FiGiTEE 5. — A nearly lk'dj,^ed yuuu;; l)ald eagle, Atka Island, Aleutian Islands, Alaska. 

 The dark plumage of the head, the dark bill, and the dark iris of the eye are in 

 marked contrast with the coloration of the adult bird with its white head and lijiht- 

 yellow bill and iris. ( Photograph by V. B. Scheff er. ) 



bald eagles including adults and 

 juveniles of both sexes. These data 

 appear in table 1. 



The adult females averaged 2.26 

 pounds lieavier than the adult males 

 and the immature females averaged 

 2.31 pounds heavier than the im- 

 mature males. In fact, tlie differ- 

 ence in weight between the sexes 

 (both adult and immature birds) 

 was so pronounced that little over- 

 lapping occurred even between 

 weights of the heaviest males and 

 tlie lightest females. 



The immature birds (1 year or 

 older) revealed average measure- 

 ments (except that of the bill) 



greater than those of the mature 

 birds of the same sex. On the other 

 hand, the average weight of the 

 immature birds was less than that 

 of adults of the same sex, indicating 

 that the greater dimensions of the 

 young birds are attributable to 

 greater length of wing and tail 

 feathers, and not to greater body 

 size. 



The greater size of the Alaskan 

 birds is reflected even in the eggs. 

 Bent (1937) has assembled data 

 showing that the average size of the 

 eggs of the bald eagle increases 

 gradually northward through the 

 bird's ranjre. 



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