496 THE CUCKOO 



Now in a well wooded district, with innumerable hedgerows, gardens, 

 and coppices, it is quite impossible for the keenest bird-nester to be 

 able to work every possible breeding-place. The best results have 

 therefore naturally been obtained in England in the case of such 

 species as the reed-warbler, which is confined to a limited area on 

 the banks of our rivers, and, as far as they go, these observations 

 tend to confirm Capek's conclusions. Of course no definite results 

 could have been arrived at if it were not for the fact, which may 

 be regarded as definitely proved, that each hen cuckoo lays eggs of 

 a similar type throughout her life. The marvellous series of eggs 

 collected by the Revs, with the index number of each hen on the 

 test-tube containing the clutch, would convince the most sceptical. 



As a general rule it may be stated that each hen cuckoo lays by 

 preference in the nest of some one species. When this species is 

 plentiful it is probable that all the eggs are laid in this way. But if 

 we suppose that a hen cuckoo is parasitic on the reed-warbler, and 

 after successfully depositing four or five eggs she finds the supply of 

 foster-parents exhausted, as the colony of reed-warblers is only a small 

 one, it is natural that she should make use of a sedge-warbler's nest 

 with fresh eggs in the same locality. This we know from experience 

 does frequently take place, and in all probability many of the rarer 

 foster-parents are only made use of owing to the fact that the cuckoo 

 can find nothing really suitable for the purpose. I am inclined to 

 think that in some cases they are merely intended as a temporary 

 convenience, for cases have fallen within my own experience in which 

 a cuckoo's egg has proved to be incubated for some days, while the 

 eggs of the foster-parent were quite fresh. 1 Unless the cuckoo's 

 egg had been left for a day or two in the nest of some other 

 species, it is difficult to account for this, as it is hardly credible that 

 a bird would brood over a cuckoo's egg for some days before she 

 had begun to lay. 



1 Cf. also H. Reeks, Zoologist, 1863, p. 8681 : J. G. Tuck, Zoologist, 1899, p. 323 ; 1901, 

 p. 317. 



