Introduction

Adult Sooty Tern, breeding plumage; Florida

Figure 2. Breeding distribution of Sooty Terns in the Hawaiian Archipelago.

Figure 1. Breeding distribution of the Sooty Tern in the Caribbean region.

Editor’s Note: Study of the mitochondrial DNA of terns, along with their plumage characteristics, have suggested that the heretofore broadly defined genus Sterna is paraphyletic. Reclassification of this genus now places Sooty Tern in the genus Onychoprion. See the 47th Supplement to the AOU Check-list of North American Birds for details. Future revisions of this account will account for this change.

This tern inhabits tropical and subtropical oceans around the world, nesting on remote islands. It is common throughout the Caribbean Sea, the Hawaiian Archipelago up through Kure Atoll, and on islands off most Central American countries. It generally nests in areas little visited by humans, making accurate determination of its status difficult. This is a species that lives on the wing—well known for its ability to stay airborne for years at a time between fledging and first breeding, never coming to land during the nonbreeding season, and essentially never seen resting on the water. At sea, the Sooty Tern may perch on flotsam or the backs of surfaced sea turtles, and it is able to alight on a calm sea surface briefly and take wing again. But Sooty Tern plumage apparently has little waterproofing; individuals quickly become waterlogged when held on the water.

Most terns (Sterna spp.) feed by plunge-diving, but this species feeds either by “dipping” (often merely brushing the water surface) or by snatching small fish in midair as they are escaping from predatory fish below. It feeds in flocks, often with other species. Sooty Tern colonies are among the largest, densest seabird colonies in the world, at times numbering more than 1 million birds. Pairs nest on the ground, generally in sandy substrate with sparse vegetation. Colonies can be extremely noisy as neighbors communicate their intentions, defend their territory, and interact with their mates or chicks. Parent and chick recognize each other’s voices and often call back and forth to locate each other when a parent returns with food. One of the most commonly heard calls in a Sooty Tern colony is the “wideawake” call, and these birds are often referred to as Wideawakes.

The Sooty Tern once bred on practically every island group in the Tropics but is now extirpated from many, owing mainly to alteration of habitat, persecution by humans, and the introduction of predators into colonies. Its eggs are a popular human food source and are still taken in many places today, often with no control or thought to preservation of the resource. The worldwide population is thought to be between 60 million and 80 million birds and the number of nests each year between 18 million and 23 million (Appendix).

W. B. Robertson and M. J. Robertson spent 40 years studying the breeding biology of Sooty Terns in the Dry Tortugas, Florida. They were beginning work on this account when both passed away. In addition to published literature, this account includes information from their field notes and various unfinished manuscripts.