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. [Illustration: CROSSBILLS, ADULT AND YOUNG (_Loxia curvirostra_.) JEREZ, July 1910.] 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.