Understanding Rules of Assembly and Species Interactions in Mixed-species Bird Flocks
Abstract
In mixed-species bird flocks (flocks hereafter), participants vary in their degree of similarity
with each other. Flock participants can gain group size (supplementary) benefits by choosing
similar flock partners, or complementary benefits from dissimilar partners. The nature of
benefits, therefore varies based on overall similarity in the flock. Earlier research has shown
that flocks world over tend to be phenotypically clumped and that intraspecifically gregarious
species are important benefit providers. In this thesis, I examine changing patterns of
associations and species importance with respect to group size in mixed-species bird flocks.
In my first chapter, I examine the relationship between flock size and phenotypic clumping. I
find that small flocks are more phenotypically clumped than expected by chance but as flocks
become larger, the phenotypic variation does not differ from what’s expected by chance. At a
global scale, I find that, flocks in regions with lower average flock size are more
phenotypically clumped. In the second chapter, I examine the importance of intra-specifically
gregarious species. I find that flocks with less than or equal to two gregarious species have
lower richness of non-gregarious species than expected by chance. I also study traits of
intraspecifically gregarious species that are linked to functional importance and find that
individual behavioural traits are not directly correlated to species importance. In the third
chapter, I construct emergent networks of flock participant species based on flock cooccurrence. I find that a few species are structurally important in flocks of all sizes, while a
few are important only in networks of large flocks. I also find that flock components that are
unconnected in smaller flock networks, merge in large flock networks. Overall, I find that
species similarity and presence of important species is crucial in smaller flocks whereas large
flocks are heterogenous groups that resemble random phenotypic assemblages of flocking
birds
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