Parrot - Morphology

Morphology

Extant species range in size from the Buff-faced Pygmy Parrot, at under 10 g (0.4 oz) in weight and 8 cm (3.1 in) in length, to the Hyacinth Macaw, at 1 m (3.3 ft) in length, and the Kakapo, at 4.0 kg (8.8 lb) in weight. Among the superfamilies, the three extant Strigopoidea species are all large parrots, and the cockatoos tend to be large birds as well. The Psittacoidea parrots are far more variable, ranging the full spectrum of sizes shown by the family.

The most obvious physical characteristic is the strong, curved, broad bill. The upper mandible is prominent, curves downward, and comes to a point. It is not fused to the skull, which allows it to move independently, and contributes to the tremendous biting pressure the birds are able to exert. The lower mandible is shorter, with a sharp, upward-facing cutting edge, which moves against the flat portion of the upper mandible in an anvil-like fashion. There are touch receptors along the inner edges of the kerantinised bill, which are collectively known as the 'bill tip organ', allowing for highly dextrous manipulations. Seed-eating parrots have a strong tongue (containing similar touch receptors to those in the bill tip organ), which helps to manipulate seeds or position nuts in the bill so that the mandibles can apply an appropriate cracking force. The head is large, with eyes positioned high and laterally in the skull, so the visual field of parrots are unlike any other birds. Without turning its head, a parrot can see from just below its bill tip, all above its head, and to quite far behind its head. Parrots also have quite a wide frontal binocular field for a bird, although this is nowhere near as large as primate binocular visual fields.

Parrots have strong zygodactyl feet with sharp, elongated claws, which are used for climbing and swinging. Most species are capable of using their feet to manipulate food and other objects with a high degree of dexterity, in a similar manner to a human using his hands. A study conducted with Australian parrots has demonstrated that they exhibit "handedness"—that is a distinct preference with regards to the foot used to pick up food, with adult parrots being almost exclusively "left-footed" or "right footed", and with the prevalence of each preference within the population varying from species to species.

Cockatoo species have a mobile crest of feathers on the top of their heads which can be raised for display, and retracted. No other parrots can do so, but the Pacific lorikeets in the genera Vini and Phigys are able to ruffle the feathers of the crown and nape and the Red-fan Parrot (or Hawk-headed Parrot) has a prominent feather neck frill which can be raised and lowered at will. The predominant colour of plumage in parrots is green, though most species have some red or another colour in small quantities. Cockatoos are the main exception to this, having lost the green and blue plumage colours in their evolutionary history they are now predominately black or white with some red, pink or yellow. Strong sexual dimorphism in plumage is not typical among parrots, with some notable exceptions, the most striking being the Eclectus Parrot.