Swine serve as a mixing vessel for generating pandemic strains of human influenza virus. All hemagglutinin subtypes of IAVs can infect swine; however, only sporadic cases of infection with avian IAVs are reported in domestic swine. The molecular mechanisms affecting the ability of avian IAVs to infect swine are still not fully understood. From the findings of phenotypic analyses, this study suggests that the tissue tropisms (i.e., in swine upper respiratory tracts) of avian IAVs affect their spillovers from wild birds to pigs. It was found that this phenotype is determined not by receptor binding preference but is determined by other markers across genomic segments, such as those in the ribonucleoprotein complex. In addition, our results show that such a phenotypic trait was sporadically and randomly distributed among IAVs across multiple avian species and geographic and temporal orders. This study suggests an efficient way for assessment of the risk posed by avian IAVs, such as in evaluating their potentials to be transmitted from birds to pigs.