Arthropod detectability play an important role over group foraging behavior of birds: a new theoretical framework for mixed-species flocks.

GABRIELA GISELLE MANGINI; KARL MOKROSS; FACUNDO ARIEL GANDOY; ARETA JUAN IGNACIO

Simposio; Mixed-species animal groups 2021 online symposium; 2021

Mixed-species flocks presumably provide birds with antipredator and foraging benefits. The foraging benefits hypothesis predicts that less food will trigger flocking activity; however, flocking activity may also respond to the difficulty of detecting food, which has not been evaluated. We found that flocking propensity of birds was more strongly correlated with arthropod detectability than arthropod abundance after two years in Yungas forest studying 129 mixed-species flocks, recording 1344 birds? foraging sequences, and capturing 25591 arthropods. We performed a first analysis to evaluate whether environmental traits (temperature and foliage density), or arthropod abundance, or rather the combination of both influenced the frequency of arthropod detections made by birds. We found that the combination of environmental traits and arthropod abundance explained food detection of birds. Prey detection was negatively influenced by ambient temperature and foliage density but positively by arthropod abundance. Based on these results, we define our flocking behavioral trigger model that allowed us to compare the relative importance of the difficulty in detecting prey items using a proxy latent variable, arthropod crypsis, and arthropod abundance as predictors of flocking propensity. Flocking propensity peaked when arthropod abundance was greatest but especially when the arthropod community was constituted by a higher proportion of immature and non-flying arthropods, the temperature was low and the foliage density was higher. Lastly we assessed whether birds within mixed flocks experienced increased foraging efficiency compared to birds outside such flocks. On average, individuals within mixed flocks increased their prey-capture attempt rate by 40% whilst the search rate increased by 16%. Our research add a new perspective on the drivers of mixed-species flocking, showing that the capacity to find and recognize prey items may have a greater effect on sociality than prey abundance when deciding whether to join a mixed flock to obtain the associated foraging benefits.