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analogous to, but distinct from, American species. Fourthly a
swallow, which though differing from the Progne purpurea of both
Americas, only in being rather duller coloured, smaller, and
slenderer, is considered by Mr. Gould as specifically distinct.
Fifthly there are three species of mocking-thrush - a form highly
characteristic of America. The remaining land-birds form a most
singular group of finches, related to each other in the structure
of their beaks, short tails, form of body and plumage: there are
thirteen species which Mr. Gould has divided into four sub-groups.
All these species are peculiar to this archipelago; and so is the
whole group, with the exception of one species of the sub-group
Cactornis, lately brought from Bow Island, in the Low Archipelago.
Of Cactornis the two species may be often seen climbing about the
flowers of the great cactus-trees; but all the other species of
this group of finches, mingled together in flocks, feed on the dry
and sterile ground of the lower districts. The males of all, or
certainly of the greater number, are jet black; and the females
(with perhaps one or two exceptions) are brown.

(PLATE 81. FINCHES FROM GALAPAGOS ARCHIPELAGO. 1. Geospiza
magnirostris. 2. Geospiza fortis. 3. Geospiza parvula. 4. Certhidea
olivasea.)

The most curious fact is the perfect gradation in the size of the
beaks in the different species of Geospiza, from one as large as
that of a hawfinch to that of a chaffinch, and (if Mr. Gould is
right in including his sub-group, Certhidea, in the main group)
even to that of a warbler. The largest beak in the genus Geospiza
is shown in (Plate 81) Figure 1, and the smallest in Figure 3; but
instead of there being only one intermediate species, with a beak
of the size shown in Figure 2, there are no less than six species
with insensibly graduated beaks. The beak of the sub-group
Certhidea, is shown in Figure 4. The beak of Cactornis is somewhat
like that of a starling, and that of the fourth sub-group,
Camarhynchus, is slightly parrot-shaped. Seeing this gradation and
diversity of structure in one small, intimately related group of
birds, one might really fancy that from an original paucity of
birds in this archipelago, one species had been taken and modified
for different ends. In a like manner it might be fancied that a
bird, originally a buzzard, had been induced here to undertake the
office of the carrion-feeding Polybori of the American continent.

Of waders and water-birds I was able to get only eleven kinds, and
of these only three (including a rail confined to the damp summits
of the islands) are new species. Considering the wandering habits
of the gulls, I was surprised to find that the species inhabiting
these islands is peculiar, but allied to one from the southern
parts of South America. The far greater peculiarity of the
land-birds, namely, twenty-five out of twenty-six being new
species, or at least new races, compared with the waders and
web-footed birds, is in accordance with the greater range which
these latter orders have in all parts of the world. We shall
hereafter see this law of aquatic forms, whether marine or fresh
water, being less peculiar at any given point of the earth's
surface than the terrestrial forms of the same classes, strikingly
illustrated in the shells, and in a lesser degree in the insects of
this archipelago.

Two of the waders are rather smaller than the same species brought
from other places: the swallow is also smaller, though it is
doubtful whether or not it is distinct from its analogue. The two
owls, the two tyrant-flycatchers (Pyrocephalus) and the dove, are
also smaller than the analogous but distinct species, to which they
are most nearly related; on the other hand, the gull is rather
larger. The two owls, the swallow, all three species of
mocking-thrush, the dove in its separate colours though not in its
whole plumage, the Totanus, and the gull, are likewise duskier
coloured than their analogous species; and in the case of the
mocking-thrush and Totanus, than any other species of the two
genera. With the exception of a wren with a fine yellow breast, and
of a tyrant-flycatcher with a scarlet tuft and breast, none of the
birds are brilliantly coloured, as might have been expected in an
equatorial district. Hence it would appear probable that the same
causes which here make the immigrants of some species smaller, make
most of the peculiar Galapageian species also smaller, as well as
very generally more dusky coloured. All the plants have a wretched,
weedy appearance, and I did not see one beautiful flower. The
insects, again, are small-sized and dull coloured, and, as Mr.
Waterhouse informs me, there is nothing in their general appearance
which would have led him to imagine that they had come from under
the equator. (17/1. The progress of research has shown that some of
these birds, which were then thought to be confined to the islands,
occur on the American continent. The eminent ornithologist, Mr.
Sclater, informs me that this is the case with the Strix
punctatissima and Pyrocephalus nanus; and probably with the Otus
galapagoensis and Zenaida galapagoensis: so that the number of
endemic birds is reduced to twenty-three, or probably to
twenty-one. Mr. Sclater thinks that one or two of these endemic
forms should be ranked rather as varieties than species, which
always seemed to me probable.) The birds, plants, and insects have
a desert character, and are not more brilliantly coloured than
those from southern Patagonia; we may, therefore, conclude that the
usual gaudy colouring of the intertropical productions is not
related either to the heat or light of those zones, but to some
other cause, perhaps to the conditions of existence being generally
favourable to life.

We will now turn to the order of reptiles, which gives the most
striking character to the zoology of these islands. The species are
not numerous, but the numbers of individuals of each species are
extraordinarily great. There is one small lizard belonging to a
South American genus, and two species (and probably more) of the
Amblyrhynchus - a genus confined to the Galapagos Islands. There is
one snake which is numerous; it is identical, as I am informed by
M. Bibron, with the Psammophis Temminckii from Chile. (17/2. This
is stated by Dr. Gunther "Zoological Society" January 24, 1859, to
be a peculiar species, not known to inhabit any other country.) Of
sea-turtle I believe there are more than one species, and of
tortoises there are, as we shall presently show, two or three
species or races. Of toads and frogs there are none: I was
surprised at this, considering how well suited for them the
temperate and damp upper woods appeared to be. It recalled to my
mind the remark made by Bory St. Vincent, namely, that none of this
family are found on any of the volcanic islands in the great
oceans. (17/3. "Voyage aux Quatres Iles d'Afrique." With respect to
the Sandwich Islands see Tyerman and Bennett's "Journal" volume 1
page 434. For Mauritius see "Voyage par un Officier" etc. Part 1
page 170. There are no frogs in the Canary Islands, Webb et
Berthelot "Hist. Nat. des Iles Canaries." I saw none at St. Jago in
the Cape de Verds. There are none at St. Helena.) As far as I can
ascertain from various works, this seems to hold good throughout
the Pacific, and even in the large islands of the Sandwich
archipelago. Mauritius offers an apparent exception, where I saw
the Rana Mascariensis in abundance: this frog is said now to
inhabit the Seychelles, Madagascar, and Bourbon; but on the other
hand, Du Bois, in his voyage in 1669, states that there were no
reptiles in Bourbon except tortoises; and the Officier du Roi
asserts that before 1768 it had been attempted, without success, to
introduce frogs into Mauritius - I presume for the purpose of
eating: hence it may be well doubted whether this frog is an
aboriginal of these islands. The absence of the frog family in the
oceanic islands is the more remarkable, when contrasted with the
case of lizards, which swarm on most of the smallest islands. May
this difference not be caused by the greater facility with which
the eggs of lizards, protected by calcareous shells, might be
transported through salt-water, than could the slimy spawn of
frogs?

I will first describe the habits of the tortoise (Testudo nigra,
formerly called Indica), which has been so frequently alluded to.
These animals are found, I believe, on all the islands of the
Archipelago; certainly on the greater number. They frequent in
preference the high damp parts, but they likewise live in the lower
and arid districts. I have already shown, from the numbers which
have been caught in a single day, how very numerous they must be.
Some grow to an immense size: Mr. Lawson, an Englishman, and
vice-governor of the colony, told us that he had seen several so
large that it required six or eight men to lift them from the
ground; and that some had afforded as much as two hundred pounds of
meat. The old males are the largest, the females rarely growing to
so great a size: the male can readily be distinguished from the
female by the greater length of its tail. The tortoises which live
on those islands where there is no water, or in the lower and arid
parts of the others, feed chiefly on the succulent cactus. Those
which frequent the higher and damp regions eat the leaves of
various trees, a kind of berry (called guayavita) which is acid and
austere, and likewise a pale green filamentous lichen (Usnera
plicata), that hangs from the boughs of the trees.

The tortoise is very fond of water, drinking large quantities, and
wallowing in the mud. The larger islands alone possess springs, and
these are always situated towards the central parts, and at a
considerable height. The tortoises, therefore, which frequent the
lower districts, when thirsty, are obliged to travel from a long
distance. Hence broad and well-beaten paths branch off in every
direction from the wells down to the sea-coast; and the Spaniards,
by following them up, first discovered the watering-places. When I
landed at Chatham Island, I could not imagine what animal travelled
so methodically along well-chosen tracks. Near the springs it was a
curious spectacle to behold many of these huge creatures, one set
eagerly travelling onwards with outstretched necks, and another set
returning, after having drunk their fill. When the tortoise arrives
at the spring, quite regardless of any spectator, he buries his
head in the water above his eyes, and greedily swallows great
mouthfuls, at the rate of about ten in a minute. The inhabitants
say each animal stays three or four days in the neighbourhood of
the water, and then returns to the lower country; but they differed
respecting the frequency of these visits. The animal probably
regulates them according to the nature of the food on which it has
lived. It is, however, certain that tortoises can subsist even on
those islands where there is no other water than what falls during
a few rainy days in the year.

I believe it is well ascertained that the bladder of the frog acts
as a reservoir for the moisture necessary to its existence: such
seems to be the case with the tortoise. For some time after a visit
to the springs, their urinary bladders are distended with fluid,
which is said gradually to decrease in volume, and to become less
pure. The inhabitants, when walking in the lower district, and
overcome with thirst, often take advantage of this circumstance,
and drink the contents of the bladder if full: in one I saw killed,
the fluid was quite limpid, and had only a very slightly bitter
taste. The inhabitants, however, always first drink the water in
the pericardium, which is described as being best.

The tortoises, when purposely moving towards any point, travel by
night and day and arrive at their journey's end much sooner than
would be expected. The inhabitants, from observing marked
individuals, consider that they travel a distance of about eight
miles in two or three days. One large tortoise, which I watched,
walked at the rate of sixty yards in ten minutes, that is 360 yards
in the hour, or four miles a day, - allowing a little time for it to
eat on the road. During the breeding season, when the male and
female are together, the male utters a hoarse roar or bellowing,
which, it is said, can be heard at the distance of more than a
hundred yards. The female never uses her voice, and the male only
at these times; so that when the people hear this noise, they know
that the two are together. They were at this time (October) laying
their eggs. The female, where the soil is sandy, deposits them
together, and covers them up with sand; but where the ground is
rocky she drops them indiscriminately in any hole: Mr. Bynoe found
seven placed in a fissure. The egg is white and spherical; one
which I measured was seven inches and three-eighths in
circumference, and therefore larger than a hen's egg. The young
tortoises, as soon as they are hatched, fall a prey in great
numbers to the carrion-feeding buzzard. The old ones seem generally
to die from accidents, as from falling down precipices: at least,
several of the inhabitants told me that they never found one dead
without some evident cause.

The inhabitants believe that these animals are absolutely deaf;
certainly they do not overhear a person walking close behind them.
I was always amused when overtaking one of these great monsters, as
it was quietly pacing along, to see how suddenly, the instant I
passed, it would draw in its head and legs, and uttering a deep
hiss fall to the ground with a heavy sound, as if struck dead. I
frequently got on their backs, and then giving a few raps on the
hinder part of their shells, they would rise up and walk away; - but
I found it very difficult to keep my balance. The flesh of this
animal is largely employed, both fresh and salted; and a
beautifully clear oil is prepared from the fat. When a tortoise is
caught, the man makes a slit in the skin near its tail, so as to
see inside its body, whether the fat under the dorsal plate is
thick. If it is not, the animal is liberated; and it is said to
recover soon from this strange operation. In order to secure the
tortoises, it is not sufficient to turn them like turtle, for they
are often able to get on their legs again.

There can be little doubt that this tortoise is an aboriginal
inhabitant of the Galapagos; for it is found on all, or nearly all,
the islands, even on some of the smaller ones where there is no
water; had it been an imported species this would hardly have been
the case in a group which has been so little frequented. Moreover,
the old Bucaniers found this tortoise in greater numbers even than
at present: Wood and Rogers also, in 1708, say that it is the
opinion of the Spaniards that it is found nowhere else in this
quarter of the world. It is now widely distributed; but it may be
questioned whether it is in any other place an aboriginal. The
bones of a tortoise at Mauritius, associated with those of the
extinct Dodo, have generally been considered as belonging to this
tortoise; if this had been so, undoubtedly it must have been there
indigenous; but M. Bibron informs me that he believes that it was
distinct, as the species now living there certainly is.

(PLATE 82. AMBLYRHYNCHUS CRISTATUS. a. Tooth of natural size, and
likewise magnified.)

The Amblyrhynchus, a remarkable genus of lizards, is confined to
this archipelago; there are two species, resembling each other in
general form, one being terrestrial and the other aquatic. This
latter species (A. cristatus) was first characterised by Mr. Bell,
who well foresaw, from its short, broad head, and strong claws of
equal length, that its habits of life would turn out very peculiar,
and different from those of its nearest ally, the Iguana. It is
extremely common on all the islands throughout the group, and lives
exclusively on the rocky sea-beaches, being never found, at least I
never saw one, even ten yards in-shore. It is a hideous-looking
creature, of a dirty black colour, stupid, and sluggish in its
movements. The usual length of a full-grown one is about a yard,
but there are some even four feet long; a large one weighed twenty
pounds: on the island of Albemarle they seem to grow to a greater
size than elsewhere. Their tails are flattened sideways, and all
four feet partially webbed. They are occasionally seen some hundred
yards from the shore, swimming about; and Captain Collnett, in his
Voyage says, "They go to sea in herds a-fishing, and sun themselves
on the rocks; and may be called alligators in miniature." It must
not, however, be supposed that they live on fish. When in the water
this lizard swims with perfect ease and quickness, by a serpentine
movement of its body and flattened tail - the legs being motionless
and closely collapsed on its sides. A seaman on board sank one,
with a heavy weight attached to it, thinking thus to kill it
directly; but when, an hour afterwards, he drew up the line, it was
quite active. Their limbs and strong claws are admirably adapted
for crawling over the rugged and fissured masses of lava which
everywhere form the coast. In such situations a group of six or
seven of these hideous reptiles may oftentimes be seen on the black
rocks, a few feet above the surf, basking in the sun with
outstretched legs.

I opened the stomachs of several, and found them largely distended
with minced sea-weed (Ulvae), which grows in thin foliaceous
expansions of a bright green or a dull red colour. I do not
recollect having observed this sea-weed in any quantity on the
tidal rocks; and I have reason to believe it grows at the bottom of
the sea, at some little distance from the coast. If such be the
case, the object of these animals occasionally going out to sea is
explained. The stomach contained nothing but the sea-weed. Mr.
Bynoe, however, found a piece of a crab in one; but this might have
got in accidentally, in the same manner as I have seen a
caterpillar, in the midst of some lichen, in the paunch of a
tortoise. The intestines were large, as in other herbivorous
animals. The nature of this lizard's food, as well as the structure
of its tail and feet, and the fact of its having been seen
voluntarily swimming out at sea, absolutely prove its aquatic
habits; yet there is in this respect one strange anomaly, namely,
that when frightened it will not enter the water. Hence it is easy
to drive these lizards down to any little point overhanging the
sea, where they will sooner allow a person to catch hold of their
tails than jump into the water. They do not seem to have any notion
of biting; but when much frightened they squirt a drop of fluid
from each nostril. I threw one several times as far as I could,
into a deep pool left by the retiring tide; but it invariably
returned in a direct line to the spot where I stood. It swam near
the bottom, with a very graceful and rapid movement, and
occasionally aided itself over the uneven ground with its feet. As
soon as it arrived near the edge, but still being under water, it
tried to conceal itself in the tufts of sea-weed, or it entered
some crevice. As soon as it thought the danger was past, it crawled
out on the dry rocks, and shuffled away as quickly as it could. I
several times caught this same lizard, by driving it down to a
point, and though possessed of such perfect powers of diving and
swimming, nothing would induce it to enter the water; and as often
as I threw it in, it returned in the manner above described.
Perhaps this singular piece of apparent stupidity may be accounted
for by the circumstance that this reptile has no enemy whatever on
shore, whereas at sea it must often fall a prey to the numerous
sharks. Hence, probably, urged by a fixed and hereditary instinct
that the shore is its place of safety, whatever the emergency may
be, it there takes refuge.

During our visit (in October) I saw extremely few small individuals
of this species, and none I should think under a year old. From
this circumstance it seems probable that the breeding season had
not then commenced. I asked several of the inhabitants if they knew
where it laid its eggs: they said that they knew nothing of its
propagation, although well acquainted with the eggs of the land
kind - a fact, considering how very common this lizard is, not a
little extraordinary.

We will now turn to the terrestrial species (A. Demarlii), with a
round tail, and toes without webs. This lizard, instead of being
found like the other on all the islands, is confined to the central
part of the archipelago, namely to Albemarle, James, Barrington,
and Indefatigable islands. To the southward, in Charles, Hood, and
Chatham Islands, and to the northward, in Towers, Bindloes, and
Abingdon, I neither saw nor heard of any. It would appear as if it
had been created in the centre of the archipelago, and thence had
been dispersed only to a certain distance. Some of these lizards
inhabit the high and damp parts of the islands, but they are much
more numerous in the lower and sterile districts near the coast. I
cannot give a more forcible proof of their numbers, than by stating
that when we were left at James Island, we could not for some time
find a spot free from their burrows on which to pitch our single
tent. Like their brothers the sea-kind, they are ugly animals, of a
yellowish orange beneath, and of a brownish-red colour above: from
their low facial angle they have a singularly stupid appearance.
They are, perhaps, of a rather less size than the marine species;
but several of them weighed between ten and fifteen pounds. In
their movements they are lazy and half torpid. When not frightened,
they slowly crawl along with their tails and bellies dragging on
the ground. They often stop, and doze for a minute or two, with
closed eyes and hind legs spread out on the parched soil.





They inhabit burrows which they sometimes make between fragments of
lava, but more generally on level patches of the soft
sandstone-like tuff. The holes do not appear to be very deep, and
they enter the ground at a small angle; so that when walking over
these lizard-warrens, the soil is constantly giving way, much to
the annoyance of the tired walker. This animal, when making its
burrow, works alternately the opposite sides of its body. One front
leg for a short time scratches up the soil, and throws it towards
the hind foot, which is well placed so as to heave it beyond the
mouth of the hole. That side of the body being tired, the other
takes up the task, and so on alternately. I watched one for a long
time, till half its body was buried; I then walked up and pulled it
by the tail; at this it was greatly astonished, and soon shuffled
up to see what was the matter; and then stared me in the face, as
much as to say, "What made you pull my tail?"

They feed by day, and do not wander far from their burrows; if
frightened, they rush to them with a most awkward gait. Except when
running down hill, they cannot move very fast, apparently from the
lateral position of their legs. They are not at all timorous: when
attentively watching any one, they curl their tails, and, raising
themselves on their front legs, nod their heads vertically, with a
quick movement, and try to look very fierce; but in reality they
are not at all so: if one just stamps on the ground, down go their
tails, and off they shuffle as quickly as they can. I have
frequently observed small fly-eating lizards, when watching
anything, nod their heads in precisely the same manner; but I do
not at all know for what purpose. If this Amblyrhynchus is held and
plagued with a stick, it will bite it very severely; but I caught
many by the tail, and they never tried to bite me. If two are
placed on the ground and held together, they will fight, and bite
each other till blood is drawn.

The individuals, and they are the greater number, which inhabit the
lower country, can scarcely taste a drop of water throughout the
year; but they consume much of the succulent cactus, the branches
of which are occasionally broken off by the wind. I several times
threw a piece to two or three of them when together; and it was
amusing enough to see them trying to seize and carry it away in
their mouths, like so many hungry dogs with a bone. They eat very
deliberately, but do not chew their food. The little birds are
aware how harmless these creatures are: I have seen one of the
thick-billed finches picking at one end of a piece of cactus (which
is much relished by all the animals of the lower region), whilst a



Online LibraryCharles DarwinThe Voyage of the Beagle → online text (page 38 of 51)