skimmer, common name for certain sea birds resembling the related tern. Skimmers (genus Rhynchops ) have long, laterally compressed bills of which the lower mandible is one fourth longer than the movable upper mandible. This bill is adapted to their technique of skimming the water's surface to catch the shrimp and small fish that form their diet. Skimmers are gregarious and partly nocturnal; their sensitive eyes narrow to slits while they roost during the day. The black skimmer, R. nigra (black back and white belly), the largest (20 in./50 cm) of the family and the only American member, is found on the Atlantic coast of North America and on both coasts of South America. Skimmers are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Charadriiformes, family Rhynchopidae.