PREFACE. 



ALL the district round a little house in the 

 country, to which I removed from London, 

 now getting on to twenty years ago, abounds with 

 cuckoos, as well as with nightingales. I -^vas thus 

 led to pay more attention than I had before done to 

 both these birds and to two others, to which I do not 

 here at all refer. I have lain half-days in woods and 

 coppices to watch and observe as best 1 could the 

 ways of the cuckoos, and in doing this I could not 

 help seeing other things ; and sometimes I have been 

 so struck with what I have seen that I became very 

 anxious to know in how far other observers had 

 witnessed the same or similar occurrences. 



This led me on and on, in a wide track of reading 

 and inquiry, till I found myself launched on a piece 

 of big and rather difficult research about the various 

 different cuckoos in Europe and further afield, and 

 even about other parasitical birds. I was constantly 

 forced on attempts at comparative survey, and the 

 endeavour to form sufficing theories, based on rational 

 explanations of habit, or, at all events, working hy- 



