Cosmoledo is a raised coralline atoll in the Aldabra group, lying c.120 km east-south-east of Aldabra atoll, 700 km east of Africa and 400 km north-west of Madagascar. It comprises 13 islands and a few tiny islets (460 ha) surrounding a roughly circular lagoon (c.14,500 ha). The lagoon dries out extensively at low tide. Much of the interior of the atoll is characterized by irregular limestone formations known as ‘champignon’. The vegetation is similar to Aldabra (SC020), dominated by salt-resistant Pemphis acidula, but there are some extensive open grassy areas suitable for three species of ground-nesting seabirds not present on Aldabra (Sula dactylatra, S. leucogaster and Sterna fuscata). The islands of Menai and Grand Ile used to have resident human populations engaged in agriculture, fishing and the exploitation of seabirds, seabird eggs and turtles. However, the atoll has now been abandoned. It is visited by boats from both within Seychelles and from Comoros for the illegal poaching of seabirds, eggs and turtles. Two of the three largest islands (Grand Ile and Ile Sud Ouest) do not appear to have rats and, probably, most or even all islets are rat-free.
See Box for key species. The site holds Seychelles’ largest colonies of Sula sula and S. dactylatra, both of which have suffered drastic reductions in numbers elsewhere in the Indian Ocean, including extinction on some islands. Cosmoledo is now the only site in Seychelles with a viable population (c.60 pairs) of S. leucogaster, nesting mainly on Ile du Sud Ouest, with a few on Ile du Nord. Exploitation has greatly reduced numbers of breeding Fregata minor to 10–20 pairs, down from hundreds of pairs in the 1970s. Fregata ariel also once bred, but now may be extinct. Nevertheless, 200–400 non-breeding Fregata minor regularly occur, as do similar numbers of Fregata ariel. The site is the only breeding area in the Aldabra group for Sterna fuscata. It is the largest colony in Seychelles and, perhaps, in the western Indian Ocean. Some 15–30 pairs of Egretta dimorpha also breed. Resident landbirds include three endemic Seychelles races, Zosterops maderaspatana menaiensis (restricted to Cosmoledo and Astove), Nectarinia sovimanga buchenorum (restricted to Cosmoledo and Astove) and a form of Streptopelia picturata. This has been assumed to be coppingeri, but its status is currently under investigation and may prove to be a race restricted to Cosmoledo. Cisticola cherina, believed to be a relatively recent natural colonizer, is common on most islands; it occurs in Seychelles only on Cosmoledo and Astove.
Non-bird biodiversity: Green turtle Chelonia mydas (EN) nest all around the outside of the atoll. They have been heavily exploited and numbers are reduced.
BirdLife International (2021) Important Bird Areas factsheet: Cosmoledo. Downloaded from http://www.birdlife.org on 14/04/2021.