Species cumulative impacts to mixed assemblages of Neotropical parrots

Abstract

Mixed-species aggregations at fixed resources may demonstrate complex social structure and behaviors. However, these systems are underappreciated in behavioral ecology, ultimately limiting our understanding of population and community processes. Here we observed 13 species of parrots, macaws, and parakeets in foraging assemblages at exposed cliffs in southeast Perú. For each species, we developed a multivariate index of group impact by accumulating 9 separate metrics of abundance, chronology, functions, and interactions. This index appreciates species that join aggregations in large numbers, participate early, serve in functional roles, interact with others, and are socially dominant. We used Random Forest ("RF") algorithms to build nonlinear multiple regressions to assess and rank the influence of a suite of taxonomic and morphometric factors on this index. The RF models (R2 = 0.96) indicate parrots with smaller brains (controlled for body size) have the highest impact scores, with several potential underlying mechanisms. We further document a distinct sequence of group participation where subordinate species serve as pioneers that initiate group assembly and foraging, while dominant species serve as sentinels, foraging after subordinates. This result suggests that sequenced tradeoffs and reciprocal altruism may be important in these mixed-species groups.