveniles had reached full independence, they exhibited social strategies similar to those of adults by establishing stable social ties based on familiarity that persisted through winter into the next spring. Overall, this research demonstrates dynamic changes in social networks during ontogeny in a species with a fast life history and limited parental care, which likely reflect changes in selective pressures. It further highlights the importance of long-term social bonds based on familiarity in this species.

Variation in local population size predicts social network structure in wild songbirds

The structure of animal societies is a key determinant of many ecological and evolutionary processes. Yet, we know relatively little about the factors and mechanisms that underpin detailed social structure. Among other factors, social structure can be influenced by habitat configuration. By shaping animal movement decisions, heterogeneity in habitat features, such as vegetation and the availability of resources, can influence the spatiotemporal distribution of individuals and subsequently key socioecological properties such as the local population size and density. Differences in local population size and density can impact opportunities for social associations and may thus drive substantial variation in local social structure. Here, we investigated spatiotemporal variation in population size at 65 distinct locations in a small songbird, the great tit (Parus major) and its effect on social network structure. We first explored the within-location consistency of population size from weekly samples and whether the observed variation in local population size was predicted by the underlying habitat configuration. Next, we created social networks from the birds' foraging associations at each location for each week and examined if local population size affected social structure. We show that population size is highly repeatable within locations across weeks and years and that some of the observed variation in local population size was predicted by the underlying habitat, with locations closer to the forest edge having on average larger population sizes. Furthermore, we show that local population size affected social structure inferred by four global network metrics. Using simple simulations, we then reveal that much of the observed social structure is shaped by social processes. Across different population sizes, the birds' social structure was largely explained by their preference to forage in flocks. In addition, over and above effects of social foraging, social preferences between birds (i.e. social relationships) shaped certain network features such as the extent of realized social connections. Our findings thus suggest that individual social decisions substantially contribute to shaping certain social network features over and above effects of population size alone.

Factors affecting captive female giraffe stress response: Male presence, small enclosure, and low temperature

To improve animal welfare based on suitable social housing conditions, it is important to understand the factors that trigger high-stress responses. Wild giraffes live in a fission-fusion society and males and females are rarely in the same herd for a long period. The captive condition of belonging to a herd with the same individuals for months or years is uncommon in nature. To understand the effect of male presence on female stress levels, fecal glucocorticoid metabolite (fGCM) levels and social interactions in two captive female giraffes were investigated. Additionally, the effect of enclosure size and temperature on fGCM level and social interactions were examined. The results showed no significant difference in the fGCM levels of females based on male presence. The frequency of agonistic behavior by the dominant female toward the subordinate female was significantly increased when a male was present. The subordinate female was significantly less likely to approach the dominant female and showed decreased affiliative and agonistic interactions toward the dominant female when a male was present. The frequencies of agonistic interactions between females were higher in the small enclosure regardless of male presence. Low temperature triggered higher fGCM levels and increased agonistic interaction in an aged female. The findings of this study suggest that these multiple factors should be considered individually to promote the welfare of captive giraffes.

Parental breeding decisions and genetic quality predict social structure of independent offspring

Across the animal kingdom, newly independent juveniles form social associations that influence later fitness, mate choice and gene flow, but little is known about the ontogeny of social environments, particularly in wild populations. Here we test whether associations among young animals form randomly or are influenced by environmental or genetic conditions established by parents. Parents' decisions determine natal birth sites, which could affect who independent young initially encounter; secondly, mate choice determines genetic condition (e.g. inbreeding) of young and the parental care they receive, which can affect sociability. However, genetic and environmental factors are confounded unless related offspring experience different natal environments. Therefore, we used a long-term genetic pedigree, breeding records and social network data from three cohorts of a songbird with high extra-pair paternity (hihi, Notiomystis cincta) to disentangle (1) how nest location and relatedness contribute to association structure once juveniles disperse away from birth sites, and (2) if juvenile and/or parental inbreeding predicts individual sociability. We detected positive spatial autocorrelation: hihi that fledged closer by were more likely to associate even after dispersing, irrespective of genetic relatedness. Juvenile inbreeding did not predict sociability, but those raised by more inbred fathers formed more, stronger, associations, which did not depend on whether that male was the genetic parent or not. These results suggest that the natal environment created by parents, rather than focal genetic condition, establishes the foundation for social associations. Overall, we highlight how social inheritance may play an important role in population dynamics and evolutionary potential in wild animals.

Identifying the social context of single- and mixed-species group formation in large African herbivores

Despite continued interest in mixed-species groups, we still lack a unified understanding of how ecological and social processes work across scales to influence group formation. Recent work has revealed ecological correlates of mixed-species group formation, but the mechanisms by which concomitant social dynamics produce these patterns, if at all, is unknown. Here, we use camera trap data for six mammalian grazer species in Serengeti National Park. Building on previous work, we found that ecological variables, and especially forage quality, influenced the chances of species overlap over small spatio-temporal scales (i.e. on the scales of several metres and hours). Migratory species (gazelle, wildebeest and zebra) were more likely to have heterospecific partners available in sites with higher forage quality, but the opposite was true for resident species (buffalo, hartebeest and topi). These findings illuminate the circumstances under which mixed-species group formation is even possible. Next, we found that greater heterospecific availability was associated with an increased probability of mixed-species group formation in gazelle, hartebeest, wildebeest and zebra, but ecological variables did not further shape these patterns. Overall, our results are consistent with a model whereby ecological and social drivers of group formation are species-specific and operate on different spatio-temporal scales. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Social network inheritance and differentiation in wild baboons

Immatures' social development may be fundamental to understand important biological processes, such as social information transmission through groups, that can vary with age and sex. Our aim was to determine how social networks change with age and differ between sexes in wild immature baboons, group-living primates that readily learn socially. Our results show that immature baboons inherited their mothers' networks and differentiated from them as they aged, increasing their association with partners of similar age and the same sex. Males were less bonded to their matriline and became more peripheral with age compared to females. Our results may pave the way to further studies testing a new hypothetical framework: in female-philopatric societies, social information transmission may be constrained at the matrilineal level by age- and sex-driven social clustering.

Social network analysis reveals context-dependent kin relationships in wild sulphur-crested cockatoos Cacatua galerita

A preference to associate with kin facilitates inclusive fitness benefits, and increased tolerance or cooperation between kin may be an added benefit of group living. Many species exhibit preferred associations with kin; however, it is often hard to disentangle active preferences from passive overlap, for example caused by limited dispersal or inheritance of social position. Many parrots exhibit social systems consisting of pair-bonded individuals foraging in variably sized fission-fusion flocks within larger communal roosts of hundreds of individuals. Previous work has shown that, despite these fission-fusion dynamics, individuals can exhibit long-term preferred foraging associations outside their pair bonds. Yet the underlying drivers of these social preferences remain largely unknown. In this study, we use a network approach to examine the influence of kinship on social associations and interactions in wild, communally roosting sulphur-crested cockatoos, Cacatua galerita. We recorded roost co-membership, social associations and interactions in 561 individually marked birds across three neighbouring roosts. We then collected genetic samples from 205 cockatoos, and conducted a relationship analysis to construct a kinship network. Finally, we tested correlations between kinship and four social networks: association, affiliative, low-intensity aggression and high-intensity aggression. Our result showed that while roosting groups were clearly defined, they showed little genetic differentiation or kin structuring. Between roost movement was high, with juveniles, especially females, repeatedly moving between roosts. Both within roosting communities, and when visiting different roosts, individuals preferentially associated with kin. Supporting this, individuals were also more likely to allopreen kin. However, contrary to expectation, individuals preferred to direct aggression towards kin, with this effect only observed when individuals shared roost membership. By measuring social networks within and between large roosting groups, we could remove potential effects of passive spatial overlap on kin structuring. Our study reveals that sulphur-crested cockatoos actively prefer to associate with kin, both within and between roosting groups. By examining this across different interaction types, we further demonstrate that sulphur-crested cockatoos exhibit behavioural and context-dependent interaction rules towards kin. Our results help reveal the drivers of social association in this species, while adding to the evidence for social complexity in parrots.

Community structure of the solitary giant pandas is maintained by indirect social connections

BACKGROUND

Indirect interactions between individual solitary mammals, such as the giant panda, are often overlooked because of their nature, yet are important for maintaining the necessary sociality in solitary species.

METHODS AND RESULTS

Here, we determined the genetic identity of all giant panda individuals in a local population and matched these identities with their associations to determine social network of this solitary animal. Total thirty-five giant panda individuals were found in our field survey, and we constructed genetic and social networks for thirty-three individuals who successfully obtained genetic, age and sex information. The results showed that sex had great impact on both social network and genetic network, and age may have the potential to influence the social network of the giant pandas. Adult males, mostly in the central of the social network, which appeared significantly larger network connections than adult females. Due to the female-biased dispersal pattern of wild giant pandas, male-male pairs showed higher relatedness than female-female ones and multi-generational patrilinear assemblages are expected in the study area.

CONCLUSIONS

The relatedness of individuals has an influence on the formation of community social structure of giant pandas, and indirect interactions among solitary giant pandas potentially function to reduce competition for resources and inbreeding.

Adaptive Party Choice of Low-Ranking Males in Fission–Fusion Dynamics of Chimpanzees in Kalinzu Forest Reserve, Uganda

Simple Summary

Various mammalian species, including primates, exhibit fission–fusion dynamics (FFD), which alters the size of subgroups through splitting and merging. Among primates, chimpanzees (Pan troglodytes) have been particularly studied as a species that exhibits a high degree of FFD, wherein members of the same group form temporary subgroups (parties) that vary in both size and composition. Most studies on the FFD of chimpanzees have focused on its role in reducing food competition among individuals. In this study, we focused on the association patterns of each adult male chimpanzee and examined whether the social factors, including male dominance rank and aggression from other males, affect their party attendance behavior. Low-ranking males spent more time alone than other males when mating opportunities were absent. When females were available for mating, males of all ranks showed a similar party attendance behavior. The aggression increased with the number of males in the party, and low-ranking males received more aggression than higher-ranking males. These results suggest that low-ranking males frequently traveled alone to avoid aggression from other males unless they attended parties to seek mating opportunities. The FFD seemed to offer alternative tactics for low-ranking males to balance the costs and benefits of attending parties.

Abstract

Several studies have examined factors that regulate fission–fusion dynamics (FFD) in chimpanzee communities, such as receptive females, predation risks, and food availability. However, the effects of these factors vary between populations. In this study, we conducted focal animal observations of adult males in the M group in Kalinzu to examine the influence of male dominance rank, aggression from other males, the presence of females exhibiting maximum sexual swelling (MS), and fruit abundance on male tendencies of party attendance. We found that low-ranking males spent more time alone than other males when females with MS were absent. In contrast, when females with MS were present, males of all ranks showed a similar tendency of party attendance. We also found that the aggressive interactions increased with the number of males irrespective of the presence or absence of females with MS, and low-ranking males attracted aggression more frequently than higher-ranking males. These results suggest that low-ranking males frequently ranged alone to avoid aggression from other males unless they attended parties to seek mating opportunities. We conclude that low-ranking males have alternative tactics to balance the costs and benefits incurred or gained when attending parties.

Adolescence and the development of social behaviour in giraffes

All mammals experience different life stages as they develop, each of which is characterised by particular physical and behavioural changes. Despite the emergence of sophisticated behaviour analysis techniques, the ways in which social behaviour varies by life stage, and how this is influenced by an individual’s sex, is relatively understudied in most social mammals other than primates and elephants. Understanding the social requirements of mammals should be a central and critical component to their conservation, captive management and welfare. Here, we apply social network analysis techniques to understand how social behaviour differs with life stage in the giraffe, a gregarious fission–fusion mammal. We studied two wild populations of giraffes in Kenya and found that adolescents have significantly stronger associations with adolescents of their own sex first and foremost, then adults of their own sex. Other associations were significantly lower than would be expected, or non-significant. Our results suggest that adolescence in both male and female giraffes shares similar features to adolescence in other social mammal species. We discuss how the application of such knowledge might improve the management and welfare of captive giraffes.

Contact call acoustic structure is associated with inter-individual distances during antiphonal vocal exchanges in wild red-tailed monkeys (Cercopithecus ascanius schmidti)

Contact calls allow animals to maintain group cohesion when visibility is restricted. To maximise call detection, animals should produce calls that are audible to closest neighbours or respond to individuals that produce preceding calls (i.e., antiphony). Antiphonal exchanges are more likely to occur between older conspecifics that respond more reliably or close neighbours that are more likely to detect calls when groups are travelling. Because animals should produce calls that are optimised for propagation, call structure should be associated with the distance between individuals calling in antiphonal exchanges. I investigated whether acoustic structures of red-tailed monkey (Cercopithecus ascanius) contact calls (phrased grunts) reflected increased sound propagation as nearest neighbour distances increased, depending on three factors: (1) the occurrence of a preceding grunt, (2) neighbour age-sex class, and (3) group travel speed. I recorded grunts from five habituated monkey groups at Kibale National Park, Uganda. Per grunt, I measured five parameters associated with sound propagation. Grunt mean entropy and frequency related negatively to neighbour distance when the neighbour produced a preceding grunt or when there was no preceding grunt, but not when a more distant individual grunted prior. Neighbour age-sex class and group travel speed did not influence whether grunt structure was associated with neighbour distance, but monkeys produced grunts with higher mean entropy and frequency as groups travelled faster. Variation in grunt mean entropy and frequency was associated with propagation to either nearest neighbours or more distant individuals that produced preceding calls, providing quantitative evidence for antiphonal calling. By calling antiphonally, animals in cohesive groups can spread out to avoid intra-group competition while maintaining contact with other group members. Higher grunt entropy and frequency as groups travel faster may counteract more variable sound attenuation as animals move through acoustically complex (e.g., densely vegetated) environments.

How do genetic relatedness and spatial proximity shape African swine fever infections in wild boar?

The importance of social and spatial structuring of wildlife populations for disease spread, though widely recognized, is still poorly understood in many host-pathogen systems. In particular, system specific kin relationships among hosts can create contact heterogeneities and differential disease transmission rates. Here, we investigate how distance-dependent infection risk is influenced by genetic relatedness in a novel host-pathogen system: wild boar (Sus scrofa) and African swine fever (ASF). We hypothesized that infection risk would correlate positively with proximity and relatedness to ASF-infected individuals but expected those relationships to weaken with distance between individuals due to decay in contact rates and genetic similarity. We genotyped 323 wild boar samples (243 ASF-negative and 80 ASF-positive) collected in north-eastern Poland in 2014-2016 and modeled the effects of geographic distance, genetic relatedness, and ASF virus transmission mode (direct or carcass-based) on the probability of ASF infection. Infection risk was positively associated with spatial proximity and genetic relatedness to infected individuals with generally stronger effect of distance. In the high-contact zone (0-2 km), infection risk was shaped by the presence of infected individuals rather than by relatedness to them. In the medium-contact zone (2-5 km), infection risk decreased but was still associated with relatedness and paired infections were more frequent among relatives. At farther distances, infection risk further declined with relatedness and proximity to positive individuals, and was 60% lower among unrelated individuals in the no-contact zone (33% in10-20 km) compared with among relatives in the high-contact zone (93% in 0-2 km). Transmission mode influenced the relationship between proximity or relatedness and infection risk. Our results indicate that the presence of nearby infected individuals is most important for shaping ASF infection rates through carcass-based transmission, while relatedness plays an important role in shaping transmission rates between live animals. This article is protected by copyright. All rights reserved.

Research Highlight: Social dispersal in giraffes

Dispersal is a critical process that shapes the structure of wild animal populations. In species that form multi‐level societies, natal dispersal might be social (associating with a different social community while remaining near the natal area), spatial (moving away from the natal area while continuing to associate with the same community) or both social and spatial (associating with a different community and moving away from the natal area).

For such species, classical spatial measures of dispersal, such as distance moved, might not capture social dispersal.

We examined dispersal outcomes for 67 male and 70 female giraffe calves over 7 years in a large, unfenced, ecologically heterogeneous landscape. We tested predictions about the influence of sex, food availability, low‐ and high‐impact human settlements, and local giraffe population density on social or spatial dispersal, dispersal distance, and age of dispersal.

We found that dispersal is sex‐specific, with females being predominately philopatric. When dispersing, both sexes did so at a mean of 4 years of age. Most (69% of total) young males dispersed, with 84% of male dispersers associating with a different adult female social community than that of their mother, but one in four of these dispersers remained spatially near to their natal area. For adolescent males that dispersed socially but not spatially, overlapping female social communities may represent a potential pool of unrelated mating partners without the risks of travelling to unfamiliar areas. Just 26% of young females dispersed and half of these continued to associate with the adult female social community into which they were born, confirming the importance of maintaining ties among females from calf to adulthood. Furthermore, individuals born farther from high‐impact human settlements were more likely to spatially or socially‐and‐spatially disperse, move greater distances from their natal areas, and disperse at a younger age.

Our study highlights the potential importance of social structure in dispersal decisions, and of tracking social structure when studying dispersal in multi‐level societies, as effective dispersal can be attained without large‐scale spatial displacements.

Comparing single- and mixed-species groups in fruit flies: differences in group dynamics, but not group formation

Mixed-species groups describe active associations among individuals of 2 or more species at the same trophic level. Mixed-species groups are important to key ecological and evolutionary processes such as competition and predation, and research that ignores the presence of other species risks ignoring a key aspect of the environment in which social behavior is expressed and selected. Despite the defining emphasis of active formation for mixed-species groups, surprisingly little is known about the mechanisms by which mixed-species groups form. Furthermore, insects have been almost completely ignored in the study of mixed-species groups, despite their taxonomic importance and relative prominence in the study of single-species groups. Here, we measured group formation processes in Drosophila melanogaster and its sister species, Drosophila simulans. Each species was studied alone, and together, and one population of D. melanogaster was also studied both alone and with another, phenotypically distinct D. melanogaster population, in a nested-factorial design. This approach differs from typical methods of studying mixed-species groups in that we could quantitatively compare group formation between single-population, mixed-population, and mixed-species treatments. Surprisingly, we found no differences between treatments in the number, size, or composition of groups that formed, suggesting that single- and mixed-species groups form through similar mechanisms of active attraction. However, we found that mixed-species groups showed elevated interspecies male-male interactions, relative to interpopulation or intergenotype interactions in single-species groups. Our findings expand the conceptual and taxonomic study of mixed-species groups while raising new questions about the mechanisms of group formation broadly.

Consensus driven by a minority in heterogenous groups of the cockroach Periplaneta american a

Many social species are able to perform collective decisions and reach consensus. However, how the interplay between social interactions, the diversity of preferences among the group members and the group size affects these dynamics is usually overlooked. The collective choice between odourous and odorless shelters is tested for the following three groups of social cockroaches (Periplaneta americana) which are solitary foragers: naive (individuals preferring the odorous shelter), conditioned (individuals without preference), and mixed (combining, unevenly, conditioned, and naive individuals). The robustness of the consensus is not affected by the naive individuals' proportion, but the rate and the frequency of selection of the odorous shelter are correlated to this proportion. In mixed groups, the naive individuals act as influencers. Simulations based on the mechanisms highlighted in our experiments predict that the consensus emerges only for intermediate group sizes. The universality of these mechanisms suggests that such phenomena are widely present in social systems.

Social networks research in ex situ populations: Patterns, trends, and future directions for conservation-focused behavioral research

Social networks research using non-human animals has grown over the past decade, utilizing a wide range of species to answer an array of pure and applied questions. Network approaches have relevance to conservation, evaluating social influences on fecundity, health, fitness and longevity. While the application of network approaches to in situ populations with conservation concern appears in published literature, the degree to which ex situ and zoo-housed populations are the focus of "social networks for conservation research" is limited. Captive environments provide scientists with an ability to understand the social behavior of species that may be hard to observe consistently in the wild. This paper evaluates the scope of network research involving ex situ populations, analyzing output from 2010 to 2019 to determine trends in questions and subjects using ex situ populations. We show that only 8.2% of ex situ social network analysis (SNA) implications are of conservation-focus, apparent in papers relating to birds, carnivores, bats, primates, reptiles, and ungulates. Husbandry and welfare questions predominate in ex situ network research, but over half of these papers have nonpractical application (basic science). The chance of a citation for a basic science paper was 95.4% more than for a conservation-based paper. For taxonomic groups, primate-focused papers had the most citations. The focus of ex situ conservation-based networks research may be driven by the needs of conservation programs (e.g., population recovery outcomes) or by a need to evaluate the efficacy of ex situ conservation goals. We evaluate our findings considering the IUCN's One Plan Approach to conservation to show how in situ and ex situ network research is applicable to global conservation efforts. We have identified that there is a lack of application and evaluation of SNA to wildlife conservation. We highlight future areas of research in zoos and hope to stimulate discussion and collaboration between relevant parties.

Comparative cognition in three understudied ungulate species: European bison, forest buffalos and giraffes

Background

Comparative cognition has historically focused on a few taxa such as primates, birds or rodents. However, a broader perspective is essential to understand how different selective pressures affect cognition in different taxa, as more recently shown in several studies. Here we present the same battery of cognitive tasks to two understudied ungulate species with different socio-ecological characteristics, European bison (Bison bonasus) and forest buffalos (Syncerus caffer nanus), and we compare their performance to previous findings in giraffes (Giraffa camelopardalis). We presented subjects with an Object permanence task, Memory tasks with 30 and 60 s delays, two inference tasks based on acoustic cues (i.e. Acoustic inference tasks) and a control task to check for the use of olfactory cues (i.e. Olfactory task).

Results

Overall, giraffes outperformed bison and buffalos, and bison outperformed buffalos (that performed at chance level). All species performed better in the Object permanence task than in the Memory tasks and one of the Acoustic inference tasks (which they likely solved by relying on stimulus enhancement). Giraffes performed better than buffalos in the Shake full Acoustic inference task, but worse than bison and buffalos in the Shake empty Acoustic inference task.

Conclusions

In sum, our results are in line with the hypothesis that specific socio-ecological characteristics played a crucial role in the evolution of cognition, and that higher fission-fusion levels and larger dietary breadth are linked to higher cognitive skills. This study shows that ungulates may be an excellent model to test evolutionary hypotheses on the emergence of cognition.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12983-021-00417-w.

Lifetime stability of social traits in bottlenose dolphins

Behavioral phenotypic traits or “animal personalities” drive critical evolutionary processes such as fitness, disease and information spread. Yet the stability of behavioral traits, essential by definition, has rarely been measured over developmentally significant periods of time, limiting our understanding of how behavioral stability interacts with ontogeny. Based on 32 years of social behavioral data for 179 wild bottlenose dolphins, we show that social traits (associate number, time alone and in large groups) are stable from infancy to late adulthood. Multivariate analysis revealed strong relationships between these stable metrics within individuals, suggesting a complex behavioral syndrome comparable to human extraversion. Maternal effects (particularly vertical social learning) and sex-specific reproductive strategies are likely proximate and ultimate drivers for these patterns. We provide rare empirical evidence to demonstrate the persistence of social behavioral traits over decades in a non-human animal.

Taylor Evans et al. present analyses based on 32 years of observations of dolphin social behaviour in Shark Bay, Western Australia. Their findings indicate that individual social traits, such as preference for time spent alone vs in groups, remain stable throughout an individual’s lifetime, despite physiological and social changes through adulthood.

Further behavioural parameters support reciprocity and milk theft as explanations for giraffe allonursing

Suckling of a non-filial calf, or allosuckling, is an extreme case of allomaternal care in mammals. There have been many hypotheses postulated in an attempt to explain this behaviour; however, the supporting evidence differs, together with the conclusions drawn from the investigated variables. Previously, suckling bout rejection was analysed, and the milk theft and reciprocity hypotheses were both determined as the most appropriate explanation of allosuckling in giraffe. In this study, seven hypotheses were tested using different behavioural parameters, namely suckling bout frequency, suckling bout duration, and time spent suckling. It is well-documented that these parameters are associated with various aspects in ungulate biology; for example, suckling rejection typically reflects milk intake and parent-offspring conflict, whereas the suckling bout duration and frequency is associated with social behaviours (affiliation, bonding, social stress). In total, 22 nursing females and 47 suckling calves were observed, in four Czech zoos during a five-year period. The correlation of the observed parameters between the reciprocal female-calf dyads was found to be in line with the reciprocity hypothesis. In addition, non-filial calves tried to steal the milk from non-maternal females, supporting the milk theft hypothesis. Thus, the results support both the reciprocity and milk-theft hypotheses as the most plausible explanation of allosuckling in giraffe, and illustrates the importance of using suckling bout duration and frequency, and the time spent suckling, as behavioural parameters that may aid in explaining the extremity of maternal investment, such as allosuckling.

Biological and environmental factors as sources of variation in nocturnal behavior of giraffe

Upon a drastic decline of the giraffe population in the wild, conservation efforts and therefore the role of zoos have become more important than ever. With their unique opportunities, zoos provide excellent conditions to study animal behavior, expanding the knowledge about the giraffe's behavior repertoire and their ability to adapt. This study therefore examined the nocturnal behavior of 63 giraffe living in 13 different EAZA zoos across Germany and the Netherlands. Giraffe were observed and videos recorded via infrared sensitive cameras during the winter seasons 2015-2018. The observation period spanned nightly from 17:00 to 7:00. Thus, 198 nights, with a total of 2772 h were recorded and analyzed. Linear mixed models were then used to assess potential biological and environmental factors influencing behavior during the dark phase. Results show that individual variables such as age, subspecies and motherhood determined nocturnal activity and sleep behavior most. Among the variables studied, husbandry conditions and environmental factors complying with EAZA standards had no influence on the giraffe's nocturnal behavior. By combining nocturnal activity analyses and an assessment of potential influencing factors, our findings present a holistic approach to a better understanding of captive giraffe behavior and allow for management implications.

Kinship does not predict the structure of a shark social network

Genetic relatedness in animal societies is often a factor that drives the structure of social groups. In the marine world, most studies which have investigated this question have focused on marine mammals such as whales and dolphins. For sharks, recent studies have demonstrated preferential associations among individuals from which social communities emerge. Assortment patterns have been found according to phenotypic or behavioral traits, but the role of genetic relatedness in shaping the social structure of adult shark populations has, to the best of our knowledge, never been investigated. Here, we used a social network analysis crossed with DNA microsatellite genotyping to investigate the role of the genetic relatedness in the social structure of a blacktip reef shark (Carcharhinus melanopterus) population. Based on the data from 156 groups of sharks, we used generalized affiliation indices to isolate social preferences from nonsocial associations, controlling for the contribution of sex, size, gregariousness, spatial, and temporal overlap on social associations, to test for the influence of genetic relatedness on social structure. A double-permutation procedure was employed to confirm our results and account for issues arising from potentially elevated type I and type II error rates. Kinship was not a predictor of associations and affiliations among sharks at the dyad or community levels as individuals tended to associate independently of the genetic relatedness among them. The lack of parental care in this species may contribute to the breakdown of family links in the population early in life, thereby preventing the formation of kin-based social networks.

Sociability increases survival of adult female giraffes

Studies increasingly show that social connectedness plays a key role in determining survival, in addition to natural and anthropogenic environmental factors. Few studies, however, integrated social, non-social and demographic data to elucidate what components of an animal's socio-ecological environment are most important to their survival. Female giraffes (Giraffa camelopardalis) form structured societies with highly dynamic group membership but stable long-term associations. We examined the relative contributions of sociability (relationship strength, gregariousness and betweenness), together with those of the natural (food sources and vegetation types) and anthropogenic environment (distance from human settlements), to adult female giraffe survival. We tested predictions about the influence of sociability and natural and human factors at two social levels: the individual and the social community. Survival was primarily driven by individual- rather than community-level social factors. Gregariousness (the number of other females each individual was observed with on average) was most important in explaining variation in female adult survival, more than other social traits and any natural or anthropogenic environmental factors. For adult female giraffes, grouping with more other females, even as group membership frequently changes, is correlated with better survival, and this sociability appears to be more important than several attributes of their non-social environment.

Analysis of astrovirus transmission pathways in a free-ranging fission-fusion colony of Natterer’s bats (Myotis nattereri)

Abstract

Bats are a diverse and widespread order of mammals. They fulfill critical ecosystem roles but may also act as reservoirs and spreaders for zoonotic agents. Consequently, many recent studies have focused on the potential of bats to spread diseases to other animals and to humans. However, virus transmission networks within bat colonies remain largely unexplored. We studied the detection rate and transmission pathway of astroviruses in a free-ranging Natterer’s bat colony (Myotis nattereri) that exhibits a high fission-fusion dynamic. Based on automatic roost monitoring data of radio-frequency identification tagged bats, we assessed the impact of the strength of an individual’s roosting associations with all other colony members (weighted degree), and the number of roost sites (bat boxes) an individual used—both being proxies for individual exposure risk—on the detected presence of astrovirus-related nucleic acid in individual swab samples. Moreover, we tested to which degree astrovirus sequence types were shared between individuals that frequently roosted together, as proxy for direct transmission risk, and between bats sharing the same roost sites in close temporal succession, as proxy for indirect transmission risk. Neither roosting associations nor the number of different roost sites had an effect on detected virus presence in individual bats. Transmission network data suggest that astroviruses are transmitted both via direct and indirect contact, implying that roost sites pose a risk of astrovirus infection for several days after the bats leave them. Our study offers novel insights in the presence and transmission of viruses within social networks of bat colonies.

Significance statement

Bats provide many ecosystem services but have moved into the focus of virological research as potential carriers of zoonotic disease agents. However, the sparse information available about virus transmission within bat colonies is solely based on simulated transmission data. In this field study, we examined the daily roosting behavior in a wild bat colony in relation to the presence of viruses in individual colony members. Our findings suggest that astroviruses are transmitted by direct contact and via contaminated roost sites. Bats typically defecate in their roost sites, and astroviruses can remain infectious in feces for several days. The here observed virus diversity and roosting behavior suggest that bats can contract astroviruses even if they use contaminated roost sites days after infected individuals have left. This study provides first-time insights in the transmission of astroviruses within bat colonies in the wild.

The impact of Masai giraffe nursery groups on the development of social associations among females and young individuals

Fission-fusion social systems involve the splitting and merging of subgroups with frequent changes in membership occurring as a result of a number of ecological and social factors, such as demographic processes including birth, movement, or death. Giraffe reside in fission-fusion social systems, and we studied how reproductive status influence associations among females, as well as how associations differ between calves and juveniles. Data were collected in Katavi National Park, Tanzania, during five study periods. We used social network analysis to identify whether reproductive status and developmental stages predict differences in giraffe social association. We found that females with offspring maintain stronger associations than females without offspring. We also revealed that calves and juveniles had similar network association patterns. Our results suggest that the presence of dependent offspring influences the social associations of females and individuals less than 1.5 years of age are still maintaining strong social associations with nursery group members. We conclude that nursery groups among giraffe are co-operative rearing units that probably reduce the costs of rearing to mothers, and may provide a group structure for animals to begin to develop skills useful for their future life in a fission-fusion social system.

Mechanistic home range analysis reveals drivers of space use patterns for a non-territorial passerine

Home ranging is a near-ubiquitous phenomenon in the animal kingdom. Understanding the behavioural mechanisms that give rise to observed home range patterns is thus an important general question, and mechanistic home range analysis (MHRA) provides the tools to address it. However, such analysis has hitherto been principally restricted to scent-marking territorial animals, so its potential breadth of application has not been tested. Here, we apply MHRA to a population of long-tailed tits Aegithalos caudatus, a non-territorial passerine, in the non-breeding season where there is no clear 'central place' near which birds need to remain. The aim is to uncover the principal movement mechanisms underlying observed home range formation. Our foundational models consist of memory-mediated conspecific avoidance between flocks, combined with attraction to woodland. These are then modified to incorporate the effects of flock size and relatedness (i.e. kinship), to uncover the effect of these on the mechanisms of home range formation. We found that a simple model of spatial avoidance, together with attraction to the central parts of woodland areas, accurately captures long-tailed tit home range patterns. Refining these models further, we show that the magnitude of spatial avoidance by a flock is negatively correlated to both the relative size of the flock (compared to its neighbour) and the relatedness of the flock with its neighbour. Our study applies MHRA beyond the confines of scent-marking, territorial animals, so paves the way for much broader taxonomic application. These could potentially help uncover general properties underlying the emergence of animal space use patterns. This is also the first study to apply MHRA to questions of relatedness and flock size, thus broadening the potential possible applications of this suite of analytic techniques.

Variability in the estimation of ungulate group sizes complicates ecological inference

Foundational work has examined adaptive social behavior in animals in relation to the costs and benefits of group living. Within this context, a "group" of animals represents an organizational unit that is integral to the study of animal ecology and evolution.Definitions of animal group sizes are often subjective with considerable variability within and across species. However, investigations of both the extent and implications of such variability in the estimation of animal group sizes are currently lacking.Selecting ungulates as a case study, we conducted a literature review to assess prevailing practices used to determine group sizes among terrestrial Cetartiodactyla and Perissodactyla. Via this process, we examined group size definitions for 61 species across 171 peer-reviewed studies published between 1962 and 2018.These studies quantified group sizes via estimation of ungulate aggregations in space and time. Spatial estimates included a nearest neighbor distance ranging from 1.4 m to 1,000 m, and this variation was partially explained by a weak positive correlation (|r| = .4, p < .003) with the body size of the ungulate research subjects. The temporal extent over which group size was estimated was even broader, ranging from three minutes to 24 hr.The considerable variability in ungulate group size estimation that we observed complicates efforts to not only compare and replicate studies but also to evaluate underlying theories of group living. We recommend that researchers: (a) clearly describe the spatiotemporal extents over which they define ungulate group sizes, (b) highlight foundational empirical and ecological rationale for these extents, and (c) seek to align such extents among individual species so as to facilitate cross-system comparisons of ungulate group size dynamics. We believe an integrative approach to ungulate group size estimation would readily facilitate replication, comparability, and evaluation of competing hypotheses examining the tradeoffs of animal sociality.

Proximity to humans affects local social structure in a giraffe metapopulation

Experimental laboratory evidence suggests that animals with disrupted social systems express weakened relationship strengths and have more exclusive social associations, and that these changes have functional consequences. A key question is whether anthropogenic pressures have a similar impact on the social structure of wild animal communities. We addressed this question by constructing a social network from 6 years of systematically collected photographic capture-recapture data spanning 1,139 individual adult female Masai giraffes inhabiting a large, unfenced, heterogeneous landscape in northern Tanzania. We then used the social network to identify distinct social communities, and tested whether social or anthropogenic and other environmental factors predicted differences in social structure among these communities. We reveal that giraffes have a multilevel social structure. Local preferences in associations among individuals scale up to a number of distinct, but spatially overlapping, social communities, that can be viewed as a large interconnected metapopulation. We then find that communities that are closer to traditional compounds of Indigenous Masai people express weaker relationship strengths and the giraffes in these communities are more exclusive in their associations. The patterns we characterize in response to proximity to humans reflect the predictions of disrupted social systems. Near bomas, fuelwood cutting can reduce food resources, and groups of giraffes are more likely to encounter livestock and humans on foot, thus disrupting the social associations among group members. Our results suggest that human presence could potentially be playing an important role in determining the conservation future of this megaherbivore.

Understanding Temporal Social Dynamics in Zoo Animal Management: An Elephant Case Study

Zoo animal management procedures which lead to changes to social groups can cause disruption in social hierarchies and the temporary breakdown of social relationships. Animals have different roles in social networks. Understanding individual positions in social networks is important for effective management and ensuring positive welfare for all animals. Using elephants as a case study, the aim of this research was to investigate temporal social dynamics in zoo animals. Behavioural data were collected between January 2016 and February 2017 from 10 African and 22 Asian elephants housed at seven zoos and safari parks in the UK and Ireland. Social interactions were defined as positive physical, positive non-physical, negative physical or negative non-physical. Social network analysis explored social relationships including the fluidity of networks over time and dyadic reciprocity. Social interaction networks were found to be fluid but did not follow a seasonal pattern. Positive interaction networks tended to include the entire social group whereas negative interactions were restricted to specific individuals. Unbalanced ties were observed within dyads, suggesting potential inequalities in relationships. This could impact on individual experiences and welfare. This research highlights subtle temporal dynamics in zoo elephants with the potential for species-level differences. Similar temporal dynamics may also be present in other socially housed zoo species. This research thus provides evidence for the importance of understanding the social networks of zoo animals over longer periods of time. Understanding social networks enables pro-active and evidence-based management approaches. Further research should seek to identify the minimum sampling efforts for social networks in a range of species, to enable the implementation of regular monitoring of social networks and thus improve the welfare of social species under human care.

Predictability and variability of association patterns in sooty mangabeys

Abstract

In many group-living animal species, interactions take place in changing social environments, increasing the information processing necessary to optimize social decision-making. Communities with different levels of spatial and temporal cohesion should differ in the predictability of association patterns. While the focus in this context has been on primate species with high fission-fusion dynamics, little is known about the variability of association patterns in species with large groups and high temporal cohesion, where group size and the environment create unstable subgroups. Here, we use sooty mangabeys as a model species to test predictability on two levels: on the subgroup level and on the dyadic level. Our results show that the entirety of group members surrounding an individual is close to random in sooty mangabeys; making it unlikely that individuals can predict the exact composition of bystanders for any interaction. At the same time, we found predictable dyadic associations based on assortative mixing by age, kinship, reproductive state in females, and dominance rank; potentially providing individuals with the ability to partially predict which dyads can be usually found together. These results indicate that animals living in large cohesive groups face different challenges from those with high fission-fusion dynamics, by having to adapt to fast-changing social contexts, while unable to predict who will be close-by in future interactions. At the same time, entropy measures on their own are unable to capture the predictability of association patterns in these groups.

Significance statement

While the challenges created by high fission-fusion dynamics in animal social systems and their impact on the evolution of cognitive abilities are relatively well understood, many species live in large groups without clear spatio-temporal subgrouping. Nonetheless, they show remarkable abilities in considering their immediate social environment when making social decisions. Measures of entropy of association patterns have recently been proposed to measure social complexity across species. Here, we evaluate suggested entropy measures in sooty mangabeys. The high entropy of their association patterns would indicate that subgroup composition is largely random, not allowing individuals to prepare for future social environments. However, the existence of strong assortativity on the dyadic level indicates that individuals can still partially predict who will be around whom, even if the overall audience composition might be unclear. Entropy alone, therefore, captures social complexity incompletely, especially in species facing fast-changing social environments.

Giraffe translocation population viability analysis

Most populations of giraffes have declined in recent decades, leading to the recent IUCN decision to upgrade the species to Vulnerable status, and some subspecies to Endangered. Translocations have been used as a conservation tool to re-introduce giraffes to previously occupied areas or establish new populations, but guidelines for founding populations are lacking. To provide general guidelines for translocation projects regarding feasibility, we simulated various scenarios of translocated giraffe populations to identify viable age and sex distributions of founding populations using population viability analysis (PVA) implemented in Vortex software. We explored the parameter space for demography and the genetic load, examining how variation in founding numbers and sex ratios affected 100 yr probability of population extinction and genetic diversity. We found that even very small numbers of founders (N ≤ 10 females) can appear to be successful in the first decades due to transient positive population growth, but with moderate population growth rate and moderate genetic load, long-term population viability (probability of extinction <0.01) was only achieved with ≥30 females and ≥3 males released. To maintain >95% genetic diversity of the source population in an isolated population, 50 females and 5 males are recommended to compose the founding population. Sensitivity analyses revealed first-year survival and reproductive rate were the simulation parameters with the greatest proportional influence on probability of extinction and genetic diversity. These simulations highlight important considerations for translocation success and data gaps including true genetic load in wild giraffe populations.

A comparative approach for species delimitation based on multiple methods of multi-locus DNA sequence analysis: A case study of the genus Giraffa (Mammalia, Cetartiodactyla)

Molecular data are now commonly used in taxonomy for delimiting cryptic species. In the case of giraffes, which were treated as a single species (Giraffa camelopardalis) during half of a century, several molecular studies have suggested a splitting into four to seven species, but the criteria applied for taxonomic delimitation were not fully described. In this study, we have analysed all multi-locus DNA sequences available for giraffes using multispecies coalescent (MSC: *BEAST, BPP and STACEY), population genetic (STRUCTURE, allelic networks, haplotype network and bootstrapping, haplowebs and conspecificity matrix) and phylogenetic (MrBayes, PhyML, SuperTRI) methods to identify the number of species. Our results show that depending on the method chosen, different taxonomic hypotheses, recognizing from two to six species, can be considered for the genus Giraffa. Our results confirm that MSC methods can lead to taxonomic over-splitting, as they delimit geographic structure rather than species. The 3-species hypothesis, which recognizes G. camelopardalis sensu strico A, G. giraffa, and G. tippelskirchi, is highly supported by phylogenetic analyses and also corroborated by most population genetic and MSC analyses. The three species show high levels of nucleotide divergence in both nuclear (0.35-0.51%) and mitochondrial sequences (3-4%), and they are characterised by 7 to 12 exclusive synapomorphies (ES) detected in nine of the 21 nuclear introns analysed for this study. By contrast, other putative species, such as G. peralta, G. reticulata, G. thornicrofti or G. tippelskirchi sensu stricto, do not exhibit any ES in the nuclear genes. A robust mito-nuclear conflict was found for the position and monophyly of G. giraffa and G. tippelskirchi, which is interpreted as the result of a mitochondrial introgression from Masai to southeastern giraffe during the Pleistocene and nuclear gene flow mediated by male dispersal between southern populations (subspecies G. g. giraffa and G. g. angolensis).

Kinship and reproductive condition correlate with affiliation patterns in female southern Australian bottlenose dolphins

Social relationships in female mammals are usually determined by an interplay among genetic, endogenous, social and ecological factors that ultimately affect their lifetime reproductive success. However, few studies have attempted to control for, and integrate these factors, hampering our understanding of drivers underlying female sociality. Here, we used generalized affiliation indices, combined with social networks, reproductive condition, and genetic data to investigate drivers of associations in female southern Australian bottlenose dolphins. Our analysis is based on photo-identification and genetic data collected through systematic boat surveys over a two-year study period. Female dolphins formed preferred associations and social clusters which ranged from overlapping to discrete home ranges. Furthermore, matrilineal kinship and biparental relatedness, as well as reproductive condition, correlated with the strength of female affiliations. In addition, relatedness for both genetic markers was also higher within than between social clusters. The predictability of resources in their embayment environment, and the availability of same-sex relatives in the population, may have favoured the formation of social bonds between genetically related females and those in similar reproductive condition. This study highlights the importance of genetic, endogenous, social and ecological factors in determining female sociality in coastal dolphins.

Beyond the group: how food, mates, and group size influence intergroup encounters in wild bonobos

In social-living animals, interactions between groups are frequently agonistic, but they can also be tolerant and even cooperative. Intergroup tolerance and cooperation are regarded as a crucial step in the formation of highly structured multilevel societies. Behavioral ecological theory suggests that intergroup tolerance and cooperation can emerge either when the costs of hostility outweigh the benefits of exclusive resource access or when both groups gain fitness benefits through their interactions. However, the factors promoting intergroup tolerance are still unclear due to the paucity of data on intergroup interactions in tolerant species. Here, we examine how social and ecological factors affect the onset and termination of intercommunity encounters in two neighboring communities of wild bonobos, a species exhibiting flexible patterns of intergroup interactions, at Kokolopori Bonobo Reserve, Democratic Republic of the Congo. We recorded the timing and location of intercommunity encounters and measured fruit abundance and distribution, groups’ social characteristics, and space-use dynamics over a 19-month period. We found that intercommunity tolerance was facilitated by a decrease in feeding competition, with high fruit abundance increasing the likelihood of communities to encounter, and high clumpiness of fruit patches increasing the probability to terminate encounters likely due to increased contest. In addition, the possibility for extra-community mating, as well as the potential benefits of more efficient foraging in less familiar areas, reduced the probability that the communities terminated encounters. By investigating the factors involved in shaping relationships across groups, this study contributes to our understanding of how animal sociality can extend beyond the group level.