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Location Seychelles
Central coordinates 46o 22.00' East  9o 26.00' South
IBA criteria A1, A2, A4i, A4ii, A4iii
Area 33,180 ha
Altitude 0 - 8m
Year of IBA assessment 2001

Nature Seychelles



Site description Aldabra is the world’s largest raised coralline atoll. It is situated 640 km east of the African continent, 420 km north-west of Madagascar, and 1,100 km south-west of Mahé. It comprises four main islands circling a central lagoon, Grande Terre, Malabar, Picard and Polymnie. There are many smaller islands and islets, some of which are rat-free. The land area comprises 15,380 ha, the lagoon 22,400 ha, and the IBA also includes a coastal marine area of 10,700 ha. The terrain is characterized by irregular limestone formations called ‘champignon’. The vegetation is dense and shrubby, adapted to relatively low rainfall and strong winds, and dominated in large areas by Pemphis acidula. Around 15% of the land area is more open, and covered in low grasses known as ‘tortoise turf’. The inner rim of the lagoon is lined with mangroves. The flora is exceptionally rich in endemics, with 19 species restricted to Aldabra and 22 others found also only on other islands of the Aldabra group. There is also a pristine marine ecosystem, with an intact fringing reef and an abundant and diverse fish and invertebrate fauna. A small permanent human population is based on Picard, engaged in wardening the reserve and scientific research. There are several huts on the other main islands for the overnight accommodation of scientists and fieldworkers. In the past, the islands were exploited for mangrove wood, turtles and giant land tortoises.

Key Biodiversity See Box and for key species. The site has, unlike almost every other tropical island of comparable size in the Indian Ocean, no introduced avifauna. There is one extant endemic species, Dicrurus aldabranus (500 pairs), although the status of several other taxa, currently classed as subspecies, is unclear. Another endemic species, Nesillas aldabrana, only discovered in 1967, has not been seen since 1983, and is thought now extinct. Endemic subspecies include Dryolimnas cuvieri aldabranus (1,500–2,700 pairs), the last surviving flightless bird in the Indian Ocean. Another endemic form, Threskiornis aethiopica abbotti (100–250 pairs), is most closely related to the subspecies bernieri of Madagascar which, with it, may form a species distinct from populations on the African mainland. The other endemic subspecies of landbird include Alectroenas sganzini minor (1,000–2,500 pairs), Streptopelia picturata coppingeri (2,000–5,000 pairs), Centropus toulou insularis (400–800 pairs), Caprimulgus madagascariensis aldabrensis (500–1,000 pairs), Hypsipetes madagascariensis rostratus (4,000–8,000 pairs), Nectarinia sovimanga aldabrensis, Zosterops maderaspatana aldabrensis (4,000–10,000 pairs) and Foudia eminentissima aldabranus (1,000–3,000 pairs)—all population estimates are only very approximate. The site is also important for several breeding seabirds, including the world’s second-largest colony of frigatebirds (both Fregata minor and Fregata ariel) as well as, in addition to those listed below, Sterna bergii (60–100 pairs) and the world’s only oceanic breeding colony of Sterna caspia (6–10 pairs). Other breeding waterbirds are Butorides striatus, Ardea cinerea, Anous stolidus and Gygis alba. Aldabra is the only atoll in the world (and the only oceanic site other than Galapagos) where Phoenicopterus ruber (25–50 birds) breeds; evidence of nesting was only discovered in 1995. The lagoon forms an important feeding area for both resident seabirds and shorebirds, and for migrants, notably Dromas ardeola, Arenaria interpres and Sterna saundersi (up to 800).

Non-bird biodiversity: Aldabra has the world’s largest population of the giant tortoise Dipsochelys dussumieri, estimated to number c.100,000 individuals in 1997. It is also of global importance for the sea-turtle Chelonia mydas (EN), which comes ashore to nest throughout the year; surveys between 1981–1985 indicated 10,000–18,000 nesting emergences annually; smaller numbers of Eretmochelys imbricata (CR) also breed. There are four species of lizard, including one endemic race Phelsuma abbotti abbotti. There are also four species of bat, including one endemic race of fruit bat, Pteropus seychellensis aldabrensis. A healthy population of the coconut crab Birgus latro (DD) exists throughout the atoll.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Egretta garzetta breeding  1,000-3,000 breeding pairs  A4i  Not Recognised 
Madagascar Pond-heron Ardeola idae breeding  20-50 breeding pairs  A1, A4i  Endangered 
Red-tailed Tropicbird Phaethon rubricauda breeding  1,900 breeding pairs  A4ii  Least Concern 
White-tailed Tropicbird Phaethon lepturus breeding  2,500 breeding pairs  A4ii  Least Concern 
Great Frigatebird Fregata minor breeding  4,000 breeding pairs  A4ii  Least Concern 
Lesser Frigatebird Fregata ariel breeding  6,000 breeding pairs  A4ii  Least Concern 
Red-footed Booby Sula sula breeding  6,000-7,000 breeding pairs  A4ii  Least Concern 
Crab-plover Dromas ardeola winter  2,800 individuals  A4i  Least Concern 
Ruddy Turnstone Arenaria interpres winter  500-1,000 individuals  A4i  Least Concern 
Black-naped Tern Sterna sumatrana breeding  70-150 breeding pairs  A4i  Least Concern 
Comoro Blue-pigeon Alectroenas sganzini resident  1999  present  A2  Least Concern 
Aldabra Drongo Dicrurus aldabranus resident  1999  present  A1, A2  Near Threatened 
Aldabra Warbler Nesillas aldabrana resident  1983  present  A1, A2  Extinct 
Red-headed Fody Foudia eminentissima resident  1999  present  A2  Least Concern 
A4iii Species group - seabirds breeding  50,000-99,999 individuals  unknown  A4iii   

IBA Monitoring

2001 medium not assessed medium
  unset
-

Invasive and other problematic species and genes invasive non-native/alien species/diseases - named species happening now some of area/population (10-49%) slow but significant deterioration medium
Over-exploitation, persecution and control of species fishing & harvesting aquatic resources - unintentional effects: large scale happening now small area/few individuals (<10%) no or imperceptible deterioration low
Over-exploitation, persecution and control of species hunting & collecting terrestrial animals - intentional use (species being assessed is the target) happening now small area/few individuals (<10%) no or imperceptible deterioration low

Whole area of site (>90%) covered by appropriate conservation designation  No management plan exists but the management planning process has begun  Substantive conservation measures are being implemented but these are not comprehensive and are limited by resources and capacity  medium 

Protected areas

Protected area Designation Area (ha) Relationship with IBA Overlap with IBA (ha)  
Aldabra Special Reserve 35,000 protected area contains site 33,180  
Aldabra Atoll World Heritage Site 35,000 protected area contains site 33,180  

Land use

Land-use Extent (% of site)
nature conservation and research -

Further web sources of information 

Alliance for Zero Extinction (AZE) species/site profile. This site has been identified as an AZE due to it containing a Critically Endangered or Endangered species with a limited range.

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Recommended citation  BirdLife International (2014) Important Bird Areas factsheet: Aldabra atoll. Downloaded from http://www.birdlife.org on 18/12/2014

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