Does not go back beyond one of the most recent geological epochs. Of
course there are a large number of species (such as most of the
waders, many of the raptorial birds, some of the kingfishers,
swallows, and a few others), which range so widely over a large part
of the Archipelago that it is impossible to trace them as having come
from any one part rather than from another. There are fifty-seven such
species in my list, and besides these there are thirty-five more
which, though peculiar to the Timor group, are yet allied to wide-
ranging forms. Deducting these ninety-two species, we have nearly a
hundred birds left whose relations with those of other countries we
will now consider.
If we first take those species which, as far as we yet know, are
absolutely confined to each island, we find, in:
Lombock 4 belonging to 2 genera, of which 1 is Australian, 1 Indian.
Flores 12 " 7 " 5 are " 2 "
Timor 42 " 20 " 16 are " 4 "
The actual number of peculiar species in each island I do not suppose
to be at all accurately determined, since the rapidly increasing
numbers evidently depend upon the more extensive collections made in
Timor than in Flores, and in Flores than in Lombock; but what we can
depend more upon, and what is of more special interest, is the
greatly increased proportion of Australian forms and decreased
proportion of Indian forms, as we go from west to east. We shall show
this in a yet more striking manner by counting the number of species
identical with those of Java and Australia respectively in each
island, thus:
In Lombock. In Flores. In Timor.
Javan birds . . . . 33 23 11
Australian birds . . 4 5 10
Here we see plainly the course of the migration which has been going
on for hundreds or thousands of years, and is still going on at the
present day. Birds entering from Java are most numerous in the island
nearest Java; each strait of the sea to be crossed to reach another
island offers an obstacle, and thus a smaller number get over to the
next island. [The names of all the birds inhabiting these islands are
to be found in the "Proceedings of the Zoological Society of London"
for the year 1863.] It will be observed that the number of birds that
appear to have entered from Australia is much less than those which
have come from Java; and we may at first sight suppose that this is
due to the wide sea that separates Australia from Timor. But this
would be a hasty and, as we shall soon see, an unwarranted
supposition. Besides these birds identical with species inhabiting
Java and Australia, there are a considerable number of others very
closely allied to species peculiar to those countries, and we must
take these also into account before we form any conclusion on the
matter. It will be as well to combine these with the former table thus:
In Lombock. In Flores. In Timor.
Javan birds . . . . . . . . . . .33 23 11
Closely allied to Javan birds . . 1 5 6
Total . . . . . . . . . . . . . . 34 28 17
Australian birds . . . . . . . . . 4 5 10
Closely allied to Australian birds 3 9 26
Total . . . . . . . . . . . . . . 7 14 36
We now see that the total number of birds which seem to have been
derived from Java and Australia is very nearly equal, but there is
this remarkable difference between the two series: that whereas the
larger proportion by far of the Java set are identical with those
still inhabiting that country, an almost equally large proportion of
the Australian set are distinct, though often very closely allied
species. It is to be observed also, that these representative or
allied species diminish in number as they recede from Australia, while
they increase in number as they recede from Java. There are two
reasons for this, one being that the islands decrease rapidly in size
from Timor to Lombock, and can therefore support a decreasing number
of species; the other and the more important is, that the distance of
Australia from Timor cuts off the supply of fresh immigrants, and has
thus allowed variation to have full play; while the vicinity of
Lombock to Bali and Java has allowed a continual influx of fresh
individuals which, by crossing with the earlier immigrants, has
checked variation.
To simplify our view of the derivative origin of the birds of these
islands let us treat them as a whole, and thus perhaps render more
intelligible their respective relations to Java and Australia.
The Timor group of islands contains:
Javan birds . . . . . . . 36 Australian birds . . . 13
Closely allied species . . 11 Closely allied species . . 35
Derived from Java . . . . 47 Derived from Australia . . . 48
We have here a wonderful agreement in the number of birds belonging to
Australian and Javanese groups, but they are divided in exactly a
reverse manner, three-fourths of the Javan birds being identical
species and one-fourth representatives, while only one-fourth of the
Australian forms are identical and three-fourths representatives. This
is the most important fact which we can elicit from a study of the
birds of these islands, since it gives us a very complete clue to much
of their past history.
Change of species is a slow process - on that we are all agreed, though
we may differ about how it has taken place. The fact that the
Australian species in these islands have mostly changed, while the
Javan species have almost all remained unchanged, would therefore
indicate that the district was first peopled from Australia. But, for
this to have been the case, the physical conditions must have been
very different from what they are now. Nearly three hundred miles of
open sea now separate Australia from Timor, which island is connected
with Java by a chain of broken land divided by straits which are
nowhere more than about twenty miles wide.
