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Frequency of Mixed Species Flocking in Tropical Forest Birds and Correlates of Predation Risk: An Intertropical Comparison
Journal of Avian Biology
Vol. 30, No. 3 (Sep., 1999), pp. 282-294
Stable URL: http://www.jstor.org/stable/3677354
Page Count: 13
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The composition and frequency of occurrence of mixed flocks among foraging insectivorous birds were compared between several tropical forests from South America to the Indian Ocean and Southeast Asia, and related to forest structure, foraging behaviour and abundance of predators (diurnal raptors), to investigate relationships between flocking behaviour and antipredator defence. Foliage gleaners, the most conspicuous and least vigilant foragers, were usually the most abundant flock members and the birds with the highest flocking propensity. In contrast, species foraging low above ground or in dense vegetation were the least likely to join flocks. Flocking propensity of all insectivores pooled, or of gleaners alone, generally declined from primary lowland forest to open (semi-deciduous), disturbed (logging gaps), managed or montane forest (broken canopy), i.e. when predator detectability was likely to increase. There was also a significant positive correlation between bird-hunting raptor diversity or abundance and flocking rates of foliage gleaners or all insectivores. The results supported the hypothesis that foraging birds most vulnerable to predators were most likely to form mixed species flocks and that flocking tendency decreased when vegetation structure became more protective and/or when predator pressure became lower.
Journal of Avian Biology © 1999 Nordic Society Oikos