280 MR. E. C. STUART BAKER ON 



Cuckoos in India. These Cuckoos lay deep blue eggs which they 

 deposit in the iiests of birds of the genera Argya and Ttcrdoides, 

 two of the most common and universally distributed genera of 

 birds in the Empire of India, which also lay similarly coloured 

 eggs of about the same size and shape. Here we have two 

 Cuckoos of different genera laying eggs so closely alike that it is 

 practically impossible to separate them except by their size and 

 the colour of the yolk. Even in size^ however, they constantly 

 overlap whilst, though the Hawk Cuckoo generally laj^s earlier 

 in the year than does the Crested Cuckoo, in many places both 

 birds are laying simultaneously. The genera Argya and Tur- 

 doides both lay unicoloured blue eggs, very glossy, hard-shelled 

 and broad, blunt ovals in shape. The Cuckoos both lay eggs 

 very similar in colour but with a softer, more satiny surface, 

 less glossy and with much thicker shells. In shape they are more 

 spherical or elliptical and in size generally a trifle larger than 

 the eggs of Ttordoides and much larger than those of Argya. 

 In some instances both these eggs, as I have already said, are 

 practically indistinguishable from those of the fosterer when 

 lying side by side, though when being blown they are very easily 

 distinguishable by the great thickness of the shells of the 

 Cuckoos' eggs and by the colour of the yolks which are a much 

 paler yellow, especially in the eggs of Clamator. 



In these instances we have all the factors which seem to be 

 necessary to hasten evolution. In the first place we have as 

 suitable foster-parents two nearly allied genera containing 

 numerous species of birds which are vei-y numerous from the 

 level of the plains vip to about 4000 feet over practically the 

 whole of India, Burma, and Ceylon. In addition to this, their 

 breeding-season is very protracted and they are excellent 

 mothers and fathers. Finally, they are very clever birds, and 

 possibly elimination of dissimilar eggs would proceed with these 

 fosterers faster than with most. 



Another and almost exactly similar instance of perfect evolu- 

 tion is that of Clamator coromandus, the Red-winged Crested 

 Cuckoo. This bird has a different breeding range to that of the 

 last two, and is found from the foothills of the Eastern Hima- 

 layas, throughout the hills of Burma up to about 5000 feet, but it 

 is most common as a breeding species at 1000 to 2000 feet. The 

 most common birds Avithin this area are the Laughing Thrushes 

 of the family Timaliidce. Amongst these the genera Bryonastes 

 and Garridax contain the most numerous and most widely spread 

 species and amongst these again the two species Garridax ononi- 

 liger and G. pectoralis are the two which are found throughout 

 this great extent of country in the greatest numbers. These two 

 birds, which are outwardly extremely alike, are the ones we 

 should expect to find acting as fosterer to the Bed-winged 

 Crested Cuckoo, and so it is. These two Laughing Thrushes both 

 lay pale blue eggs, and the Cuckoo lays an egg exactly similar 

 in colour and about the same in size but differing not only in 



