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 earth. At the
eastern extremity of Sumatra, and separated from it by a strait about fifteen miles
wide, is the small rocky island of Banca, celebrated for its tin mines. One of the
Dutch residents there sent some collections of birds and animals to Leyden, and
among them were found several species distinct from those of the adjacent coast
of Sumatra. One of these was a squirrel (Sciurus bangkanus), closely allied to
three other species inhabiting respectively the Malay peninsula, Sumatra, and
Borneo, but quite as distinct from them all as they are from each other. There
were also two new ground thrushes of the genus Pitta, closely allied to, but quite
distinct from, two other species inhabiting both Sumatra and Borneo, and which
did not perceptibly differ in these large and widely separated islands. This is just