Wild ducks are the reservoir for only a limited number of influenza A subtypes.

Analysis of cloacal samples collected from 12,321 wild ducks in Alberta, Canada, from 1976 to 1990 showed influenza A infections to be seasonal, with prevalences increasing as the population became increasingly more dense. Viruses with 3 haemagglutinin (H3, H4, and H6) and 3 neuraminidase subtypes (N2, N6, and N8) were found consistently to infect both adult and juvenile ducks each year, indicating that wild ducks may be a reservoir for these viruses. In contrast, viruses with 7 haemagglutinin (H2, H5, H7, H8, H9, H11, and H12) and 3 neuraminidase subtypes (N1, N3, and N4) were not found for prolonged periods during the study; when they were found, they primarily infected juveniles at moderate levels. Whilst wild ducks appear to perpetuate some influenza A viruses, they apparently do not act as a reservoir for all such viruses.