Variation in Colour of Birds 297 



In Birds of Prey there is a good deal of variation in the 

 colour of the young birds as compared with that of the old 

 ones. Many Eagles do not greatly differ in this respect, 

 and often the colouring and barring of the tail is our only 

 guide to the determination of the age of the birds. Young 

 Kestrels of both sexes resemble the mother rather than the 

 father, but we find exceptions in many cases, as in some of 

 the Harriers, where the young birds are different in colour 

 and markings from both their parents, though they 

 resemble the old hen to a certain extent, in being brown 

 instead of grey like the male. In Buzzards, Hawks, 

 Serpent-Eagles, and Falcons, where the only differential 

 character between the old birds is one of size, the young 

 plumages are quite of another pattern, and do not resemble 

 those of either father or mother. 



In many cases where the parent birds are absolutely 

 unlike each other, the young have more likeness to the 

 plumage of the mother than that of the father. Take, for 

 instance, the familiar case of our Common Blackbird 

 (Merula mertila), where the male is perfectly black, and the 

 female is dark brown. The nestlings are much more like 

 the old hen than the cock, and it is not until after the first 

 moult that the sexes of the young birds can with certainty 

 be determined by the colour of the plumage alone. Thus 

 we are enabled to understand how remarkable is the case 

 of the Koel of Palawan referred to above. The Koels are 

 Cuckoos of the genus Eudynamis, which are sufficiently 

 plentiful in India and the Malayan countries and islands. 

 They have a peculiarly exasperating whistle, a sort of 

 pi — u pi — u, which the bird keeps on uttering inces- 

 santly in an ascending scale, beginning at the bottom again 

 as soon as it has reached the topmost notes. I was 

 introduced to the Koel in the plains of India, and one of 

 my friends called it the " brain-fever bird," as it is said to 

 produce an attack of brain-fever, if an unfortunate man 



