Not the least interesting feature of the nest is the clay which is studded about it in lumps. In one nest Jerdon found no fewer than six of these lumps, weighing in all three ounces. The clay has, I think, three uses: it helps to balance the nest, it prevents it being blown about by every gust of wind, and keeps it steady while the bird is entering it.
A story is abroad, and is repeated in nearly every popular book on ornithology, to the effect that the weaver bird sticks fireflies on these lumps of clay, and thus illuminates the nursery, or renders it terrifying to predacious creatures. Jerdon scoffs at this firefly story, and I, too, am unable to accept it. Nevertheless it is so universally believed by the natives of India that there must be some foundation for it.
Some time ago a correspondent living on the West Coast of India informed me that weaver birds are very abundant in that part of the country, that their nests are everywhere to be seen, and that he had noticed fireflies stuck into many of them. He asked if I could explain their presence. I suggested in reply that he had made a mistake and requested him to look carefully next nesting season, that is to say in August, and, if he came upon a single nest on to which a firefly was stuck, to take it down, fireflies and all, and send it to me at my expense. Since then August has come and gone thrice, and I have heard nothing from my correspondent! Thus it is that I am still among those that disbelieve the firefly story.
My theory is that the bird brings the clay to the nest in its bill in a moist condition. Now wet clay retains moisture for some time and would shine quite brightly in the moonlight, so might easily be mistaken for a firefly. Unfortunately the weaver bird is not common where I am now stationed, so that I have not had an opportunity of putting this theory to the test. I have, however, noticed how the nests built by solitary wasps shine when the clay that composes them is wet.
The natives of Northern India attribute great medicinal value to the nest of the weaver bird. They assert that a baby will never suffer from boils if it be once washed in water in which a weaver bird’s nest has been boiled!
A great many half-finished weaver birds’ nests are seen in India. Most of these are the work of the cock, who thus amuses himself while his wife is incubating. A few are nests which have gone wrong, nests which do not balance nicely and so have not been completed.