Traits That Structure Birds Following Army Ant Swarms and the Roles of Both Facilitation and Competition

Environmental changes are impacting community structure world‐wide by causing shifts in species interactions. Alterations in interactions may arise through the loss of key species and/or shifts in the costs and benefits of interacting. Here, we examined how characteristics of the swarms of two ant species and the abundance of key, dominant bird species influence the community of birds attending army ant swarms. Birds appeared to forage opportunistically at swarms of the less predictable ant species, Labidus praedator , and to use multiple cues to forage at swarms of the more predictable ant species, Eciton burchellii . Dominant bird species used swarm size to make decisions about attending ant swarms, while non‐dominant bird species used the abundance of dominant individuals. Results suggest that facilitation and competition influenced attendance at E. burchellii swarms. While dominant individuals attract other bird species to swarms, too many dominants reduce the number of individuals present. Our results suggest that dominant species have more than one role in these groups, and both the species present and swarm traits alter the costs and benefits of foraging in mixed‐species groups. As the environment continues to change, shifts in costs and benefits may arise, dramatically altering the structure of these groups and biodiversity, more broadly.