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THIRD REVISED EDITION
Pages 19 - 20
There are approximately eight thousand seven hundred species of birds living today, though Austin (1961) has pointed out that there is evidence to suggest that the Pleistocene bird fauna of the world may have numbered about eleven thousand five hundred species, so birds as a class possibly reached a peak some quarter to half a million years ago and have declined gradually ever since.
Bird species constitute the class Aves among vertebrates and are grouped into categories according to their similarities and differences. Thus the class Aves contains several major orders, each comprising related families, genera and species. It is the order Psittaciformes – the parrots – that we shall be looking at in this book. Probably the most conspicuous feature making any parrot easily recognisable to even the casual viewer or zoo visitor is the short, blunt, rounded bill with the curved upper mandible fitting neatly over the lower. The foot is zygodactyl, that is, two toes point forward and two are turned backwards. There are other less obvious characteristics – the head is large and broad, the neck is short, the tongue is thick and prehensile, the nostrils are set in a bare or feathered, fleshy cere at the base of the upper mandible, and there are powder downs scattered throughout the plumage.
It will be evident from even a cursory glance at the illustrations in this
book that parrots come in ‘all shapes and sizes’. However, despite
this superficial variation they are a really homogenous group and, as we
shall see later, this presents problems to systematists. They vary in size
from the pygmy parrots of New Guinea, which are less than 9 cm in length,
to the giant macaws of South America; the Hyacinth Macaw Andorhynchus hyacinthinus,
with a total length of approximately 100 cm, is the largest of all parrots.
Plumage colouration is also variable; most parrots are brilliantly coloured
with green, red, and yellow predominating, but there are dull coloured species
like the Vasa Parrot Coracopsis vasa from Madagascar. Tails may be long
and pointed, as in the Long-tailed Parakeet Psittacula longicauda and the
Princess Parrot Polytelis alexandrae; short and squarish, as in the Short-tailed
Parrot Graydidascalus brachyurus and some parrotlets (Touit spp.), or there
may be ornate feathers, as in the Papuan Lory Charmosyna papou and the racket-tailed
parrots (Prioniturus spp.). Wings can be narrow and pointed, as in the Swift
Parrot Lathamus discolour and the Cockatiel Nymphicus hollandicus, or broad
and rounded as in the amazons (Amazona spp.). Some parrots have head crests,
while others have elongated feathers on their hindnecks.
Forshaw, Joseph M. (1989)
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