A few comments about Martin's and Don's comments about eagle colors.

>So, an immy eagle on the ground signifies "no food"? If "food's here!"
>were the selection factor driving the contrasting plummage I'd think
>juvies would share it.

One possible explanation for conspicuous adults and inconspicuous immatures
is that adults can defend a food source more readily than immatures. The
latter are dull so they *won't* be visible to a passing bird, thus they can
eat their fish in peace. This may be the explanation for brown immature
gulls.

I don't think for a second that adult eagles are conspicuous to show "food
here" to share with all the other eagles in the area; I can't see this
working under a natural-selection paradigm. It's one thing for gulls to be
conspicuous, as they can sometimes feed more effectively on fish schools
when there are a lot of them, but I don't think eagles work this way. It
doesn't take a lot of eagles to subdue a dead salmon.

On the other hand, the white head and tail of an adult Bald Eagle make it
stand out from a mile away when it's on territory.

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416