Mallards occur in various forms and colours. The males are very recognisable with their iridescent bottle green head and neck and the narrow white ring around the base of the neck and their chestnut breast. Distinctive characteristics include orange legs and their tail feathers curl upwards. Non-breeding plumage of males resembles that of the female of being brown with darker spots and stripes. Females have a grey bill and purple speculum and orange legs.
Mallards also occur in white or variants of the green head as a result of inbreeding. To keep pure bred Mallards you need to have a permit, while all hybrids are classed as Category 1a.
The American black duck numbers have drastically declined and the Mexican duck is now extinct because of hybridization with mallard ducks. In Hawaii the Hawaiian duck is under threat from hybridization and the New Zealand grey duck once considered the most widespread and abundant duck in New Zealand, is highly threatened and now only makes up 5% of the total Mallard-hybrid-Grey duck population. If something is not done, the yellow-billed duck will soon face the same fate as these ducks.