The island of Juan Fernandez has two species, and Masafuera, an island beyond it, one; the three forming a peculiar genus. The island of Tres Marias, about 60 miles from the west coast of Mexico, possesses a peculiar species of humming-bird, and the Bahamas two species; but none inhabit either the Falkland Islands or the Galapagos.
Like most groups which are very rich in species and in generic forms, the humming-birds are generally very local, small generic groups being confined to limited districts; while single mountains, valleys, or small islands, often possess species found nowhere else. It is now well ascertained that the Trochilidæ are really insectivorous birds, although they also feed largely, but probably never exclusively, on the nectar of flowers. Their nearest allies are undoubtedly the Swifts; but the wide gap that now separates them from these, as well as the wonderful variety of form and of development of plumage, that is found among them, alike point to their origin, at a very remote period, in the forests of the once insular Andes. There is perhaps no more striking contrast of the like nature, to be found, than that between the American kingfishers—confined to a few closely allied forms of one Old World genus—and the American humming-birds with more than a hundred diversified generic forms unlike everything else upon the globe; and we can hardly imagine any other cause for this difference, than a (comparatively) very recent introduction in the one case, and a very high antiquity in the other.
General Remarks on the Distribution of the Picariæ.
The very heterogeneous mass of birds forming the Order Picariæ, contains 25 families, 307 genera and 1,604 species. This gives about 64 species to each family, while in the Passeres the proportion is nearly double, or 111 species per family. There are, in fact, only two very large families in the Order, which happen to be the first and last in the series—Picidæ and Trochilidæ. Two others—Cuculidæ and Alcedinidæ—are rather large; while the rest are all small, seven of them consisting only of a single genus and from one to a dozen species. Only one of the families—Alcedinidæ—is absolutely cosmopolitan, but three others are nearly so, Caprimulgidæ and Cypselidæ being only absent from New Zealand, and Cuculidæ from the Canadian sub-region of North America. Eleven families inhabit the Old World only, while seven are confined to the New World, only one of these—Trochilidæ—being common to the Neotropical and Nearctic regions.
The Picariæ are highly characteristic of tropical faunas, for while no less than 15 out of the 25 families are exclusively tropical, none are confined to, or have their chief development in, the temperate regions. They are best represented in the Ethiopian region, which possesses 17 families, 4 of which are peculiar to it; while the Oriental region has only 14 families, none of which are peculiar. The Neotropical region has also 14 families, but 6 of them are peculiar. The Australian region has 8, the Palæarctic 9 and the Nearctic 6 families, but none of these are peculiar. We may see a reason for the great specialization of this tropical assemblage of birds in the Ethiopian and Neotropical regions, in the fact of the large extent of land on both sides of the Equator which these two regions alone possess, and their extreme isolation either by sea or deserts from other regions,—an isolation which we know was in both cases much greater in early Tertiary times. It is, perhaps, for a similar reason that we here find hardly any trace of the connection between Australia and South America which other groups exhibit; for that connection has most probably been effected by a former communication between the temperate southern extremities of those two continents. The most interesting and suggestive fact, is that presented by the distribution of the Megalæmidæ and Trogonidæ over the tropics of America, Africa, and Asia. In the absence of palæontological evidence as to the former history of the Megalæmidæ, we are unable to say positively, whether it owes its present distribution to a former closer union between these continents in intertropical latitudes, or to a much greater northern range of the group at the period when a luxuriant sub-tropical vegetation extended far toward the Arctic regions; but the discovery of Trogon in the Miocene deposits of the South of France renders it almost certain that the latter is the true explanation in the case of both these families.
The Neotropical region, owing to its enormous family of humming-birds, is by far the richest in Picariæ, possessing nearly half the total number of species, and a still larger proportion of genera. Three families, the Bucerotidæ, Meropidæ and Coraciidæ are equally characteristic of the Oriental and Ethiopian regions, a few outlying species only entering the Australian or the Palæarctic regions. One family (Todidæ) is confined to the West Indian Islands; and another (Leptosomidæ) consisting of but a single species, to Madagascar; parallel cases to the Drepanididæ among the Passeres, peculiar to the Sandwich Islands, and the Apterygidæ among the Struthiones, peculiar to New Zealand.
Order III.—PSITTACI.
The Parrots have been the subject of much difference of opinion among ornithologists, and no satisfactory arrangement of the order into families and genera has yet been reached. Professor Garrod has lately examined certain points in the anatomy of a large number of genera, and proposes to revolutionize the ordinary classifications. Until, however, a general examination of their whole anatomy, internal and external, has been made by some competent authority, it will be unsafe to adopt the new system, as we have as yet no guide to the comparative value of the characters made use of. I therefore keep as much as possible to the old groups, founded on external characters, only using the indications furnished by Professor Garrod's paper, to determine the position of doubtful genera.
Family 76.—CACATUIDÆ. (5 Genera, 35 Species.)
| General Distribution. | |||||
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| Neotropical Sub-regions. | Nearctic Sub-regions. | Palæarctic Sub-regions. | Ethiopian Sub-regions. | Oriental Sub-regions. | Australian Sub-regions. |
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