Covariates in candidate models included: 1) Species, 2) AI Virus Prevalence (proportion of individuals testing positive for AI viruses via RT-PCR testing in spring), 3) Social Index (colonial or dispersed nesting), 4) Continental Affinity (solely North America or including Asia), 5) Wintering Habitat (marine or agriculture), and 6) Staging and Wintering Distribution (isolated or co-occurring).