Gray-backed Tern

Onychoprion lunatus
Gray back tern

Gray-backs are similar to sooty terns, except back, wings, and tail feathers are gray. Head and eye-stripe are black. White forehead extends further back behind the eye than the sooty tern. Bill and legs are black. Characteristic posture - somewhat crouched and bent over when standing, with wings and tail pointing upward.

Nesting pairs breed on Eastern and Spit Islands. Gray-backed tern populations are confined to the central tropical Pacific Ocean.

Their vocalization is a high pitched screeching, although it is softer and less harsh than the sooty tern.

Gray-backs arrive and lay eggs shortly before sooty terns on Midway (late February). They lay a single speckled egg on small depressions on the ground, usually against low vegetation or debris. They breed singly or in loose colonies.

Mean incubation period is 32 days. Both parents incubate egg. Incubation shifts range from 7-18 hours. Chicks are raised for about 46 days by both parents. Young gray-backs remain at their nesting colonies up to six weeks after fledging.

Facts About Gray-backed Tern

A plunge diver, the gray-backed tern does not depend on predatory fish to drive prey to surface. Diet consists of sea striders, crustaceans, juvenile flying fish, cowfish, and goat fish.
Life Span
18 years
Length: 35-38 cm (14-15 in); wing span: 73-76 cm (29-30 in)