"One of the greenfinches is again attacking the cones, and I can now see the way he does it more plainly. He places his beak between the clubs of the cones at their tips (I mean their outer ends), and then moves his head and beak rapidly, seeming, as it were, to flutter with his head, and as he does this you hear the grating, vibratory sound. All the time, he is clinging head downwards to the side of the cone, quite a feat for so large, at least for such a stout-built bird. I will not, however, be quite sure that it is to the cone itself that he clings. The fir-needles hang in bunches near them, and his claws may be fixed amongst these, though I do not think so, or, at least, not always. Besides this sound made with the beak on the fir-cones, there is another, which one often hears, and which is usually, I think, made by the greenfinch. To get at the cones, he often flies up underneath them, and hangs a little, thus, before clinging, on fluttering wings. When the tips of these strike amongst the bunches of needles, a sharp, thin, vibratory rattle is produced—also a very noticeable sound.
"The nut-hatch—or another one—now flies in again, uttering, as he arrives, a curious, high, sharp note—'zitch, zitch, zitch'—and again flies away with a thin brown flake in his bill, a very woody morsel it would seem. And now, later in the afternoon, I see a great-tit probing the cones with his bill, and he also pulls out a brown flake and flies away with it. Another does the same, hanging from the tip of a cone, on which he afterwards perches for a moment, before flying with it to another tree. Whilst standing, all this time, in the tree, I had noticed little hard brown seeds about the size of apple-pips, and which had all been cracked, lying in the forks formed by the junction of the branches with the trunk. There was hardly one such resting-place in which there were not a few of these cracked seeds. Pulling off a fir-cone, I began to pull it to pieces, and at once saw, at the base of every club where it had joined and helped to form the central pillar, the double indentation, one on either side of the median line—or mid-rib as it would be called in a true leaf—in which the two seeds had been lying. Soon I came upon a seed itself, and, attached to the outer end of it—that farthest from the base of the club—I at once recognised the little brown flaky leaf that I had seen in the bills of all three birds, but which none of them seemed to eat.
"Here, then, the whole mystery—for to my ignorance it had been such—was explained. The birds were picking out the seeds from the cone, and the way to do this was to seize the thin brown flake to which the seed was attached, and which lay all along inside each club or leaf of the cone, whereas the seed itself was right at the base, and the beak of the birds could not, perhaps (or not so easily), be pushed up so far between the stiff clubs, the hard edges of which would catch their foreheads uncomfortably. At least with the tit and greenfinch, whose bills are not long, this would seem to be likely. When the birds—as was evidently often the case—pulled out only the thin flake-leaf which had become detached from the seed, they let it fall negligently, thus conveying the impression that they had been taking trouble to no end. When, however, they flew away with it, it is to be presumed the seed was attached.
"Here, then, are three quite different birds, all busily occupied in extracting the seeds from the large cones of an exotic species of fir, but whilst two of them—the great-tit and the nut-hatch—effect this by first hammering on the cone, so as to loosen the seeds, or, rather, the woody flake to which they are attached, from the basal part of the club (if we may assume this to be the object) before pulling them out, the greenfinch procures them without any previous hammering, which is an action, perhaps, to which it is not accustomed. One should not, however, assume too hastily that the latter bird has no plan of his own for first loosening the seeds. Remembering the rapid, almost fluttering, motion—not at all like pecking or hammering—which he communicates to his head and bill, with the curious, vibratory sound—which again does not suggest an ordinary blow—that accompanies it, and how often when I could get a fairly good view of him, he seemed to be repeatedly seizing and letting his bill slip over the outer edges of the fir-clubs, I am inclined to think that he was making the stiff clubs vibrate on their stalks—their hinges, so to speak—in a manner that would tend to loosen the seeds as effectually, perhaps, as would tapping them.
"Judging by these limited observations, I should say that the nut-hatch was the most skilful of the three in extracting the seeds, as, on the two occasions when I saw him plainly, he flew away with a flake, soon (once almost immediately) after he had come. He looked more like a connoisseur, too, and his bill is much longer. He alone, as I should think, might possibly be able to drive it right down, so as to seize the actual seed. Yet he tapped the cone in the same quick manner as did the tit, nor did he appear to me to be probing it at such times. Moreover, I never observed him—any more than the others—to extract the seed independently of the flake."
Birds that are not tree-creepers will often behave very much as if they were so, and show different degrees of expertness in the art. It seems quite natural that a small bird, which habitually frequents trees, should sometimes cling to the trunk; but what surprises me is, that with so much raw material to have worked upon, nature should not have developed some of our small perching birds into actual tree-creepers. My observations on the blue-tit and the wren show, at least, that should anything occur to make it difficult for them to procure food in other ways, or should they (and this is easier to imagine) develop a partiality for some particular kind of insect or other creatures living in the chinks or under the bark of trees—say spiders, for instance, which are often to be found there in colonies—they would be all ready to become specialised experts. At least it appears to me so, and I think it the more curious because they do not seem often to practise what they can do so well. Here is my note, taken in October, when, perhaps, there would be a little more scarcity of the ordinary food of such birds, than in the spring and summer of the year.
"In a grove of Scotch firs this morning I noted, first a blue-tit, clinging to the trunk of one in the same manner as a nut-hatch or tree-creeper. Hardly had he flown off it when a wren flew to and commenced to ascend perpendicularly the trunk of a tree quite near me, flying thence to another which it also ascended, and so on from tree to tree. Afterwards, however, I was able to watch blue-tits acting in this manner for some little time, as well as quite closely, and I decided that they were the greater adepts of the two. They climbed the perpendicular or overhanging trunk with ease and swiftness, clinging to the roughnesses of the bark, at which they pecked from time to time, I imagine for insects. Usually they went straight upwards, but sometimes more or less slantingly. I also noted—and this I had not been able to do for certain in the wren—that they descended as well as ascended the trunks of the trees; but here the manner of progressing was not quite so scansorial, for it was with a little flutter. Whether they used the feet as well as the wings in the descent I could not actually see, but they kept quite near enough to the trunk to have done so. These little fluttering drops or drop-runs interested me very much. The bird never made them except whilst hanging on the trunk of the tree perpendicularly and head downwards, and when he stopped and clung to it again he was in precisely the same position. The drop each time might have been from four to six or seven inches. It never appeared to me to be more. Both the blue-tit, therefore, and the wren have acquired the habit of creeping about the trunks of trees, in search, presumably, of insects or spiders, as do the tree-creepers, wood-peckers, and nut-hatch. The former of them can descend the trunk, but not, it would appear, without the aid of its wings, either wholly or in part. For the wren, I saw him descend once, as I think, in a quick side-eye-shot; but some nettles intervened, and I cannot be sure."
"On the next morning I am at the same grove, and, about seven, a good many blue-tits fly into it, one of which is soon busily occupied on the trunk of a fir-tree. I now observe that this bird uses his wings even in ascending the trunk, for though he certainly crawls up it, yet he accompanies each fresh advance, after a pause, with a little flutter, and advance and flutter end commonly together, taking him but a very little way. A tree-creeper on the same tree, who moves deftly about, pressed much flatter to the trunk and never using his wings, gives a good opportunity of comparing the two birds—the professional and the amateur. Now, both according to my memory and my notes, the tits I saw yesterday did not flutter at all while ascending the tree—at any rate, that one which I saw quite close both ascending and descending, on which my note was principally based, did not; for though I saw others, this one gave me the best and longest view, and the only one of the descent. Had he fluttered in the ascent also, I must certainly have noted it, and I should not, then, have placed the two in such contradistinction. If an inference may be drawn from such limited observation, it, perhaps, is that this bird is in process of acquiring, or, at any rate, of perfecting, a habit, and that, therefore, all the individuals do not excel in it to an equal degree. The fact that I often watched and waited to see them practising the art again, but without success, may lend some colour to this. There was clinging sometimes, but not climbing."
In this competition, therefore, between the wren and the tit as tree-creepers, the tit bears off the bell; but later I had a better opportunity of observing the prowess of the latter bird, and, though I did not see it descend, yet in ease and deftness, length of time during which the part was assumed, and general fidelity of the understudy to the original, it must, I think, be pronounced the superior. It was early on a cold, rainy, cheerless morning towards the end of February, that I was so lucky as not to be in bed. I say—"Have, this morning, watched closely, and from quite near, a wren behaving just like a professional tree-creeper. It ascended the trunk of an alder, quickly and easily, and sometimes to a considerable height—twenty or thirty feet perhaps—beginning from the roots, and then flew down to the roots or base of the next one, and so on along a whole line of them. Up the sloping roots, or anywhere at all horizontal, it hopped along in the usual manner, but, when the trunk became perpendicular, it crept or crawled, just like a true tree-creeper.[19] I was, as I say, quite close, and watched it most attentively. It certainly—as far as good looking can settle it—did not assist itself with the wings. They remained close against the sides, or, if they moved at all, it was imperceptible to my eyes (which, by the way, are non-pareils). Nevertheless, at a later period—for I followed along the trees—when I watched it at only a few paces off, it as certainly appeared that it did use the wings, advancing up the trunk by flutterings, but these were so small and slight, and raised the bird so imperceptibly from the surface of the trunk, that it had all the while the appearance of creeping. As I was still closer to the bird during the latter part of my watching, it may be thought that this alone represents the actual fact; but, for my part, I cannot help thinking that my eyesight served me upon each occasion. If so, then here is more 'richness,' from a Darwinian point of view. The tits, it will be remembered, differed individually, but in this wren there was a personal variation. He could creep, in ascending, without using his wings, and generally did so; still he sometimes broke into a little flutter, which, in a more pronounced form, had been prevalent in his youth. His father always did it in this way, and there were very old wrens still living who only flew up a trunk. But this was thought very old-fashioned."
[19] I allude to the apparent motion. The tree-creeper itself, I believe, really hops.