First I tried to keep the common mole. It was easy to procure a healthy specimen, caught to order in the nursery gardens of my father-in-law, and I found no difficulty in keeping it alive. Immediately on its arrival, it devoured an almost incredible quantity of earthworms which, from the very first moment, it took from my hand. But, as an object of behaviour study, it proved most disappointing. Certainly, it was interesting to watch its method of disappearing in the space of a few seconds under the surface of the ground, to study its astoundingly efficient use of its strong, spade-shaped fore-paws, and to feel their amazing strength when one held the little beast in one’s hand. And again, it was remarkable with what surprising exactitude it located, by smell, from underground, the earthworms which I put on the surface of the soil in its terrarium. But these observations were the only benefits I derived from it. It never became any tamer and it never remained above ground any longer than it took to devour its prey; after this, it sank into the earth as a submarine sinks into the water. I soon grew tired of procuring the immense quantities of living food it required and, after a few weeks, I set it free in the garden.
It was years afterwards, on an excursion to that extraordinary lake, the Neusiedlersee, which lies on the Hungarian border of Austria, that I again thought of keeping an insectivore. This large stretch of water, though not thirty miles from Vienna, is an example of the peculiar type of lake found in the open steppes of Eastern Europe and Asia. More than thirty miles long and half as broad, its deepest parts are only about five feet deep and it is much shallower on the average. Nearly half its surface is overgrown with reeds which form an ideal habitat for all kinds of water-birds. Great colonies of white, purple, and grey heron and spoon bills live among the reeds and, until a short while ago, glossy ibis were still to be found here. Greylag geese breed here in great numbers and, on the eastern, reedless shore, avocets and many other rare waders can regularly be found. On the occasion of which I am speaking, we, a dozen tired zoologists, under the experienced guidance of my friend Otto Koenig, were wending our way, slowly and painfully, through the forest of reeds. We were walking in single file, Koenig first, I second, with a few students in our wake. We literally left a wake, an inky-black one in pale grey water. In the reed-forests of Lake Neusiedel, you walk knee deep in slimy, black ooze, wonderfully perfumed by sulphuretted-hydrogen-producing bacteria. This mud clings tenaciously and only releases its hold on your foot with a loud, protesting plop at every step.
After a few hours of this kind of wading you discover aching muscles whose very existence you had never suspected. From the knees to the hips you are immersed in the milky, clay-coloured water characteristic of the lake, which, among the reeds, is populated by myriads of extremely hungry leeches conforming to the old pharmaceutical recipe, “Hirudines medicinales maxime affamati”. The rest of your person inhabits the upper air, which here consists of clouds of tiny mosquitoes whose bloodthirsty attacks are all the more exasperating because you require both your hands to part the dense reeds in front of you and can only slap your face at intervals. The British ornithologist who may perhaps have envied us some of our rare specimens will perceive that bird-watching on Lake Neusiedel is not, after all, an entirely enviable occupation.
We were thus wending our painful way through the rushes when suddenly Koenig stopped and pointed mutely towards a pond, free from reeds, that stretched in front of us. At first, I could only see whitish water, dark blue sky and green reeds, the standard colours of Lake Neusiedel. Then, suddenly, like a cork popping up on to the surface, there appeared, in the middle of the pool, a tiny black animal, hardly bigger than a man’s thumb. And for a moment I was in the rare position of a zoologist who sees a specimen and is not able to classify it, in the literal sense of the word: I did not know to which class of vertebrates the object of my gaze belonged. For the first fraction of a second I took it for the young of some diving bird of a species unknown to me. It appeared to have a beak and it swam on the water like a bird, not in it as a mammal. It swam about in narrow curves and circles, very much like a whirligig beetle, creating an extensive wedgeshaped wake, quite out of proportion to the tiny animal’s size. Then a second little beast popped up from below, chased the first one with a shrill, bat-like twitter, then both dived and were gone. The whole episode had not lasted five seconds.
I stood open-mouthed, my mind racing. Koenig turned round with a broad grin, calmly detached a leech that was sticking like a leech to his wrist, wiped away the trickle of blood from the wound, slapped his cheek, thereby killing thirty-five mosquitoes, and asked, in the tone of an examiner, “What was that?” I answered as calmly as I could, “water-shrews”, thanking, in my heart, the leech and the mosquitoes for the respite they had given me to collect my thoughts. But my mind was racing on: water-shrews ate fishes and frogs which were easy to procure in any quantity; water-shrews were less subterranean than most other insectivores; they were the very insectivores to keep in captivity. “That’s an animal I must catch and keep”; I said to my friend. “That is easy”, he responded. “There is a nest with young under the floor mat of my tent.” I had slept that night in this tent and Koenig had not thought it worth while to tell me of the shrews; such things are, to him, as much a matter of course as wild little spotted crakes feeding out of his hand, or as any other wonders of his queer kingdom in the reeds.
On our return to the tent that evening, he showed me the nest. It contained eight young which, compared with their mother, who rushed away as we lifted the mat, were of enormous size. They were considerably more than half her length and must each have weighed well between a fourth and a third of their dam: that is to say, the whole litter weighed, at a very modest estimate, twice as much as the old shrew. Yet they were still quite blind and the tips of their teeth were only just visible in their rosy mouths. And two days later when I took them under my care, they were still quite unable to eat even the soft abdomens of grasshoppers, and in spite of evident greed, they chewed interminably on a soft piece of frog’s meat without succeeding in detaching a morsel from it. On our journey home, I fed them on the squeezed-out insides of grasshoppers and finely minced frog’s meat, a diet on which they obviously throve. Arrived home in Altenberg, I improved on this diet by preparing a food from the squeezed-out insides of mealworm larvae, with some finely chopped small, fresh fishes, worked into a sort of gravy with a little milk. They consumed large quantities of this food, and their little nest-box looked quite small in comparison with the big china bowl whose contents they emptied three times a day. All these observations raise the problem of how the female water-shrew succeeds in feeding her gigantic litter. It is absolutely impossible that she should do so on milk alone. Even on a more concentrated diet my young shrews devoured the equivalent of their own weight daily and this meant nearly twice the weight of a grown shrew. Yet, at that time of their lives, young shrews could not possibly engulf a frog or a fish brought whole to them by their mother, as my charges indisputably proved. I can only think that the mother feeds her young by regurgitation of chewed food. Even thus, it is little short of miraculous that the adult female should be able to obtain enough meat to sustain herself and her voracious progeny.
When I brought them home, my young water-shrews were still blind. They had not suffered from the journey and were as sleek and fat as one could wish. Their black, glossy coats were reminiscent of moles, but the white colour of their underside, as well as the round, streamlined contours of their bodies reminded me distinctly of penguins, and not, indeed, without justification: both the streamlined form and the light underside are adaptations to a life in the water. Many free-swimming animals, mammals, birds, amphibians and fishes, are silvery-white below in order to be invisible to enemies swimming in the depths. Seen from below, the shining white belly blends perfectly with the reflecting surface film of the water. It is very characteristic of these water animals that the dark dorsal and the white ventral colours do not merge gradually into each other as is the case in “counter-sh
aded” land animals whose colouring is calculated to make them invisible by eliminating the contrasting shade on their undersides. As in the killer whale, in dolphins, and in penguins, the white underside of the water-shrew is divided from the dark upper side by a sharp line which runs, often in very decorative curves, along the animal’s flank. Curiously enough, this border-line between black and white showed considerable variations in individuals and even on both sides of one animal’s body. I welcomed this, since it enabled me to recognize my shrews personally.
Three days after their arrival in Altenberg my eight shrew babies opened their eyes and began, very cautiously, to explore the precincts of their nest-box. It was now time to remove them to an appropriate container, and on this question I expended much hard thinking. The enormous quantity of food they consumed and, consequently, of excrement they produced, made it impossible to keep them in an ordinary aquarium whose water, within a day, would have become a stinking brew. Adequate sanitation was imperative for particular reasons; in ducks, grebes and all water-fowl, the plumage must be kept perfectly dry if the animal is to remain in a state of health, and the same premise may reasonably be expected to hold good of the shrew’s fur. Now water which has been polluted soon turns strongly alkaline and this I knew to be very bad for the plumage of water-birds. It causes saponification of the fat to which the feathers owe their waterproof quality, and the bird becomes thoroughly wet and is unable to stay on the water. I hold the record, as far as I know hitherto unbroken by any other bird-lover, for having kept dabchicks alive and healthy in captivity for nearly two years, and even then they did not die but escaped, and may still be living. My experience with these birds proved the absolute necessity of keeping the water perfectly clean; whenever it became a little dirty I noticed their feathers beginning to get wet, a danger which they anxiously tried to counteract by constantly preening themselves. I had, therefore, to keep these little grebes in crystal-clear water which was changed every day, and I rightly assumed that the same would be necessary for my water-shrews.
I took a large aquarium tank, rather over a yard in length and about two feet wide. At each end of this, I placed two little tables, and weighed them down with heavy stones so that they would not float. Then I filled up the tank until the water was level with the tops of the tables. I did not at first push the tables close against the panes of the tank, which was rather narrow, for fear that the shrews might become trapped under water in the blind alley beneath a table and drown there; this precaution, however, subsequently proved unnecessary. The water-shrew, which in its natural state swims great distances under the ice, is quite able to find its way to the open surface in much more difficult situations. The nest-box, which was placed on one of the tables, was equipped with a sliding shutter, so that I could imprison the shrews whenever the container had to be cleaned. In the morning, at the hour of general cage-cleaning, the shrews were usually at home and asleep, so that the procedure caused them no appreciable disturbance. I will admit that I take great pride in devising, by creative imagination, suitable containers for animals of which nobody, myself included, has had any previous experience, and it was particularly gratifying that the contraption described above proved so satisfactory that I never had to alter even the minutest detail.
When first my baby shrews were liberated in this container they took a very long time to explore the top of the table on which their nest-box was standing. The water’s edge seemed to exert a strong attraction; they approached it ever and again, smelled the surface and seemed to feel along it with the long, fine whiskers which surround their pointed snouts like a halo and represent not only their most important organ of touch but the most important of all their sensory organs. Like other aquatic mammals, the water shrew differs from the terrestrial members of its class in that its nose, the guiding organ of the average mammal, is of no use whatsoever in its under-water hunting. The water-shrew’s whiskers are actively mobile like the antennae of an insect or the fingers of a blind man.
Exactly as mice and many other small rodents would do under similar conditions, the shrews interrupted their careful exploration of their new surroundings every few minutes to dash wildly back into the safe cover of their nest-box. The survival value of this peculiar behaviour is evident: the animal makes sure, from time to time that it has not lost its way and that it can, at a moment’s notice, retreat to the one place it knows to be safe. It was a queer spectacle to see those podgy black figures slowly and carefully whiskering their way forward and, in the next second, with lightning speed, dash back to the nest-box. Queerly enough, they did not run straight through the little door, as one would have expected, but in their wild dash for safety they jumped, one and all, first on to the roof of the box and only then, whiskering along its edge, found the opening and slipped in with a half somersault, their back turned nearly vertically downward. After many repetitions of this manoeuvre, they were able to find the opening without feeling for it; they “knew” perfectly its whereabouts yet still persisted in the leap on to the roof. They jumped on to it and immediately vaulted in through the door, but they never, as long as they lived, found out that the leap and vault which had become their habit were really quite unnecessary and that they could have run in directly without this extraordinary detour. We shall hear more about this dominance of path habits in the water-shrew presently.
It was only on the third day, when the shrews had become thoroughly acquainted with the geography of their little rectangular island, that the largest and most enterprising of them ventured into the water. As is so often the case with mammals, birds, reptiles and fishes, it was the largest and most handsomely coloured male which played the role of leader. First he sat on the edge of the water and thrust in the fore part of his body, at the same time frantically paddling with his fore-legs but still clinging with his hind ones to the board. Then he slid in, but in the next moment took fright, scampered madly across the surface very much after the manner of a frightened duckling, and jumped out on to the board at the opposite end of the tank. There he sat, excitedly grooming his belly with one hind paw, exactly as coypu and beavers do. Soon he quietened down and sat still for a moment. Then he went to the water’s edge a second time, hesitated for a moment, and plunged in; diving immediately, he swam ecstatically about under water, swerving upward and downward again, running quickly along the bottom, and finally jumping out of the water at the same place as he had first entered it.
When I first saw a water-shrew swimming I was most struck by a thing which I ought to have expected but did not: at the moment of diving, the little black and white beast appears to be made of silver. Like the plumage of ducks and grebes, but quite unlike the fur of most water mammals, such as seals, otters, beavers or coypus, the fur of the water-shrew remains absolutely dry under water, that is to say, it retains a thick layer of air while the animal is below the surface. In the other mammals mentioned above, it is only the short, woolly undercoat that remains dry, the superficial hair-tips becoming wet, wherefore the animal looks its natural colour when under water and is superficially wet when it emerges. I was already aware of the peculiar qualities of the waterproof fur of the shrew, and, had I given it a thought, I should have known that it would look, under water, exactly like the air-retaining fur on the underside of a water beetle or on the abdomen of a water spider. Nevertheless the wonderful, transparent silver coat of the shrew was, to me, one of those delicious surprises that nature has in store for her admirers.
Another surprising detail which I only noticed when I saw my shrews in the water was that they have a fringe of stiff, erectile hairs on the outer side of their fifth toes and on the underside of their tails. These form collapsible oars and a collapsible rudder. Folded and inconspicuous as long as the animal is on dry land, they unfold the moment it enters the water and broaden, the effective surface of the propelling feet and of the steering tail by a considerable area.
Like penguins, the water-shrews looked rather awkward and ungainly on dry land but
were transformed into objects of elegance and grace on entering the water. As long as they walked, their strongly convex underside made them look pot-bellied and reminiscent of an old, overfed dachshund. But under water, the very same protruding belly balanced harmoniously the curve of their back and gave a beautifully symmetrical streamline which, together with their silver coating and the elegance of their movements, made them a sight of entrancing beauty.
When they had all become familiar with the water, their container was one of the chief attractions that our research station had to offer to any visiting naturalists or animal-lovers. Unlike all other mammals of their size, the water-shrews were largely diurnal and, except in the early hours of the morning, three or four of them were constantly on the scene. It was exceedingly interesting to watch their movements upon and under the water. Like the whirligig beetle, Gyrinus, they could turn in an extremely small radius without diminishing their speed, a faculty for which the large rudder surface of the tail with its fringe of erectile hairs is evidently essential. They had two different ways of diving, either by taking a little jump as grebes or coots do and working their way down at a steep angle, or by simply lowering their snout under the surface and paddling very fast till they reached “planing speed”, thus working their way downward on the principle of the inclined plane—in other words, performing the converse movement of an ascending aeroplane. The water-shrew must expend a large amount of energy in staying down, since the air contained in its fur exerts a strong pull upwards. Unless it is paddling straight downwards, a thing it rarely does, it is forced to maintain a constant minimum speed, keeping its body at a slightly downward angle, in order not to float to the surface. While swimming under water the shrew seems to flatten, broadening its body in a peculiar fashion, in order to present a better planing surface to the water. I never saw my shrews try to cling by their claws to any underwater objects, as the dipper is alleged to do. When they seemed to be running along the bottom, they were really swimming close above it, but perhaps the smooth gravel on the bottom of the tank was unsuitable for holding on to and it did not occur to me then to offer them a rougher surface. They were very playful when in the water and chased one another loudly twittering on the surface, or silently in the depths. Unlike any other mammal, but just like water birds, they could rest on the surface; this they used to do, rolling partly over and grooming themselves. Once out again, they instantly proceeded to clean their fur—one is almost tempted to say “preen” it, so similar was their behaviour to that of ducks which have just left the water after a long swim.
King Solomon's Ring Page 10
