Gulls and Terns are unique families in that they can be found on every continent in the world. They also have a basic pattern that with just a few exceptions is recognisable which ever species you're looking at. In the main they are grey above and with below. The above colour can vary from almost black to almost white (or in one case completely white). the general theory is that this pattern makes them difficult to see from above as far as predators are concerned and difficult to see from below, as far as prey is concerned.
Of course when you find gulls on a beach half way round the world the odds are they are different species to the ones you see at home. But even in Los Angeles two of them, one gull and one tern, were species that I've seen in Kent! Not the Western Gull above though, this Herring Gull sized bird is strictly a west coast of North America bird. It does wander up to Alaska and down to Mexico sometimes, and occasion visits some of the inland states, but compared to many gulls it isn't very much of a traveller.The dark grey mantle is similar in colour to out Lesser Black-backed Gull, but they are unlikely to be met with together!
Above two Western Gulls share the beach with at California Gull, a smaller gull, about half way in size between a Common Gull and a Herring Gull this bird winters on the West Coast of N America, but moves inland to breed in land on lakes from Canada down to Utah. The largest colonies are in Great Salt, Utah and Mono Lake, California. There are now around 200,000 pairs in total, but in 1930 they were down to 50,000 pairs due to egg collecting. Vagrants have occurred in Japan and Hawaii as well as on the American East Coast
The Ring-billed Gull has occurred in Kent, and one must beware on on-coming motorbikes when twitching one (Barry!). This is the most frequent N American Gull to visit Europe and has been recorded in many countries, with gatherings of up to 17 seen in Ireland. It is a little bit larger than a Common Gull which is a potential confusion species. I breeds across N America on fresh water lakes, and with a population of up to 2 million pairs and a migration the takes some of the population down to the Caribbean the potential for vagrancy, helped by late summer hurricanes is obvious.
The wing pattern of this late first winter/first summer plumaged bird does show some similarity to a Common Gull, so care is needed in identification.
A nice group of three species of terns with two California Gulls.
Two Caspian Gulls, another species with a large world wide distribution. Dungeness has hosted one that I saw and is probably the most likely place in Kent to turn up another of this jumbo sized tern.
Elegant Terns breed along the Pacific Coast, from Southern California to Central America. It has been recorded in Europe a few times, including one breeding with a Sandwich Tern in France. On average it it just slightly larger than a Sandwich Tern, but with the long crest and distinctively curved bill a good view should be conclusive. One at Dungeness would cause some excitement!
Another big Tern, almost the size of a Common Gull, the Royal Tern has two subspecies. One that breeds on both the east (includig the Caribbean) and west coasts of North America and one that breeds in West Africa. Occurences of large terns with orange or red bills nearly always cause confusion and debate, ofteen because the views are brief and distant. This bird is in first summer plumage, adults have a black cap and nuch paler primaries.