258 FLEAS, FLUKES AND CUCKOOS 



providing their clutch is incomplete — arc most likely to be absent. She 

 glides over the selected nest several times and then quickly alights in it 

 and lays one egg directly into the nest — the entire action occupying 

 no more than five seconds. Subsequently she destroys one or more of 

 the fosterer's eggs, either by throwing them out or by crushing and 

 eating them. Sometimes she carries one a considerable distance in her 

 beak before disposing of it. When the cuckoo deposits her egg in a small 

 domed nest with a side entrance it is impossible for her to enter and lay 

 in the usual manner. The egg is then forcibly projected into the aperture 

 from the bird's cloaca while she hovers immediately over the nest — a 

 feat which might excite envy in an Olympic athlete. Some hold the 

 view that on certain occasions it is first laid on the ground, picked up in 

 the cuckoo's beak and then dropped into the nest. Whether this some- 

 times happens is a matter of acute controversy. The majority of eggs (if 

 not all) which are seen being carried by cuckoos are not their own, but 

 eggs of the fosterers which they are about to destroy. 



If conditions are favourable and there are enough breeding pairs 

 of the right species of fosterer present, with incomplete or just completed 

 clutches, the female cuckoo will continue laying eggs at intervals of 

 about forty-eight hours until between fourteen and twenty have been 

 deposited. One female parasitising meadow-pipits has been known to 

 lay twenty-five eggs in one season. There are, however, rarely enough 

 nests available in a single territory to make such a feat possible, although 

 the cuckoo is able to keep several under observation simultaneously. 

 On occasion she will destroy a whole clutch in order that a particular 

 nest should be in a suitable condition to receive one of her eggs at a 

 later date. Some species such as the great spotted cuckoo lay several 

 eggs in the same nest, but the European cuckoo almost always distri- 

 butes her eggs singly. 



It is now a well-estabhshed fact that there are strains or "gentes" of 

 the European cuckoo which, throughout their Hves, parasitise only one 

 particular species of small birds. In Britain there are relatively few 

 regular hosts. The main fosterers used are the meadow-pipit, the robin, 

 the pied wagtail, the hedge-sparrow, the reed-warbler and the sedge- 

 warbler. In Germany a favourite host is the red-backed shrike, which is 

 rarely, if ever, attacked in Britain. In Finland, on the other hand, the 

 most popular fosterers are the redstart (which is rarely parasitised in 

 Germany), the wheatear, the whinchat and the pied flycatcher, all of 

 which lay blue eggs. In Finland 68 per cent, of cuckoos' eggs are blue, 



