Who benefits the most from a social party, those who host it or the guests?

FACUNDO ARIEL GANDOY; JUAN IGNACIO ARETA; GABRIELA GISELLE MANGINI; PEDRO GERARDO BLENDINGER

Congreso; North American Ornithological Conference VII; 2020

Mixed-flocks are a ubiquitous phenomenon across forest environments involving species with different roles and ecological requirements. Species roles have been broadly defined as central species, those who attracts and leads the movement of the flock, and those who follow the central species. But, those who leads want to be followed? Two main evolutionary advantages have been proposed as motivations behind flocking behavior: better surveillance against predators and increased foraging efficiency. However, all species perceive benefits in the same way? In order to identify the central species and to evaluate the foraging benefits that species might be perceiving and its relation to their role, we surveyed 388h in the Yungas-foothill forest across 3 years. We recorded the species that were leading the movement in each mixed-flock and the foraging efficiency of each observed bird individual regardless its social condition. Because central species behavior implies more than leading the movement, we also compiled all our mixed-flocks data and performed network analysis to rank the most central species based on the probability of each species of being central under the neighborhood inclusion criteria. We found that species with higher leading behavior were also the most central by network analysis. We also found a significant 24% global increase in the foraging efficiency when integrating mixed-flocks, being the central species those who benefited the most while some followers were hampered. This result indicates that central species are seizing the foraging benefits that mixed-flocks offers whilst follower species could be seizing the better surveillance against predators.