Studying individual-level interactions can transform our understanding of avian mixed-species flocks

Avian mixed-species flocks are ubiquitous across habitats and a model for studying how heterospecific sociality influences the behavior and composition of animal communities. Here, we review the literature on mixed-species flocks and argue that a renewed focus on individual-level interactions among flock members can transform our understanding of this iconic, avian social system. Specifically, we suggest that an individual perspective will further our understanding of (1) how inter- and intraspecific variation in flock participation links to fitness costs and benefits, (2) the implications of familiarity between individuals in structuring mixed-species flock communities, and (3) how social roles within mixed-species flocks are related to social behavior within and across species. We summarize studies that use an individual perspective in each of these areas and discuss knowledge from conspecific social behavior to posit more broadly how individuals may shape mixed-species flocks. We encourage research approaches that incorporate individual variation in traits, relationships, and social roles in their assessment of mixed-species flocking dynamics. We propose that the analysis of individual variation in behavior will be particularly important for explicitly identifying fitness outcomes that led to the evolution of mixed-species flocks, which in turn affect community structure and resilience. Lay Summary center dot Across the world, many birds form mixed-species flocks that serve as information centers, facilitating foraging, and anti-predation behaviors for multiple species. Such social groups provide a prime example of how sociality can extend beyond species boundaries. center dot Most research on this topic focuses on species-level questions (e.g., how different species fill different roles in the flock) without accounting for the importance of individual-level traits and relationships in mixed-species flocks. center dot We argue that an increased focus on the individuals in mixed-species flocks is needed to understand how flock participation is linked to the evolution of traits and behaviors, how social relationships matter in interactions between species, and to reveal hidden social structure at the level of ecological communities. center dot We demonstrate how techniques such as social network analysis can be used in conjunction with experiments and observations of individuals to explore the importance of individual variation and social recognition in the social dynamics of mixed-species flocks.

Automated summary

Avian mixed-species flocks are a common social system that can be used to study the impact of heterospecific sociality on animal communities. By focusing on individual-level interactions, we can gain a better understanding of the variation in flock participation, the influence of familiarity on the flock structure, and the relationship between social roles and behavior within and across species. Incorporating individual variation in assessments of mixed-species flock dynamics is important for identifying fitness outcomes and understanding community structure.