Some time ago I received a small parcel from a friend of mine in India. Inside the box I found a note which read: ‘I bet you don’t know what this is.’ Greatly intrigued, I lifted off the top layer of wrapping paper, and underneath I found what appeared to be two large leaves which had been rather inexpertly sewn together.
My friend would have lost his bet. As soon as I saw the large and rather amateur stitches, I knew what it was: the nest of a tailor bird, a thing I had always wanted to see. The two leaves were about six inches long, shaped rather like laurel leaves, and only the edges had been sewn together, so that it formed a sort of pointed bag. Inside the bag was a neat nest of grass and moss, and inside that were two small eggs. The tailor bird is quite small, about the size of a tit, but with a rather long beak. This is its needle. Having found the two leaves it likes, hanging close together, it then proceeds to sew them together, using fine cotton as thread. The curious thing about it is not so much that the tailor bird stitches the leaves together as that nobody seems to know where he finds the cotton material with which to do the sewing. Some experts insist that he weaves it himself, others that he has some source of supply that has never been discovered. As I say, the stitches were rather large and inartistic, but then how many people could make a success of sewing up two leaves, using only a beak as a needle?
Architecture in the animal world differs a great deal. Some animals, of course, have only the haziest idea of constructing a suitable dwelling, while others produce most complicated and delightful homes. It is strange that even among closely related animals there should be such a wide variety of taste in the style, situation and size of the home and the choice of materials used in its construction.
In the bird world, of course, one finds homes of every shape and size. They range from the tailor bird’s cradle of leaves to the emperor penguin, who, with nothing but snow for his building, has dispensed with the idea of a nest altogether. The egg is simply carried on the top of the large flat foot, and the skin and feathers of the stomach form a sort of pouch to cover it. Then you have the edible swift who makes a fragile, cup-shaped nest of saliva and bits of twigs and sticks it to the wall of a cave. Among the weaver-birds of Africa, too, the variety of nests is bewildering. One species lives in a community which builds a nest half the size of a haystack, rather like a block of flats, in which each bird has its own nesting-hole. In these gigantic nests you sometimes get an odd variety of creatures living as well as the rightful occupants. Snakes are very fond of them; so are bush-babies and squirrels. One of these nests, if taken to pieces, might display an extraordinary assortment of inmates. No wonder that trees have been known to collapse under the weight of these colossal nests. The common weaver-bird of West Africa builds a neat, round nest, like a small basket woven from palm fibres. They also live in communities and hang their nests on every available branch of a tree, until it seems festooned with some extraordinary form of fruit. In the most human way the brilliant and shrill-voiced owners go about the business of courting, hatching the eggs, feeding their young and bickering with their neighbours, so that the whole thing rather resembles an odd sort of council estate.
To construct their nests, the weaver-birds have become adept not only at weaving but at tying knots, for the nest is strapped very firmly to the branch and requires considerable force to remove it. I once watched a weaver-bird starting its nest, a fascinating performance. He had decided that the nest should hang from the end of a delicate twig half-way up a tree, and he arrived on the spot carrying a long strand of palm fibre in his beak. He alighted on the branch, which at once swung to and fro so that he had to flap his wings to keep his balance. When he was fairly steady he juggled with the palm fibre until he got to the centre of it. Then he tried to drape it over the branch, so that the two ends hung one side and the loop hung the other. The branch still swayed about, and twice he dropped the fibre and had to fly down to retrieve it, but at last he got it slung over the branch to his satisfaction. He then placed one foot on it to keep it in position and leaning forward precariously he pulled the two dangling ends from one side of the branch through the loop on the other and tugged it tight. After this he flew for some more fibre and repeated the performance. He went on in this way for the whole day, until by evening he had twenty or thirty pieces of fibre lashed to the branch, the ends dangling down like a beard.
Unfortunately I missed the following stages in the construction of this nest, and I next saw it empty, for the bird had presumably reared its young and moved off. The nest was flask-shaped – a small round entrance, guarded by a small porch of plaited fibre. I tried to pull the nest off the branch, but it was impossible, and in the end I had to break the whole branch off. Then I tried to tear the nest in half so that I could examine the inside. But so intricately interlaced and knotted were the palm fibres that it took me a long time and all my strength before I could do so. It was really an incredible construction, when you consider the bird had only its beak and its feet for tools.
When I went to Argentina four years ago I noticed that nearly every tree-stump or rail-post in the pampa was decorated with a strange earthenware construction about the size and shape of a football. At first, I believed they were termite nests, for they were very similar to a common feature of the landscape in West Africa. It was not until I saw, perched on top of one of them, a small tubby bird about the size of a robin with a rusty-red back and grey shirt-front that I realized they were the nests of the oven-bird.
As soon as I found an unoccupied nest, I carefully cut it in half and was amazed at the skill with which it had been built. Wet mud had been mixed with tiny fragments of dried grass, roots and hair to act as reinforcement. The sides of the nest were approximately an inch and a half thick. The outside had been left rough – unrendered, as it were – but the inside had been smoothed to a glass-like finish. The entrance to the nest was a small arched hole, rather like a church door, which led into a narrow passage-way that curved round the outer edge of the nest and eventually led into the circular nesting-chamber lined with a pad of soft roots and feathers. The whole thing rather resembled a snail-shell.
Although I searched a large area, I was never lucky enough to find a nest that had been newly started, for it was fairly well into the breeding season. But I did find one half-completed. Oven-birds are very common in Argentina, and in the way they move and cock their heads on one side and regard you with their shining dark eyes, they reminded me very much of the English robin. The pair building this nest took no notice of me whatever, provided I remained at a distance of about twelve feet, though occasionally they would fly over to take a closer look at me, and after inspecting me with their heads on one side, they would flap their wings as though shrugging, and return to their building work. The nest, as I say, was half-finished: the base was firmly cemented on to a fence-post and the outer walls and inner wall of the passage-way were already some four or five inches high. All that remained now was for the whole thing to be covered with the domed roof.
The nearest place for wet mud was about half a mile away at the edge of a shallow lagoon. They would hop round the edge of the water in a fussy, rather pompous manner, testing the mud every few feet. It had to be of exactly the right consistency. Having found a suitable patch, they would hop about excitedly, picking up tiny rootlets and bits of grass until their beaks were full and they looked as though they had suddenly sprouted large walrus moustaches. They would carry these beakfuls of reinforcement down to the mud patch, and then, by skilful juggling, without dropping the material, pick up a large amount of mud as well. By a curious movement of the beak they matted the two materials together until their walrus moustaches looked distinctly bedraggled and mudstained. Then, with a muffled squeak of triumph, they flew off to the nest. Here the bundle was placed in the right position and pecked and trampled on and pushed until it had firmly adhered to the original wall. Then they entered the nest and smoothed off the new patch, using their beaks, their breasts and even the sides of their wings to get the required shining finish.
When only a small patch on the very top of the roof needed to be finished, I took some bright scarlet threads of wool down to the edge of the lagoon and scattered them around the place where the oven-birds gathered their material. On my next trip down there, to my delight, they had picked them up, and the result, a small russet bird apparently wearing a bright scarlet moustache, was quite startling. They incorporated the wool into the last piece of building on the nest, and it was, I feel sure, the only Argentinian oven-bird’s nest on the pampa flying what appeared to be a small red flag at half-mast.
If the oven-bird is a master-builder, whose nest is so solid that it takes several blows of a hammer to demolish it, members of the pigeon family go to the opposite extreme. They have absolutely no idea of proper nest-making. Four or five twigs laid across a branch: that is the average pigeon’s idea of a highly complicated structure. On this frail platform the eggs, generally two, are laid. Every time the tree sways in the wind this silly nest trembles and shakes and the eggs almost fall out. How any pigeon ever reaches maturity is a mystery to me.
I knew that pigeons were stupid and inefficient builders, but I never thought that their nests might prove an irritating menace to a naturalist. When I was in Argentina I learned differently. On the banks of a river outside Buenos Aires I found a small wood. The trees, only about thirty feet high, were occupied by what might almost be called a pigeon colony. Every tree had about thirty or forty nests in it. Walking underneath the branches you could see the fat bellies of the young, or the gleam of the eggs, through the carelessly arranged twigs. The nests looked so insecure that I felt like walking on tip-toe for fear that my footsteps would destroy the delicate balance.
In the centre of the wood I found a tree full of pigeons’ nests but for some odd reason devoid of pigeons. At the very top of the tree I noticed a great bundle of twigs and leaves which was obviously a nest of some sort and equally obviously not a pigeon’s nest. I wondered if it was the occupant of this rather untidy bundle of stuff that had made the pigeons desert all the nests in the tree. I decided to climb and see if the owner was at home. Unfortunately, it was only when I had started to climb that I realized my mistake, for nearly every pigeon’s nest in the tree contained eggs, and as I made my way slowly up the branches my movements created a sort of waterfall of pigeon eggs which bounced and broke against me, smearing my coat and trousers with yolk and bits of shell. I would not have minded this so much, but every single egg was well and truly addled, and by the time I had reached the top of the tree, hot and sweating, I smelt like a cross between a tannery and a sewage farm. To add insult to injury, I found that the occupant of the nest I had climbed up to was out, so I had gained nothing by my climb except a thick coating of egg and a scent that would have made a skunk envious. Laboriously I climbed down the tree again, looking forward to the moment when I would reach ground and could light a cigarette, to take the strong smell of rotten egg out of my nostrils. The ground under the tree was littered with broken eggs tastefully interspersed with the bodies of a few baby pigeons in a decomposed condition. I made my way out into the open as quickly as possible. With a sigh of relief, I sat down and reached into my pocket for my cigarettes. I drew them out dripping with egg yolk. At some point during my climb, by some curious chance, an egg had fallen into my pocket and broken. My cigarettes were ruined. I had to walk two miles home without a smoke, breathing in a strong aroma of egg and looking as though I had rather unsuccessfully taken part in an omelette-making competition. I have never really liked pigeons since then.
Mammals, on the whole, are not such good builders as the birds, though, of course, a few of them are experts. The badger, for example, builds the most complicated burrow, which is sometimes added to by successive generations until the whole thing resembles an intricate underground system with passages, culs-de-sac, bedrooms, nurseries and feeding-quarters. The beaver, too, is another master-builder, constructing his lodge half in and half out of the water: thick walls of mud and logs with an underground entrance, so that he can get in and out even when the surface of the lake is iced over. Beavers also build canals, so that when they have to fell a tree some distance inland for food or repair work on their dam, they can float it down the canal to the main body of water. Their dams are, of course, masterpieces – massive constructions of mud and logs, welded together, stretching sometimes many hundreds of yards. The slightest breach in these is frantically repaired by the beavers, for fear that the water might drain away and leave their lodge with its door no longer covered by water, an easy prey to any passing enemy. What with their home, their canals and their dams, one has the impression that the beaver must be a remarkably intelligent and astute animal. Unfortunately, however, this is not the case. It appears that the desire to build a dam is an urge which no self-respecting beaver can repress even when there is no need for the construction, and when kept in a large cement pool they will solemnly and methodically run a dam across it to keep the water in.
But, of course, the real master-architects of the animal world are, without a doubt, the insects. You need only look at the beautiful mathematical precision with which a common-or-garden honeycomb is built. Insects seem capable of building the most astonishing homes from a vast array of materials – wood, paper, wax, mud, silk and sand – and they differ just as widely in their design. In Greece, when I was a boy, I used to spend hours searching mossy banks for the nest of the trapdoor-spiders. These are one of the most beautiful and astonishing pieces of animal architecture in the world. The spider itself, with its legs spread out, would just about cover a two-shilling piece and looks as though it has been made out of highly polished chocolate. It has a squat fat body and rather short legs, and does not look at all the sort of creature you would associate with delicate construction work. Yet these rather clumsy-looking spiders sink a shaft into the earth of a bank about six inches deep and about the diameter of a shilling. This is carefully lined, so that when finished it is like a tube of silk. Then comes the most important part, the trapdoor. This is circular and with a neatly bevelled edge, so that it fits securely into the mouth of the tunnel. It is then fixed with a silken hinge, and the outside of it camouflaged with springs of moss or lichen; it is almost indistinguishable from the surrounding earth when closed. If the owner is not at home and you flip back the door, you will see on its silken underside a series of neat little black pinpricks. These are the handles, so to speak, in which the spider latches her claws to hold the door firmly shut against intruders. The only person, I think, who would not be amazed at the beauty of a trapdoor-spider’s nest is the male trapdoor-spider himself, for once he has lifted the trapdoor and entered the silken shaft, it is for him both a tunnel of love and death. Once having gone down into the dark interior and mated with the female, he is promptly killed and eaten by her.
One of my first experiences with animal architects was when I was about ten years old. At that time I was extremely interested in freshwater biology and used to spend most of my spare time dredging about in ponds and streams, catching the minute fauna that lived there and keeping them in large jam-jars in my bedroom. Among other things, I had one jam-jar full of caddis larvae. These curious caterpillar-like creatures encase themselves in a sort of silken cocoon with one end open, and then decorate the outside of the cocoon with whatever materials they think will produce the best camouflage. The caddis I had were rather dull, for I had caught them in a very stagnant pool. They had merely decorated the outside of their cocoons with little bits of dead water-plant.
I had been told, however, that if you remove a caddis larva from its cocoon and place it in a jar of clean water, it would spin itself a new cocoon and decorate the outside with whatever materials you cared to supply. I was a bit sceptical about this, but decided to experiment. I took four of my caddis larvae and very carefully removed them, wriggling indignantly, from their cocoons. Then I placed them in a jar of clean water and lined the bottom of the jar with a handful of tiny bleached seashells. To my astonishment and delight the creatures did exactly what my friend said they would do, and by the time the larvae had finished the new cocoons were like a filigree of seashells.
I was so enthusiastic about this that I gave the poor creatures a rather hectic time of it. Every now and then I would force them to manufacture new cocoons decorated with more and more improbable substances. The climax came with my discovery that by moving the larvae to a new jar with a new substance at the bottom when they were half-way through building operations, you could get them to build a parti-coloured cocoon. Some of the results I got were very odd. There was one, for example, who had half his cocoon magnificently arrayed in seashells and the other half in bits of charcoal. My greatest triumph, however, lay in forcing three of them to decorate their cocoons with fragments of blue glass, red brick and white seashells. Moreover, the materials were put on in stripes – rather uneven stripes, I grant you, but stripes nevertheless.
Since then I have had a lot of animals of which I have been proud, but I never remember feeling quite the same sort of satisfaction as I did when I used to show off my red, white and blue caddis larvae to my friends. I think the poor creatures were really rather relieved when they could hatch out and fly away and forget about the problems of cocoon-building.