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Birds of Midway Atoll

Sooty Tern / Onychoprion fuscatus

	Description Upperparts, legs, and bill black. Underparts and forehead white. Long, narrow wings and deeply forked tail, with white edged outer feathers. A black stripe running through eye to base of bill. Length: 41-45 cm (16-18 in); wingspan: 86-94 cm (34-37 in); average life span: 32 years.
Sooty Tern Photo credit: Robert Shallenberger

Midway Population

Approximately 45,000 nesting pairs on Eastern and Spit Islands were documented in 2005. Wide distribution throughout tropical oceans.

Vocalization

Incessant high pitched, screeching wacky-wack calls.

Feeding Habits

Skim water, take food on the wing, rarely touching down on the ocean. Poor oil glands, can become waterlogged if they alight on water for long duration. Feed offshore with predatory fish that drive smaller fish to the surface. Flying fish (primarily) and other fish constitute diet. Seem to feed extensively at night.

Breeding

Breeding takes place from April through September. Birds start to breed at 6-8 years of age. Highly ritualized and vocal aerial displays are conducted over nesting area prior to settling down to lay eggs. Nesting locations change slightly from season to season. A single speckled egg is laid on ground. No nest is prepared.

Incubation period averages 30 days. Individual incubation shifts are approximately 5 days. Heat stress may cause terns to abandon eggs for short periods to drink seawater. Sooty terns are easily disturbed by human activity, and repeated disturbance may result in permanent abandonment.

Chicks are shaded by parents during hot hours and brooded only when cool. Chicks are fed every 16 hours with regurgitated food. Parents locate chicks through vocalizations, and will feed only their own. Fledging occurs at about 8 weeks. Offspring continue to be fed by parents for several weeks after fledging.