The Roseate Tern (pictured above) can be distinguished from the Common Tern by checking out a couple of key features. First note that the mantle (back of bird) is more pale along with the lighter, white edged outer primary feathers. Also, the tail extends well beyond the wing tips.
You can also see the darker colored wing tips of the Common Terns in the background, compared to the paler tips of the Roseate Tern. These two species often nest together in colonies. Soon, both of these species will begin their southern journey to overwinter along the northern coast of South America.
I will begin my own journey south tomorrow as I board a plane to Tucson for the Southwest Wings Birding Festival. I've got more tales to tell about my recent trip to New England as well, so stay tuned.