It is not enough that animal industry should be able, to a certain extent, to adapt itself to casual exigencies when choosing the site of a nest; if the race is to thrive, something else is required, something which hide-bound instinct is unable to provide. The Chaffinch, for instance, introduces a great quantity of lichen into the outer layer of his nest. This is his method of strengthening the edifice and making a stout framework in which to place first the bottom mattress of moss, fine straw and rootlets and then the soft bed of feathers, wool and down. But, should the time-honoured lichen be lacking, will the bird refrain from building its nest? Will it forgo the delight of hatching its brood because it has not the wherewithal to settle its family in the orthodox fashion?
No, the chaffinch is not perplexed by so small a matter; he is an expert in materials, he understands botanical equivalents. In the absence of the branches of the evernias, he picks the long beards of the usneas, the wartlike rosettes of the parmelias, the membranes of the stictises torn away in shreds; if he can find nothing better, he makes shift with the bushy tufts of the cladonias. As a practical lichenologist, when one species is rare or lacking in the neighbourhood, he is able to fall back on others, varying greatly in shape, colour and texture. And, if the impossible happened and lichen failed entirely, I credit the Chaffinch with sufficient talent to be able to dispense with it and to build the foundations of his nest with some coarse moss or other.
What the worker in lichens tells us the other weavers of textile materials confirm. Each has his favourite flora, which hardly ever varies when the plant is easily accessible and which can be supplemented by plenty of others when it is not. The bird's botany would be worth examining; it would be interesting to draw up the industrial herbal of each species. In this connection, I will quote just one instance, so as not to stray too far from the subject in hand.
The Red-backed Shrike (Lanius collurio), the commonest variety in my district, is noteworthy because of his savage mania for forked gibbets, the thorns in the hedgerows whereon he impales the voluminous contents of his game-bag--little half-fledged birds, small Lizards, Grasshoppers, caterpillars, Beetles--and leaves them to get high. To this passion for the gallows, which has passed unnoticed by the country-folk, at least in my part, he adds another, an innocent botanical passion, which is so much in evidence that everybody, down to the youngest bird's-nester, knows all about it. His nest, a massive structure, is made of hardly any other materials than a greyish and very fluffy plant, which is found everywhere among the corn. This is the Filago spathulata of the botanists; and the bird also makes use, though less frequently, of the Filago germanica, or common cotton-rose. Both are known in Provencal by the name herbo dou tarnagas, or Shrike-herb. This popular designation tells us plainly how faithful the bird is to its plant. To have struck the agricultural labourer, a very indifferent observer, the Shrike's choice of materials must be remarkably persistent.
Have we here a taste that is exclusive? Not in the least. Though cotton-roses of all species are plentiful on level ground, they become scarce and impossible to find on the parched hills. The bird, on its side, is not given to journeys of exploration and takes what it finds to suit it in the neighbourhood of its tree or hedge. But on arid ground, the Micropus erectus, or upright micropus, abounds and is a satisfactory substitute for the Filago so far as its tiny, cottony leaves and its little fluffy balls of flowers are concerned.
True, it is short and does not lend itself well to weaver's work. Afew long sprigs of another cottony plant, the Helichrysum staechas, or wild everlasting, inserted here and there, will give body to the structure. Thus does the Shrike manage when hard up for his favourite materials: keeping to the same botanical family, he is able to find and employ substitutes among the fine cotton-clad stalks.
He is even able to leave the family of the Compositae and to go gleaning more or less everywhere. Here is the result of my botanizings at the expense of his nests. We must distinguish between two genera in the Shrike's rough classification: the cottony plants and the smooth plants. Among the first, my notes mention the following: Convolvulus cantabrica, or flax-leaved bindweed; Lotus symmetricus, or bird's-foot trefoil; Teucrium polium, or poly; and the flowery heads of the Phragmites communis, or common reed. Among the second are these: Medicago lupulina, or nonesuch; Trifolium repens, or white clover; Lathyrus pratensis, or meadow lathyrus;Capsella bursa pastoris, or shepherd's purse; Vicia peregrina, or broad-podded vetch; Convolvulus arvensis, or small bindweed;Pterotheca nemausensis, a sort of hawkweed; and Poa pratensis, or smooth-stalked meadow-grass. When it is downy, the plant forms almost the whole nest, as is the case with the flax-leaved bindweed; when smooth, it forms only the framework, destined to support a crumbling mass of micropus, as is the case with the small bindweed. When making this collection, which I am far from giving as the birds' complete herbarium, I was struck by a wholly unexpected detail: of the various plants, I found only the heads still in bud; moreover, all the sprigs, though dry, possessed the green colouring of the growing plant, a sign of swift desiccation in the sun. Save in a few cases, therefore, the Shrike does not collect the dead and withered remains:
it is from the growing plants that he reaps his harvest, mowing them down with his beak and leaving the sheaves to dry in the sun before using them. I caught him one day hopping about and pecking at the twigs of a Biscayan bindweed. He was getting in his hay, strewing the ground with it.
