Chapter XXI: The Cement of Bird Masons

Birds may be divided into two classes—those which build nests and those which do not. To the latter belong the parasitic starlings and cuckoos, which drop their eggs in the nests of other birds; those, such as plovers, which lay their eggs on the bare ground; and those which deposit them in holes, in the earth, in trees, in banks, or in buildings, as, for example, the Indian roller or blue jay (_Coracias indica_).

Intermediate between the birds that build nests and those which do not—for there are no sudden transitions, no sharply defined lines of division in nature—are those birds which merely furnish, more or less cosily, the ready-made holes in which they deposit their eggs. The common myna (_Acridotheres tristis_) affords a familiar instance of this class of birds. Some of the nest-builders are really excavators; they dig out their nests in a tree or bank. The woodpeckers and the bee-eaters are examples of these. The rest of the nest-builders actually construct their nurseries. These buildings are of various degrees of complexity. Crows, doves, birds of prey, herons, and a few other families are content with a mere platform of sticks and twigs, which rests in the fork of a tree, or on a ledge or other suitable surface. The birds which build primitive nests of this description are not put to the trouble of seeking or manufacturing any cohesive materials. It is only when the nest takes some definite shape and form that means have to be found of binding together the materials of which it is composed, and of attaching the whole to that which supports the nest. In such cases the component materials are either woven or cemented together. It is among the woven nests that we find the highest examples of avian architecture. The homes of the weaver-bird (_Ploceus baya_) and of the Indian wren-warbler (_Prinia inornata_) are constructed with a skill that defies competition. But it is not with these wonderful nests that we are concerned to-day. It must suffice to say that woven nests have to be supported; they cannot float in the air. There are various methods of supporting them. The nest may be firmly wedged into a forked branch. It may be bound to its supports, as in the case of the nest of the king crow (_Dicrurus ater_). The supporting branches may be worked into its structure, as is done by _Prinia inornata_. The nest may hang, as does that of _Ploceus baya_. It may be cemented to its support, as in the case of the nests of the various swifts; or it may rest on supporting fibres which are slung on to a forked branch, just as a prawn net is slung on to its frame. The golden oriole (_Oriolus kundoo_) resorts to this ingenious device.

Coming now to those nurseries in which the building materials are cemented together, we must first consider the nests of the swallows and swifts. These birds secrete a very sticky saliva, which quickly hardens when it is exposed to the air. This constitutes an excellent cement. Watch a swift working at its nest under the eaves of a house. It flies to it with a feather or piece of straw carried far back in the angle of its mouth, hangs itself by means of its four forwardly directed toes on to the half-completed nest, which is stuck on to the wall of the house, and, having carefully placed the feather or straw in the required position, holds it there until the sticky saliva it has poured over it has had time to harden and thus firmly glue the added piece of material to the nest. The bits of straw, feathers, etc., may be said to constitute the bricks, and the saliva the cement of the swift’s nest. Some swifts build their nests exclusively of their saliva. These constitute the “edible birds’ nests” of commerce, and may be likened to houses built entirely of cement. The martin (_Chelidon urbica_), the common swallow (_Hirundo rustica_), and the wire-tailed swallow (_H. smithii_) construct their nests of clay and saliva. They repair to some puddle and there gather moist clay, which they stick on to some building, so as to form a projecting saucer-shaped shelf. In this the eggs are laid. But nature has not vouchsafed sticky saliva to all birds, so that many of them have to find their cement just as they have to seek out the other building materials they use.

The chestnut-bellied nuthatch (_Sitta castaneiventris_), which nestles in holes in trees, fills up all but a small part of the entrance with mud “consolidated with some viscid seed of a parasitical plant.”

The hornbills close up the greater part of the orifice of the hole in which they nest with their droppings mixed with a little earth.

Hume informs us the rufous-fronted wren-warbler (_Franklinia buchanani_) utilises a fungus as its cement. “In all the nests that I have seen,” he writes, “the egg-cavity has been lined with something very soft. In many of the nests the lining is composed of soft, felt-like pieces of some dull salmon-coloured fungus, with which the whole interior is closely plastered.”

The cement which is most commonly used is cobweb. I do not think that I am exaggerating when I say that cobweb enters extensively into the structure of the nests of more than one hundred species of Indian birds. What birds would do without our friend the spider I cannot imagine.

The nest of some birds is literally a house of cobwebs. The beautiful white-browed fan-tail fly-catcher (_Rhipidura albifrontata_) is a case in point. Its nursery is so thickly plastered with cobweb as to sometimes look quite white. It is a tiny cup that rests on a branch of a bush or small tree, and is composed of fine twigs and roots, which are cemented to the supporting branch and to one another by cobweb. This the bird takes from the webs of those trap-door spiders which weave large nets on the ground.

Utterly regardless of the feelings of the possessor of the web, the fly-catcher takes beakful after beakful of it, and smears it over the part of the branch on which the nest will rest. It then sticks to this some dried grass stems or other fine material, next adds more cobweb, and continues in this manner until the neat little cup-shaped nest is completed. This, as I have already said, is thickly coated exteriorly with cobweb to give it additional strength.

The sunbirds or honeysuckers make nearly as extensive use of cobweb in nest construction as do the fan-tailed fly-catchers. Loten’s honeysucker (_Arachnechthra lotenia_) seeks until it finds a large spider’s web stretched horizontally across some bush; it then proceeds to build its nursery in the middle of this. As the material is added the nest grows heavier, and thus depresses the middle of the web until it at last assumes the shape of a V, in the angle of which the mango-shaped nest is situated. The nursery is thus suspended from the bush by the four corners of the cobweb.

A spider’s web looks such a flimsy affair that it does not seem possible that it could support a nest peopled by a number of birds. Sometimes the nest derives additional support by being attached to other branches. Moreover, a tiny creature such as a sunbird is almost as light as the proverbial feather. Then cobweb is exceedingly elastic, and, considering its attenuity, is able to support a surprising amount of weight. It occasionally happens that the common garden spider (_Epeira diadema_) is not able to find a _point d’appui_ to which it can attach the lower part of its web; it then utilises a stone (which may be as much as a quarter-inch in each dimension) as a plummet to make the nest taut. This comparatively heavy stone hangs by a single thread.

I have sometimes amused myself by testing the strength of a strand of cobweb stretched across a path, by hanging bits of match or other light material on it. In one experiment a gossamer thread, thirty feet in length, stretched across a road, bore the weight of five blades of grass which were hung upon it. The sixth blade proved to be the last straw that broke the camel’s back.

The strength of cobweb is proved by the fact that many of the birds that build hanging nests use it as cement to attach them to the supports from which they are suspended. The Indian white-eye (_Zosterops palbebrosa_) fixes its tiny oriole-like nest to the supporting branches, not by fibres, but by cobweb. In the same way the yellow-eyed babbler (_Pyctorhis sinensis_), whose nest is shaped like an inverted cone, attaches this by cobweb to the stems of the crop in which it is situated.

The common honeysucker (_Arachnechthra asiatica_), whose nest looks like a tangle of dried twigs and other rubbish, uses much cobweb in the construction thereof. The little nursery is suspended by means of cobweb from some projecting branch of a bush, and the various materials which compose it are stuck together with spider’s web; but in this case some sticky resinous substance is usually used in addition to the cobweb.

The tailor-bird (_Orthotomous sutorius_) always uses cobweb to draw together the edges of the leaf or leaves that compose its nest. Having made a series of punctures along the edges of the leaf to be utilised, it procures some cobweb, and, having attached it to one edge of the leaf, carries the strand across to the other edge and, before attaching it to this, pulls it so tightly as to draw the two edges together. When the nest has taken its final shape the bird strengthens the first attenuated strands of cobweb by adding more cobweb or some threads of cotton.

Many birds which weave their nests plaster the exterior more or less thickly with cobweb so as to add strength to the structure.

It would be wearisome to detail all the kinds of nest into the composition of which cobweb enters. Sufficient has been said to show that this very useful substance is the favourite cement of bird masons.