The study of the extinct organisms of any country leads to a proper
appreciation of its existing flora and fauna; while, on the other hand,
a due consideration of the plants and animals which may predominate
within its bounds cannot fail to throw more or less light on the changes
it has in the course of ages undergone. That is to say, the distribution
of forms in time is a subject so much connected with the distribution of
forms in space, that the one can hardly be separated from the other.
Granting this is a general truth, it must yet be acknowledged as a
special fact, that in fossil birds we have as yet but scanty means of
arriving at any precise results which will justify bold generalization
in the matter of avine distribution. Remains of extinct birds are,
compared with those of other classes of vertebrates, exceedingly scarce,
and these have been found in very few, widely separated countries. The
great problems involved in the study of geographical distribution must
therefore be based mainly upon the other classes, both vertebrate and
invertebrate, which, moreover, enjoy less great facilities of locomotion
than the birds.
Yet it so happens that the great zoogeographical regions of the world,
now more or less generally accepted, have been based upon the
distribution of birds. The whole subject was properly introduced by
Treviranus,[1] who in his large philosophical work devotes considerable
space to the "geographical distribution of animals." Next we have to
mention F. Tiedemann,[2] the Heidelberg anatomist, who has been
generally ignored, although he surpassed many a recent zoogeographer by
the wide view he took of the problem; in fact he was the first to
connect distribution with environmental or bionomic factors; e.g. the
remark on p. 481 of his work that "the countries of the East Indian
flora have no kinds of birds in common with America which are vegetable
feeders." L.K. Schmarda[3] divided the land into twenty-one realms,
characterizing these mainly by their birds. P.L. Sclater[4] was the
first to divide the world into a few great "regions," the Palaearctic,
Ethiopian, Indian and Australian forming one group, the "Old World"
(_Palaeogaea_); and the Nearctic and Neotropical forming a second, the
New World (_Neogaea_). Birds being of all animals most particularly
adapted for extended and rapid locomotion, it became necessary for him
to eliminate from his consideration those groups, be they small or
large, which are of more or less universal occurrence, and to ground his
results on what was at that time commonly known as the order Insessores
or Passeres, comprehending the orders now differentiated as
Passeriformes, Coraciiformes and Cuculiformes, in other words the mass
of arboreal birds. His six main divisions--practically adopted by A.R.
Wallace[5] in his epoch-making work--are excellent, taken separately.
They express the main complexes of land with their dependencies in
well-chosen terms; for instance the "Neotropical region" stands short
for South and Central America with the Antilles.
But these six divisions of Sclater and Wallace are not all equivalent,
only some are of primary importance; they require co- and
sub-ordination. This most important advance was made by T.H. Huxley.[6]
Some of the "regions" have now to be called subregions, e.g. the
Nearctic and the Palaearctic. The reduction of the Oriental to a
subregion, with consequent "provincial" rank of its main subdivisions,
will probably be objected to, but these are matters of taste and
prejudice. Above all it should be borne in mind that nearly all the last
subdivisions or provinces are of very little real value and most of them
are inapplicable to other classes of animals.
Besides some occasional references in the text, only a few more of the
general works dealing with the distribution of birds can here be
mentioned. Especial attention has to be drawn to the article
"Geographical Distribution," in Newton's _Dictionary of Birds_. See
also A. Heilprin, _The Geographical and Zoological Distribution of
Animals_ (New York, 1887); W. Marshall and A. Reichenow, two maps with
much detail, although badly arranged, in Berghaus' _Physikalischer
Atlas_, pt. vi. (_Atlas d. Thierverbreitung_), (Gotha, 1887); A.
Reichenow, "Die Begrenzung zoogeographischer Regionen vom
ornithologischen Standpunkte," _Zoolog. Jahrb._ iii., 1888, pp.
671-704, pl. xxvi.; E.L. Trouessart, _La Geographie zoologique_.
(Paris, 1890).