PREFACE 
The claim made by the title of this book* is based 
upon the fact that never before in the history of 
ornithology has any observer been able to foretell 
the time, place, and circumstances of the laying of 
a Cuckoo’s egg, and thus designedly to witness the 
act itself. It will be evident to readers of this 
book that, without the necessary preparation which 
foreknowledge alone can make possible, all purely 
casual observations of the deposition of Cuckoos’ 
eggs must lack the precision of detail which is 
essential to accurate knowledge, and which my 
system has secured. 
The value of photography in corroborating the 
record of eye-witnesses is obvious to all. Whereas 
the instantaneous “ snap ” shows but a single 
instant of arrested movement, cinematography 
enables the naturalist of to-day to secure a con- 
tinuous record of a bird’s incessant activities. Yet 
* I am indebted to Sir William Beach Thomas for originating 
this title in an article by him in the Daily Mail early in 1921. 
