220 BRITAIN'S BIRDS AND THEIR NESTS. 



all. The most striking feature about it is its undeni- 

 able outward resemblance to a Hawk. This resemblance 

 extends to the various stages of the plumage, and is 

 apparently sufficiently close to deceive small birds, who 

 will mob a Cuckoo as they would a Hawk. That they 

 have any natural instinct warning them against the 

 Cuckoo, as such, can scarcely be believed, in view of the 

 complete success of the deception practised by the species 

 on the birds it makes the foster-parents of its young. 

 The resemblance is too remarkable to be a mere coincidence, 

 and it must be regarded as a real example of mimicry. 

 The advantage gained by this mimicry is rather obscure, 

 however. At least part of the truth may lie in the 

 suggestion that the hawk-like appearance of the Cuckoo 

 frightens away victims of its parasitic habits, and allows 

 it time to work its nefarious purpose on their nests. 

 But this does not explain the resemblance between the 

 immature stages of Cuckoo and Hawk. Apart from 

 plumage, the birds have nothing in common. The Cuckoo 

 is a weak bird, and, apart from its parasitism, a harm- 

 less species, subsisting on insects and their larvae. The 

 resemblance in plumage, it may be mentioned, has 

 probably suggested the popular superstition, explaining 

 away migration, that Cuckoos become Hawks in winter ! 



It is, of course, in its nesting habits that the Cuckoo 

 is most remarkable, these being absolutely unique so far 

 as indigenous British birds are concerned. Other members 

 of the family foiuid in other parts of the world show 

 similar habits, often with special modifications. One 

 species, for instance, displays an extremely close mimicry 

 of the very bird it usually victimises. Other kinds of 

 Cuckoos, however, incubate their own eggs, and rear their 

 own yoiuig in a more or less ordinary manner. On the 

 other hand, certain utterly different kinds of birds possess 



