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*AMERICAN BLACK TERN  Chlidonias [niger] surinamensis 23–25cm. Small

tern of inshore marine waters, adjacent beaches, river mouths, coastal lagoons.

Flocks of 100s occur off Pacific coast, often associating with other terns

(especially Common). Flight buoyant and slightly floppy, swooping to pick

food from near water surface; often rests on flotsam, sea turtles. Very small size,

dusky gray upperparts, dark spur on sides of breast, and habits distinctive; birds

in full breeding plumage rare in Costa Rica. SOUNDS: Quiet piping whistles;

quacking kek in alarm. STATUS: Fairly common to common Sep–May over

Pacific inshore and shelf waters, small numbers of imms. may occur in summer.

Uncommon to fairly common spring and fall off and along Caribbean coast. (Breeds N America, winters

Mexico to S America.)

WESTERN BRIDLED TERN  Onychoprion [anaethetus] melanopterus 33–36cm

(+ 5–6.5cm adult tail streamers). Marine waters, rarely seen from shore. Nests

on inshore rocky islets. Singles or small groups occur with feeding flocks of

boobies, shearwaters, other terns. Flight buoyant and graceful, swooping to

pick from surface; often rests on flotsam. Adult has dark gray-brown upperparts,

extensively white tail and underwings, long white brow, cf. Sooty Tern.

SOUNDS:  Varied braying and clucking calls. STATUS:  Uncommon to fairly

common off Pacific coast, breeding locally Mar–Aug in northwest. Scarce off

Caribbean coast, mainly fall. (Tropical Americas and Atlantic.)

SOOTY TERN  Onychoprion fuscatus 36–39cm (+ 6.5–7.5cm adult tail streamers). Offshore waters; very

unlikely to be seen from land. Feeds over schooling tuna or dolphins with shearwaters, boobies, noddies.

Adult clean black-and-white with extensive dark on underside of primaries, cf. Western Bridled Tern.

Juv. distinctive: note whitish underwing coverts; cf. Common Brown Noddy. SOUNDS: Clucking wed-

a-wek; juv. gives high lisping whistles. STATUS: Scarce year-round off Pacific coast, mainly well offshore;

exceptional on Caribbean coast (storm-blown). (Pantropical.)

COMMON BROWN NODDY  Anous stolidus 36–42cm. Marine waters, un­

likely to be seen from shore. Often with feeding flocks of boobies, other terns,

shearwaters. Flight typically low to the water, swooping to pick from the

surface; transiting flight low and direct, when can suggest small jaeger. Rests on

flotsam, sea turtles. Habits and uniform dark brown plumage distinctive; adult

has variable whitish forecrown. Rarely vocal away from breeding grounds.

STATUS: Uncommon to fairly common Apr–Nov over Pacific waters, mainly

offshore (breeds Cocos I.); may nest locally on rocky inshore islets; rare in

winter. Rare on Caribbean coast (mainly storm-blown). (Pantropical.)

SKIMMERS (LARIDAE; 1 SPECIES) Small pantropical group, sometimes treated as a

distinct family. Resemble large angular terns with deep bills that have the elongated mandible

adapted to aerial foraging by ‘skimming’ it through the water surface. Ages differ, attaining adult

appearance in 1st year; sexes similar but male has appreciably larger bill.

BLACK SKIMMER  Rynchops niger 43–45.5cm, WS 115–123cm. Distinctive,

angular, and boldly patterned waterbird of river mouths, tidal flats, salt ponds,

coastal lagoons, beaches. Often rests with gulls and terns, usually in closely

spaced groups. Flocks typically fly in rather compact, wheeling formation.

Feeds in flight, mainly at night, by slicing elongated mandible through water

surface and snapping shut on contact with food. Breeding plumage has solidly

black hindneck; juv. has pale edgings to upperparts. Comprises 2 groups that

may represent species: American Black Skimmer R. [n.] niger with extensive

white on tail and wings, white underwing coverts; Amazonian Black Skimmer

R. [n.] cinerascens with mostly dark tail, narrow white trailing edge to wings, dusky underwings.

SOUNDS: Nasal laughing and barking clucks, mainly in flight, including at night. STATUS: American is

fairly common but very local nonbr. migrant Sep–May on Pacific coast (mainly Gulf of Nicoya), scarce

inland in nw. lowlands and on Caribbean coast; a few birds oversummer locally. Amazonian is scarce and

irregular nonbr. migrant May–Oct on s. Pacific coast. (Americas.)