INTRODUCTORY 
7 
The results of our own investigation will doubt- 
less be regarded as proof of the soundness of Rey’s 
reasoning. Clearly the only possible way of 
discovering definitely, as we claim to have done — 
(1) The normal interval a Cuckoo requires 
between the laying of her eggs ; 
(2) The number of eggs which an individual 
Cuckoo can, under favourable circumstances, 
lay in a season ; and 
(3) The incidents preceding and during the process 
of the laying of an egg by a Cuckoo — 
is to find the whole of the possible fosterers’ nests 
throughout the laying season in the whole of a par- 
ticular Cuckoo’s laying area, and to create in that 
area throughout the season a continuous supply 
of nests of the species of fosterer most favoured 
by the particular Cuckoo under observation. 
Valuable as Dr. Rey’s careful investigations 
undoubtedly are, I am unable to share many of his 
conclusions. The majority of his observations 
would appear to have been confined to Cuckoos 
whose dupes were Red-backed Shrikes (Lanius 
collurio, L.) ; and I would commend to the notice 
of naturalists, for their emulation, Dr. Rey’s sane 
attitude in refusing to generalise about all types 
