http://www.cdc.gov/flu/avian/gen-info/avian-influenza.htm
Centers for Disease Control and Prevention, U.S. Department of Health and Human Services
Influenza viruses that infect birds are called avian influenza viruses. Only influenza A viruses infect birds, and all known subtypes of influenza A viruses can infect birds. This fact sheet discusses the three types prominent subtypes of avian influenza A viruses, including influenza A H5, influenza A H7, and influenza A H9.