78 THE GROUSE IN HEALTH AND IN DISEASE 



having all the primaries moulted except the two most distal 

 ones. The third then will be found to be a short feather actively 

 growing, and if it is pulled out the growing root will be full 

 of blood. Therefore not every bird that gives this sign is 

 necessarily a bird of the year. 



jwerbill. Another sign often used to test the age of a bird is the 

 strength of the lower mandible. The weight of the bird is allowed 

 to hang without support by holding the tip of the lower bill 

 only. The bone of an old bird's jaw easily stands this test, but 

 the soft jaw of a young bird of three or four months cannot 

 carry its weight, and the jaw either bends or breaks. 



tull. Yet another test often used is that of trying to crush in the 



skull with the finger and thumb ; in the young bird the soft 

 skull gives way readily, in the old bird it requires very con- 

 siderable force. 



In dissection, the age of an old bird is apparent, perhaps 

 as plainly upon the table as elsewhere. The fibrous tissues all 

 toughen with age and use, and the bones become harder. The 

 grits of the gizzard in an old bird seem to be larger and more 

 worn into rounded pebble shapes the reason for this has been 

 discussed elsewhere. 1 The question, therefore, of deciding 

 whether a bird is less than a year or more than a year old, is 

 possible, but it seems almost impossible to judge more exactly 

 of the age of an older bird by any sign to be discovered either 

 externally or internally. 



1 Vide chap. iii. pp. 107 d scg. 



