An experimental investigation of the effects of human intrusion into breeding colonies of Bridled Terns Sterna anaethetus in the Great Barrier Reef

Abstract

Many studies have demonstrated that recreational visitors impede the breeding success of nesting seabirds, although recently some authors challenged the view that human visitation is always detrimental to the breeding birds. This emerging lack of consensus, as well as the fact that almost all disturbance studies to date were conducted in habitats and on species of high latitudes, presents a challenge to managers of Australia's Great Barrier Reef World Heritage Area. The present study used an experimental approach to examine the impact of recreational visitors on aspects of the reproductive biology of a tropical tern, the Bridlled Tern, Sterna anaethetus, at Rocky Islets in the Far Northern Section of the Great Barrier Reef World Heritage Area. Two levels of human disturbance schedules were implemented over five experimental sites and over three breeding seasons. The dependent variables were hatching success, body mass and bill length of chicks at both 12-13 and 21-22 days of age. Chicks at 12-13 days of age were significantly heavier and hatching success was higher at sites exposed to higher level disturbance than at sites exposed to lower level disturbance. The results suggest that the early development of Bridled Tern chicks may be adversely affected by non-lethal human disturbance and that such adverse effects may be ameliorated by habituation to human intrusion into nesting areas.