Data from: Evidence for facilitation among avian army-ant attendants: specialization and species associations across elevations

Mixed-species assemblages can involve positive and negative
interactions, but uncertainty about high-value patchy resources can
increase the value of information sharing among heterospecific co-foragers.
I sampled species composition of bird-flocks attending army ant raids in
three adjacent elevation zones in Costa Rica, across multiple years, to
test for positive and negative associations among raid-attending bird
species. My goal was to test whether the most frequent and specialized
raid-attending species showed evidence of facilitating or excluding other
bird species. I quantified elevational variation in avian community
composition at raids, then asked whether species composition was associated
with variation in flock characteristics (flock size and species richness).
I identified the most frequent raid-attending species (those that attended
raids most frequently relative to their mistnet capture rates), and bird
species that performed specialized army ant-following behavior
(bivouac-checking, which allows birds to memorize and track mobile army ant
colonies). There was significant turnover of bird species among zones
(including the frequent and specialized attendants); patterns of species
overlap suggested a gradual transition from a Pacific-slope to an
Atlantic-slope raid-attending bird fauna. Raid attendance frequency was
positively correlated with bivouac-checking behavior. With few exceptions,
the most frequent raid-attending bird species, and the bivouac-checking
species, also participated in the most species-rich flocks. High
species-gregariousness suggests many of the frequently attending and/or
bivouac-checking species functioned as core flock members. However, some
bird species pairs were significantly negatively associated at raids.
Despite species turnover, per-flock numbers of birds at raids did not
differ among geographic zones, but flocks on the Pacific slope were heavier
because larger-bodied bird species attended raids. Previous studies showed
that the size (biomass) of bird-flocks corresponds to the amount of food
the birds cleptoparasitize from ant raids, and the heavier Pacific-slope
bird-flocks could have greater negative cleptoparasitic impacts.