138 EXTRACTS FROM NOTE-BOOKS. CH. XXVIII. 



a well-authenticated case of a mule bird bred be- 

 tween the grouse and blackcock being killed. In 

 most instances in which birds supposed to be 

 hybrids between these two species have fallen under 

 my observation, they appeared to me to be merely 

 gray hens, whose plumage had become like that of 

 the cock. I have seen birds of this kind in the 

 Edinburgh Museum and elsewhere ; and I saw one 

 killed this autumn (1848), which had very much 

 the appearance of a hybrid, but on closer exami- 

 nation I came to the conclusion that it was merely 

 an old gray hen, who had changed her appearance, 

 as the hen-pheasant does. This latter bird, we all 

 know, is very frequently killed in different stages 

 of change towards the male plumage. The same 

 is the case with the common domestic fowl and the 

 peahen. It is difficult to account for the cause 

 of this transformation. "We know that it does 

 not arise from any disease or ill-health, as the 

 birds in their borrowed plumage are always in as 

 good condition as any others. 



It is very rare indeed to find any wild animal 

 subject to illness, with the exception of the 

 epidemics before alluded to. Unless they are 

 wounded and unable to hunt for their own food, 

 all wild birds and animals keep themselves plump 

 and healthy. The wood-pigeon is indeed frequently 



