In addition to the SA2,6-linkage glycan, SA2,3-linked oligosaccharides with Galb1-3GalNAc subterminal residues, which show a MAL-II preference, may be present in the goblet cells (Table 1) [4, 5, 6, 23] . Notably, although AIVs can bind to the terminal SAa2-3Gal, duck and chicken influenza viruses exhibit different affinities for glycans with different subterminal residues [7, 8] . For example, duck influenza viruses prefer Galb1-3GlcNAc or Galb1-3GalNAc, but chicken influenza viruses prefer Galb1-4GlcNAc or Galb1-4(6OSO3)GlcNAc [7, 8] . Our study suggests that SAa2,3-capped oligosaccharides following a Galb1,3-linkage [6] are candidate sugars conjugated to the chicken tracheal mucin protein. Determining the SA composites of chicken mucin protein and the neutralizing effect of chicken mucin on duck influenza viruses will be an interesting task that will provide important information about the innate defense mechanisms in the chicken trachea and about the interspecies transmission of influenza viruses between ducks and chickens.