Resources and seasonality drive the composition of mixed-species bird flocks along an elevational gradient in the Himalaya

Mixed-species bird flocks are cohesive networks of interacting insectivorous bird species that benefit from reduced predation risk and/or enhanced resource access. We studied how species' propensity to participate in mixed flocks, and the number and strength of interspecific associations within flocks, changed along elevational (low, mid, high) and seasonal (winter, spring) gradients in the western Himalaya. We expected species to have high propensities, and greater number and strength of interspecific associations when resources are scarce, and to decline when resources are abundant. We first used species occurrence within and outside mixed flocks to calculate species-specific flocking propensity and then performed network analyses to quantify the proportion of realized interspecific associations (network density) and their strength (weighted degree), using an abundance-based null model to control flocking species' availability. Further, we quantified arthropod prey availability in win...