The Australian Subregion comprises Australia and Tasmania. In the north it is influenced, of course, by its proximity to Papuasia, whence there is a considerable admixture of genera which do not proceed beyond the tropics, and of these Casuarius is a striking example. The Cape York peninsula practically belongs to Papuasia. As a whole, Australia is rich in parrots, of which it has several very peculiar forms, but Picarians in old-fashioned parlance, of all sorts—certain kingfishers excepted—are few in number, and the pigeons are also comparatively scarce, no doubt because of the many arboreal predaceous marsupials. The continent, however, possesses the two important genera of the Pseudoscines, namely the lyre-birds (Menura) and the scrub-birds (Atrichia). Among the more curious forms of other land-birds may be especially mentioned the Megapodiidae, Lipoa and Talegallus, the rail Tribonyx and Pedionomus, which represents the otherwise palaeotropical Turnices in Australia. The presence of bustards (Eupodotis) is a curious example of interrupted distribution, since none other of the Otididae are found nearer than India. The Ratitae are represented by two species of emeu (Dromaeus), besides the cassowary of Cape York peninsula, and the extinct Dromornis and Genyornis with its enormous skull.
The Papuan Subregion, chiefly New Guinea with its dependencies, the Timor group of islands, the Moluccas and Celebes. On the whole its avifauna presents some very remarkable features. Its most distinctive characteristic is the presence of the birds of paradise, which are almost peculiar to it; for, granting that the bower-birds, Chlamydodera and others, of Australia, belong to the same family, they are far less highly specialized than the beautiful and extraordinary forms which are found, within very restricted limits, in the various islands of the subregion. Another chief feature is the extraordinary development of the cassowaries, the richness and specialization of the kingfishers, parrots, pigeons, honey-suckers and some remarkable flycatchers. It has several marked deficiencies compared with Australia, among which are the babblers (Timeliidae), weaver birds (Ploceidae), the Platycercinae among parrots, diurnal birds of prey and the emeus. As a whole, the birds of Papua are remarkable for their brilliance of plumage, or their metallic colouring. The birds of paradise, the racquet-tailed kingfishers, Tanysiptera, the largest and smallest of parrots, Calyptdrhynchiis and Nasiterna, and the great crowned pigeons, Goura, are very characteristic; and so are the various Megapodes.
(B) Neogaea, or the Neotropical region.—Excepting towards the north, where, in Mexico, it meets, and inosculates with the Nearctic subregion, the boundaries of the Neotropical region are simple enough to trace, comprehending as it does the whole of South America and all Central America; besides including the Falkland islands to the south-east and the Galapagos under the equator to the west, as well as the Antilles or West India islands up to the Florida channel.
Owing to the comparatively scanty number of harmful mammalian types, the birds play a considerable part in this large region, and some authorities consider its avifauna the richest in the world. The entire number of species amounts to about 3600. Of these 2000, or a good deal more than half, belong to the order Passeriformes. But the characteristic nature of the avifauna is more clearly brought out when we learn that of the 2000 species just mentioned only about 1070 belong to the higher suborder of Oscines, that means to say, nearly one-half belong to the lower suborder Clamatores. This is a state of things which exists nowhere else; for except in Australia, where a few indigenous and peculiar low non-Oscines are found, and in the Nearctic country, whither one family of Clamatores, viz. the Tyrannidae, has evidently been led by the geographical continuity of its soil with that of the Neotropical region, such forms do not occur elsewhere. Accordingly their disproportionate prevalence in South America points unerringly to the lower rank of the avifauna of the region as a whole, and therefore to the propriety of putting it next in order to that of the Australian region, the general fauna of which is admittedly the lowest in the world. Huxley has urged with his wonted perspicuity the alliance of these two regions as Notogaea, basing his opinion, besides other weighty evidence, in great measure on the evidence afforded by the two main sections of the Galli, viz. the Peristeropodes and the Alectoropodes, the former composed of the families Megapodiidae, almost wholly Australian, and the Cracidae, entirely Neotropical. (Cf. P.Z.S., 1868. pp. 294-319.)
Leaving, however, this matter as in some degree hypothetical, we have as genera, families, or perhaps even larger groups, a great many very remarkable forms which are characteristic of, or peculiar to, the Neotropical region in part, if not as a whole. Of families we find twenty-three, or maybe more, absolutely restricted thereto, besides at least eight which, being peculiar to the New World, extend their range into the Nearctic region, but are there so feebly developed that their origin may be safely ascribed to the southern portion of America. First in point of importance comes the extraordinarily beautiful family of humming-birds (Trochilidae), with nearly 150 genera (of which only three occur in the Nearctic region) and more than 400 species. Then the tyrants (Tyrannidae), with more than seventy genera (ten of which range into the northern region), and over 300 species. To these follow the tanagers (Tanagndae), with upwards of forty genera (only one of which crosses the border), and about 300 species; the piculules (Dendrocolaptidae), with as many genera, and over 200 species; the ant-thrushes, (Formicariidae), with more than thirty genera, and nearly 200 species; together with other groups which, if not so large as those just named, are yet just as well defined, and possibly more significant, namely, the tapaculos (Pteroptochidae), the toucans (Rhamphastidae), the jacamars (Galbulidae), the motmots (Monotidae), the todies (Todidae), the trumpeters (Psophiidae), and the screamers (Palamedeidae); besides such isolated forms as the seriema (Cariama), and the sun-bittern (Eurypyga).
The nature of the South American avifauna will perhaps become still more evident if we arrange the characteristic members as follows:—
1. Birds which are restricted to, probably indigenous of the region: Rhea; Palamedea and Chauna, the screamers; Tinami; Psophia, Dicholophus, Eurypyga, Heliornis of the Gruiform assembly; Thinocorys and Attagis; Cracidae; Opisthocomus; of parrots Ara and Conurus with their allies; Monotidae, incl. Todus; Steatornis; Galbulinae and Bucconinae; Rhamphastidae; Formicariidae, Pteroptochidae, and of the Tyrannidae the Cotinginae.
2. Birds which are indigenous, but extend far into North America: Cathartae, Trochilidae, Tyrannidae.
3. Birds which are originally immigrants from North America: Podicipedidae, with the flightless Centropelma on Lake Titicaca; Ceryle, the only genus of kingfishers in the New World; all the Oscines.
More or less cosmopolitan groups like herons, Falconidae, Anseres, Columbae, &c., and circumtropical families like Parridae, Trogonidae, Capitonidae, are to be excluded from these lists as indifferent. The differences between the Neotropical avifauna and that of North America are fundamental and prove the independence or superior value of the Neotropical region as one of the principal realms.