Mixed species flocks of birds as strategy: behavior and seasonality in Yungas Foothill of North-west Argentina.

GANDOY F; MANGINI G; ARETA JI

Iguazu

Congreso; Ornithological Congress of the Americas; 2017

It has been long recognized that bird mixed-species flocks are seasonal in temperateforests and annual in tropical forests, however, seasonality of mixed flocks in thesubtropical forests remains poorly studied despite their potential role to clarify howintermediate climatic conditions affect flocking behavior. We surveyed the number ofmixed flocks, number of species and number of individuals in mixed flocks in Yungas-foothill of Northwest Argentina, to examine seasonality of mixed flocks and flockingbehavior in response to climatic elements (temperature, humidity, wind speed) andfragmentation, to test the hypothesis that birds flock more frequently under harshconditions. In both, continuous forest and forest fragments, mixed flock formation wasseasonal (they occurred more frequently and had more species and individuals duringthe harsh dry season, than during the more benign wet season), and harsh climaticconditions lead to flocking (the number of mixed flocks, and number of species andindividuals in them increased as temperature and humidity decreased within andbetween seasons). Although forest fragments were climatically harsher (drier andwindier) than continuous forest, fragments had fewer mixed flocks with fewer speciesand individuals. Since flock formation was a function of the number of species andindividuals, either reduced connectivity has limited the number of individuals reachingthe forest fragments or forest fragments were so harsh that birds could not thrive inthem. The benefits gained by flocking remain to be elucidated, but whichever thosebenefits are they should be understood in the context of seasonal variation in life-historytraits.