For higher definition: http://vimeo.com/25429598
I guess The Creator had a lot of niches to fill, but flying over the surface of the water at speed to catch little fish seems an improbable one. Indeed, how often have you seen a skimmer that has actually caught something? The Black Skimmer (there are two similar species, one in Africa, one in Asia) is well adapted to do this job. First of all, the birds know where to fish. They are so mobile that they can search large areas for concentrations of small fish forced close to the surface by evaporation or tides. They even hunt for fish or invertebrates temporarily washed onto beaches by wave action. They have one huge advantage over terns. Since skim-fishing is a tactile, not a visual activity, they can fish at night. Schools of little fish often rise to the surface at night. Doesn't sound like such a silly hunting strategy any more.
Another feeding adaptation these birds have is their hugely long wings. When you are flying an inch or two above the water, you can't produce a full wing stroke. Forty five degrees of movement is all you get. It's like running with your legs tied together. So the extra lift provided by their length is necessary.
Of course the beak of a skimmer is its most obvious attribute, but look at it head on (at 13 seconds in the video). It's a knife edge offering very little resistance to the water. Babies are born with both mandibles equal in length, and do not look "skimmery" until they fledge. Here are some shots made at a rookery and beach on Marco Island, Florida.