The black skimmer is the largest of the three skimmer species. It measures 40–50 cm (16–20 in) long with a 107–127 cm (42–50 in) wingspan. This species ranges from 212 to 447 g (7.5 to 15.8 oz), with males averaging about 349 g (12.3 oz), as compared to the smaller females 254 g (9.0 oz).[6] The basal half of the bill is red, the rest mainly black, and the lower mandible is much-elongated. The eye has a dark brown iris and catlike vertical pupil, unique for a bird. The legs are red.
Skimmers have a light graceful flight, with steady beats of their long wings. They usually feed in large flocks, flying low over the water surface with the lower mandible skimming the water for (in order of importance) small fish, insects, crustaceans and molluscs caught by touch.