ANATOMY OF BIRDS
GEOGRAPHICAL DISTRIBUTION
MIGRATIONS OF BIRDS
CLASSIFICATION OF BIRDS
LIZARD-TAILED BIRD
AMERICAN TOOTHED-BIRDS
THE OSTRICHES
THE RHEAS
EMEUS AND CASSOWARIES
THE TINAMOUS
THE KIWIS
THE PENGUINS
LOONS AND GREBES
ALBATROSSES & PETRELS
STORK-LIKE BIRDS
GOOSE-LIKE BIRDS
FALCON-LIKE BIRDS
FOWL-LIKE BIRDS
CRANE-LIKE BIRDS
PLOVER-LIKE BIRDS
CUCKOO-LIKE BIRDS
THE ROLLER-LIKE BIRDS
SPARROW-LIKE BIRDS
Birds and Birding's Guide to:
Watching GEOGRAPHICAL DISTRIBUTION OF BIRDS
Effect of Oceans in Bird Distribution
Oceanic bodies of water have of course a powerful effect on distribution, especially of land birds, but even here certain limitations must be borne in mind. To purely terrestrial animals the presence of even a moderate width of open water may prove an efficient barrier, but to birds, endowed as they are with the power of flight, it is less so than might be supposed.
The Galapagos Islands lying six hundred miles off the coast of Peru have been stocked with an abundant fauna of land birds, evidently of South American and West Indian origin, and the Azores, seven hundred miles distant from South Europe, have a fauna of one hundred and twenty species and subspecies of birds, all Old World forms, the ranks of which are being yearly augmented by fresh arrivals. Within the last fifty years the White-eye {Zosterops ccerulescens), a small passerine bird about the size of our Parula Warbler, has crossed over the twelve hundred miles of open water separating Australia from New Zealand, and has extensively and permanently colonized the latter; the European Widgeon and Ruff have again and again been found in the middle and western United States, and the American Catbird has been taken in Italy. Examples of this erratic wandering, or apparently regular journeying, might be continued almost indefinitely, but enough has been given to show that the sea is not an insuperable barrier in all cases.
It has been found possible to divide the land-masses of the world into a number of faunal (and floral) areas, each of which is more or less strongly characterized by the presence or marked absence of certain dominant or peculiar forms of life.
The failure of early attempts at such delimitation was due, as already pointed out, to the effort to make them conform to the lines of political division, or to degrees of latitude and longitude; and while naturalists are even now not in accord as to the number of primary divisions that should be recognized, Mr. P. L. Sclater was the first to put the subject on a scientific basis by applying to it a logical principle.
The contention that”convenience, intelligibility, and custom should largely guide us”in prescribing life areas has long been discredited, for it is now obvious that the mere size of an area can have no real weight so long as it is sufficiently characterized. It should not be inferred, however, that these life areas, whatever their size and grade, are always sharply circumscribed by hard and fast lines; for while it is possible to define them with considerable definiteness in a general way, it rarely happens that a change from one to another is abrupt.
Perhaps the most notable example of a sharp line of demarcation is that passing between the islands of Bali and Lombok and separating the Australian and Indian Regions. There is usually an area of greater or less width in which there is a commingling of the life forms of adjacent divisions, a neutral ground or transition area, as it is called. On the whole, however, it is found that these lines correspond quite closely to isothermal lines, or the lines of equal temperature.
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