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To this list Dr. Baldamus, from other sources,
has added the following :1
Great Reed Warbler.
And lastly, in a foot-note to Mr. Dawson Rowley's article on the Cuckoo,2 in which the above lists were quoted, Professor Newton has pointed out the authority which exists for including the following, at least occasionally, amongst the foster parents of the young Cuckoo :—
1 "Naumannia," 1853, p. 307.
s On certain facts in the economy of the Cuckoo, "Ibis," 1865, pp. 178—186.
He confirms, moreover, Mr. Rowley's remark that the Cuckoo's egg is occasionally found in the nest of the Brambling (Fringilla montifringilld).
I have still to name four species which are not included in any of the above lists, viz., the Spotted Flycatcher, Yellow Wagtail, Grey Wagtail, and Wheatear. They were noticed by me some years ago in the first work I ever published.2 In the case of the Wheatear, a nest of that bird containing three eggs of the Wheatear and one of the Cuckoo was placed under a
1 This species, however, is included in Dr. Thienemann's list above given.
2 "The Birds of Middlesex," 1866, p. 120.
clod, and in such a position as strongly to favour the opinion of some naturalists that the Cuckoo first lays her eggs and then deposits them with her bill in the nest.
Considering the amount of attention which has been bestowed upon the Cuckoo by naturalists in every age down to the present, one would suppose that every fact in connection with its life-history was now pretty generally known. Such, however, is not the case. There are still certain points which require investigation, and which, owing chiefly to the vagrant habits of the bird, are not easily determined.
How can it be ascertained with certainty, for example, whether the same hen Cuckoo always lays eggs of the same colour, or whether (admitting this to be the case) she invariably lays in the nest of the same species—that is, in the nest of that species whose eggs most nearly approximate in colour to her own?
And yet we must be satisfied on these points if we are to accept the ingenious theory of Dr. Baldamus. If I understand the learned German rightly, he states that, with a view to insure the preservation of species which would otherwise be exposed to danger, Nature has endowed every hen Cuckoo with the faculty of laying eggs similar in colour to those of the species in whose nest she lays, in order that they may be less easily detected by the foster parents, and that she only makes use of the nest of some other species [i.e. of one whose eggs do not resemble her own) when, at the time she is ready to lay, a nest of the former description is not at hand. This statement, which concludes a long and interesting article on the subject in the German ornithological journal "Naumannia," for 1853, has deservedly attracted much attention. English readers were presented with an epitome of this article by Mr. Dawson Rowley in the "Ibis" for 1865, and the Rev. A. C. Smith, after bringing it to the notice of the Wiltshire Archaeological Society in the same year, published a literal translation of it in the "Zoologist" for 1868. More recently, an article on the subject, by Professor Newton, appeared
in "Nature" and elicited various critical remarks from Mr. H. E. Dresser, Mr. Layard, and other ornithologists which deserve perusal.1
To enter fully upon the details of this interesting subject would require more space than can here be accorded; one can only glance therefore at the general opinions which have been expressed in connection with it.
If the theory of Dr. Baldamus be correct, is it possible to give a reasonable and satisfactory explanation of it? This question has been answered by Professor Newton in the article to which we have just referred. He says :— "Without attributing any wonderful sagacity to the Cuckoo, it does seem likely that the bird which once successfully deposited her eggs in a Reed Wren's or a Titlark's nest, should again seek for another Reed Wren's, or a Titlark's nest (as the case may be) when she had an egg to dispose of, and that she should continue her practice from one season to another. We know that year after year the same migratory bird will
1 See "Nature," 18th Nov. and 23rd Dec, 1869, 6th Jan., 7th July, and 18th Aug. 1870.