THEORIES AND CONCLUSIONS 223 
living creatures exhibit ; amongst which, birds, 
owing to their power of flight and the phenomena 
of migration, are peculiarly elusive and difficult to 
identify. 
Identification of Cuckoo from Egg 
When one finds in a mud-lined nest blue eggs 
with black spots on the larger end, one does not 
hesitate until one has seen the parent bird to say, 
“ This is a Song Thrush’s nest.” In the same way, 
readers of this book will have gathered, there is 
among practical students of the Cuckoo a consensus 
of opinion, amounting to a certainty no longer in 
need of proof, that a particular hen Cuckoo may be 
identified from the appearance of her egg , within 
reasonable limits of time and place. The limitations 
of time and place are mentioned, because if, for 
example, one found the same type of Cuckoo’s egg 
being laid in the same territory, season after 
season for (say) twenty years, it would be reasonable 
to question whether a daughter had not succeeded 
to her mother’s realm ; and if, again, one found in 
the same season, but in widely separated terri- 
tories, the same type of Cuckoo’s egg in the same 
species of fosterer’s nest, it would be a reasonable 
