Selection for territory acquisition is modulated by social network structure in a wild songbird

The social environment may be a key mediator of selection that operates on animals. In many cases, individuals may experience selection not only as a function of their phenotype, but also as a function of the interaction between their phenotype and the phenotypes of the conspecifics they associate with. For example, when animals settle after dispersal, individuals may benefit from arriving early, but, in many cases, these benefits will be affected by the arrival times of other individuals in their local environment. We integrated a recently described method for calculating assortativity on weighted networks, which is the correlation between an individual's phenotype and that of its associates, into an existing framework for measuring the magnitude of social selection operating on phenotypes. We applied this approach to large‐scale data on social network structure and the timing of arrival into the breeding area over three years. We found that late‐arriving individuals had a reduced probability of breeding. However, the probability of breeding was also influenced by individuals’ social networks. Associating with late‐arriving conspecifics increased the probability of successfully acquiring a breeding territory. Hence, social selection could offset the effects of nonsocial selection. Given parallel theoretical developments of the importance of local network structure on population processes, and increasing data being collected on social networks in free‐living populations, the integration of these concepts could yield significant insights into social evolution.     

Do Pied Flycatchers Use Personal or Social Information for Replacement Clutch Decisions? A Field Experiment

Life is a continuous stream of decisions: organisms are repeatedly confronted with multiple options from which to choose. To make the best decisions and maximise their fitness, individuals need to collect information: from direct interactions with the environment (personal information) or from observing other individuals interacting with the environment (social information). Yet, very little is known about the details of decision‐making by animals in their natural environments, including the sources of information they use in the process. We set out to determine the relative importance of social and personal information in breeding habitat decisions in the migratory pied flycatcher, Ficedula hypoleuca. In a field experiment in Finland, we manipulated flycatcher breeding success and then allowed individuals to choose among breeding sites labelled with artificial cues (arbitrary symbols) associated with their own (manipulated) and neighbour's reproductive success, respectively, for laying a replacement clutch. Birds did not appear to distinguish among the symbols representing their own, their neighbour's or a neutral symbol, indicating that they did not use either information source when deciding about a replacement clutch. Also, the choice did not influence subsequent investment into breeding (clutch size). This may suggest that pied flycatchers utilise other cues (e.g. breeding success or predation risk on larger scales) when having to make a decision about replacement clutches. We discuss our results in light of constraints imposed by a short breeding season of migratory birds.     

Consistent sociality but flexible social associations across temporal and spatial foraging contexts in a colonial breeder

When the consequences of sociality differ depending on the state of individual animals and the experienced environment, individuals may benefit from altering their social behaviours in a context‐dependent manner. Thus, to fully address the hypotheses about the role of social associations it is imperative to consider the multidimensional nature of sociality by explicitly examining social associations across multiple scales and contexts. We simultaneously recorded > 8000 associations from 85% of breeding individuals from a colony of Australasian gannets (Morus serrator) over a 2‐week period, and examined gregariousness across four foraging states using multilayer social network analysis. We found that social associations varied in a context‐dependent manner, highlighting that social associations are most prevalent during foraging (local enhancement) and in regions expected to provide clustered resources. We also provide evidence of individual consistency in gregariousness, but flexibility in social associates, demonstrating that individuals can adjust their social behaviours to match experienced conditions.     

Testing the conspecific attraction hypothesis with Dupont's Larks,a resident species of songbird in central Spain

Some birds use social cues, such as the presence of conspecifics, when selecting breeding habitat. This phenomenon, known as conspecific attraction, has been well‐documented in migratory species, but has not been assessed for resident species of birds. We used Dupont's Larks (Chersophilus duponti) as a model species to determine if conspecific attraction plays a role in habitat selection by resident species of birds. At our study site in Soria province in central Spain, we monitored two potential habitat patches and one managed site where management actions had provided apparently suitable habitat. At each site, we broadcast recordings of the songs and calls of male Dupont's Larks, and monitored their presence during the breeding season and dispersal period in 2018 using automated recorders and field surveys. No birds were attracted to our study sites. Our results suggest that management of patches of suitable habitat should occur close to areas (within 1 km) already occupied by Dupont's Larks to encourage natural colonization because, based on our results, playback of conspecific vocalizations may not attract the species to new breeding areas. However, additional studies are needed before drawing conclusions about the effectiveness of conspecific attraction for this and other resident species of birds.     

Social carry‐over effects underpin trans‐seasonally linked structure in a wild bird population

Spatial structure underpins numerous population processes by determining the environment individuals' experience and which other individuals they encounter. Yet, how the social landscape influences individuals' spatial decisions remains largely unexplored. Wild great tits (Parus major) form freely moving winter flocks, but choose a single location to establish a breeding territory over the spring. We demonstrate that individuals' winter social associations carry‐over into their subsequent spatial decisions, as individuals breed nearer to those they were most associated with during winter. Further, they also form territory boundaries with their closest winter associates, irrespective of breeding distance. These findings were consistent across years, and among all demographic classes, suggesting that such social carry‐over effects may be general. Thus, prior social structure can shape the spatial proximity, and fine‐scale arrangement, of breeding individuals. In this way, social networks can influence a wide range of processes linked to individuals' breeding locations, including other social interactions themselves.     

Social network structure in wintering golden‐crowned sparrows is not correlated with kinship

Stable social organization in a wide variety of organisms has been linked to kinship, which can minimize conflict due to the indirect fitness benefits from cooperating with relatives. In birds, kin selection has been mostly studied in the context of reproduction or in species that are social year round. Many birds however are migratory, and the role of kinship in the winter societies of these species is virtually unexplored. In a previous study, we discovered striking social complexity and stability in a wintering population of migratory golden‐crowned sparrows (Zonotrichia atricapilla) – individuals repeatedly form close associations with the same social partners, including across multiple winters. Here, we test the possibility that kinship might be involved in these close and stable social affiliations. We examine the relationship between kinship and social structure for two of the consecutive wintering seasons from the previous study. We found no evidence that social structure was influenced by kinship. Relatedness between most pairs of individuals was at most that of first cousins (and mostly far lower). Genetic networks based on relatedness do not correspond to the social networks, and Mantel tests revealed no relationship between kinship and pairwise interaction frequency. Kinship also failed to predict social structure in more fine‐grained analyses, including analyses of each sex separately (in the event that sex‐biased migration might limit kin selection to one sex), and separate analyses for each social community. The complex winter societies of golden‐crowned sparrows appear to be based on cooperative benefits unrelated to kin selection.     

The effects of data collection and observation methods on uncertainty of social networks in wild primates

In social species, network centralities of group members shape social transmission and other social phenomena. Different factors have been found to influence the measurement of social networks, such as data collection and observation methods. In this study, we collected data on adults and juveniles and examined the effect of data collection method (ad libitum sampling vs. focal animal sampling) and observation method (interaction—grooming; play—vs. association—arm-length; 2 m; 5 m proximities—) on social networks in wild vervet monkeys. First, we showed using a bootstrapping method, that uncertainty of ad libitum grooming and play matrices were lesser than uncertainty of focal matrices. Nevertheless, grooming and play networks constructed from ad libitum and focal animal sampling were very similar and highly correlated. We improved the certainty of both grooming and play networks by pooling focal and ad libitum matrices. Second, we reported a high correlation between the proximity arm-length network and the focal grooming one making an arm-length proximity network a reasonable proxy for a grooming one in vervet monkeys. However, we did not find such a correlation between proximity networks and the play one. Studying the effects of methodological issues as data collection and observation methods can help improve understanding of what shapes social networks and which data collection method to choose to study sociality.     

A guide to choosing and implementing reference models for social network analysis

Analysing social networks is challenging. Key features of relational data require the use of non-standard statistical methods such as developing system-specific null, or reference, models that randomize one or more components of the observed data. Here we review a variety of randomization procedures that generate reference models for social network analysis. Reference models provide an expectation for hypothesis testing when analysing network data. We outline the key stages in producing an effective reference model and detail four approaches for generating reference distributions: permutation, resampling, sampling from a distribution, and generative models. We highlight when each type of approach would be appropriate and note potential pitfalls for researchers to avoid. Throughout, we illustrate our points with examples from a simulated social system. Our aim is to provide social network researchers with a deeper understanding of analytical approaches to enhance their confidence when tailoring reference models to specific research questions.     

Space use and social association in a gregarious ungulate: Testing the conspecific attraction and resource dispersion hypotheses

Animals use a variety of proximate cues to assess habitat quality when resources vary spatiotemporally. Two nonmutually exclusive strategies to assess habitat quality involve either direct assessment of landscape features or observation of social cues from conspecifics as a form of information transfer about forage resources. The conspecific attraction hypothesis proposes that individual space use is dependent on the distribution of conspecifics rather than the location of resource patches, whereas the resource dispersion hypothesis proposes that individual space use and social association are driven by the abundance and distribution of resources. We tested the conspecific attraction and the resource dispersion hypotheses as two nonmutually exclusive hypotheses explaining social association and of adult female caribou (Rangifer tarandus). We used location data from GPS collars to estimate interannual site fidelity and networks representing home range overlap and social associations among individual caribou. We found that home range overlap and social associations were correlated with resource distribution in summer and conspecific attraction in winter. In summer, when resources were distributed relatively homogeneously, interannual site fidelity was high and home range overlap and social associations were low. Conversely, in winter when resources were distributed relatively heterogeneously, interannual site fidelity was low and home range overlap and social associations were high. As access to resources changes across seasons, caribou appear to alter social behavior and space use. In summer, caribou may use cues associated with the distribution of forage, and in winter caribou may use cues from conspecifics to access forage. Our results have broad implications for our understanding of caribou socioecology, suggesting that caribou use season‐specific strategies to locate forage. Caribou populations continue to decline globally, and our finding that conspecific attraction is likely related to access to forage suggests that further fragmentation of caribou habitat could limit social association among caribou, particularly in winter when access to resources may be limited.     

Experimental manipulation of avian social structure reveals segregation is carried over across contexts

Our current understanding of animal social networks is largely based on observations or experiments that do not directly manipulate associations between individuals. Consequently, evidence relating to the causal processes underlying such networks is limited. By imposing specified rules controlling individual access to feeding stations, we directly manipulated the foraging social network of a wild bird community, thus demonstrating how external factors can shape social structure. We show that experimentally imposed constraints were carried over into patterns of association at unrestricted, ephemeral food patches, as well as at nesting sites during breeding territory prospecting. Hence, different social contexts can be causally linked, and constraints at one level may have consequences that extend into other aspects of sociality. Finally, the imposed assortment was lost following the cessation of the experimental manipulation, indicating the potential for previously perturbed social networks of wild animals to recover from segregation driven by external constraints.     

Giraffe (Giraffa camelopardalis) social networks in areas of contrasting human activity and lion density

The adaptive value of close social bonds and social networks has been demonstrated in a variety of vertebrate taxa. While the effect of predators on populations is well established, disturbance by humans is increasingly being identified as affecting the behaviour and reproductive success of animals and can have significant impacts on their survival. We used a concurrent analysis of two adjacent giraffe Giraffa camelopardalis populations in Kenya to determine whether human activities and high predation affected their social networks. One study site was a premier tourist destination with a high volume of human activity in the form of tourist traffic and lodge infrastructure, alongside a high density of lions which preferentially prey on giraffe calves; the other was a private wildlife conservancy with minimal human activity and no lion population. Giraffes in both networks showed preferred associations and avoidances of other individuals, which were independent of space use. Bond strength was lower in the population exposed to high levels of human activity and lions, and the network had lower density and clustering, and shorter path lengths, suggesting that it was more fragmented. We suggest that human activity and predator density may influence the patterns of social interactions in giraffes and highlight the importance of understanding the impact of tourism and management on the survival and success of wild animal populations.     

From social network (centralized vs. decentralized) to collective decision-making (unshared vs. shared consensus)

Relationships we have with our friends, family, or colleagues influence our personal decisions, as well as decisions we make together with others. As in human beings, despotism and egalitarian societies seem to also exist in animals. While studies have shown that social networks constrain many phenomena from amoebae to primates, we still do not know how consensus emerges from the properties of social networks in many biological systems. We created artificial social networks that represent the continuum from centralized to decentralized organization and used an agent-based model to make predictions about the patterns of consensus and collective movements we observed according to the social network. These theoretical results showed that different social networks and especially contrasted ones--star network vs. equal network--led to totally different patterns. Our model showed that, by moving from a centralized network to a decentralized one, the central individual seemed to lose its leadership in the collective movement's decisions. We, therefore, showed a link between the type of social network and the resulting consensus. By comparing our theoretical data with data on five groups of primates, we confirmed that this relationship between social network and consensus also appears to exist in animal societies.     

Composition and structure of a large online social network in The Netherlands

Limitations in data collection have long been an obstacle in research on friendship networks. Most earlier studies use either a sample of ego-networks, or complete network data on a relatively small group (e.g., a single organization). The rise of online social networking services such as Friendster and Facebook, however, provides researchers with opportunities to study friendship networks on a much larger scale. This study uses complete network data from Hyves, a popular online social networking service in The Netherlands, comprising over eight million members and over 400 million online friendship relations. In the first study of its kind for The Netherlands, I examine the structure of this network in terms of the degree distribution, characteristic path length, clustering, and degree assortativity. Results indicate that this network shares features of other large complex networks, but also deviates in other respects. In addition, a comparison with other online social networks shows that these networks show remarkable similarities.     

Testing hypotheses about the sister group of the passeriformes using an independent 30-locus data set

Although many phylogenetic studies have focused on developing hypotheses about relationships, advances in data collection and computation have increased the feasibility of collecting large independent data sets to rigorously test controversial hypotheses or carefully assess artifacts that may be misleading. One such relationship in need of independent evaluation is the position of Passeriformes (perching birds) in avian phylogeny. This order comprises more than half of all extant birds, and it includes one of the most important avian model systems (the zebra finch). Recent large-scale studies using morphology, mitochondrial, and nuclear sequence data have generated very different hypotheses about the sister group of Passeriformes, and all conflict with an older hypothesis generated using DNA-DNA hybridization. We used novel data from 30 nuclear loci, primarily introns, for 28 taxa to evaluate five major a priori hypotheses regarding the phylogenetic position of Passeriformes. Although previous studies have suggested that nuclear introns are ideal for the resolution of ancient avian relationships, introns have also been criticized because of the potential for alignment ambiguities and the loss of signal due to saturation. To examine these issues, we generated multiple alignments using several alignment programs, varying alignment parameters, and using guide trees that reflected the different a priori hypotheses. Although different alignments and analyses yielded slightly different results, our analyses excluded all but one of the five a priori hypotheses. In many cases, the passerines were sister to the Psittaciformes (parrots), and taxa were members of a larger clade that includes Falconidae (falcons) and Cariamidae (seriemas). However, the position of Coliiformes (mousebirds) was highly unstable in our analyses of 30 loci, and this represented the primary source of incongruence among analyses. Mousebirds were united with passerines or parrots in some analyses, suggesting an additional hypothesis that needs to be considered in future studies. There was no clear evidence that base-compositional convergence, saturation, or long-branch attraction affected our conclusions. These results provide independent evidence excluding four major hypotheses about the position of passerines, allowing the extensive studies on this group to be placed in a more rigorous evolutionary framework.     

A framework to evaluate whether to pool or separate behaviors in a multilayer network

A multilayer network approach combines different network layers,which are connected by interlayer edges,to create a single mathematical object.These networks can contain a variety of information types and represent different aspects of a system.However,the process for selecting which information to include is not always straightforward.Using data on 2 agonistic behaviors in a captive population of monk parakeets(Myiopsitta monachus),we developed a framework for investigating how pooling or splitting behaviors at the scale of dyadic relationships(between 2 individuals)affects individual-and group-level social properties.We designed 2 reference models to test whether randomizing the number of interactions across behavior types results in similar structural patterns as the observed data.Although the behaviors were correlated,the first reference model suggests that the 2 behaviors convey different information about some social properties and should therefore not be pooled.However,once we controlled for data sparsity,we found that the observed measures corresponded with those from the second reference model.Hence,our initial result may have been due to the unequal frequencies of each behavior.Overall,our findings support pooling the 2 behaviors.Awareness of how selected measurements can be affected by data properties is warranted,but nonetheless our framework disentangles these efforts and as a result can be used for myriad types of behaviors and questions.This framework will help researchers make informed and data-driven decisions about which behaviors to pool or separate,prior to using the data in subsequent multilayer network analyses.     

Individual personalities predict social behaviour in wild networks of great tits (Parus major)

Social environments have an important effect on a range of ecological processes, and form a crucial component of selection. However, little is known of the link between personality, social behaviour and population structure. We combine a well‐understood personality trait with large‐scale social networks in wild songbirds, and show that personality underpins multiple aspects of social organisation. First, we demonstrate a relationship between network centrality and personality with ‘proactive’ (fast‐exploring) individuals associating weakly with greater numbers of conspecifics and moving between flocks. Second, temporal stability of associations relates to personality: ‘reactive’ (slow‐exploring) birds form synergistically stable relationships. Finally, we show that personality influences social structure, with males non‐randomly distributed across groups. These results provide strong evidence that songbirds follow alternative social strategies related to personality. This has implications not only for the causes of social network structure but also for the strength and direction of selection on personality in natural populations.     

Social Context Modulates Predator Evasion Strategy In Guppies

Social context is a powerful mediator of behavioral decisions across animal taxa, as the presence of conspecifics comes with both costs and benefits. In risky situations, the safety conferred by the presence of conspecifics can outweigh the costs of competition for resources. How the costs and benefits of grouping influence decisions among alternative antipredator behaviors remains largely unexplored. We took advantage of the Trinidadian guppy (Poecilia reticulata) to examine the influence of social context on alternative behavioral responses to threats. We compared the frequency of active (startle) versus passive (freeze) responses to sudden acoustic stimuli in the presence and absence of conspecifics. We found that fish were relatively less likely to startle and more likely to freeze when in a group than when alone, indicating that immediate social context modulates predator evasion strategy in guppies. We suggest that these social context‐dependent changes reflect trade‐offs between survival and energy expenditure. To our knowledge, an effect of immediate social environment on startle probability has not been previously demonstrated in a teleost.     

Sex,growth rate,rank order after brood reduction,and hatching date affect first‐year survival of long‐lived Herring Gulls

Among most species of birds, survival from hatching throughout the first year of life is generally lower than subsequent survival rates. Survival of young birds during their first year may depend on a combination of selection, learning, unpredictable resources, and environmental events (i.e., post‐fledging factors). However, knowledge about post‐fledging development in long‐lived species is usually limited due to a lengthy immature stage when individuals are generally unobservable. Therefore, pre‐fledging characteristics are often used to predict the survival of young birds. We assessed effects of nestling growth rates, hatching date, hatching asynchrony, brood size and rank order after brood reduction, and sex on first‐year survival of 137 fledglings using a mark‐resighting analysis. We found that the survival probability (Φ_1yr = 0.39) of first‐year Herring Gulls (Larus argentatus) in our study colony located at the outer port of Zeebrugge (Belgium) was lower than that of older individuals (Φ_>1yr = 0.75). All 10 models best supported by our data included nestling growth rate, suggesting that variability in first‐year survival may be linked primarily to individual variation in growth. First‐year survival was negatively correlated with hatching date and rank order after brood reduction. Hence, carry‐over effects of breeding season events such as timing of breeding, early development, and social status had an influence on survival of Herring Gulls after fledging. Furthermore, we found sex‐biased mortality in first‐year Herring Gulls, with females (Φ_1yr = 0.45) surviving better than males (Φ_1yr = 0.38). Although adult survival is generally regarded as the key parameter driving population trajectories in long‐lived species, juvenile survival has recently been acknowledged as an important source of variability in population growth rates. Thus, increasing our knowledge of factors affecting age‐specific survival rates is necessary to improve our understanding of population dynamics and ultimately life‐history variation.     

What's in a crowd? Analysis of face-to-face behavioral networks

The availability of new data sources on human mobility is opening new avenues for investigating the interplay of social networks, human mobility and dynamical processes such as epidemic spreading. Here we analyze data on the time-resolved face-to-face proximity of individuals in large-scale real-world scenarios. We compare two settings with very different properties, a scientific conference and a long-running museum exhibition. We track the behavioral networks of face-to-face proximity, and characterize them from both a static and a dynamic point of view, exposing differences and similarities. We use our data to investigate the dynamics of a susceptible-infected model for epidemic spreading that unfolds on the dynamical networks of human proximity. The spreading patterns are markedly different for the conference and the museum case, and they are strongly impacted by the causal structure of the network data. A deeper study of the spreading paths shows that the mere knowledge of static aggregated networks would lead to erroneous conclusions about the transmission paths on the dynamical networks.