My measurements show that the bald eagles in our area, southern British
Columbia, generally weigh between 5 and 12 pounds (closer average 7 -11 pounds) . When I repeat this to my Alaskan colleagues they point out they have caught several 13 pound birds. And I believe they do.
I actually suspect many are seasonally bigger here as well. An eagle stuffing itself for days on end on salmon gains great weight. Most of the eagles I caught were during the summer when food was less available – and they had to work harder to get it. The general breakdown is 5 - 8 pounds for males and 8 -12 pounds for females.
It is interesting to note that in each of the first 5 years of an eagles life its wingspan gets shorter and has less width. The big soaring wings of the juveniles, so necessary to get them to their first free food, which might be 1000 miles (1600km) with minimal energy expansion -- the northern salmon runs -- get shorter and better adapted to fast maneuverable flight to match the eagles flying needs which become greatest when it has to be able to hunt within a home range to support a family. Before that it has more freedom to soar and the larger sails are obviously better adapted to that. A female just off the nest might have 6'4" wing span but at maturity it might only be 6'.
Hancock Wildlife Foundation