The geographical distribution of animals, with a study of the relations ...

chap, xiii.] THE AUSTRALIAN REGION. 395peculiar to the Australian region.Another of the universally distributedfamilies which have their metropolis here, is that of theColumbidse or pigeons.Three-fourths of the genera have representativesin the Australian region, while two-fifths of the whole areconfined to it ;other two regions combined.and it possesses as many species of pigeons as anyIt also possesses the most remarkableforms, as exemplified in the great crowned pigeons(Goura)and the hook-billed Didunculus, while the green fruit-pigeons(Ptilopus) are sometimes adorned with colours vying with thoseof the gayest parrots or chatterers.This enormous developmentof a family of birds so defenceless as the pigeons, whose rudenests expose their eggs and helpless young to continual danger,may perhaps be correlated, as I have suggested elsewhere (Ibis,1865, p. 366), with the entire absence of monkeys, cats, lemurs,weasels, civets and other arboreal mammals, which prey on eggsand young birds. The very prevalent green colour of the upperpart of their plumage, may be due tothe need of concealmentfrom their only enemies,—birds of prey ; and this is renderedmore probable by the fact that it is among the pigeons of thesmall islands of the Pacific (where hawks and their allies are exceedinglyscarce) that we alone meet with specieswhose entireplumage is a rich and conspicuous yellow. Where the need ofconcealment is least, the brilliancy of colour has attained itsmaximum. We may therefore look upon the genus Ptilopus,with its fifty species whose typical coloration is green, withpatches of bright blue, red, or yellow on the head and breast,as a special development suited to the tropical portion of theAustralian region, to which it is almost wholly confined.It will be seen from the sketch just given, that the ornithologicalfeatures of the Australian region are almost as remarkableas those presented by its Mammalian fauna ; and from thefuller development attained by the aerial class of birds, muchmore varied and interesting. None of the other regions of theearth can offer us so many families with special points ofinterest in structure, or habits, or general relations. Theparadise-birds, the honeysuckers, the brush-tongued paroquets,the mound-builders, and the cassowaries—all strictly peculiar