Ilhéu Raso (6147)
Cape Verde, Africa

Site overview

KBA status: confirmed

Global KBA criteria: A1e, B1, D1a

Year of last assessment: 2018

National site name: Ilhéu Raso

Central coordinates: Latitude: 16.6185, Longitude: -24.5891

System: marine, terrestrial

Elevation (m): 0 to 164

Area of KBA (km²): 10.41482

Protected area coverage (%): 81.80

KBA classification: Global

Legacy site: Yes

Site details

Site description: The island of Raso is primarily flat, with some small peaks in central-northern parts of the island, which rise to a maximum of 164 m. The entire south-western area is a flat, rocky plain, parts of which are covered with large boulders. Dry riverbeds cross the island. There is little vegetation except for a grassy area in the south-west. The coastline is entirely composed of rocky cliffs.

Rationale for qualifying as KBA: This site qualifies as a Key Biodiversity Area of international significance that meets the thresholds for at least one criterion described in the Global Standard for the Identification of KBAs. Alliance for Zero Extinction (2018): site confirmed as an AZE site during the AZE project (2015-2018). Taxonomy, nomenclature and Red List category follow the IUCN 2016 Red List.

Additional biodiversity: See Box and Table 2 for key species. The most famous bird of the island is, without doubt, the endemic Alauda razae, which is entirely confined to Raso and has a total population of c.45 pairs. The species roams all over the island, but breeding is largely confined to the grassy area in the south-west. Calonectris (diomedea) edwardsii is the most numerous seabird on the island, with thousands of pairs breeding on the cliffs along the southern shore and more breeding inland in holes under boulders. Other breeding procellarids are Puffinus (assimilis) boydi, Bulweria bulwerii and Oceanodroma castro. There is a colony of c.125 pairs of Sula leucogaster and 25–40 pairs of Phaethon aethereus, numbers which are only a shadow of those recorded c.100 years ago. Egretta garzetta, Pandion haliaetus, Falco (tinnunculus) neglectus, Tyto (alba) detorta and Passer iagoensis also breed. Non-bird biodiversity: The endemic giant skink Macroscincus coctei is thought to have become extinct early in the twentieth century (see site CV010). The endemic geckos Tarentola caboverdiana and T. gigas still occur in good numbers. Other lizards include Mabuya stangeri and Hemidactylus bouvieri.

Delineation rationale: Type 1 marine IBA: suitable for the seaward extension approach.

Habitats

Land use: nature conservation and research

Threats

Summary of threats to biodiversity at KBA: The island was designated a Nature Reserve by law in 1990 and may now only be visited under special permit. In practice, however, the law is difficult to enforce. Large numbers of eggs and young of Calonectris (diomedea) edwardsii are still taken each year for food, as are young and adults of Sula leucogaster and Phaethon aethereus. The frequency of visits by fishermen carries the associated risk of the introduction of rats, cats or other domestic animals, which could be fatal to the ground-breeding Alauda razae. This risk was illustrated in February 1994, when a stray dog was seen on the island. Such an introduction could (or may have had) serious consequences for ground-nesting birds, including the lark and the boobies, as well as the endemic reptiles. Indeed, the extinction of the giant skink has been, at least partly, ascribed to the introduction of dogs during the first decade of the twentieth century. Abundant cat faeces, containing many bird remains, were found on Raso in February 1998. To prevent further over-exploitation of C. (diomedea) edwardsii, some form of wardening during the critical period (September–October, just before fledging) is necessary.

Additional information