686 CUCKOO has probably given rise to the vulgar, but seemingly groundless, belief that they suck the eggs of other kinds of birds. More than this, Mr Rowley, who has had much experience of Cuckovvs, declares (Ibis, 1865, p. 186) his opinion to be that traces of violence and of a scuffle between the intruder and the owners of the nest at the time of introducing the egg often appear, whence we are led to suppose that the Cuckow ordinarily, when inserting her egg, excites the fury (already stimulated by her Hawk like appearance) of the owners of the nest by turning out one or more of ths eggs that may be already laid therein, and thus induces the dupe to brood all the more readily and more strongly what is left to her. Of the assertion that the Cuckow herself takes any interest in the future welfare of the egg she has foisted on her victim, or of its product, there is no evidence worth a moment s attention. But a much more curious assertion has also been made, and one that at first sight appears so incomprehensible as to cause little surprise at the neglect it long encountered. To this currency was first given more than a hundred years ago by Salerne (UHist. Nat. <kc., Paris: 1767, p. 42), who was, however, hardly a believer in it, and it is to the effect, as he was told by an inhabitant of Sologne, that the egg of a Cuckow resembles in colour that of the eggs normally laid by the kind of bird in whose nest it is placed. In 1853 the same notion was prominently and indepen dently brought forward by Dr Baldarnus (Naumannia, 1853, pp. 307-325), and in time became known to English ornithologists, most of whom were sceptical as to its truth, as well they might be, since no likeness whatever is ordinarily apparent in the very familiar case of the blue- green egg of the Hedge-Sparrow and that of the Cuckow, which is so often found beside it. 1 Dr Baldamus based his notion on a series of eggs in his cabinet, 2 a selection from which he figured in illustration of his paper, and, however the thing may be accounted for, it seems impossible to resist, save on one supposition, the force of the testimony these specimens afford. This one supposition is that the eggs have been wrongly ascribed to the cuckow, and that they are only exceptionally large examples of the eggs of the birds in the nests of which they were found, for it cannot be gainsaid that some such abnormal examples are occasionally to be met with. But it is well known that abnormally-large eggs are not only often deficient in depth of colour, but still more often in stoutness of shell. Apply ing these rough criteria to Dr Baldamus s series, most of the specimens stand the test very well, and, though no doubt more precise and delicate examination, than any to which they seem to have been submitted, were desirable, there are some other considerations to be urged. For instance, Herr Braune, a forester at Greiz in the principality of Reuss (Naumannia, torn. cit. pp. 307, 313), shot a hen Cuckow as she was leaving the nest of an Icterine Warbler (Hypolais -icterind). In the oviduct of this Cuckow he found an egg coloured very like that of the Warbler, and on looking into the nest he found there an exactly similar egg, which there can be no reasonable doubt had just been laid by that very Cuckow. Moreover Herr Gruuack (Journ. fur Orn., 1873, p. 454) has since found one of the most abnormally-coloured specimens, quite unlike the ordinary egg- of the Cuckow, to contain an embryo so fully formed as to show the characteristic zygodactyl feet of the bird, thus proving unquestionably its parentage. Now these being both of them extreme cases, Dr Baldamus may fairly claim attention to his assertion ; for short of absolutely disbelief ing his word we must admit that he has ground for it. 1 An instance to the contrary has been recorded by Mr A. C. Smith (Zoologist, 1873, p. 3516) on Mr Brine s authority. 2 This series was seen iu 1861 by the writer. On the other hand, we must bear in mind the numerous instances in which not the least similarity can be traced as in the not uncommon case of the Hedge-Sparrow already mentioned, and if we attempt any explanatory hypothesis it must be one that will fit all round. Such a one then seems to be this. We know that certain kinds of birds resent interference with their nests much less than others, and among them it may be asserted that the Hedge-Sparrow will patiently submit to various experiments. She will brood with complacency the egg of a Redbreast (Eritkacus rubecula), so unlike her own, and for aught we know to the contrary may even be colour-blind. In the case of such a species there would be no need of anything further to insure success the terror of the nest-owner at seeing her home invaded by a Hawk-like giant, and some of her treasures tossed out, would be enough to stir her motherly feelings so deeply that she would without misgiving, if not with joy that something had been spared to her, resume the duty of incubation so soon as the danger was past. But with, other species it may be, nay doubtless it is, different. Here assimilation of the introduced egg to those of the- rightful owner may be necessary, for there can hardly be a doubt as to the truth of Dr Baldamus s theory (the only theory, by the way, he has put forth), as to the object of the assimilation being to render the Cuckow s egg " less easily recognized by the foster-parents as a substituted one." But in this place it is especially desirable to point out that theic is not the slightest ground for imagining that the Cuckow, or any other bird, can voluntarily influence the colour of the egg she is about to lay. Over that she can have no control, but its destination she can determine. It would seem also impossible that a Cuckow having laid an egg, should look at it, and then decide from its appearance in what bird s nest she should put it. That the colour of an egg-shell can be in some mysterious way affected by the action of external objects on the perceptive faculties of the mother is a notion too wild to be seriously entertained. Consequently, only one explanation of the facts can here be suggested. Every one who has sufficiently studied the habits of animals will admit the tendency of some of those habits to become hereditary. That there is a reasonable probability of each Cuckow mostcommonly putting her eggs in the nest of the same species of bird, and of this habit being transmitted to her posterity, does not seem to be a very violent supposition. Without attributing any wonder ful sagacity to her, it does not seem unlikely that the Cuckow which had once successfully foisted her egg on a Reed-Wren or a Titlark should again seek for another Reed- Wren s or another Titlark s nest (as the case may be), when she had another egg to dispose of, and that she should con tinue her practice from one season to another. It stands on record (Zoologist, 1873, p. 3648) that a pair of Wagtails built their nest for eight or nine years running in almost exactly the same spot, and that in each of those years they fostered a young Cuckow, while many other cases of like kind, though not perhaps established on authority so good, are believed to have happened. Such a habit could hardly fail to become hereditary, so that the daughter of a Cuckow which always put her egg into a Reed-Wren s, Titlark s, or Wagtail s nest would do as did her mother. Furthermore it is unquestionable that, whatever variation there may be among the eggs laid by different individuals of the same species, there is a strong family likeness between the eggs laid by the same individual, even at the interval of many years, and it can hardly be questioned that the eggs of the daughter would more or less resemble those of her mother. Hence the supposition may be fairly regarded that the habit of laying a particular style of egg is also likely to become hereditary. Combining this supposition with that
as to the Cuckow s habit of using the nest of the same