Coexistence in Mixed Species Antwren Flocks

Abstract

Morphological and behavioral data were collected for 9 spp. [Microrhopias quixensis, Myrmotherula fulviventris, M. axillaris, Thamnophilus punctatus, Wilsonia canadensis, Xenops minutus, Myrmeciza exsul, Hylophylax naevioides, Hylophilus decurtatus] seen most frequently in tropical mixed species antwren flocks. Ratios of bill size differ by .ltoreq. 1.14 for 1/3 of the species-pairs. Values of potential overlap in diet (.alpha.), based on body weight ratios are .gtoreq. 0.63 for all species-pairs. Each behavioral aspect of foraging strategy and microhabitat selection, substrate searched, vertical forging height, foraging method, foliage density and position is significantly different among > 1/2 species-pairs. Mean length and rate of foraging movements differ significantly among 12/28 and 18/28 species-pairs, respectively. The correlation between species ranked with respect to behavioral vs. morphological differences is highly significant. Twenty-one intraspecific aggressive encounters occurred, each when a species attempted to join a flock for which that species was already present. Coefficient of Association (CA) is used to quantify interspecific association: 94% of the values of CA are positive, 11 of which are significant. No negative values of CA are significant. CA is not significantly correlated with .alpha. in behavioral parameters.