A comparative study of the hemagglutinin (HA) receptor binding site (RBS) of a number of H13 influenza viruses isolated from Laridae family of birds (gulls) and other influenza viruses obtained from the Anatidae family (ducks) was conducted. The affinity of all viruses to alpha N-acetylneuraminic acid (Neu5Acα), 3′sialyllactose (3′SL), and sialylglycopolymers bearing 3′-sialyl(N-acetyllactosamine) (3′SLN-PAA), [Neu5Acα(2-3)Galβ(1-4)][-Fucα(1-3)]GlcNAcβ (SLex-PAA), and [Neu5Acα(2-3)Galβ(1-3)][-Fucα(1-4)]GlcNAcβ (SLea-PAA), was determined. The last three polymer glycoconjugates were synthesized for determining the contribution of carbohydrate chains after the galactose link to the binding with the receptor. The difference in affinity between 3′SL and Neu5Acα in all studied H13 viruses is small, which indicates a less significant role of the galactose moiety in the binding to the receptor. The results of virus binding with polymer sialylglycoconjugates indicates that the method of linking, the third monosaccharide moiety, and the presence of an extra fucose substitute in this moiety may influence the binding considerably. For viruses isolated from ducks, the suitable polymer is SLea-PAA (i.e., a 1-3 linkage between galactose and glucosamine is optimal). This finding is in accord with the data that H13 viruses isolated from the gulls differ based on their ability to interact with polymer sialylglycoconjugates. The affinity to all three polymers is uniform, and the presence of GlcNAc-linked fucose does not prevent the binding. A comparative analysis of six sequenced HA H13 viruses and other subtype viruses showed presence of substantial differences in the composition of amino acids of this region in H13 viruses.