… are sea birds, occurring down the Atlantic and southern Pacific coasts.Chicks hatch with mandibles of the same length; the distinctive uneven bill only develops as the young birds grow. The bill is knife-thin, allowing it to slice cleanly through water, and is touch-sensitive. The birds fly just above the water’s surface with the lower mandible in the water; the moment it contacts something - usually a small fish, but crustaceans or other invertebrates are also taken - the bill snaps shut. Skimmers also have another adaptation unique among birds: their pupils are vertical slits, as in cats’ eyes. This is thought to help with glare from the water’s surface, allowing the birds to more easily spot potential prey.