cuckoos' eggs and evolution, 277 



20. Cuckoos' Eggs and Evolution. 

 By E. C. Stuart Bakee, F.Z S. 



[Received March 19, 1923 : Read April 24, 1923.] 



(Plates I.-IY.*) 



Much has recently been written on Cuckoos and Cuckoos' 

 eggs, in some cases the writers having laid down laws and 

 accepted facts as proved on very insufficient data. Certain of 

 these writers, who have watched the actions of individual 

 Cuckoos and who have spent much time and money on their 

 valuable observations, have theorized on the presumption that 

 what one Cuckoo does all Cuckoos do. Other writers, also from 

 watching one bird, essay to prove that the former are wrong 

 because their observations do not have the same result as their 

 own. As a matter of fact both are equally correct, the result of 

 their observations are of great value, and their work worthy of 

 all praise so long as they do not pose as authorities, able to prove 

 or disprove theories, until their experiences are far wider. 



For over forty years now I have studied Cuckoos, and the 

 older I grow and the more I know about these birds, the more 

 certain I am that I have not yet sufficient data to enable me to 

 do more than roughly outline certain theories and point out what 

 there is in support of them. 



Curiously enough, the most interesting of all Cuckoo subjects 

 is the one which seems to have been most avoided. I refer to 

 the evolution of Cuckoos' eggs resembling the eggs of their foster 

 parents sufficiently well to enable them to escape destruction. 

 Perhaps this is because our British Cuckoo, Ctoculus canorns 

 canorus, is only a very i-ecently evolved type of Cuckoo and 

 within its few thousand years of existence has not yet had time to 

 eliminate those members of its species which lay eggs dissimilar 

 to those of the birds it selects as fosterers. To find really satis- 

 factory instances of perfected or far advanced evolution, or of 

 evolution in an obvious stage of transition, we have to go abroad 

 and examine the eggs of such genera as Olamator, Coccystes, 

 Eierococcyx, etc. Amongst these we may hope to find sufficient 

 evidence to enable us to show what has already taken place and, 

 by analogy, to learn what is probably taking place at the present 

 day amongst other genera and species. 



The material from which I have drawn my deductions consists 

 of some 2500 Cuckoos' eggs collected from Europe, Asia, and 

 Australia (not Africa), but principally from India where Cuckoos, 

 of many species, are exceedingly common. As I have already 



* For explanation of the Plates see pages 293, 294. 



Proc. Zool. Soc— 1 923, No. XIX 1 9 



