These birds have no monopoly of these careful dwellings; a considerable number of genera have carried this industry to the same degree of perfection.
When animals apply themselves in association to any work, they nearly always exhibit in it a marked superiority over neighbouring species among whom the individuals work in isolation. The construction of dwellings is no exception, and the nests of the Sociable Weaver Birds of South Africa are the best constructed that can be found. These birds live together in considerable colonies; the members of an association are at least two hundred in number, and sometimes rise to five hundred. The city which they construct is a marvel of industry. They first make with grass a sloping roof; giving it the form of a mushroom or an open umbrella, and they place it in such a way that it is supported by the trunk of a tree and one or two of the branches. ([Fig. 29.]) This thatch is prepared with so much care that it is absolutely impenetrable to water. Beneath this protecting shelter each couple constructs its private dwelling. All the individual nests have their openings below, and they are so closely pressed against one another that on looking at the construction from beneath, the divisions cannot be seen. One only perceives a surface riddled with holes like a skimmer; each of these holes is the door of a nest. The work may endure for several years; as long as there is room beneath the roof the young form pairs near their cradle; but at last, as the colony continues to increase, a portion emigrate to found a new town on another tree in the forest.[97]
The industry of the woven dwelling does not flourish among mammals; but there is one which excels in it. This is the Dwarf Mouse (Mus minutus), certainly one of the smallest Rodents. It generally lives amidst reeds and rushes, and it is perhaps this circumstance which has impelled it to construct an aërial dwelling for its young, not being able to deposit them on the damp and often flooded soil. This retreat is not used in every season; its sole object is for bringing forth the young. It is therefore a genuine nest, not only by the manner in which it is made, but by the object it is intended to serve. The mouse chooses in the midst of its usual domain a tuft with leaves more or less crossed; but not too inextricable, so that there may remain in the midst an empty space, in the centre of which the work will be arranged. Great ingenuity is shown in the preliminaries; the mouse simplifies its task by utilising material within its reach instead of going afar to collect them with trouble. The little animal examines the thicket, and on reflection chooses some thirty leaves which appear suitable. Then, without detaching them, it tears each into seven or eight threads which are held together by the base, and remain attached to the reeds. It is a clever idea to avoid losing a natural point of support. The little bands being thus prepared, they are interlaced and crossed with much art, the animal comes and goes, placing first one of them, then another above, taken from a different leaf. It has soon woven a ball about the size of the fist, and hollowed out the interior. ([Fig. 30.]) Delicate materials are not lacking around to make a soft bed. The mouse gleans and constantly brings in the light down of the willow, grains with cottony crests, and the petals of flowers. This is all carefully fitted, and when the edifice is completed the female retires into it to bring forth her young, which are there well sheltered against the dangers without, and the caprices of storms and floods. The nest is made with as much delicacy as that of any bird, and no other mammal except Man is capable of executing such weaver’s work.
The art of sewing among birds. — There are birds which have succeeded in solving a remarkable difficulty. Sewing seems so ingenious an art that it must be reserved for the human species alone. Yet the Tailor Bird, the Orthotomus longicauda, and other species possess the elements of it. They place their nests in a large leaf which they prepare to this end. With their beaks they pierce two rows of holes along the two edges of the leaf; they then pass a stout thread from one side to the other alternately. With this leaf, at first flat, they form a horn in which they weave their nest with cotton or hair. ([Fig. 31.]) These labours of weaving and sewing are preceded by the spinning of the thread. The bird makes it itself by twisting in its beak spiders’ webs, bits of cotton, and little ends of wool. Sykes found that the threads used for sewing were knotted at the ends.[98] It is impossible not to admire animals who have skilfully triumphed over all the obstacles met with in the course of these complicated operations.[99]
