THE EUROPEAN CUCKOO 259 



whereas in England they are almost all of the spotted type. The number 

 of eggs laid by individual cuckoos depends to a certain extent on the 

 species of host favoured. Thus, in Germany "red-backed shrike" 

 cuckoos lay fewer eggs than "robin" cuckoos, for the breeding season of 

 the former host is much shorter. Sometimes, when nests are scarce or 

 an accident occurs, a cuckoo is compelled to lay in any nest she can 

 find. Also some cuckoos are eccentric and select unusual hosts and 

 others fail to establish a territory and have to lay at random in a wide 

 variety of nests. Thus, over fifty hosts have been recorded from Britain 

 alone, but nevertheless, the overwhelming majority of cuckoos in this 

 country lay their eggs in the nests of the five or six regular fosterers 

 mentioned above. It is, however, not known why a female cuckoo selects 

 a certain specific fosterer for her initial laying, and generally continues 

 to select similar fosterers throughout her period of reproductive 

 activity. Why does a "meadow-pipit" cuckoo in Britain, for example, 

 regularly select the nests of meadow-pipits rather than other small birds 

 in which to lay her first tgg ? This is one of the unsolved mysteries of 

 the cuckoo's life history. One possible explanation is that she has a 

 strong inclination to parasitise the same species by which she herself 

 was reared. Much of the recent work on bird behaviour has shown that 

 certain sights and sounds and general situations can act as stimuli 

 which release inborn and well formed patterns of behaviour. Thus it is 

 quite possible that the plumage and song of birds exactly similar to 

 those which reared her and the general appearance of their nest "rings 

 a bell," and acts as a "releaser" of this type (habitat imprinting which 

 in this case might be called host imprinting), and thus stimulates the 

 female cuckoo to foist her eggs upon them rather than any other species. 

 But this is pure conjecture. 



The eggs of the species as a whole are very variable both in regard 

 to colour and markings, but all the eggs from one individual bird are 

 similar. The various strains or gentes of cuckoos, such as "wagtail" 

 cuckoos and "pipit" cuckoos, have developed eggs which, to a greater 

 or lesser degree, resemble the eggs of the regular fosterers. 



Many small birds have an inherited fear and dislike of the adult 

 cuckoo. They will mob it and drive it off in the same w^ay in which they 

 attack birds of prey. Pliny wrote : "They know how all birds hate them 

 for even very little birds are readie to war with them." Some interesting 

 experiments could be done with models and stuffed specimens to try to 

 determine by what features the cuckoo is recognised. 



FFC— c 



