Читать книгу The Courtship of Animals - W. P. Pycraft - Страница 8

Table of Contents

The Birth of Weapons—All Flesh is Grass—Utility and Ornament—The Fever of Love—The “Challenge” of the Deer—What it means—More about “Hormones”—“Hummel” Stags—The Age of Deer—The “Courtship” of the Moose—Types of Antlers—Antlered Females—Fighting Topi—The Lance of the Oryx in the Lion’s Flanks—Happiness and Hartebeestes—Odoriferous Suitors—The Bloody Sweat of the Hippopotamus—The Elephant in Love—Concerning Tusks—Polygamy.

From Apes to Antelopes is a far cry, but contrasts are always helpful. Antelopes and Deer, Zebras and Elephants, Rhinoceroses and Swine, are types, taken at random, of that great and important group of animals known as the “Ungulates,” or “Hoofed” animals. These illustrate in a very striking manner what is meant by the term “Secondary Sexual Characters.” They demonstrate no less forcibly what is meant by the term “Sexual Selection.” They are valuable in this connection, because of the often formidable weapons, in the shape of horns and tusks, which so many species have developed during the struggle for mates.

But “Sexual Selection” will not explain their origin, and it is difficult, in the present state of our knowledge, to discover any clues which will reveal this. In seeking these there are certain broad aspects of the problem which are not to be lost sight of. In the first place, horns, at any rate, are confined to the hoofed animals. That the various types of hoofed animals, living and extinct, have had a common ancestry, no one at the present day will probably call in question. The relationship, however, of the various living types, one to another, is by no means always apparent: the missing links are to be sought in the records of the rocks.

When the whole of the evidence comes to be surveyed, and not till then, it becomes apparent that this wonderful diversity is the result of complex factors. That the conditions of existence have controlled the results is beyond question; but it is equally certain that these conditions have been merely controlling and not causative. In other words, we must regard each of these different groups or types—Deer, Antelopes, Horses, Elephants, Swine, and so on—as witnesses of what we call “Heredity.” They are so many “Diathetic types.” That is to say, the forms, or individuals, belonging to each type have inherited certain peculiarities in common; they display a “Diathesis” as the doctors call it: an inherent, inborn tendency, or habit of growth, in a definite direction: a tendency which, ever and anon, develops new qualities, takes new directions. And thus it is that we get Oxen—using this term in its widest sense and not in its special sense—Antelopes, Goats and Sheep, for example. These have, among other things, a “diathesis” in the direction of horn production, and each, too, of a different type. What is meant by this apparently mystifying term “diathesis” will perhaps be made clear by taking the case of the Ox and the Sheep. While very different in appearance, these live on precisely similar food; yet no one has any difficulty in discriminating between the taste of beef and mutton. In the marvellous chemical laboratory of the body the grass gathered in the same field is converted into flesh which even in its uncooked state is easily distinguishable. Though for the purposes of this illustration domesticated animals have been used, the same is true of their wild relations. Sportsmen tell us that the various types of Antelopes and the Zebra, which may be seen feeding together, have yet flesh of very different qualities. These qualities are to be attributed neither to “Natural” nor to “Sexual” selection; they are “accidents.” Similarly, their horns are the witness of a horn-producing “diathesis”: the various divergencies in curvature, and in the form of their spirals, or the number of their encircling rings—as in the horns of Antelopes—are to be interpreted in like fashion. These twists and turns vary in the same way that the taste of the flesh varies, and for the same reason; that is to say, they are not the outcome of “Sexual Selection,” nor have they been brought about by “Natural Selection” to serve the purpose of “Recognition marks,” as Wallace would have us believe.

But horns, as horns, apart from their “accidents” of curvature and ornament, must certainly be regarded as the product of Sexual selection, for having once started into being those individuals had the best chance of leaving descendants which were best armed. The possession of horns was not necessary to the maintenance of the species; but such armature was essential among the males in securing possession of the females. Other things being equal, the male with the biggest horns wins the prize. Since these are also used as weapons of offence, or rather of defence, in warding off the attacks of beasts of prey, it might be contended that they are as much the product of Natural selection as of Sexual selection.

It soon becomes apparent that this interpretation must fail. In the first place, if it were true, the females should be similarly armed. In the second, in the presence of many of their enemies they are useless. The Cape hunting-dog, for example, is more than a match for any antelope. This ferocious animal kills his victim by running it down, persistently tearing at its flanks, until at last the entrails protrude and the horrid chase is ended. Furthermore, the horns are a comparatively late acquirement of the species, as is shown in the case of the Deer; for the earliest known fossil species were hornless. That the females among the Oxen and many of the Antelopes possess horns is an interesting fact, but it can only be regarded as another instance of a character first acquired by the male and later, in successive generations, transferred to the female. And it is to be noticed that this transference is never found save in the cases where the character in question has attained its maximum in the male. The transference of weapons to the female is the more remarkable because there is no evidence that they play any part in the struggle for existence, either in securing mates or in warding off the attacks of enemies. Moreover, these weapons in the female may exceed those of the male, in length, though they are never so massive. They are to be regarded solely in the light of ornaments. There are few more striking instances indeed where the purely ornamental and the strictly utilitarian are so closely associated.

Plate 4.

By the courtesy of Rowland, Ward, Ltd.

WEAPONS OF OFFENCE.

Horns of various types furnish the most conspicuous of the “Secondary Sexual Characters” of the ruminants. In the Deer only are these branched. In the “hollow-horned” ruminants they are either lance-like or more or less spirally curved, or they may form more or less open loops.

1. Black-tailed Deer. 2. Hangul or Kashmir Barasingha Deer. 3. Greater Kudu. 4. Black-buck. 5. Saiga Antelope, remarkable also for its curiously swollen nose. 6. Marco-Polo’s Sheep.

[Face page 52.

Attention may now profitably be turned to the behaviour of these interesting tribes when under the alluring influences of love.

Tradition and the poets have contrived to persuade us that the fever of Love becomes epidemic in the spring. This, however, is by no means true, at any rate in so far as what we are pleased to call the “lower animals” are concerned. For with many, as for example the Deer and the Bats, this fever is not aroused till the time of autumn plenty. With regard to the deer, we can find a reason for this. It is determined in part by the period of gestation, and in part by the peculiar character of the most conspicuous of the male secondary sexual characters—the antlers. The deer, at any rate of the northern hemisphere, carry their young about eight months. Now it is important that they should make their entry into the world just as the food supply is increasing and the temperature is rising. With the summer before them the young have time to gather strength for the encounter with their first winter. We have a striking witness to the truth of this contention in the fact that when the Indian Spotted Deer, or Chital, was first introduced into Europe, nearly all the fawns perished owing to having been born in winter; later, the females took to calving in spring, and from thence onwards the species has held its own among us.

As touching the stags. The antlers, as everybody knows, are shed annually, and their renewal entails a very considerable strain on the system. As a consequence, it is necessary that this period of stress should fall after the trial of winter is overpast, and with the genial summer before them. From the end of March, when the old weapons are shed, till July, the masterful males of the community wander at large, seeking seclusion and avoiding all occasion of quarrel; for they are not only defenceless, but threatened with disaster should any accident befall the growing horns, which, during their formation, are exceedingly sensitive. Even a slight blow would not only spoil their shapely proportions, but, further, might render them useless in the warfare that is before them.

With some species this desire to go into retreat is more marked than in others. The Red-deer, and the Wapiti, on the one hand, and the Moose on the other, well illustrate this. The two first-named pass the winter in herds, in the case of the Wapiti numbering many thousand individuals; no other species, indeed, is so markedly gregarious. With the advance of the spring, however, all is changed, for the males withdraw from their companions to suffer humiliation in seclusion. As chill October arrives, a striking alteration in their demeanour becomes apparent, at any rate in the case of the older males. The new antlers are now hardened, and the blood supply, which has hitherto been building up the new weapons, is cut off. As a consequence, the “velvet,” which till now has been directly concerned with the growth of the antlers, dies, and peels off the underlying bone. To facilitate this work of cleaning, the animal rubs them, first against the stems of saplings, and, later, against larger trees, and even rocks, till at last they are ready for “battle, murder and sudden death.” The “rutting” season, in short, has commenced. And with the final completion of the antlers other signs of that approaching frenzy, which is soon to establish itself, become apparent. The most striking of these are the swelling of the neck, and a marked increase in the mane thereof; while the voice enlarges its compass enormously, whereby the females, so long neglected, are now feverishly sought for.

Plate 5.

Photo by G. IF. Wilson Co. Ltd., from “The Living Animals of the World.”

MANCHURIAN WAPITI “CALLING.”

The “stags” do not begin to call for mate’s until the horns have more or less completely shed their velvet.

[Face page 54.

The Red-deer, maddened with desire, scours the country, calling as he travels with a loud musical roar, ever and anon impatiently listening for the tremulous response of females hardly less anxious to mate than himself. One after another is speedily added to his harem, but not without conflict. For sooner or later he catches the call of another stag in like case. A jealous fury at once takes possession of him, and the call, intended as a message to mateless hinds, becomes translated into a challenge to fight for the mates possessed. Each of the now infuriated challengers makes all haste to come to blows, and speedily they are rushing headlong on one another to meet in a crash of antlers. Then follows a test of strength, a sort of tug-of-war reversed, for each strives to push the other to his knees, and succeeding, to deal a deadly sideways thrust at the kneeling adversary’s heart with the spike-shaped brow-tines. This attempt, however, is rarely achieved. Yet not seldom such encounters become a duel to the death, and one in which both die, for in the remorseless tilt at one another the antlers of one may spring apart, and then close in on those of the other. Once this happens, it seems to be rare indeed that they can be extricated from this close embrace. With heads thus locked, they sway, and twist, and tug, not now for the mastery, but for life itself. But as the hours run they become more and more exhausted by their efforts, weaker and weaker from loss of food and rest, till finally death releases both.

A male having once succeeded in forming a harem, will commonly contrive to repeat his success year after year, withstanding all comers. But sooner or later his vigour wanes and he is ousted by another and younger male. Not else would the stamina of the race be preserved. It is considered a moot point, however, whether physical strength and sexual potency run at the same pace; for it is believed by some that a stag will often contrive to hold a harem against all rivals after his fertility has declined. This, however, is extremely improbable. A lowering of fertility means a decline in the potency of the hormones, and in the development of the secondary sexual characters, among which are the antlers, which are by no means negligible factors. That they are not all-important, however, seems to be shown by the fact that, occasionally, stags appear in a herd which are congenitally unable to produce antlers—a reversion to the ancestral condition—and such are said, occasionally at any rate, to be able to oust their formidably armed rivals. This may be so, but the fact that “hummel” stags, as they are called, are so rare is surely to be regarded as eloquent testimony of the disadvantages of their unarmoured state. They become speedily eliminated, in short, by “Sexual Selection.”

After this outburst of sexual activity has spent itself, the various harems, with their lords, amalgamate; all living in peace through the winter. The stags retain their antlers at this season, partly as a protection against predatory enemies, such as wolves, and other large carnivores, which would otherwise play havoc in their ranks, and partly because the cold of winter and scanty fodder would inhibit the growth of new antlers or reduce their size. With the return of spring the dangers of attack are lessened, temperature rises, and food becomes once more plentiful. Then the inevitable disarmament takes place.

The Red-deer, though mature at six, does not reach his prime till his eleventh year, and from thence till his fifteenth or sixteenth year is at his best. The hinds mature earlier, and appear to be fertile for a much longer period. At any rate, a wild hind in Jura, known by certain peculiarities of its ears, during twenty-one years produced twenty calves. She was killed at last with a calf at her side, but was thin and haggard-looking. She was, therefore, not less than six-and-twenty at her death. The calves, it may be mentioned, are born in May and June.

Old stags shed their antlers, it is remarked, earlier than young ones. And this is an advantage to the species, since it prevents premature breeding on the part of sexually precocious but immature males, and limits competition to the adults.

What obtains in the case of the Red-deer obtains also with minor variations due to environment, climate, and so on, in the case of all other deer. The life-history of the Wapiti, as might be supposed, differs only in detail from that of the Red-deer. But during the winter they form vast herds, numbering thousands. It may be that in primitive times the Red-deer was no less numerous. But in this country, at any rate, conditions favourable to the maximum development, either in bodily size, or in the massiveness of the antlers, have long since passed away. Even in the Highlands of Scotland the conditions of existence have entirely changed owing to disafforestation. Deer are essentially forest dwellers. But the “deer forests” are such only in name, and for the most part the wild stags of to-day must get what shelter they can from rocks and inequalities of the ground. From this cause, and from the very natural desire of the owners of such “forests” to secure the finest heads in each year, the whole race has deteriorated. How great a change has come over it may be seen by comparing the heads of British Stags with those from German forests, where the conditions of existence are more favourable. If we turn to the records of the past we find that the antlers found in the fens, turbaries, and caverns of our islands are vastly larger, heavier, and carry a greater number of points on the sur-royals, than do those of the existing Scotch stags.

Having regard to the fact that hundreds, and in the distant past thousands, of antlers were shed annually, the comparative rarity of these weapons in the haunts of deer excites comment. This is accounted for by the fact that they are greedily eaten by their late owners, apparently, though unconsciously, for the sake of their bone-producing qualities.

By way of contrast with the Red-deer and Wapiti, we may take the Moose (Alces machlis), which at no time, and nowhere, attains to large herds. This is explained by the relatively restricted food supply which obtains in the haunts of these creatures. For they frequent the margins of streams, feeding largely on willows and birch. From the shortness of their necks, and the great length of their legs, they cannot crop grass and other short herbage, for unless they kneel they cannot reach the ground. Hence it is obvious that though their geographical range may be wide, their numbers are kept rigidly in check. They would be fewer still but for the fact that, unlike other deer, they glean no small amount of food from the water, wading out to feed upon aquatic vegetation. The roots of water-lilies are especially sought for, and to obtain these the animal will often disappear entirely under water.

As a consequence of the limited food supply the Moose lead solitary lives. On the Eastern side of America, where the winter is severe, a few individuals, generally a family party, will “yard up,” or make a fortress for their mutual protection by trampling down the snow over a restricted area. But in the Yukon district, my friend Mr. F. C. Selous tells me this is never done.

The rutting season of the bulls begins as soon as the antlers begin to “peel.” What follows is practically a repetition of what has already been related in regard to the Red-deer and Wapiti. And in this connection it is interesting to note that the natives take advantage of the period of desire in the bull to entice him to his death. Generally this is done by imitating the call of the cow in response to the bull’s anxious bellowing. But in Southern Alaska the opposite side of his nature is played upon. This is done by scraping or beating the bushes with the shoulder-blade of a Moose in such a way as to reproduce the sound of a bull cleaning his horns. The very suspicion of a rival enrages him, and, rushing in a blind fury in the direction of the tell-tale sounds, he speedily falls a victim to the trick which has been played him.

That the mating period is the most critical, and most searching in the whole life-history there can be no doubt. Every faculty during this time is put to the test, and from the time of sexual maturity until old age is at last attained it is an annual test. Alertness is all important. Other things being equal, success falls most certainly to those individuals with the keenest perception, and quickest interpretation of sight, sound and smell.

One is puzzled at what seems a concession of Darwin’s to the Lamarckian theory of the inherited effects of use in this connection. For in discussing the bellowing of the stag in “The Descent of Man,” he remarks that it “does not seem to be of any special service to him, either during courtship or battles, or in any other way. But may we not believe that the frequent use of the voice, under the strong excitement of love, jealousy and rage, continued during many generations, may at last have produced an inherited effect on the vocal organs of the stag, as well as of other male animals?” All the evidence goes to show that the production of sound, and the instant interpretation of its significance, is a matter of the highest importance. In the case of the Moose, for example, the noise occasioned by the cleaning of antlers provokes the same frenzy as at another time is aroused by the voice. Dullness of perception not only in these matters, but at all times, is fatal.

As touching the less conspicuous secondary sexual characters of Deer more must be said presently. For the moment the antlers must retain our attention. Time was when the Deer lacked these appendages. When they first appeared, in the now extinct species of the Middle Miocene period, they were no more than short prongs. Later, one of the prongs became elongated, and developed short branches or “tines,” which, in succeeding species, became more numerous, while at the same time, with the gradual evolution of more and more species, these antlers assumed new features both in the matter of size and in the character and number of the “tines,” a development which has reached its maximum to-day. But apart from these specific variations, which have given us such types as those of the Roe-deer, Red-deer, Wapiti, Caribou, Moose, Fallow-deer, Sambar, Schombergk’s deer, the strange Milou-deer, Elds-deer and Mule-deer, each species displays a quite remarkable range of variation in regard to its particular type of antler. Nowhere, perhaps, is this more strikingly marked than in the case of the Caribou and Moose. No doubt this feature is due largely to the fact that the horns are shed annually, and that the variations are due, in part at any rate, to temporary environmental conditions, such as food and weather. But these apart, individual peculiarities are constant, reappearing with more or less exactness each year.