The observed population crash in a colony located on Ascension Island, one of the UK Overseas Territories (UKOTs), is partly due to poor diet, research led by the University of Birmingham has found.
The findings provide fresh evidence of the fragility of marine ecosystems and lend weight to the scientific case for creating the Ascension Island Ocean Sanctuary (AIOS), set to be one of the largest fully protected reserves in the Atlantic Ocean.
The most numerous seabird of tropical waters, Sooty Tern is an abudant species. The colony on Ascension Island is the largest in the entire Atlantic Ocean. However its population has declined from several million in the middle of the last century to just a few hundred thousand today. A team based in the University's School of Biosciences believes the birds' plight is closely linked to changes in populations of predatory fish, such as tuna. The terns follow these large fish across vast expanses of ocean to feed on the small fish driven to the surface as they hunt.
The terns had been expected to benefit from conservation work carried out on the island between 2002 and 2004 by the RSPB. This involved a feral cat eradication scheme in a bid to restore nesting populations of seabird species, including the rare .
However, while many seabird species subsequently began to thrive, the tern population did not recover as expected and the Birmingham team, together with researchers from the University of Exeter, the Ascension Island Government Conservation Department (AIGCD) and the Army Ornithological Society (AOS), set out to find out why.
Dr Jim Reynolds, lead author on the paper, commented: "We believe that a number of factors might influence the size of the breeding population of sooty terns on the island but we wanted to understand such factors in greater detail, resulting in causal explanations of the tern population decline over the past 60 years."