On the beaches of Southwest Florida, amidst the innumerable [and perfectly ignorable] laughing gulls and royal terns, some choicer species may be found by the discerning observer.
Consider firstly the gulls:
A massive gull with a very dark back is seen on a sandbar -- this, the appropriately named Great Black-Backed Gull: it is certainly "Great" -- being the largest gull in the world; and its back is truly very dark; deep charcoal if not jet black.
A coastal gull, it is found from the shores of the Baltic states through Northern Europe to Northern Canada and the US; where it is expanding its presence.
Like most gulls, the greater black-backed gull will scavenge for food; but, unlike most gulls, it is also a vicious predator and will hunt down other birds as well as small mammals.
In contrast to the massive black-backed, the ring-billed is a pale gull with yellow legs and a black ring at the tip of its bill. In gull identification, it is useful to look at leg, bill, and back color in addition to size.
Compared to the pale pink of the great black-backed, the Herring Gull's legs are pinker. It is also much larger in size than the ring-billed.
Treated by the British Ornithologists' Union as a separate species unrelated to the European Herring Gull, the American Herring Gull, although superficially alike, has several variations in plumage to the European as both an adult as well as a juvenal.
Another gull is found grooming -- sharing the yellow legs and bill of the ring-billed gull, but much larger in size and with a darker back: this is the lesser black-backed gull.
This pose shows the light streaking on the neck and head that is typical in their winter plumage.
A little further down the sandbar, another similar tern -- but brighter orange legs and paler on the back.
Now seen side by side, the difference (and similarities) become more apparent:
First the similarities: similar size and orange legs; fading black on the head and dark bills. Readily apparent are also the differences: The Common Tern [left] stands a little squatter than the Forster's which stands taller. The Forster's [right] has brighter legs and the familiar black "comma" shape on the side of the head. The common tern also has black [more prominent in the first photograph] on the shoulder; and, the black on the head goes all the way down the nape but recedes on the forehead. Of course, distinguishing them in the field is a bit more challenging and any carelessness in observation could easily prevent disambiguation.
Lastly, the ubiquitous Royal Tern. A larger tern with black legs and orange bill. The only other tern that it could possibly be confused with would perhaps be the Caspian but that is much larger, and with more scarlet in the bill.
Here's where these birds were seen based on the GPS tag in the JPEG files: Map Link