history, and is rendered probable by the remarkable fact that a rise of
only three hundred feet would convert the wide seas that separate them
into an immense winding valley or plain about three hundred miles wide
and twelve hundred long. It may, perhaps, be thought that birds which
possess the power of flight in so pre-eminent a degree, would not be
limited in their range by arms of the sea, and would thus afford few
indications of the former union or separation of the islands they
inhabit. This, however, is not the case. A very large number of birds
appear to be as strictly limited by watery barriers as are quadrupeds;
and as they have been so much more attentively collected, we have more
complete materials to work upon, and are able to deduce from them still
more definite and satisfactory results. Some groups, however, such
as the aquatic birds, the waders, and the birds of prey, are great
wanderers; other groups are little known except to ornithologists.
I shall therefore refer chiefly to a few of the best known and most
remarkable families of birds as a sample of the conclusions furnished by
the entire class.
The birds of the Indo-Malay region have a close resemblance to those
of India; for though a very large proportion of the species are quite
distinct, there are only about fifteen peculiar genera, and not a single
family group confined to the former district. If, however, we compare
the islands with the Burmese, Siamese, and Malayan countries, we shall
find still less difference, and shall be convinced that all are closely
united by the bond of a former union. In such well-known families as
the woodpeckers, parrots, trogons, barbets, kingfishers, pigeons, and
pheasants, we find some identical species spreading over all India, and
as far as Java and Borneo, while a very large proportion are common to
Sumatra and the Malay peninsula.
The force of these facts can only be appreciated when we come to treat
the islands of the Austro-Malay region, and show how similar barriers
have entirely prevented the passage of birds from one island to another,
so that out of at least three hundred and fifty land birds inhabiting
Java and Borneo, not more than ten have passed eastward into Celebes.
Yet the Straits of Macassar are not nearly so wide as the Java sea, and
at least a hundred species are common to Borneo and Java.
I will now give two examples to show how a knowledge of the distribution
of animals may reveal unsuspected facts in the past history of the
122