292 THE STRUCTURE AND LIFE OF BIRDS chap. 



and neck. The young bird is blackish, speckled with 

 white, and at each moult some of the incorrect feathers 

 are weeded out. These changes, it is believed, give a 

 rapid recapitulation of the history of the Gannets. At 

 one time they had throughout their lives these blackish 

 feathers ; in the course of generations they attained to 

 their present spotless white. It is probably not till 

 the fifth autumn that the .plumage reaches the per- 

 fection of maturity, and the next spring the bird 

 makes his first nest. In the photograph at South 

 Kensington of Gannets sitting on their eggs, there is 

 apparently not one whose plumage shows any sign of 

 immaturity. The youth of a Golden Eagle lasts ten 

 years, or even longer. The rate of mortality is great 

 among young birds, and but few Golden Eagles, prob- 

 ably, survive to build a nest and rear young. And 

 this leads us on to the subject of the age attained by 

 birds, for there is no doubt that there is a connection 

 between this and the age of maturity. There is a good 

 deal of evidence that Eagles and their allies live to a 

 great age — to ioo years and more ; and even if parti- 

 cular cases are doubtful, yet on the principle that a 

 number of weak sticks make a strong faggot, I think 

 we may accept it. Suppose that an Eagle lives to 

 only sixty years, and becomes mature at ten, then a 

 pair will produce ioo eggs in the fifty years, the 

 number laid being usually two, and of the hundred 

 birds hatched only two will live to grow up. This 

 calculation, which I quote from Professor Weissmann, 

 even if only roughly correct, is valuable as bringing 

 together three facts which must be viewed in con- 

 nection— (i) the great length of an eagle's natural 



