The speculum is a patch of colour on the secondary flight feathers of many species of duck. Each type of duck has a specific colour and often this is iridescent. It can be a useful clue to bird identification, particularly when birds are immature or in moult. The photograph shows the speculum of Britain's most common duck, the mallard. It is iridescent purple/blue with black and white edges. This species has interbred with domestic ducks and frequently the speculum of the hybrid is a clue to the parentage of one half of the union.
photo © T. Boughen Camera: Nikon P900
