Midway Atoll National Wildlife Refuge
Pacific Region
 

Birds of Midway Atoll

Gray-backed Tern / Sterna lunata

photo of gray-backed tern

Description

Similar to Sooty Terns, except back, wings, and tail feathers gray. Head and eye-stripe are black. White forehead extends further back behind the eye than the sooty tern. Bill and legs black. Characteristic posture somewhat crouched and bent over when standing, with wings and tail pointing upward. Length: 35-38 cm (14-15 in); wing span: 73-76 cm (29-30 in); average life span: 18 years.

Gray-backed Tern
Photo credit: Robert Shallenberger
  

Midway Population

Approximately 315-487 nesting pairs (2006) breed on Eastern and Spit Islands. Gray-backed Tern populations are confined to the central tropical Pacific Ocean.

Vocalization

High pitched screeching. Softer and less harsh than the Sooty Tern.

Feeding Habits

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.

Breeding

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. Breeds 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.
Last updated: May 21, 2009