IF we look at a map of the Archipelago, nothing seems more unlikely than
that the closely connected chain of islands from Java to Timor should
differ materially in their natural productions. There are, it is true,
certain differences of climate and of physical geography, but these
do not correspond with the division the naturalist is obliged to make.
Between the two ends of the chain there is a great contrast of climate,
the west being exceedingly moist and leaving only a short and irregular
dry season, the east being as dry and parched up, and having but a short
wet season. This change, however, occurs about the middle of Java, the
eastern portion of that island having as strongly marked seasons as
Lombock and Timor. There is also a difference in physical geography; but
this occurs at the eastern termination of the chain where the volcanoes
which are the marked feature of Java, Bali, Lombock, Sumbawa, and
Flores, turn northwards through Gunong Api to Banda, leaving Timor with
only one volcanic peak near its centre, while the main portion of the
island consists of old sedimentary rocks. Neither of these physical
differences corresponds with the remarkable change in natural
productions which occurs at the Straits of Lombock, separating the
island of that name from Bali, and which is at once so large in amount
and of so fundamental a character, as to form an important feature in
the zoological geography of our globe.
The Dutch naturalist Zollinger, who resided a long time on the island of
Bali, informs us that its productions completely assimilate with those
of Java, and that he is not aware of a single animal found in it which
does not inhabit the larger island. During the few days which I stayed
on the north coast of Bali on my way to Lombock, I saw several birds
highly characteristic of Javan ornithology. Among these were the
yellow-headed weaver (Ploceus hypoxantha), the black grasshopper thrush
(Copsychus amoenus), the rosy barbet (Megalaema rosea), the Malay oriole
(Oriolus horsfieldi), the Java ground starling (Sturnopastor jalla), and
the Javanese three-toed woodpecker (Chrysonotus tiga). On crossing over
to Lombock, separated from Bali by a strait less than twenty miles wide,
I naturally expected to meet with some of these birds again; but during
a stay there of three months I never saw one of them, but found a
totally different set of species, most of which were utterly unknown
not only in Java, but also in Borneo, Sumatra, and Malacca. For example,
among the commonest birds in Lombock were white cockatoos and three
species of Meliphagidae or honeysuckers, belonging to family groups
which are entirely absent from the western or Indo-Malayan region of the
Archipelago. On passing to Flores and Timor the distinctness from the
Javanese productions increases, and we find that these islands form a
natural group, whose birds are related to those of Java and Australia,
but are quite distinct from either. Besides my own collections in
Lombock and Timor, my assistant Mr. Allen made a good collection in
Flores; and these, with a few species obtained by the Dutch naturalists,
enable us to form a very good idea of the natural history of this group
of islands, and to derive therefrom some very interesting results.
The number of birds known from these islands up to this date is: 63 from
Lombock, 86 from Flores, and 118 from Timor; and from the whole group,
188 species. With the exception of two or three species which appear
to have been derived from the Moluccas, all these birds can be traced,
either directly or by close allies, to Java on the one side or to
Australia on the other; although no less than 82 of them are found
nowhere out of this small group of islands. There is not, however,
a single genus peculiar to the group, or even one which is largely
represented in it by peculiar species; and this is a fact which
indicates that the fauna is strictly derivative, and that its origin
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. Evidently there are now great facilities for the natural
productions of Java to spread over and occupy the whole of these
islands, while those of Australia would find very great difficulty in
getting across. To account for the present state of things, we should
naturally suppose that Australia was once much more closely connected
with Timor than it is at present; and that this was the case is rendered
highly probable by the fact of a submarine bank extending along all the
north and west coast of Australia, and at one place approaching within
twenty miles of the coast of Timor. This indicates a recent subsidence
of North Australia, which probably once extended as far as the edge
of this bank, between which and Timor there is an unfathomed depth of
ocean.
I do not think that Timor was ever actually connected with Australia,
because such a large number of very abundant and characteristic groups
of Australian birds are quite absent, and not a single Australian mammal
has entered Timor--which would certainly not have been the case had
the lands been actually united. Such groups as the bower birds
(Ptilonorhynchus), the black and red cockatoos (Calyptorhynchus),
the blue wrens (Malurus), the crowshrikes (Cracticus), the Australian
shrikes (Falcunculus and Colluricincla), and many others, which abound
all over Australia, would certainly have spread into Timor if it
had been united to that country, or even if for any long time it had
approached nearer to it than twenty miles. Neither do any of the most
characteristic groups of Australian insects occur in Timor; so that
everything combines to indicate that a strait of the sea has always
separated it from Australia, but that at one period this strait was
reduced to a width of about twenty miles.
But at the time when this narrowing of the sea took place in one
direction, there must have been a greater separation at the other end of
the chain, or we should find more equality in the numbers of identical
and representative species derived from each extremity. It is true that
the widening of the strait at the Australian end by subsidence, would,
by putting a stop to immigration and intercrossing of individuals from
the mother country, have allowed full scope to the causes which have
led to the modification of the species; while the continued stream of
immigrants from Java, would, by continual intercrossing, check such
modification. This view will not, however, explain all the facts; for
the character of the fauna of the Timorese group is indicated as well by
the forms which are absent from it as by those which it contains, and is
by this kind of evidence shown to be much more Australian than Indian.
No less than twenty-nine genera, all more or less abundant in Java, and
most of which range over a wide area, are altogether absent; while of
the equally diffused Australian genera only about fourteen are wanting.
This would clearly indicate that there has been, until recently, a wide
separation from Java; and the fact that the islands of Bali and Lombock
are small, and are almost wholly volcanic, and contain a smaller number
of modified forms than the other islands, would point them out as of
comparatively recent origin. A wide arm of the sea probably occupied
their place at the time when Timor was in the closest proximity to
Australia; and as the subterranean fires were slowly piling up the now
fertile islands of Bali and Lombock, the northern shores of Australia
would be sinking beneath the ocean. Some such changes as have been here
indicated, enable us to understand how it happens, that though the birds
of this group are on the whole almost as much Indian as Australian, yet
the species which are peculiar to the group are mostly Australian in
character; and also why such a large number of common Indian forms
which extend through Java to Bali, should not have transmitted a single
representative to the island further east.
The Mammalia of Timor as well as those of the other islands of the
group are exceedingly scanty, with the exception of bats. These last are
tolerably abundant, and no doubt many more remain to be discovered. Out
of fifteen species known from Timor, nine are found also in Java, or the
islands west of it; three are Moluccan species, most of which are also
found in Australia, and the rest are peculiar to Timor.
The land mammals are only seven in number, as follows: 1. The common
monkey, Macacus cynomolgus, which is found in all the Indo-Malayan
islands, and has spread from Java through Bali and Lombock to Timor.
This species is very frequent on the banks of rivers, and may have
been conveyed from island to island on trees carried down by floods. 2.
Paradoxurus fasciatus; a civet cat, very common over a large part of
the Archipelago. 3. Felis megalotis; a tiger cat, said to be peculiar
to Timor, where it exists only in the interior, and is very rare. Its
nearest allies are in Java. 4. Cervus timoriensis; a deer, closely
allied to the Javan and Moluccan species, if distinct. 5. A wild pig,
Sus timoriensis; perhaps the same as some of the Moluccan species. 6.
A shrew mouse, Sorex tenuis; supposed to be peculiar to Timor. 7. An
Eastern opossum, Cuscus orientalis; found also in the Moluccas, if not a
distinct species.
The fact that not one of these species is Australian or nearly allied to
any Australian form, is strongly corroborative of the opinion that Timor
has never formed a part of that country; as in that case some kangaroo
or other marsupial animal would almost certainly be found there. It is
no doubt very difficult to account for the presence of some of the few
mammals that do exist in Timor, especially the tiger cat and the deer.
We must consider, however, that during thousands, and perhaps hundreds
of thousands of years, these islands and the seas between them have
been subjected to volcanic action. The land has been raised and has sunk
again; the straits have been narrowed or widened; many of the islands
may have been joined and dissevered again; violent floods have again and
again devastated the mountains and plains, carrying out to sea hundreds
of forest trees, as has often happened during volcanic eruptions in
Java; and it does not seem improbable that once in a thousand, or ten
thousand years, there should have occurred such a favourable combination
of circumstances as would lead to the migration of two or three land
animals from one island to another. This is all that we need ask to
account for the very scanty and fragmentary group of Mammalia which now
inhabit the large island of Timor. The deer may very probably have been
introduced by man, for the Malays often keep tame fawns; and it may
not require a thousand, or even five hundred years, to establish new
characters in an animal removed to a country so different in climate and
vegetation as is Timor from the Moluccas. I have not mentioned horses,
which are often thought to be wild in Timor, because there are no
grounds whatever for such a belief. The Timor ponies have every one an
owner, and are quite as much domesticated animals as the cattle on a
South American hacienda.
I have dwelt at some length upon the origin of the Timorese fauna
because it appears to be a most interesting and instructive problem. It
is very seldom that we can trace the animals of a district so clearly as
we can in this case to two definite sources, and still more rarely that
they furnish such decisive evidence of the time, the manner, and the
proportions of their introduction. We have here a group of Oceanic
Islands in miniature--islands which have never formed part of the
adjacent lands, although so closely approaching them; and their
productions have the characteristics of true Oceanic Islands slightly
modified. These characteristics are: the absence all Mammalia except
bats; and the occurrence of peculiar species of birds, insects, and land
shells, which, though found nowhere else, are plainly related to those
of the nearest land. Thus, we have an entire absence of all Australian
mammals, and the presence of only a few stragglers from the west which
can be accounted for in the manner already indicated. Bats are tolerably
abundant.
Birds have many peculiar species, with a decided relationship to those
of the two nearest masses of land. The insects have similar relations
with the birds. As an example, four species of the Papilionidae are
peculiar to Timor, three others are also found in Java, and one in
Australia. Of the four peculiar species two are decided modifications
of Javanese forms, while the others seem allied to those of the Moluccas
and Celebes. The very few land shells known are all, curiously enough,
allied to or identical with Moluccan or Celebes forms. The Pieridae
(white and yellow butterflies) which wander more, and from frequenting
open grounds, are more liable to be blown out to sea, seem about equally
related to those of Java, Australia, and the Moluccas.
It has been objected to in Mr. Darwin's theory, of Oceanic Islands
having never been connected with the mainland, that this would imply
that their animal population was a matter of chance; it has been termed
the "flotsam and jetsam theory," and it has been maintained that nature
does not work by the "CHAPTER of accidents." But in the case which I
have here described, we have the most positive evidence that such has
been the mode of peopling the islands. Their productions are of that
miscellaneous character which we should expect from such an origin; and
to suppose that they have been portions of Australia or of Java will
introduce perfectly gratuitous difficulties, and render it quite
impossible to explain those curious relations which the best known group
of animals (the birds) have been shown to exhibit. On the other hand,
the depth of the surrounding seas, the form of the submerged banks,
and the volcanic character of most of the islands, all point to an
independent origin.
Before concluding, I must make one remark to avoid misapprehension. When
I say that Timor has never formed part of Australia, I refer only to
recent geological epochs. In Secondary or even Eocene or Miocene times,
Timor and Australia may have been connected; but if so, all record of
such a union has been lost by subsequent submergence, and in accounting
for the present land-inhabitants of any country we have only to consider
those changes which have occurred since its last elevation above the
waters. Since such last elevation, I feel confident that Timor has not
formed part of Australia.