The Tinhosas Islands are two islands situated in the waters of São Tomé e Príncipe (STP). They host probably the most important seabird breeding colony in the Gulf of Guinea, but information on the islands’ recent conservation status and population trends was hitherto unpublished or anecdotal. Four of the five seabird species known to breed in São Tomé e Príncipe, namely Brown Booby Sula leucogaster, Sooty Tern Sterna fuscata, Brown Noddy Anous stolidus, and Black Noddy Anous minutus, breed in the Tinhosas. The Madeiran Storm-petrel Oceanodroma castro is suspected to breed in STP. The last assessment of the Tinhosas colony was completed in 1997; since then anecdotal accounts of exploitation of the birds for human consumption has raised concern about
its conservation status. We completed a two day expedition to the Tinhosas islands, estimating status and trends of breeding seabirds. We circumnavigated Tinhosa Pequena, which is ~3 ha in area and is inaccessible by sea due to sheer cliffs. We spent 24 hrs on Tinhosa Grande, which is approximately 20.5 ha in area and is accessible in good sea conditions. We did not encounter any Madeiran Storm-petrels, and the presence of a large population of land crabs makes it extremely unlikely that stormpetrels could breed there. We estimated a breeding population of 300 pairs of Brown Booby, which is 80% less than what was found in the 1997 expedition. There was no direct evidence of exploitation of seabirds. We estimated that 140 000 pairs of Sooty Tern were breeding on Tinhosa Grande, which is 30% more than in 1997. Therefore the site holds ~36% of the species’ regional breeding population, and qualifies as an IBA under the A4i and A4iii Criteria for the species. There were approximately 10 000 (±8
500) Common Noddies on the island, but breeding remains unconfirmed. Finally we estimated a Black Noddy breeding population of 3 500 pairs, which is 12,5% less than was counted in 1997. The site does not qualify as an IBA for this species, as previously thought, because it falls well below the threshold of 1% of the regional population. Apart from a moderate amount of disturbance by fishermen, who land on Tinhosa Grande, there seem to be no immediate threats to the Tinhosas colony. Nevertheless we recommend that multiple visits within and between years should be performed, to census breeders, monitor threats and establish breeding phenologies.