Bird mixed-species flock formation is driven by low temperatures between and within seasons in a Subtropical Andean-foothill forest

MANGINI, GABRIELA GISELLE; ARETA, JUAN IGNACIO; MANGINI, GABRIELA GISELLE; ARETA, JUAN IGNACIO

BIOTROPICA

WILEY-BLACKWELL PUBLISHING, INC

Año: 2018 p. 816 - 825

0006-3606

According to both the predation avoidance and foraging efficiency hypotheses, birds within mixed flocks increase their foraging effi-ciency and/or can spend more time feeding and less time looking out for predators. These hypotheses predict that birds in mixed flocksobtain benefits. Thus, mixed flock formation could serve as a strategy to cope with difficult conditions imposed on birds such as cli-matic conditions that ultimately result in a change in predation pressure or food resources. We evaluate the hypotheses that forming partof a flock confers benefits to its members and the associated prediction that birds will take advantage of these benefits and flock moreoften under cold and dry weather conditions between and within seasons to cope with such conditions. We surveyed the presence ofmixed flocks, flocking propensity, number of species and individuals in mixed flocks in the Subtropical Yungas foothill of Argentina, toexamine seasonality, flocking behavior of birds and their responses to two climatic variables: temperature and humidity. Bird species pre-sented a higher flocking propensity and mixed flocks occurred more frequently during the dry and cold seasons than during the morebenign seasons, and lower values of temperature within seasons triggered the flocking behavior. Although effects between seasons wereexpected, birds also showed a short-term response to small chang es in temperature within seasons. These results strengthen the ideasproposed by the foraging hypothesis. Although benefits derived from flocking have yet to be determined, whatever they are should beunderstood in the context of seasonal variation in life-history traits.