Introduction
The social relationships among animals emerge from interactions in multiple ecological and social situations. Relationships can result from both affiliative interactions, such as grooming and food sharing, and agonistic encounters, such as direct aggression and indirect supplanting (Whitehead 2008). Social structures have important population-level outcomes such as disease dynamics and the spread of information. Traditionally, different types of interactions have been studied either separately or in aggregate, without distinguishing among them (Croftet al. 2008; Wey et al. 2008; Krause et al. 2010; Pinter-Wollman et al. 2014). However, observed social relationships are a product of interactions that take place in different social and ecological situations (Finn et al. 2019; Dragićet al. 2021) (Fig. 1). Social animals can benefit from certain types of associations by gaining knowledge about the location, availability, and quality of resources (Dall et al. 2005; Giraldeau & Caraco. 2018). However, the potential costs of sociality, such as fast depletion of resources, competition over mates, and increased exposure to pathogens all impact social dynamics (Silk 2007). The balance between the costs and benefits of sociality can determine how each social situation contributes to the global social structure (Evans et al. 2020). Thus, a closer examination of interactions that occur in different social situations and their relative contribution to the social structure of a population may provide more accurate information about the mechanisms that underlie social structures and the function of sociality in population-level processes (Silk et al 2018).
Each social and ecological situation may contribute differently to the position of an individual in a society because individuals may differ in how much they engage with others in each social situation. For example, certain individuals may be important for stabilizing a social group (Flack et al . 2006), or are important in foraging situations, leading groups to scarce resources (Mccomb et al. 2001; Foleyet al. 2008; Brent et al. 2015). However, those individuals may play a more peripheral social role in other situations, such as caring for offspring, or group defense. The common approach of aggregating all interaction types makes it impossible to distinguish between an individual that has many interactions in one particular situation and an individual that has few interactions with unique individuals in a diverse set of situations. Thus, treating social interactions in different situations as components of a unified social structure can produce unexpected inferences about the role of individuals in their society (Finn et al. 2019). For example, in a recent study of paper wasps, the potential of an individual to become a queen was revealed only when social interactions in multiple situations were considered simultaneously, but not when interactions in each situation were considered separately or when all interactions were aggregated without distinguishing among situations (Sharma et al.2022). Similarly, in primate societies, certain individuals were identified as important in the social structure only when multiple social situations were considered together, but not when each social situation was examined separately (Barrett et al. 2012; Smith-Aguilar et al. 2019). By considering multiple situations, certain situations emerge as more important in shaping the sub-structure of the society than others (Smith-Aguilar et al. 2019). Thus, uncovering which social and ecological situations influence individuals’ social roles in each situation has important implications for determining survival and exposure to pathogens (VanderWaal et al.2016) as well as social foraging (Boogert et al 2014), which are important for wildlife conservation and management.
Griffon vultures (Gyps fulvus ) interact in different social situations to share social information about the location of roosts and feeding sites. Like most other vulture species, griffons are large obligate scavengers that search for and consume large carcasses (Houston 1974). Because carcasses are an unpredictable resource, griffons rely heavily on social information and recruitment to locate food (Jacksonet al. 2008; Spiegel et al. 2013a; Cortés-Avizandaet al. 2014). Recruitment to food results in local enhancements and feeding aggregations of tens of individuals, which may share food and/or engage in aggressive interactions (Mundy 1992; Carrete et al. 2010). Griffons roost and nest in communal roosts, which can serve as information centers for locating resources (Harel et al.2017). Thus, interactions in different situations may provide different information and contribute in different ways to the relationships that vultures form. Furthermore, individuals may differ in their need for food as well as in their knowledge about the location and quality of current resources, which depend on their recent movements and their interactions with conspecifics in different situations (Spiegel et al. 2013b). For example, if information about food location is obtained through co-flying (e.g. Cortés-Avizanda et al. (2014), vultures that spend much time flying with others might have greater access to food than those who tend to fly in smaller groups or alone. In contrast, if information sharing at the roost is more important for locating food, then individuals that roost with more individuals and/or with better informed ones will have greater access to food (Harel et al.2017). In addition, interactions on the ground (e.g., when roosting or feeding) may expose vultures to information about social status and potential mates, but also to pathogens. Thus, individuals that spend more time in ground-based interactions might have more exposure to certain information and to disease compared to those that interact predominantly during flight. Because the population of griffons that we study is of extreme conservation concern (Hatzofe 2020), uncovering what types of social interactions are important for structuring the social relationships in the population and identifying which individuals are exposed to different types of information and risks (pathogens and poisoning) can inform wildlife management actions. The prevalence of poisoning as the main mortality reason for griffons and many other vulture species (Ogada et al . 2012) highlights the importance of social foraging and of identifying the social situations that affect social aggregations and individuals’ unique roles in these social structures.
The goal of our study is to examine how different behavioral situations contribute to the social structure of a vulture population and to determine how individuals differ in their social position based on the social situations in which they interact. Specifically, we consider three social situations: diurnal interactions on the ground (e.g., while co-feeding), diurnal interactions in the air (co-flying), and nocturnal interactions on the ground (e.g., while co-roosting). We ask if individuals that have a central role in one social situation, carry over their social role to other situations. We further ask if social situations contribute in different ways to the population-level social structure. We predict that social situations with brief interactions, such as co-flying, will have a lower impact on the strength of social bonds compared to situations in which interactions are long, such as those that occur on the ground. We further predict that social situations in which movements are shorter (i.e., on the ground) will result in fewer unique interactions relative to situations in which vultures move larger distances (i.e., when flying). Disentangling the role of social interactions in different situations, both at the individual and the population levels, will shed light on the complexities of animal societies and may guide wildlife management actions.