356 



SCIENCE-GOSSIP. 



acl'.ial obseivation of tlie cuckoo's methods, there 

 can be no doubt that the egg is never actually laid 

 in the nest, but is invariably deposited upon the 

 ground or elsewhere, and then conveyed by the 

 female in its gullet to a nest previously selected. It 

 is in this fact that we find the real explanation of 

 the remaikably small size of the egg in proportion to 

 that of the cuckoo itself. It would he impossible for 

 the bird to carry safely the egg in its mouth if its 

 burden were in the least degree larger. 



Before it became known that the cuckoo's egg was 

 not laid directly in the nest, it was commonly sup- 

 posed that the reason for the egg beir^ so small was 

 that it could thereby be introduced among those of 

 small insectivorous birds that would provide the 

 young cuckoo with its proper food. The fact that 

 the egg is frequently found in the nests of seed- 

 eaters, as well as in those of birds,, that lay larger 

 eggs, such as the blackbird, &c. , renders the ex- 

 planation given above far more probable. A veiy 

 interesting fact in this connection, and one which 

 seems to have been generally overlooked, is that the 

 shell of the cuckoo's egg is very much harder than a 

 similar-sized egg of any Passerine bird, obviously a 

 provision of Nature against the peculiar usage to 

 which the egg is subjected. j\s might be expected, 

 this extra strength results in a correspondingly greater 

 density and weight in the shell. Thus a trustworthy 

 means of identifying cuckoos' eggs, formerly a diffi- 

 cult matter, is to take a suspected "cuckoo clutch "' 

 to a chemist and get hinr to weigh all the eggs 

 accurately, when the cuckoo's egg, if really there, 

 will be indicated by its extra weight, on account of 

 proving 25 per cent, heavier than a similar-sized egg 

 of a Passerine bird. I am indebted to Mr. II. .W. 

 Marsden, of Clifton, for the following table -illustra- 

 tive of proportionate weights, based upon practical 

 experiments, which will no doubt be found- helpful 

 by oologists. The weights are in centigrammes : — 



Cuckoo'-s of same 

 Species Weiglit size 



should \veigh 

 .Skylark .. .. .. 21c.gr... 24 to 26 c.gr. 



17 ., •■ „ 



, 18 ,, .. 



19 .. •• „ ,, 



„ (very large egg) . . 22 „ .. 281030 „ 

 House-sparrow (very 



heavy for the .specie.s) 21 ,, .. 24 to 26 ,, 



House-sparrow .. .. ig ,, .. 221024 



" " •• •• is .. •• „ „ !! 



Tree-pipit .. .. i6.i,, .. 201023 >. 



Tree-sparrow .. .. 15 ,, .. 20 to 2i 



The eggs of the cuckoo are rather more globular 

 than those of most of the birds in whose, nests they 

 are found, and, moreover, usuall)- show little or no 

 gloss. The Re\-. Julian (_;. Tuck writes that he has 

 always noticed that the yolk is peculiar in colouring, 

 with either a greenish or brownish tinge. 



Among the various species whose nests are selected 

 by the cuckoo as receptacles for its eggs may be 

 envnnerated the hedge-sparrow, house-sparrow, tree- 



sjiarrow, wren, linnet, bullfinch, swallow, wheatear, 

 nightingale, willow-wren, wood-wren, skylark, tree- 

 pipit, whitethroat, meadow-pipit, pied wagtail, sedge- 

 warbler, reed-warbler, yellow-bunting, cirl-bunting, 

 blackbird, garden-warbler, blackcap, redstart, red- 

 backed shrike, spotted flycatcher, redbreast, green- 

 finch, reed-tunting, chafifinch, song-thrush, mistle- 

 thrush, ring-ouzel, stonechat, and whinchat. 



The existence of a remarkable number of widel}' 

 dissimilar \'arieties of eggs of the cuckoo is a point 

 around which a good deal of controversy has at times 

 been waged. Much careful observation is necessar)- 

 still to elucidate facts out of the many existing theories. 

 To describe all the different varieties in the limited 

 space at my comiriand would be an impossibility. I 

 will therefore merely say that the more connnon 

 varieties vary from greenish-white to pale rufous-gre_\', 

 spotted and mottled closely or otherwise with olive- 

 brown or rufous-brown of different shades. The 

 average size is -90 by 75 of an inch ; but they var\- 

 a good deal. Among the principal varieties may be 

 mentioned eggs almost precisely like those of the 

 skylark, pied wagtail, house-sparrow, tree-sparrow, 

 sedge-warbler, tree-pipit, reed-warbler, cScc. In Con- 

 tinental collections a pale blue egg without markings 

 is not uncommon, although I have never known one 

 of this variety to be taken in Britain. This remark- 

 able and wholesale mimicry has gi\-en rise to an 

 absurd theory, still held to some extent, that the 

 female cuckoo has the power to lay an egg of any 

 particular colour or markings she chooses, in order 

 to make it match those amongst which she intruded. 

 Thus when she selected a nest with blue eggs, such as 

 a hedge-sparrow's, she would lay a blue egg, and so 

 on. A far more natural theory, however, is that 

 certain individuals lay eggs of a certain type, and 

 therefore instinctively endeavour to select nests con- 

 taining eggs of a similar appearance to their own — 

 the fact that they sometimes deposit their egg with 

 a clutch of dissimilar eggs being, of course, explained 

 by the supposition of difficulty in finding an appro- 

 priate nest ; therefore it was put into the first likely 

 one. 



A very interesting fact is that the nest selected 

 never contains incubated eggs at the time the in- 

 trusion takes place. This is, no doubt, usuall)- made 

 sure through the cuckoo's habit of watching when 

 the eggs of the rightful owner are laid. This fact is 

 very necessary, for otherwise the eggs of the rightful 

 owner of the nest might be hatched before the 

 cuckoo's, and the foster-brethren thus enabled to 

 becon)e too strong for their eviction by the parasite, 

 which event invariably takes place soon after the 

 latter is hatched. The unfortunate occupants are 

 then ejected from the nest one after the other, in 

 which way the young cuckoo provides insensibly for 

 the receipt of the enormous quantity of food ii 

 requires, and withotrt which it would inevitably 

 starve. It has been ' said that this ejection takes 

 place when the parasite is nine or ten days old ; Ijut 

 my experience is that it .always occurs before the 



