Islands Have Always Fascinat
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TEXT AND PHOTOGRAPHS BY PHIL HOCKEY slands have always fascinat- because many occurred before this time, ed biologists. Charles Darwin’s visit to following the earliest colonisations by Ithe Gala pagos Islands was instrumen- man. In the African regions, these extinc- tal in shaping his evolutionary (and, at tions are well documented for the endem- the time, revolutionary) thinking. Chance ic birds of St Helena. Prior to 1600, three colonisations of islands by plants and species of seabirds (as well as five non- animals, and their subsequent isolation, endemic species – a rail, crake, dove, have given rise to unique biological com- cuckoo and hoopoe) were driven to munities. Sometimes, as with the lemurs extinction by man and his introduced and vangas of Mada gascar, spectacular animals. Today, all of the nine land-bird radiations occur, giving rise to high levels species breeding on the island are aliens of endemism. Following approximately and only one endemic, the St Helena 120 million years of isolation from Africa Plover, survives. The Hawai ian Islands and India, all of Madagascar’s 50 primate and New Zealand have similar dismal taxa are unique to the island – as are 88 histories. per cent of the reptiles, 80 per cent of the Some of the post-1600 extinctions, plants, and 56 per cent of the resident such as those of the Great Auk Alca breeding birds. impennis of the north Atlantic and the Although isolation creates unique com- dodos and solitaires of the Mascarene munities, it brings with it a unique suite Islands, are fairly well known. Others of problems. Should conditions change, have been less well documented and, in species unable to adapt or disperse else- some instances, it is almost certain that where are doomed. Some changes are unrecorded extinctions have taken natural, such as the desertification of the place: the figure of 124 extinctions on east ern Canary Islands, but others are islands is therefore a minimum. This man-made, such as habitat alteration for article endeavours to summarise extinc- agriculture, the introduction of alien pre- tions that have occurred on African dators and the introduction of disease. islands and to identify where possible Globally, approximately 136 species of their causes and the lessons they hold birds (and a further 90 locally endemic for the future. The serenity of tropical islands, such as the subspecies) dwindled to extinction in the I have defined ‘African islands’ as Seychelles, belies the looming extinctions 400 years from 1600 to 2000. One hun- being those lying to the east of the Mid- of many endemic birds. dred and twenty four of these post-1600 Atlantic Ridge, west of the Mid-Indian ex tinc tions (91 per cent) occurred on Ridge and north of 40˚S. This encom- islands. This figure is not representative passes islands from Madeira in the of the total number of extinctions, north-west to Tristan da Cunha in ISLAND EXTINCTIONS 33 the south and Socotra in the north-east. quite clearly that local extinctions of An analysis of the chronology and geog- native land birds on many islands have raphy of extinc tions, and the numbers frequently exceeded 50 per cent of the of currently endangered species, reveals original species’ complement. some very obvious patterns. • The average rate of extinction on • The number of extinctions has African islands to date has been one spe- de creased progressively since 1600. cies every 11.5 years. Should 50 per cent There were 14 extinctions in the 17th of the 20 surviving critically endangered century, 12 in the 18th, six in the 19th species become extinct over the course of and three in the 20th. On the face of it the next 10 years, this rate would have this might appear to be encouraging, increased to one species every year. but bear in mind that as the number of (Critically endangered species are defined extinct species increases, fewer species by the IUCN as having a probability of remain to become extinct. By contrast, extinction greater than 50 per cent in the not one bird species has become extinct on the African mainland during the same period, although some local popu- Why should the Mascarenes lations have disappeared, such as the Moroccan guineafowl. have suffered so badly? • Overall, the islands that have the next 10 years.) most endangered species today are The widely introduced Madagascar Fody those that have experienced few or no Many early travellers waxed lyrical about competes with several Red Data Book spe- extinctions. This suggests that these the diversity and abundance of birds on cies for nest sites and food. islands may now face an imminent all three Mascarene islands, reporting extinction crisis. dodos and ducks, rails and herons, par- • The geography of extinctions is rots, pigeons and starlings. With pre- un even. Of the 35 species lost, all except cious few exceptions, these species are A combination of felling and burning has five have been on the Mascarene Islands now consigned to history. Edible bird fragmented the forests of Madagascar into of Mauri tius, Réunion and Rodrigues. species were hunted mercilessly – the almost treeless landscapes. How ever, the table on page 39 shows flightless ones soon succumbing to such pressure. As early as 1613, Samuel Book (RDB). Idyllic tourist paradise... but cultivation Castleton wrote that on Réunion, 10 By 2000, the human population of and reclamation have totally transformed men armed with sticks and stones could Mauri tius – a smaller and less rugged the lowland forests and mangrove swamps kill sufficient White Dodos to feed 40 island – had reached 1 179 500, an of Mahé, Seychelles. people – 160 years later, the White Dodo average density of almost 670 people per was no more. Over time, rats, mongoos- square kilometre. Ten of the Mauritian es, macaques and others (including en de mics are extinct, two are critically many alien birds) were also introduced endangered, three are endangered (20 per to the Mascarenes, where they continue cent chance of extinction in 20 years) and Translocations almost certainly saved the to cause immense harm to native birds. four are vulnerable. Today, the only sur- Seychelles Warbler from becoming extinct. Today, more than 60 per cent of the viving endemic bird on Mauritius that is land area of Mauritius is under inten- not included in the RDB is the Mauritius sive agriculture, and the few remaining Grey White-eye Zosterops mauritianus. patches of indigenous forest are heavily The story of the Masca renes is a chilling infested with alien trees. The human col- parallel to that of the St Helena extinc- onisation of Réunion also tells a chilling tions – the only difference is that human story. The first permanent settlement of colonisation of St Helena happened the island took place in 1663 and by 1671 about 100 years earlier. the human population had reached 76. São Tomé and Principé, by contrast, In 1735 there were 8 150 residents, and have experienced no documented extinc- 140 years later this had swelled to tions and between them have 26 en 67 000. By this time, seven Réunion demic taxa, of which 12 are included in endemics had been driven to extinction. the RDB. These islands are far less isolated In July 2000, the human population had than the Mascarenes and the adaptations reached 730 000; of the four remaining of their birds may therefore be less endemic species, only the Réunion Bul extreme. Additionally, the human popu- bul Hypsipetes borbonicus (whose specific lation density is only one quarter that of status is questionable) and the Réunion Mauritius and much primary forest Stonechat Saxicola tectes have escaped remains on Principé, although São Tomé’s inclusion in the International Red Data primary forest is reduced to two patch- TO PAGE 38 34 ISLAND EXTINCTIONS AFRICA – BIRDS & BIRDING APRIL/MAY 2001 ZANZIBAR and PEMBA Locations and approximate dates of global extinctions EXTINCT SPECIES on African islands, 1600–2000, and a comparison with No extinctions or endangered species species classified as ‘Critically Endangered’ or * COMORO ISLANDS ‘Endangered’ by BirdLife International in 2000 EXTINCT SPECIES CRITICALLY ENDANGERED AND ENDANGERED SPECIES No extinctions Anjouan Scops Owl Otus capnodes 1 Grand Comoro Scops Owl O. pauliani 1 Moheli Scops Owl O. moheliensis 1 Grand Comoro Flycatcher Humblotia flavirostris Grand Comoro Drongo Dicrurus fuscipennis Mayotte Drongo D. waldenii SOCOTRA EXTINCT SPECIES No extinctions or endangered species MADEIRA EXTINCT SPECIES SEYCHELLES (including ALDABRAS) No extinctions or endangered species EXTINCT SPECIES DATE OF LOSS CRITICALLY ENDANGERED AND ENDANGERED SPECIES White Mascarene Seychelles Parrot Psitticula wardi 1870-1881 Seychelles Scops Owl Otus insularis 1 Aldabra Warbler Nesillas aldabrensis 1986 Seychelles Magpie-Robin Copsychus sechellarum 1 Starling 1 CANARY ISLANDS Seychelles Paradise Flycatcher Terpsiphone corvina Seychelles White-eye Zosterops modestus 1 EXTINCT SPECIES DATE OF LOSS MASCARENES (more than one island) EXTINCT SPECIES DATE OF LOSS Mascarene Coot Fulica newtoni 1693 Mascarene Parrot Mascarinus mascarinus 1834-1840 White Mascarene Starling Necropsar leguati 2 1840 MAURITIUS EXTINCT SPECIES DATE OF LOSS CRITICALLY ENDANGERED AND ENDANGERED SPECIES CAPE VERDE ISLANDS Mauritius Night Heron Nycticorax mauritianus Pre-1700 Mauritius Parakeet Psittacula echo 1 EXTINCT SPECIES CRITICALLY ENDANGERED AND ENDANGERED SPECIES Mauritian Duck Anas theodori 1696 Mauritius Fody Foudia rubra 1 1 Mauritian Red Rail Aphanapteryx bonasia 1693 Pink Pigeon Columba meyeri No