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

Abstract

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

Projected impacts of climate change on functional diversity of frugivorous birds along a tropical elevational gradient

“…Under such a scenario, the immigration of species with similar or new sets of functional traits could compensate for the loss of other species 4,54,55 . However, upward movements does not only depend on climate, but also on interactions among birds, such as interspecific competition 56 or foraging interactions in mixed species flocks 57 . While knowledge on biotic factors shaping species’ distributions is available for some species, comprehensive information is currently lacking for species-rich tropical systems.…”

Using social network analysis of mixed-species groups in African savannah herbivores to assess how community structure responds to environmental change

“…Among the few studies that have attempted to tease apart the nature of these adaptations, most results indicate a shift in community structures in response to changes in resource availability (e.g. [27][28][29][30]).…”

Social dynamics of core members in mixed-species bird flocks change across a gradient of foraging habitat quality

“…It is important to keep in mind that the results from this study and [ 24 ] are based on the four primary species found in mixed-species flocks in north temperate forests (see [ 9 , 31 , 76 ]. The behavioral responses to habitat degradation observed in these flocks may differ from that found in tropical forests (e.g., [ 77 ], where seasonal variation in food availability and energetic stress is typically less than in temperate climates [ 78 ]. Moreover, the patterns we describe here may result from an increased importance of species-specific associations where species diversity is quite low [ 23 ].…”