As a rule this cuckoo disappears in early autumn, but we have an exceptional record of its occurrence in winter. One was shot at San Lucar de Barraméda, December 19, 1909.
This cuckoo, like all its old-world congeners,[70] is parasitic in its domestic ménage—that is, it adopts a system of reproduction by proxy—relying, as Canon Tristram long ago put it, on finding a “foundling hospital” for its young. But even the keen intellect quoted was at first at fault. For the great spotted cuckoo differs in one essential point from that “wandering voice” with which we are familiar at home. The latter deposits a single egg in casual nest of titlark, hedge-sparrow, wagtail—in short, of any small bird, regardless of the fact that its own egg may differ conspicuously from those of its selected foster-parent. The spotted cuckoo is more circumspect. Everywhere it restricts the delegated duty to some member of the Corvidae,[71] and in Spain exclusively to the magpies. Moreover, whether by accident or evolution, the cuckoo has so admirably adapted the coloration of its own egg to resemble that of its victim, as to deceive even so cute a bird as the magpie. Earlier ornithologists (as above suggested) failed for a moment to distinguish the difference—it was, in fact, the zygodactylic foot of an unhatched embryo that first betrayed the secret (Tristram, Ibis, 1859). On close examination the cuckoo’s eggs differ in their more elliptic form and granular surface; but, unless previously fore-warned and specially alert, no one would suspect that these were not magpies’ eggs, any more than does the magpie itself.
The spotted cuckoo deposits two, three, and even four eggs in the same magpie’s nest, sometimes leaving the lawful owner’s eggs undisturbed, in other cases removing all or part of them—we have noticed spilt yoke at the entrance. It would appear difficult, in these domed nests, for the young cuckoos to eject their pseudo-brothers and sisters; but this detail of their life-history remains, as yet, unsolved.
Crossbills.—Nature delights in presenting phenomena which no tangible cause appears to warrant. Such were the thrice-repeated invasions of Europe by “Tartar hordes”—they were only sand-grouse—that occurred during the past century (in 1863, 1872, and 1888); and in 1909 an analogous problem, though on minor scale, was offered by crossbills. From north to extreme south of our Continent these small forest-dwellers precipitated themselves bodily westwards. This was in July. All the west-European countries, from Norway to Spain, recorded an unwonted irruption. In Andalucia (at Jerez) crossbills were first noticed about mid-July, and their appearance so impressed country-folk little accustomed to discriminate small birds, as to suggest to them the idea that the strangers must have fled from Morocco to avoid the fighting then raging around Melilla! But in Spain a further and anomalous complexity followed. For the Spanish specimens we sent home, on being submitted to Dr. Ernst Hartert, proved to belong to a purely Spanish subspecies—a race distinguishable by its weaker mandibles and other minor variations. Hence the movement in Spain had been purely internal, and it became difficult to suppose that (although simultaneous) it could have been predisposed and actuated by precisely the same motives as those which compelled a more extensive exodus farther north. Thus results the curious issue—that presumably different causes, operating over a wide geographical area, produced similar and simultaneous effects. These immigrant crossbills disappeared from Andalucia at the end of August.
Crossbills we used to observe in winter in our pine-forests of Doñana; but owing to local causes they have now missed several years. Their migrations within Spain are rather on the vertical than the horizontal plane—that is, merely seasonal movements between the higher lands and the lower. In Spain, denuded of natural forest, the habitat of such birds is narrowly restricted. Hence their sudden appearance in new areas (such as this, at forestless Jerez) is at once conspicuous.
Glossy Ibis (Plegadis falcinellus).—Birds, as a rule, are strict geographists. They recognise fixed range-boundaries and abide thereby. But exceptions occur, and an instance has been offered by the glossy ibis. This bird has always been a conspicuous member of the teeming pajaréras, or mixed heronries, of our wooded swamps of Andalucia. But it was only as a spring-migrant that the ibis was known. It arrived in April and departed, after nesting, in September. A diluvial winter in 1907-8, however, apparently induced it to reconsider its “standing orders.” Already, that autumn, the ibises had departed—as usual. But in December (the whole country meanwhile having been inundated) they suddenly reappeared. Small parties distributed themselves over the marismas, and with them came an unwonted profusion of other waders, stilts and curlews, whimbrels and godwits, the latter a month or two before their usual date. All availed the occasion to frequent far-inland spots, normally dry bush and forest, nota quae sedes fuerat columbis, and one saw flights of waders and even ducks, such as teal and shoveler, circling over flooded forest-glades.
The changed quarters evidently met with approval, for each succeeding year since then we have had the company of ibises during winter.
An immature ibis, shot January 30, otherwise in normal plumage, had the head and neck brownish grey with curlew-like striations.
Slender-billed Curlew (Numenius tenuirostris).—Years ago we wrote in our wrath, moved thereto by the constant misuse of the term, that such a thing as a “rare bird” does not exist, save only in a relative sense. Go to its proper home, wherever that may be, and the supposed rarity is found abundant as its own utility and nature’s balances permit. Should some lost wanderer straggle a few hundred miles thence, it is proclaimed a “rare bird.”