Smallest cockatoo

The smallest species of cockatoo (and hence the smallest member of the entire taxonomic superfamily Cacatuidea) is the cockatiel (Nymphicus hollandicus). Native to Australia, but an extremely common and popular pet species worldwide, it measures 30–33 centimetres (11.8–12.9 inches) long, with its long tail feathers accounting for roughly half of its total length, in contrast to other cockatoo species whose tail feathers are proportionately much shorter.

There has been much controversy in the past as to the cockatiel's precise taxonomic position within the parrot order, with some ornithologists classing it as a cockatoo-like parakeet rather than as a true cockatoo. However, a series of quite recent molecular and biochemical studies have independently corroborated one another in confirming that genetically it really is a true cockatoo after all, with its superficially parakeet-like appearance probably being due to its decrease in size during its evolution and occupation of its specific ecological niche. Also, again like all true cockatoos, it possesses facial feathers covering its beak's lateral edges, an erectile crest, and powder-down, its feathers lack Dyck texture (thereby precluding the display of blue and green structural colours), and it possesses a gall bladder.