Terns and skimmers are related to gulls (they're all in the family Laridae), but terns tend to be smaller and 'sleeker'. Like many gulls, they'll feed near the surface by plunge-diving to snag small fish that are close to the surface, but they don't tend to scavenge in the same way as gulls, kittiwakes, and skuas do. Terns are also renowned for their migratory behaviours - the Arctic tern holds the record for long-distance migrations, and will spend the boreal summer in the Arctic, and the austral summer in the Antarctic, travelling around 25,000 miles each way. Terns are ground-nesting birds and so can be vulnerable to egg-stealing predators like rats and foxes, and so nesting sites are often carefully protected. If you know you're in an area with nesting birds, make sure and watch where you step - nests and eggs can be extremely well camouflaged.