Prompted by the recent Bald Eagle sightings in Melvin Village, I found a wing profile diagram that shows how the three largest birds on Lake Winnipesaukee can be identified in flight—
even while one mile distant! 
I've seen Bald Eagles from one mile away while perched on a branch. (Without binoculars—a handy guide being my former lake location in Florida, which is exactly one mile across!)
Now, note the
purple image "in-flight":
Ospreys soar with their wings held in a shallow "m" shape—like a seagull's.
Turkey Vultures' wings are held in a deep "V" shape while soaring and will appear somewhat unsteady in flight. (But they DO know what they're doing—they are absolute masters at avoiding the multiple utility wires strung all over my present location). Again, note the
purple image "in-flight":
Note the
purple image "in-flight" again: The
Bald Eagle's two wings could be made from one piece of plywood, they're held so straight!
Since birding IS recreation—and although it's certainly possible to identify Bald Eagles from indoors—I put this new thread in "Outdoor Recreation". 
Credit to sources:
http://www.in.gov/dnr_old/fishwild/endangered/id.htm
and
http://www.onlinephotographers.com/y...topic=111462.0