Which of these are the smallest members of the parrot order?

Pygmy parrots are the smallest members of the parrot order. The six species of pygmy parrots are all in the genus Micropsitta, which is the only genus in the Micropsittini tribe.

Pygmy parrots are native to the forests of New Guinea and nearby islands. They are tiny birds, fast-moving, and mostly green with bright highlights. A pygmy parrot spends a good deal of time climbing through foliage, using its large feet and beak, and stiffened tail feathers. At a little over 8 cm (3.1 in) long, the buff-faced pygmy parrot is the smallest parrot species.

Pygmy parrots are also among the few species in the order (other examples include Pyrilia and Nannopsittaca species) that have never been successfully kept, let alone bred, in captivity. All attempts to do so have resulted in the quick deaths of the little birds. Stress and dietary deficiencies are probably to blame. Pygmy parrots are among the few birds that feed on fungi and lichens, which play a major role in their diet. Their precise dietary needs are poorly understood.