Caspian Tern

When I saw this Tern circling the ponds at Fernhill Wetlands on Thursday, I thought it would be easy to identify as I remember seeing Terns like this as a youth. But when I started looking at my field guide I discovered just how many Terns look like this. Worse yet, the image above is the only decent shot I got although others where good enough to help with identification.
After studying the differences of the various Terns, the conclusion I came to is that this is a Caspian Tern. I based this on the following characteristics; relatively large size, short tail and a thick, bright red-orange, black-tipped beak.
Still not certain I was correct, I submitted this picture to Greg Gillson at Pacific NW Backyard Birder and he agreed with my conclusion. Greg is a wealth of birding information and has helped me identify birds in the past.