I love Northern Pintails! I love their rich coloring, their elegant style, and the way water sticks to their bills and heads like a shiny, acrylic coating. With their slender build and migrating speed of about 50 mph, some people call them the "greyhounds of the air". The name Pintail comes from the drake's (male's) central tail feathers. The feathers are quite long, constituting about a fourth of the drake's body length.
Take a look at the photo with the two females swimming side-by-side. The one with the yellow bill is a female Mallard. The one with the dark bill is a female Pintail. Note the subtle but distinct differences.