Phylum Chordata Bateson, 1885 - chordates
   Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
     Subclass Neornithes Gadow, 1893 see Clade Neornithes Gadow, 1893
       Superorder Neognathae Pycraft, 1900 see Cohort Neognathae Pycraft, 1900
         Order Anseriformes Wagler, 1831 - waterfowl and screamers
           Family Anatidae Vigors, 1825 - ducks, geese, swans
             Subfamily Anatinae Vigors, 1825 - pond ducks
               Genus Aythya Boie, 1822 - hardhead
                 01 Aythya valisineria (Wilson, 1814) - canvasback
                 02 Aythya ferina (Linnaeus, 1758) - common pochard
                 03 Aythya americana (Eyton, 1838) - redhead
                 04 Aythya collaris (Donovan, 1809) - ring-necked duck
                 05 Aythya australis (Eyton, 1838) - hardhead
                 06 Aythya baeri (Radde, 1863) - Baer's pochard
                 07 Aythya nyroca (Güldenstädt, 1770) - ferruginous duck
                 08 Aythya innotata (Salvadori, 1894) - Madagascan pochard
                 09 Aythya novaeseelandiae (Gmelin, 1789) - New Zealand scaup
                 10 Aythya fuligula (Linnaeus, 1758) - tufted duck
                 11 Aythya marila (Linnaeus, 1761) - greater scaup
                 12 Aythya affinis (Eyton, 1838) - lesser scaup