138 NA TURE NO TES 
April 2. — Lark 4.30, thrush 4.55, blackbird 4.35, hedge sparrow 4.39, robin 
4.45. Morning clear, warm. 
,, 3. — Lark 4.30, thrush 4.33, blackbird 4.40, robin 4.46. 
,, 4. — Lark 4.25, thrush 4.40, blackbird 4.45, robin 4.45. 
Free Public Library, Worksop. J. T. Houghton. 
June 10, 1902. 
Cuokoo. — In his interesting article on the cuckoo, in Nature Notes for 
May, Mr. Westell tells us that it has been proved that the cuckoo lays its egg on 
the ground, and then carries it in its mouth to the nest of the foster parent. It has 
also been shown* that the cuckoo’s egg is in many cases coloured like those beside 
which it is placed. Are we, then, to suppose that the cuckoo having laid an egg of 
a certain colour and pattern, seeks for a nest with similar eggs? This seems rather 
a clever performance for a bird of small brains, as I fancy the cuckoo has been 
proved to be. Or has the cuckoo already made its choice of a nest, and does 
the colour of her egg follow (« la Mrs. Nickleby, re Stratford-on-Avon)? But 
I blush to make the suggestion in a scientific paper. 
The writer of the article referred to quotes with approval Mr. Craig’s explana- 
tion of the cuckoo’s strange breeding habits. They result, he thinks, from the 
fact that the young cuckoo turns out the other occupants of the nest. This habit 
of the young necessitated the mother placing her eggs in the nests of other birds ; 
or, in the phraseology of natural selection, those which did so succeeded better 
in the struggle for existence, and lived down those which did not. 
We mwsX asstme, then, that the ancestral cuckoo built a nest and sat on its 
eggs like other birds. It is necessary also to assume that the young cuckoos in 
this case struggled together in the nest, and that one was able to turn some, or all, 
of the others out. Now we know that the cuckoo is able to throw out of the 
nest the smaller and weaker hedge sparrow or titlark. But according to the 
descriptions of those who have seen the operation it takes the young cuckoo all 
its time to do so. It would be a more difficult task to turn out a bird approxi- 
mately its own size and strength. Thus out of a number of eggs the cuckoo was 
able to rear only 07 te young bird. 
Then we must assume that in one or more cuckoos some spontaneous variations 
in brain structure caused them to put their eggs into the nests of other birds. 
These individuals obtained so great an advantage in the struggle for existence that 
they gradually lived down those that retained the habit of building their own nests. 
Notice the appalling amount of assumption required — the usual thing in 
attempts to explain facts on the principles of natural selection. But, supposing 
the ancestral cuckoo did build its own nest, and that its young did struggle 
together in the nest till one had turned out the others, and that the rest followed 
in the usual facile way indicated by the theory of natural selection, are we any 
nearer to a final solution ? Is the extraordinary fact of the young struggling 
together, and some being turned out, any easier of explanation? Such a habit 
must have been a disadvatitage, or else those birds which avoided the contingency 
by laying in the nests of others would have reaped no advantage. We must go 
back, then, to the time before the habit was acquired — when the cuckoo was like 
other birds, which — 
“ In their little nests agree.” 
Then, according to the usual formula of natural selection, certain individuals 
appeared with the curious instinct of struggling together in the nest. The 
strongest survived, .and obtained an advantage in the struggle for existence. So 
the habit was perpetuated and perfected. But we have already been obliged to 
assume that such a habit is a disadvantage ! 
To revert for a moment to the actual habits of the cuckoo as it is, one would 
like to know if a cuckoo which has once laid a blue egg and placed it in a hedge- 
sparrow’s nest will always lay blue ecgs ? 
G. W. Bulman. 
Last month a little hedge-sparrow built in a cluster rose-bush against the wall, 
close to our dining-room window. When we found the nest there were only two 
Letter from Sir Wm. Flower, quoted in “ Birds from Moidart,” p. 105. 
