Where Did "Birdie" Originate?

Golfers, ever wonder how the name "birdie" or "eagle" originated? You know that an "eagle" is two strokes under par on a golf course, usually occurring when golfers hit the ball far enough to reach the green, usually on par fives or the rare hole-in-one on a par-three. The name came about, so says legend, because a simple "birdie" needed to be a larger bird for the two stroke-advantage. Hence, "eagle."