Swallows are small, graceful birds with long, pointed wings, tiny bills, and small feet. They eat flying insects and forage over open water or ground. Many are well adapted to living near humans and use man-made structures for nesting. Swallows make their nests out of mud attached to a structure, or build in sandy burrows or in available cavities. Most swallows are social, foraging and migrating in flocks; many nest colonially, but a few are solitary. Most are monogamous, although extra-pair copulations are common in many species. The males of some species help incubate the eggs while others do not. Both parents provide care for the young. All North American species migrate.