At night each of the habitations is lighted up by a fire-fly stuck on the top with a bit of clay. The nest consists of two rooms; sometimes there are three or four fire-flies, and their blaze in the little cells dazzles the eyes of the bats, which often kill the young of these birds.
While this work is passing through the press I meet with the following, which appears to refer to some independent, and therefore corroborative observation concerning the above-stated fact, and in any case is worth adding, on account of the observation concerning the rats, which, if trustworthy, would furnish a sufficient reason for the instinct of the birds. The extract is taken from a letter to 'Nature' (xxiv., p. 165), published by Mr. H. A. Severn:
I have been informed on safe authority that the Indian bottle-bird protects his nest at night by sticking several of these glow-beetles around the entrance by means of clay; and only a few days back an intimate friend of my own was watching three rats on a roof rafter of his bungalow when a glow-fly lodged very close to them; the rats immediately scampered off.
The Talegallus of Australia is, in the opinion of Gould,—
Among the most important of the ornithological novelties which the exploration of Western and Southern Australia has unfolded to us, and this from the circumstance of its not hatching its own eggs, which, instead of being incubated in the usual way, are deposited in mounds of mixed sand and herbage, and there left for the heating of the mass to develop the young, which, when accomplished, force their way through the sides of the mound, and commence an active life from the moment they see the light of day.[168]
Sir George Grey measured one of these mounds, and found it to be 'forty-five feet in circumference, and if rounded in proportion on the top (it being at the time unfinished) would have been full five feet high.' The heat round the eggs was taken to be 89°.
A curious aberration of the nest-building instinct is sometimes shown by certain birds—particularly the common wren—which consists in building a supernumerary nest. That is to say, after one nest is completed, another is begun and finished before the eggs are laid, and the first nest is not used, though sometimes it is used in preference to the second.
As showing at once the eccentricity which birds sometimes display in the choice of a site, and also the determination of certain birds to return to the same site in successive years, I may allude to the case published by Bingley, of a pair of swallows which built their nest upon the wings and body of a dead owl, which was hanging from the rafters of a barn, and so loosely as to sway about with every gust of wind. The owl with the nest upon it was placed as a curiosity in the museum of Sir Ashton Lever, and he directed that a shell should be hung upon the rafters in the place which had been previously occupied by the dead owl. Next year the swallows returned and constructed their new nest in the cavity of the shell.[169]
The following is quoted from Thompson's 'Passions of Animals,' p. 205:—
The sociable grosbeak of Africa is one of the few instances of birds living in community and uniting in constructing one huge nest for the whole society. L. Valiant's account has been fully confirmed by other travellers. He says: 'I observed on the way a tree with an enormous nest of these birds, which I have called republicans; and as soon as I arrived at my camp I despatched a few men with a waggon to bring it to me, that I might open and examine the hive. When it arrived, I cut it in pieces with a hatchet, and saw that the chief portion of the structure consisted of a mass of Boshman's grass, without any mixture, but so compact and firmly basketed together as to be impenetrable to the rain. This is the commencement of the structure, and each bird builds its particular nest under this canopy. But the nests are formed only beneath the eaves, the upper surface remaining void, without, however, being useless; for as it has a projecting rim, and is a little inclined, it serves to let the water run off, and preserves each little dwelling from the rain. Figure to yourself a huge irregular sloping roof, all the eaves of which are covered with nests, crowded one against another, and you will have a tolerably accurate idea of these singular edifices. Each individual nest is three or four inches in diameter, which is sufficient for the bird; but, as they are all in contact with one another around the eaves, they appear to the eye to form but one building, and are distinguishable from each other only by a little external aperture which serves as an entrance to the nest; and even this is sometimes common to three different nests, one of which is situated at the bottom and the other two at the sides. This large nest, which was one of the most considerable I had anywhere seen in the course of my journey, contained 320 inhabited cells, which, supposing a male and female to each, would form a society of 640 individuals; but as these birds are polygamous, such a calculation would not be exact.'