Bird Bulletin 4 - “About Terns”

A key element in re-habilitating Denis’ ecosystem is developing an understanding of what the island was like in its pristine state. De Trobriand’s original description is very informative but not down to the species level of seabird. It is reasonable to conclude however that terns formed a major component of the original seabird colony.

• Brown Noddy (Anous stolidus): breeds in quite large numbers on the island. No census has been undertaken as yet, but practically every coconut crown in the hotel grounds has at least one pair during the breeding season. How dense the populations are in the areas of coconut-dominated forest needs to be assessed, but Denis has the potential to be one of the major breeding colonies in the Seychelles. Though no birds are yet actively breeding on the ground, as they do in some other colonies, what is noticeable is the number of chicks that continue to receive parental care and now fledge successfully despite falling from their nest, something that would never have happened prior to the rat and cat eradications.
• White Tern (Gygis alba): quite abundant and to be found breeding all year round on Denis. Again we currently have no indices as to the actual population on the island, though there is considerable anecdotal evidence to suggest that numbers have increased considerably since rat eradication in 2002. In recent months however there have been a large number of chicks and juveniles that have been left to starve suggesting a problem with the food supply.
• Lesser Noddy (Anous tenuirostris): are quite likely to have bred on the island in the past, large numbers (C 30,000) are to be seen roosting on the island and there are reports of occasional individuals breeding but I have yet to be able to confirm this. It is to be hoped that a breeding colony will establish itself on the island in the coming seasons.
• Sooty Tern (Onychoprion fuscata): known to have bred on the island in the past (see posts dated : July 2nd and August 17th 2008 for updates on the ongoing project to re-establish a colony on the island). This season has seen numerous landings of birds in the trial area including 5 birds on a single occasion. This bodes well for years 2-4 of the project.
• Bridled tern (Sterna anaethetus): In Seychelles Bridled tern breeding colonies are typically associated with rocky habitats and thus Denis may not be suitable for breeding. The birds however certainly frequent the island with at least 200-300 observed roosting in casuarinas on the south and south western coasts from November 07 through to February 08.
• Roseate Tern (Sterna dougallii): though we have no records, it is possible that the Roseate Tern used to breed on Denis as it once did on the neighbouring Bird Island. Certainly they are seen round the island, I most recently noted a pair, on the 24th July 08 soaring in the breeze over the southern point of the island and then swooping low over the water and calling distinctively.