CUCKOO'S EGGS.
(To THE EDITOR OF THE " SPECTATOR ".1
Sut,—My attention has been drawn to your recent correspond- ence re cuckoos' eggs. Without laying claim to any exceptional knowledge of cuckoos in general, I have been favoured with an opportunity, probably without parallel, of studying one individual cuckoo. Since the majority of those who rush into print upon all and sundry subjects appear to have had little or no practical experience of the subject upon which they write, the following record of what I have personally been privileged to see may interest those of your readers who really are seeking after the truth in regard to this most Interesting problem. Unfortunately, for reasons which will be obvious to ornithologists, a similar opportunity of observing any indi- vidual cuckoo is extremely unlikely to come the way of any naturalist, except on the rarest occasions. That reason alone sufficed to carry one through, with cheerful heart and the requisite patience, the many long and weary periods of monotonous waiting. The full story is a long one, most detailed notes having been made on the spot throughout the season, and as soon as compiled will be supplied to the editor of British Birds in pursuance of my report on last years experiences, published in September, 1919, but briefly the results achieved are as follows : During the last three consecutive seasons I have found (and possess to substantiate my claim) no less than dg eggs laid by the same cuckoo, all alike and readily distinguish- able from all other cuckoos' eggs, i.e., 9 in 1918, 16 in 1919, and 21 In 1920. To my knowledge one, almost certainly two, and possibly more, young from the same bird were successfully reared in 1918; again two young, but almost certainly no more than two, were also reared in 1919, whereas I am of the opinion that the 21 eggs deposited this year not only constitute the record number ever known to have been laid by one cuckoo in a season, but are, in fact, the total number laid by that cuckoo this year.
Last year's study enabled me to express the opinion that, provided the facilities, a cuckoo—or, at least, this cuckoo— would lay approximately every forty-eight hours. Fortunate], the return of this cuckoo for a third season's study enabled me this year to prove that, with extraordinary regularity, she would, and when enabled did, lay every other day, and ty the time the cuckoo had laid 10 eggs this season she had taught me so much that I actually watched her lay and deposit nine of the remaining 11 eggs of the series. I question whether ever before any one has been possessed of the necessary information to be able to foretell both when and where a ceckoo would lay her eggs so as to have had the satisfaction, as I had this season, of taking friends out on different days to see the cuckoo take up her position often in a given tree, watch her previously selected victim, and finally glide down beside the appointed nest, lay, and deposit with her beak the egg, and fly away with an egg in her beak which she had removed from the nest in exchange for her own. Having achieved my ambition this year to break all previous records in the number of eggs laid, I hope if the same cuckoo returns next season to get the whole egg-laying process filmed. On no occasion has this cuckoo deposited more than one egg in any one nest, even though force of circumstances must several times have sorely tempted her to adopt this suicidal habit. On The contrary, as suitable nests appeared unlikely to be available when required, she twice temporarily dis- continued laying this year. Or, to express the same thing rather differently, this cuckoo only persisted in laying every other day so long as a fresh nest (as opposed to one she had already victimised) of the meadow pipit (her favourite dupe) was made available for her.
A generally accepted theory amongst ornithologists is that a cuckoo will tend to deposit her eggs in nests of the same species as that by which she herself was reared. A moment's thought shows this to be most natural, and consequently probable. For example, a cuckoo reared by a hedge sparrow would naturally acquire a considerable knowledge of the habits of a hedge sparrow, which would stand her in good stead when desirous ef finding nests for her own eggs. That practice pursued down the generations might tend to cause the eggs of cuckoos to assimilate in many instances to those of their foster parents. On the other hand, I confess that experience teaches that by no means every cuckoo restricts herself to laying all her eggs in t he nests of one species, and this is one of the reasons why this particular record is likely to remain unique for a very long time. The much discussed theory that a cuckoo is possessed at the remarkable power of colouring her eggs to suit those of her dupes is, of course, too obviously childish to be believed by any recognised ornithologist. In due course I will advise you where a detailed record of my experiences of this cuckoo may be obtained so that those of your readers who are sufficiently interested may be notified.—I am, Sir, he., 9 Hay Hill, Berkeley Square, W. 1.
EDGAR CHANCE, B.O.U.
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