Logistic regression models of variation in avian influenza virus (AIV) seroprevalence in waterfowl sampled in Alaska, USA, 1998–2010 (n = 3405), examining the effects of age while controlling for sex and species.

ak = number of parameters in model.bThe best approximating model has the lowest Akaike's Information Criterion (AIC) value and the highest model weight (ωi), relative to others in the model set.Ages classes included “sub-adult”, representing hatch year (HY) birds for northern pintails and second year (SY) birds for all other species, and “adults”, representing after hatch year (AHY) birds for northern pintails and/or after second year (ASY) birds for other species. Species include tundra swan (TUSW; Cygnus columbianus), cackling goose (CACG; Branta hutchinsii), greater white-fronted goose (GWFG; Anser albifrons), Pacific black brant (BLBR; B. bernicla nigricans), and northern pintail (NOPI; Anas acuta).