8 
THE CUCKOO’S SECRET 
of Cuckoo on the strength of the facts gathered 
by him regarding the habits of the Shrike-Cuckoo. 
It is outside the scope of this book to discuss 
all Rev’s theories ; but I must quote one more 
passage from his work, before leaving it with a 
strong recommendation to all ornithologists to 
make its better acquaintance. 
In an interesting chapter on the uniformity of 
the eggs laid by one and the same Cuckoo, Rey 
gives the answer to the question so often put to me 
as to how and why I know that it is one and the 
same Cuckoo that I studied throughout four 
seasons. Rey’s words are these — 
“ As there is an immense difference between 
the eggs of different female birds in the case of the 
Cuckoo, the correspondence between the eggs of 
each individual bird furnishes us with an excellent 
means of studying the life habits of the individual, 
because its eggs serve us as proof of identity. And 
such an aid to identification is especially valuable 
in the case of the Cuckoo, which shows local and 
individual differences in its habits very much 
greater than those observed in the case of any 
other bird.” 
In fact, any one who challenges the ability of an 
oologist to identify individual Cuckoos by their 
