Sooty Terns (Sterna fuscata) have been extirpated from some islands in the Seychelles through habitat modification, introduction of exotic predators and over-exploitation of their eggs. Recently, removal of exotic predators and habitat restoration have made some islands available for the re-introduction of or re-colonization by former breeding birds. Attempts will be made to encourage Sooty Terns to re-colonize formerly occupied islands that are now deemed suitable to support colonies, using decoy models and broadcasts of recorded vocalizations. As a prelude to these attempts, this study measured the sound levels produced within a Sooty Tern colony at different times of day and season, in order that broadcasts can reasonably well simulate the sounds produced naturally. Statistically significant diurnal and seasonal differences in sound levels were recorded, related to differing activities of the adult birds during the breeding season. Our results suggested that broadcasting equipment should be capable of producing Sooty Tern colony vocalizations at sound levels at least 85-90 dB, at a distance of about three m from the speakers, in the intended nesting area. Potential human health risks of prolonged exposure to vocalizations within Sooty tern colonies are highlighted.
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Vol. 26 • No. 4