CUCKOW. 403 



that, as before stated, would be here out of place.* It is 

 however especially necessary to guard against the error, into 

 which some writers have fallen, of supposing that the Cuckow 

 has the power of diversifying the colour of her eggs at will ; 

 that, having laid it, she should look at it, and then decide 

 into what bird's nest she should put it ; or further that its 

 colour can, in any mysterious way, be affected by the action 

 of external objects on her perceptive faculties. Such suppo- 

 sitions are wholly unreasonable. The assimilationf, if such 

 there be, must be involuntary on her part, and its only object 

 be to render it less easily recognized by the foster-parents 

 as supposititious. This and nothing more is the " theory " 

 of Dr. Baldamus. It remains to say that, in depositing her 

 eggs, the Cuckow (vagrant though she be) will, season after 

 season, resort to the same spot, or as near thereto as maybe. 

 Among many instances of this fact which might be cited, it 

 will be sufficient to refer to Mr. Gurney's statement, on 

 Mr. E. Fountaine's authority (Zool. s.s, p. 3648), that a 

 pair of Pied Wagtails nested twice every season with a single 

 exception for eight or nine years, ending in 1871, in the ivy 



* Yet an hypothesis has been proposed (Encycl. Brit. ed. 9, vi. pp. 686, 687), 

 which in outline is this: — Some birds resent interference with their nests much 

 less than others : among the former is the Hedge-Sparrow, and in her case no 

 assimilation is needed, in others it may be wanted. The tendency of habits to 

 become hereditary is admitted, and since it is probable that a Cuckow commonly 

 puts her eggs into the nest of the same species, it is no violent supposition that 

 her posterity should have the same habit. Again, the family likeness between 

 the eggs laid by the same individual is unquestionable, and therefore the habit of 

 laying a particular style of egg is probable to be hereditary also. Combining 

 this supposition with the last, it will be seen that on the principle of ' ' Natural 

 Selection" the asserted facts would follow. This principle would operate most 

 strongly in species which are not easily duped, that is in the cases which occur 

 least frequently. Here it is we find it, for Cuckows' eggs deposited in nests of 

 the Red-backed Shrike, the Redstart, the Icterine Warbler, and the Great Bunting 

 approximate most nearly to the eggs of those species — species in whose nests the 

 Cuckow rarely (in comparison with others) deposits eggs. The assimilation of 

 the eggs of the Great Spotted Cuckow (the species next to be described) to those of 

 the birds in whose nests they are found, is in some cases very remarkable, and 

 will in due time be mentioned. 



f This word, like "mimicry", as implying the idea of consciousness, is open 

 to objection on the part of those who do not know its technical meaning. 

 That idea must be excluded from both words, whenever either is employed 

 by a natiiralist. 



