Social partners and temperature jointly affect morning foraging activity of small birds in winter

Daily foraging activity of small wintering birds is classically thought to be driven by the need to gather enough energy reserves to survive each night. A separate line of research has shown that sociality is a major driver in winter foraging activities in many species. Here, we used wintering birds as a study system to move toward an integrative understanding of the influence of energy requirements and sociality on foraging ecology. We used RFID-enabled feeders in Lincoln, Nebraska, USA in January–March 2019 to measure foraging activity in two species (downy woodpeckers, Dryobates pubescens, and white-breasted nuthatches, Sitta carolinensis). We analyzed the relationship between overnight temperature and morning foraging activity and found that lowest overnight temperature was weakly correlated with morning visitation at feeders. We then used a network approach to ask if flock associations explain similarity in birds’ foraging activity. In both species, individuals with stronger associations in a social network were more likely to share similar feeder activity, and an index of social partners’ activity explained foraging activity better than overnight temperature. This brings forth new questions about the interplay between individual response to temperature and social factors in shaping how small animals cope with harsh winter conditions

Flock-species richness influences node importance and modularity in mixed-species flock networks

Interdependencies in social groups of animals are a combination of multiple pairwise interactions. Heterospecific groups are often characterized by important species that contribute more to group initiation, maintenance or function than other species. However, in large heterospecific groups, many pairwise interactions are not realised, while others may not be biologically significant, confounding inferences about species importance. Hence, in this study, we examine context dependent changes in species importance and assortment in mixed-species bird flocks from a tropical field site in Southern India using social network analysis. Specifically, we ask how the structural importance of a species and the clustering patterns of species relationships depends on species richness in mixed-species flocks. We constructed both raw and filtered networks; while our results are largely correlated, we believe that filtered networks can provide insights into community-level importance of species in mixed-flocks while raw networks depict flock-level patterns. We find significant differences in flocks of different richness in that different species emerge as structurally important across flocks of varying richness. We also find that assortment is higher in two-species flocks and decreases with an increase in the number of species in the flock (‘flock richness’ hereafter). We argue that the link between structural importance of species in mixed-species flock networks and their functional significance in the community critically depends on the social context: namely, the species richness of the mixed-species flock. We propose that examining species structural importance at different flock-richness values provides insights into biologically meaningful functional roles of species. More generally, we suggest that it is important to consider context when interpreting species centrality and importance in network structure

Avian Interspecific Interactions Across Scales: Communities, Mixed-Species Flocks, and Individuals

In ecological communities, heterospecific interactions are shaped not only by the costs of competition but also by the facilitative benefits of social interactions. Avian communities have served as a key system for investigating the interplay between these interactions both in the communities as a whole and within the mixed-species flocks found within these communities. Here I investigate heterospecific avian interactions across three levels of social organization – interactions between individuals, species-level interactions within mixed-species flocks and patterns of species co-occurrence at supplemental feeding sites across a region. I review the importance of individual-level interactions in understanding complex social systems like mixed-species flocks, emphasizing that variation in traits and relationships between individuals underpin all species-level patterns we see at broader scales. I look at behavioral flexibility within mixed-species flocks and find that species in mixed-species flocks have varied strategies to control their foraging height in relation to that of their flock mates. Some species flexibly adjust their foraging height to be closer to their flock mates, others selectively join flock mates foraging at certain heights and some utilize both strategies concurrently. When delving deeper into how these strategies may impact social roles and positioning in a network of interactions within the flock, I find that – surprisingly – a species’ flexibility does not relate to the number of connections it has within the flock network. Finally, I examine how patterns of species similarity across two axes – body size and beak shape – relate to patterns of co-occurrence at bird feeders and how that relationship has changed over time. I find that across two decades species pairs with less similar beak shapes and more similar body sizes have significantly higher rates of co-occurrence over time. Thus, indicating a reduction in niche overlap while maintaining the potential anti-predation benefits of co-occurring with species of similar size. By looking at interactions across social scales I hope to bring depth and nuance to our knowledge of species interactions

Sociable Weavers Increase Cooperative Nest Construction after Suffering Aggression.

The major transitions in evolution rely on the formation of stable groups that are composed of previously independent units, and the stability of these groups requires both cooperation and reduced conflict. Conflict over group resources may be common, as suggested by work in both cichlids and humans that has investigated how societies resolve conflict regarding investment in group resources, i.e. public goods. We investigated whether sociable weavers (Philetairus socius) use aggressive behaviors to modulate the cooperative behavior of group mates. We find that the individuals that build the communal thatch of the nest, i.e. the individuals most at risk of exploitation, are the most aggressive individuals. We show that individuals that invest in interior chamber maintenance, possibly a more selfish behavior, suffer relatively more aggression. After suffering aggression individuals significantly increase cooperative construction of the communal nest thatch. We show that cooperative individuals target aggression towards selfish individuals, and the individuals suffering aggression perform cooperative behaviors subsequent to suffering aggression. In addition to other evolutionary mechanisms, these results suggest that aggression, possibly via the pay-to-stay mechanism, is possibly being used to maintain a public good