Due to the fixed pattern of glycosite, many programs and software provide the prediction of glycosites [43] , such as the ''NetNGlyc 1.0 Server'' (www.cbs.dtu.dk/services/NetNGlyc). By submitting the alignment files to a prediction server, we obtained a series scores for the potential glycosites. In consideration of experimental error, those occasional glycosites, which may result from the genomic sequencing or translated by different genetic codes, were excluded. For example, the 429NLS in the HA of A/ duck/Hunan/3315/2006(H5N1) only appears in H5 set once, and it is also embedded inside of HA trimer [44] . Statistics of the position, pattern and the levels of conservation in various subtypes were used for further discussion (Table S1 , File S2).