African Nature Notes and Reminiscences 6

African Nature Notes and Reminiscences 6

The cock ostrich is, I think, the only exception to this rule, and

in the case of this remarkable bird the influence of sexual selection

has probably been more potent than that of a dull-coloured, monotonous

environment.

 

To my mind the loss of stripes in the quagga was entirely due to the

environment in which this species had lived for long ages; for on the

karoos of the Cape Colony everything is of one dull brown colour,

whether on hill or plain, and no shade is to be found anywhere, for

the whole country is without trees. The air, too, is intensely hot and

dry, and the rainfall scanty. In these semi-deserts of South-Western

Africa, not only did the quaggas lose their black stripes, but the

elands also lost the white stripes of their immediate ancestors, whilst

the blesboks had already lost much of the white to be seen in the body

colouring of the bonteboks, from which they are descended, and had

become of a much duller colour generally. In East Africa, however, the

plains are surrounded by well-wooded hills, which give some colour to

the landscape, whilst the rainfall every year is heavy. If it is not

the influence of their several environments which has brought about the

differences between the well-striped elands and zebras of East Africa

and their dull-coloured relatives that once lived in the karoos of the

Cape Colony, the theory of protective coloration must be equally at

fault, for in spite of the fact that in both countries both races of

these animals have been hunted by lions from time immemorial on open

plains, and under precisely similar conditions, they developed very

different schemes of coloration.

 

The Barbary sheep, again, which inhabits the dry hills bordering

the deserts of Northern Africa, where the vegetation is parched and

scanty at all seasons of the year, and the rocks of a red brown colour,

is itself of a uniform reddish brown which harmonises exactly with

its surroundings, and makes it very difficult to detect when lying

at rest amongst rocks. This perfect harmony of coloration with its

surroundings in the Barbary sheep may have been brought about by the

need of protection from enemies, but seems to me far more likely to

have been caused by the influence of the colour of its environment, for

its four-footed foes hunt by scent and by night far more than by sight

during the daytime.

 

The male moufflon of Sardinia, which lives in a temperate climate where

the colours of its surroundings are much brighter and more diversified

than is the case in the habitat of the Barbary sheep, is a much more

conspicuously coloured animal than the latter, or than the females

of its own kind. As the females and young of the Sardinian moufflon,

which are of a uniform brown colour, are more difficult to see than

the males in their somewhat conspicuous autumn and winter coats, the

latter cannot be said to be protectively coloured. Either through the

influence of sexual selection or that of an environment the general

colour of which varies very greatly at different seasons of the year,

the male of the Sardinian moufflon becomes during autumn and winter

conspicuously coloured compared with the female, without detriment,

however, to the well-being of the species.

 

During my long sojourn in the interior of South Africa, I made large

collections of butterflies. There was one species (_Precis artaxia_,

Hewits) which always puzzled me. This handsome insect is only found

in shady forests, is seldom seen flying until disturbed, and always

sits on the ground amongst dead leaves. Though handsomely coloured

on the upper side, when its wings are closed it closely resembles a

dead leaf. It has a little tail on the lower wing which looks exactly

like the stalk of a leaf, and from this tail a dark brown line runs

through both wings (which on the under sides are light brown) to the

apex of the upper wing. One would naturally be inclined to look upon

this wonderful resemblance to a dead leaf in a butterfly sitting with

closed wings on the ground amongst real dead leaves as a remarkable

instance of protective form and coloration. And of course it may be

that this is the correct explanation. But what enemy is this butterfly

protected against? Upon hundreds of different occasions I have ridden

and walked through the forests where _Precis artaxia_ was numerous, and

I have caught and preserved many specimens of these butterflies, but

never once did I see a bird attempting to catch one of them. Indeed,

birds of all kinds were scarce in the forests where these insects were

to be found. I now think that the form and colour of the under wings of

_Precis artaxia_ have more probably been produced by the influence of

its environment than by the need for protection.

 

During the rainy season in South Africa, the open glades in the

forests bordering the rivers are gay with multitudes of brightly

coloured butterflies of many different species, and after a night's

rain butterflies of various kinds may often be seen settling in masses

round pools of water along waggon roads. Most of these butterflies are

conspicuously coloured, though they are in perfect harmony with the

sunlit flowers which spring up at the time of year when they appear. I

cannot, however, believe that the need for protection against birds or

other enemies has had anything whatever to do with the determination of

their various colours, as in all my experience (and I have been all my

life a close observer of nature) I have never once seen a bird feeding

upon butterflies in Africa.

 

The coloration of certain animals in the Arctic and sub-Arctic Regions

is somewhat remarkable, as at certain seasons it is conspicuously out

of harmony with its surroundings, and cannot therefore be protective.

The musk ox retains its dark brown coat the whole year round, although

it lives almost constantly amidst a snowy environment. Mr. Wallace

tells us that the reason why the musk ox does not turn white is because

it has no enemies to fear, and therefore has no need of a protective

coloration. He says: "Then we have that thoroughly Arctic animal

the musk sheep, which is brown and conspicuous; but this animal is

gregarious, and its safety depends on its association in small herds.

It is therefore of more importance for it to be able to recognise its

kind at a distance than to be concealed from its enemies, against which

it can well protect itself so long as it keeps together in a compact

body." As, however, according to the experience of Arctic travellers,

large numbers of young musk oxen are annually killed by wolves, this

explanation of a case in which an animal is manifestly not protectively

coloured does not seem altogether satisfactory. Mr. Wallace, it may be

noted, calls special attention to the coloration of the giraffe, which

he considers to be protective; yet nothing, I think, is more certain

than that a far smaller percentage of giraffes are killed annually by

lions in Africa than of musk oxen by wolves in Arctic America. If this

is so, the musk ox has more need of protective coloration than the

giraffe. The musk ox is, I think, the only one amongst the few truly

Arctic mammals which does not turn white during the winter months,

for, unlike the barren ground caribou, it does not migrate southwards

in the autumn to the dark spruce forests, which change of habitat

no doubt has had an influence on the colour of the latter animals;

since Peary's caribou, the most northerly form of the genus, whose

habitat lies far within the Arctic Circle, where trees of any kind are

non-existent, is almost absolutely white in colour. In spite, however,

of the fact that the caribou inhabiting Ellesmere Land and the adjacent

land masses are white, and therefore harmonise well in colour with the

snowy wastes amongst which they live, they form the principal food of

the white wolves inhabiting the same regions, which hunt them by scent

and run them down just as easily as the grey and black wolves of Alaska

capture the dark-coloured and very conspicuous caribou which frequent

the mountain ranges of that country. It appears to me that the colour

of a caribou's coat, whether it be white, black, or brown, cannot

afford it any protection against wolves, which probably possess as keen

a sense of scent as any animals in the world, and must surely hunt

entirely by scent during the long dark months of the Arctic winter. If

this is so, then the great diversity in the coloration of the various

species of caribou inhabiting the North American Continent must be due

to some other cause than the necessity for protection against wolves,

practically their only four-footed enemies.

 

Speaking of other Arctic animals, Mr. Wallace believes that the

Arctic fox _of necessity_ turns white in winter in order to enable it

to capture the white Arctic hares upon which it chiefly lives. Very

little, however, is known as to the life-history of these two animals.

But if the Arctic foxes hunt by scent, as they almost certainly do,

during the constant darkness of the long Arctic winter, and the hares

burrow beneath the snow, and are caught as a rule when completely

hidden from sight below its surface, I think it is arguable that the

influence of environment has been at least as potent a factor in

bringing about the white coloration of these animals in winter as the

necessity for protective coloration. At any rate, in Alaska and the

Yukon Territory of Canada, where the country is covered with snow for

more than half the year, and where the hares are white throughout

the long winter, the foxes are red, black, or a mixture of these two

colours, all the year round, and the lynxes grey; yet these two species

of carnivorous animals depend almost entirely on the hares for their

food supply. It is somewhat remarkable that in the sub-Arctic forests

of Alaska and the Yukon Territory, where the cold is intense and the

ground covered with snow for so many months of every year, only the

hares and the stoats amongst mammals turn white in winter. But in

these countries the land is covered for the most part with dark spruce

forests, the influence of which--if there is anything in the influence

of environment--may have been greater in determining the coloration of

the mammals of this district than that of the snow-covered ground.

 

During winter in the Yukon Territory, moose turn very dark in colour

on the under parts of the body, and at this season of the year leave

the thick forests and live in the comparatively open valleys amongst

willow and birch scrub, where they are said to stand out like haystacks

amidst their snowy surroundings. The local race of caribou (_Rangifer

osborni_), which live all the year round on the treeless mountain

plateaus, are very dark in colour (with the exception of their necks),

and, as I myself can testify, stand out very plainly when the open

ground they frequent is covered with snow. Of the various races of

wild sheep inhabiting the mountains of Alaska, the Yukon Territory,

and Northern British Columbia, some are white all the year round,

and therefore very conspicuous in summer when there is no snow on

the ground, though difficult to detect in the winter; some are grey,

with white heads, necks, and rumps; whilst others are nearly black,

and therefore very conspicuous in winter. Of the predatory animals

the large timber wolves are, as a rule, pale greyish brown with black

hairs on their backs and shoulders, but a considerable number are

quite black; the foxes are either red or black, or of the intermediate

coloration known as "cross"; whilst the wolverines, martens, and minks

are rich dark brown, and the lynxes neutral grey. The stoat or ermine

is the only carnivorous animal which turns white in winter in these

countries.

 

It would thus appear that in the sub-Arctic Regions of North America

the coloration of mammals does not obviously serve the purpose of

concealing the herbivorous species from their enemies, or of enabling

carnivorous animals to approach their prey unperceived. To come nearer

home, we find that whereas in the Alpine regions of Europe the mountain

hare turns white in winter, the chamois living in the same snow-covered

ground becomes deep black. It is true that in winter chamois often

leave the open mountains and live amongst the higher forests, where

it may be said that their dark colour harmonises well with the dark

foliage of the spruce trees; but I have hunted chamois in December in

the mountains of Transylvania, when they were in full winter coat,

and I certainly found that their dark coloration often made them

conspicuous.

 

Turning to Africa, we have many instances of what seen in the open

and at short range cannot possibly be called anything but conspicuous

coloration, such as the jet black and pure white striping of the East

African form of Burchell's zebra; the deep glossy black body and neck,

with snow-white belly and parti-coloured face, of the sable antelope;

the black and white face of the gemsbuck; the pure white face and rump

of the bontebok, combined with the beautiful dark brown neck and sides

and lilac tinted back; or the juxtaposition of the black and white

in Thomson's gazelle--only to mention a few of the most noteworthy examples.