The Hawaiian Duck or koloa, is generally mottled brown and has a green to blue speculum (the distinctive feathers on the secondary wing feathers) with white borders. Adult males tend to have a darker head and neck feathers (sometimes green). Both sexes have orange legs and feet. Females have a dull orange bill. The male koloa is 19 to 20 inches in length while the female is 16 to 17 inches. Their quack is a little softer than the mallard and koloa are not as vocal.