Obo – Lowland Primary Rainforest
Lowland rainforest extends from sea level to 800m. Much of this has now been cultivated in the past and only a small amount of virgin habitat remains. The only primary rainforest occurs in the central and south-western parts of São Tomé and Príncipe and in São Tomé is only accessible by following rivers such as the Ana Chaves, Xufexufe or Quija.
Four specialist birds occur only in lowland forest – the São Tomé Grosbeak, São Tomé Short-tail, São Tomé Fiscal Shrike and Dwarf Olive Ibis. In Príncipe the rare Príncipe White-eye, Príncipe Thrush and endemic subspecies of the Olive Ibis are confined to primary areas.
Montane and Mist Forest
This picture taken at Lagoa Amelia shows a typical cloudforest scene. The fog has come down into the forest and the whole habitat is dripping with condensation.
The Montane Forest Region, extends from 800 to 1,400m, is very different to lowland forest due to the different edaphic conditions. The trees are tall, with a high dense canopy and are covered with epiphytes. Exell notes the abundance of ferns as being remarkable. Much of this type of habitat is intact on the south and west side of São Tomé; development has destroyed most of this type of habitat on the north and eastern sides. These areas in the north are now being used for the production of coffee and the farming of vegetables. This zone is the most at threat from agricultural development.
The Mist Forest Region from 1,400 m to 2,024 m. Forest cover extends to the top of the Pico de São Tomé, where the trees are stunted and the canopy open. The Pico is virtually always covered with mist and the temperatures get extremely low though frosts are unknown. This is probably the only habitat that has not been altered and is also one of the least known mainly due to the difficulty of access.
High altitude forest is home to the Giant Sunbird, Maroon Pigeon, Sao Tome White-eye and also the Sao Tome Scops Owl is easy to see up here.
Secondary Forest and Abandoned Plantations
One of the most common habitats on the island and extremely valuable as it holds all the endemic birds apart from the primary forest specialists. São Tomé Scops Owl are common and it is a stonghold of the São Tomé Weaver.
Most of the forest along rivers in the south-east and south-west is old secondary growth dating back to the 1930s. On satellite images and aerial photographs this type of forest is virtually indistinguishable from primary forest. It is only through plantation and government archives, which are difficult to obtain, and by visiting these areas that it is possible to distinguish between primary forest and previously cultivated areas.
Working plantations are extremely important to many of the common endemic birds. In symapathetically managed cocoa plantations, São Tomé Paradise Flycatcher densities are more than double that found in mature forest.
Shade trees are important in maintaining a forest structure with both an understorey and a canopy – ideal for many insectivorous species.
Savanna areas in the north and east of São Tomé have developed as a result of the clearance of the original dry deciduous forest in the early years of colonisation. Today the savanna is home to non-endemic bird species such as the Vitelline Masked Weaver, Bishops, Pintailed Whydahs etc as well as being home to the endemic sub-species of quail.
Remaining areas of Mangrove are few, with small areas in the north and east. Malanza, an extensive brackish lagoon in the very south of São Tomé, is the largest remaining area of mangrove and has been proposed for protection.
Threats to the Avifauna in
Gulf of Guinea Islands
This is the single most important threat facing the endemic species. Twelve of the endemic species on São Tomé and Príncipe would be seriously at risk from the alteration or destruction of a single habitat type.
Primary forest of all types covers 28.5% of the islands. This forest type is now restricted to a few areas in south-western and central São Tomé, particularly along the Rios Xufexufe and Ana Chaves (0-400 m). There is none along the Rio Quija or the lower reaches of the Rio Io Grande which border the remaing area which is very small and constitutes only a small percentage of the total remaining area of primary rainforest.
Despite its limited area this habitat is uniquely important. It supports the only known populations of Dwarf Olive Ibis, São Tomé Fiscal Shrike, São Tomé Short-tail and São Tomé Grosbeak. In addition it holds a major proportion of the populations of São Tomé Scops Owl, São Tomé Green Pigeon, São Tomé Oriole, Giant Sunbird and São Tomé White-eye. A small population of Maroon Pigeons exists, the only one outside high altitude primary rainforest. All the remaining endemics also occur.
No other habitat on the island contains populations of every one of the endemic species. All the species named above, except possibly Maroon Pigeon, would be seriously threatened by any loss of lowland primary rainforest. Major losses of habitat would almost certainly see the extinction of the four lowland primary forest specialists, the ibis, short-tail, shrike and grosbeak.
Whilst this habitat is not immediately threatened with destruction, because of its remoteness and a lack of finances for development, the small size of the remaining areas leaves them very vulnerable to even limited development. Clearance for plantations is unlikely at the moment as so many existing plantations are in disrepair.
Timber extraction, mainly for fuel and building materials, is a major threat despite a recommendation in a 1990 Interforest report that remaining primary rainforest be protected from exploitation. The forest that has survived is mainly on steep slopes but these are not steep enough to prevent logging. Of particular concern are plans to sell off forested areas, currently owned by the government, to private sources. With no forest protection laws this habitat would be at the mercy of private developers.
Montane and Mist Forest
Montane primary forest constitutes the majority of the primary forest area, although the total area is small. Much of it remains unsurveyed as it is confined to the centre of São Tomé, around the source of the Rios Xufexufe and Ana Chaves and south from Lagôa Amélia. The threats to this habitat are the same as those for its lowland equivalent.
Mist forest is limited to Lagoa Amélia / Calvario area and the Pico de São Tomé, where it extends upwards into mist forest. Forest at Lagoa Amélia is the stronghold of the Maroon Pigeon and also supports substantial populations of São Tomé Scops Owl, Giant Sunbird, São Tomé Oriole and São Tomé White-eye together with the commoner endemics. This area is immediately at risk from encroaching agriculture.
Its proximity to the island’s main centres of population, and a climate that allows year round cultivation, make it an obvious site for agricultural expansion. However, there is a great deal of land outside the forest block which would be equally suitable for cultivation without impinging on the area around the Lagôa itself. However, the ease of access, the unusual flora and fauna and the areas outstanding natural beauty make it the ideal site for the creation of a reserve.
Extensive areas of secondary forest now exist in areas which were formerly plantations. 30.2% of the forest cover on the islands is secondary forest (Interforest 1990). The primary forest in the southwest of the island is buffered by secondary growth along the Rio Quija and south from Santa Catarina.
Mature Secondary Forest and Shade Forest
Secondary regrowth, particularly where it is mature, is important not only as a buffer zone against development, but it also holds substantial populations of several endemic species. Mature secondary forest is especially important to the São Tomé Scops Owl, São Tomé Thrush and Giant Weaver, species which occur at low densities. The owl and the thrush are equally common in primary rainforest but would suffer significant population reductions if secondary forest were destroyed.
The Giant Weaver appears to prefer secondary forest and shade forest and whilst it is not totally confined to secondary habitats it would be put at risk if large areas of of secondary forest were cleared. This habitat also provides a valuable subsidiary habitat for the São Tomé Oriole, though it was usually only found in mature secondary forest. All the remaining endemics, except the primary forest specialists (Dwarf Olive Ibis, Maroon Pigeon, São Tomé Short-tail, São Tomé Fiscal Shrike, Giant Sunbird, São Tomé Grosbeak), also occur in secondary forest.
Whilst exploitation of this habitat is currently low, the development of agriculture and an increasing demand for timber will pose a serious threat to it and its associated bird community. It would be impossible to protect all areas of secondary forest but mature regrowth needs to be protected, as do all areas which buffer primary forest. Where areas are developed, work should, where possible, be carried out so as to preserve the forest type structure of the vegetation. This will be particularly important where old plantations, currently overrun with secondary regrowth, are once again brought back into production, or developed for alternative crops.
Wood is the basic building material used on the island and is the most commonly used fuel source both for domestic purposes and commercially in the drying of cocoa. An opportunity exists for sustainably exploiting the areas of secondary forest of least conservation value as a source of timber. This would limit the damage to bird populations as the commoner endemics could probably cope with limited disturbance. However, the São Tomé Scops Owl and the São Tomé Oriole would be lost from an area that was selectively logged.
32.4% of the islands are covered with shade forest (Interforest 1990). Apart from the destruction of primary forest the major threat facing the islands’ endemic birds is the removal of shade trees from cocoa plantations. This crop has traditionally been grown beneath trees whose canopy provides shade. This creates a forest&endash;type structure to the habitat with upper and lower storeys. In turn this provides suitable conditions for many of the commoner endemics, especially São Tomé Sunbird, São Tomé Paradise Flycatcher, São Tomé Thrush and São Tomé Weaver.
Our work showed that a lack of shade trees reduces not only populations of many species found in cocoa plantations it also reduces species diversity (see Table 3.2). The threat to shade trees is increasing as agricultural aid to São Tomé and Príncipe from the EC, World Bank and Portuguese interests also increases (Jones and Tye 1988). The aid is designed to increase cocoa production and to encourage diversification into oil-palm plantations and market gardening. Shade trees in plantations are a valuable source of timber.
If, as suggested by Interforest (1990), a rotational system were adopted, with the replanting of shade trees after removal, this would provide a sustainable timber resource as well as minimizing the damage to associated bird populations. Such a system would also reduce the pressure to remove trees from the major forest blocks. This habitat will be under the most pressure in the near future and is likely to be substantially altered. Without planning these alterations could destroy valuable wildlife habitat and a very valuable social and economic resource.
This is an extremely scarce habitat on the island being confined to a few small patches on the north and east coasts. It is extensively exploited for wood as a fuel source and is severely threatened by this practice. None of the bird species are confined to mangrove but complete loss of the habitat would be detrimental to other fauna.
Birds, wild pigs, monkeys and other species are hunted for food. Currently hunting is on a limited scale and does not pose an immediate threat to any one species, although an escalation in hunting pressure would pose a threat to some species. Various species of pigeon and dove are the most favoured bird quarry. São Tomé Green Pigeon is the most commonly hunted species, and is shot wherever it occurs close to human habitation and is also taken by hunters sho sometime spend several days in the forest. São Tomé Bronze-naped Pigeon is also frequently shot, particularly in the south-west of the island. The similar Lemon Dove is also a quarry species.
The species most at risk from any increase in hunting pressure is the Maroon Pigeon, which is considered tame and easy to kill, particularly as it is attracted to smoke (Jones and Tye 1988). At Santo Antônio hunters reported killing this species whenever they encountered it, although this was rarely. It has also been hunted at Lagoa Amélia by local villagers and inhabitants of the nearby roça at Monte Café. De Naurois (1983) considered it to have become rare by 1973 due to hunting.
If high-altitude plantations are rehabilitated, the associated increase in the human population will mean that hunting pressure on the Maroon Pigeon is certain to increase. Only a moderate increase in hunting would start to threaten the species, especially in view of its restricted range, small total population size and the ease with which it can be killed.
Hunting pressures may also increase if cartridges, at present expensive and hard to obtain, become cheap and readily available. At present most cartridges are ‘home-made’ from black powder (Jones and Tye 1988).
3. Pesticide Application
During the early 1970’s massive quantities of pesticides were used in the plantations. This greatly reduced the population of the São Tomé Paradise Flycatcher and the São Tomé Oriole (de Naurois 1984) and probably affected other insectivorous species, particularly the São Tomé Thrush and São Tomé Speirops. Although the paradise flycatcher population has recovered, now that pesticide use has declined, the oriole population has not and it is no longer found in plantations. On Príncipe, the Príncipe Drongo and Príncipe Speirops would be threatened by an increase in pesticide use.
Rehabilitation of plantations will almost certainly involve a dramatic increase in the use of pesticides and this will have a major impact on the aforementioned species and possibly other insectivores such as the São Tomé Weaver, São Tomé Seedeater and São Tomé Speirops.
4. Trapping of the Cagebird Trade
Red-headed Lovebirds, Grey Parrots, Common Waxbill, Bronze Mannikin and Cordon-bleu are all trapped for keeping as pets both locally and for export. It is likely that this practice contributed to the extinction of the Red-headed Lovebird on Príncipe. The effect of the trade on the island’s Grey Parrot population is unclear. The reason for the decrease in numbers from those reported by Keulemans (1866) is also unclear. Both habitat destruction and wildlife trade may be the major factors behind the decline. It is likely that the birds we saw on São Tomé were escapes that originated in Príncipe.
Tourism developments are concentrated on the north-east and east coasts and present little threat to São Tomé’s avifauna. Increased tourism might encourage the trade in wild birds and an escalation of hunting activities. The impact of tourism on the avifauna can be easily minimized by ensuring responsible behavior from developers, travel operators and airlines.
Tourism may also be beneficial to the islands’ avifauna. São Tomé e Príncipe’s host of rare endemic species are an attraction to specialist natural history and bird tours. If this industry can be encouraged and responsibly managed it will place an economic value on the islands’ forests and wildlife encouraging the government to conserve them.
6. Introduction of Mammals
Dogs, cats, civets, weasels, monkeys, wild pigs and rats have all been introduced to São Tomé. Most of these species have been present for a century or more and there are no records of their effect on the endemic birds. Collar and Stuart (1985) reported old stories of wild dogs taking the eggs and young of Dwarf Olive Ibis. Rats, and the weasels and civets introduced to control them (Bocage 1903; Frade 1958), are very likely to have had a deleterious effect upon nesting birds. Rats and civets have both colonised primary forest. Not enough is known about the effects of these introductions on the island’s avifauna to quantify any threat they pose.
7. Small Population Size
Several of the endemic species have very small known populations. Only a single fiscal shrike and ibis were seen during the 1991 University of East Anglia expedition and more recent records from Sargeant (1992) involve only a single shrike and seven ibises. They also recorded two grosbeaks. The known population of the short-tail is also small; 25-37 birds along the Rio Xufexufe and 14 birds along the Rio Ana Chaves. Given the restricted habitat requirements of these four endemics, the actual population size must be numbered in hundreds or if they can survive in mid-altitude forest, probably in the low thousands.
The Maroon Pigeon, Giant Sunbird, São Tomé Scops Owl, São Tomé Oriole and São Tomé White-eye also have very restricted populations. Not only do these species have small populations but their distribution within São Tomé is very restricted, most being confined to one or two habitat types. This makes these species very vulnerable to extinction be it from habitat destruction or hunting or some other agent.
The capacity for recovery from a major catastrophe is very poor in small populations and extinction is very likely following such an event. Small populations are also liable to inbreeding and genetic problems.
Endemic Birds of São Tomé and Príncipe
São Tomé and Príncipe contain 28 species of bird that are endemic to one or both of the islands. These include 21 single island endemics, 15 on São Tomé and 6 on Príncipe with a further 5 being found on both islands. Two monospecific genera are endemic to São Tomé, Amaurocichla and Neospiza, and one to Príncipe, Horizorhinus. The taxonomy of some of the endemic species and sub-species is unclear. Sibley and Monroe (1990) classify the two Alcedo kingfishers as full species.
Other authors regard them as subspecific forms only and we follow that treatment here. There seems little justification for retaining the monospecific genera Thomasophantes and Dreptes and in most treatments they are subsumed within Ploceus and Nectarinia respectively.
Of the mainland African species represented on the islands, eleven have developed subspecies. In addition, a possibly undescribed subspecies of the Maderian Petrel Oceanodroma castro may breed on offshore islets (Harris 1969).
The level of endemism is high on the islands with over half of the breeding landbirds either being an endemic species or subspecies.On São Tomé 57% (28 out of 49) of the breeding landbirds are either endemic species or subspecies. For Príncipe the level of endemism is similar with 54% (19 out of 35) of the resident landbirds being endemic species or subspecies.
Collar and Stuart (1988) ranked the rainforests of south-western and central São Tomé second in a list of 75 of the most important forests for conservation in tropical Africa, mainly due to their high threatened species score. More recently both islands have been designated as individual Endemic Bird Areas (EBAs) (ICBP 1992). The importance of these two EBAs is such that they are rated as Critical. This rating is based upon the highest restricted-range bird species richness score, with both islands being three times or more richer in species than expected for their area.
The rating also takes account of the degree of threat to the EBA. Both EBAs score the highest rating, with less than 5% of the area of each EBA being found in protected areas. Finally the degree of threat to birds is rated as Medium (Birdlife International 1992) although this must be revised in the light of the development plans for Príncipe.
Status of the Endemic Birds on São Tomé
At present, most of the endemic birds are common.
The primary forest specialists on the island are the São Tomé Fiscal Shrike, Dwarf Olive Ibis, Giant Sunbird, Maroon Pigeon, São Tomé Short-tail and the São Tomé Grosbeak. Destruction of even the smallest amounts of the rather limited area of remaining primary forest would jeopardise the future existence of all these species. In addition, the São Tomé Oriole and São Tomé Scops Owl would become seriously endangered if the remaining primary forest was lost. It is of immediate importance that these areas be given protection.
At present the forests of the south-western areas are not under threat as access to them is difficult. However destruction is occurring where the forest is close to centres of human population, especially around the northern edge near Lagôa Amélia. The high altitude primary forest at Lagôa Amélia is the stronghold of the Maroon Pigeon and supports populations of the Giant Sunbird, São Tomé Scops Owl and São Tomé Oriole. It is also the area most at threat; agriculture has been encroaching for the last ten years around the Lagôa.
The abandoned plantations have regenerated into secondary forest and provide suitable habitat for several endemic species and also buffers the primary forest from development. Mature secondary forest is especially important for the São Tomé Scops Owl, São Tomé Thrush and Giant Weaver, species which occur at lower densities elsewhere. The owl and thrush are as common in primary forest but a major part of their population would be destroyed if secondary habitats are removed. The Giant Weaver seems to be a secondary habitat specialist.
Whilst not totally confined to secondary habitats it would become seriously endangered if all areas of secondary forest were cleared. This habitat also provides a valuable subsidiary habitat for the São Tomé Oriole. The extent of forest regrowth on the island at present and the low exploitation rates mean that it is a relatively secure habitat. BDPA (1985) and Interforest (1990) both recommend that the secondary forest be used as a timber resource and if exploitation is not carefully managed populations of several species could be threatened. If plantations are replanted then this should be done in such a way that the endemic species can exist in them.
Apart from the forest destruction the major problem facing the islands’ endemic birds is the removal of shade trees from cocoa and coffee plantations. These crops have been traditionally grown beneath trees whose canopy provides shade. This provides a forest type habitat and provides suitable conditions for many of the commoner endemics, especially the São Tomé Weaver, São Tomé Paradise Flycatcher, São Tomé Seedeater and the São Tomé Sunbird.
Our surveys showed that removal of shade trees reduces not only the numbers recorded but also species diversity. Shade trees in plantations are a great source of timber for the islands. If a rotational cut system were adopted with replanting after removal this would provide a sustainable timber resource as well as minimizing the damage to the associated bird community.
The Gulf of Guinea Conservation Group (GGCG)
The Gulf of Guinea Islands’ Biodiversity Network was set up as an informal network of scientists, conservationists and organizations interested in the biodiversity of the Gulf of Guinea islands of Bioko, Príncipe, São Tomé and Annobón.
Network participants came from a wide range of disciplines including botanists, geologists, herpetologists, entomologists, malacologists, primatologists … and those just interested! The network distributed news of research, scientific and conservation developments and initiatives, environmental issues, publications, web resources etc that were relevant to the Gulf of Guinea islands and was also a forum for putting researchers with similar interests in contact.
The Gulf of Guinea Conservation Group had its origin at a workshop on the biodiversity of the islands held at the Jersey Wildlife Preservation Trust in June 1993 entitled Biodiversity and Conservation of the Gulf of Guinea Islands. The workshop reviewed current knowledge on species richness and endemism in the islands and identified issues that threaten the conservation of the islands’ unique fauna and flora. Papers delivered at the workshop were published in a special issue of the journal Biodioversity and Conservation (1994 Vol. 3 No. 9).
Another notable event resulting from the Jersey meeting was the declaration by the assembled specialists to support actions taken by the islands’ governments in protecting biodiversity and to develop future collaboration amongst themselves. In deciding to constitute the Gulf of Guinea Conservation Group, a unanimous commitment was made to find common ways of studying and protecting the islands’ environments by:
- furthering research on protection and rational use of the region’s natural resources.
- fostering inter-island cooperation for environmental protection
- identifying ways of stimulating funding for species and ecosystem conservation
Since a small but auspicious beginning at the 1993 workshop, the Gulf of Guinea Conservation Group grew into an informal network of more than 100 scientists, conservationists and organizational representatives interested in the biodiversity of the Gulf of Guinea islands. Many of the network’s participants were either actively working in the region or are researching specific taxon found on the islands. For several years the group operated as an email network, known as the Gulf of Guinea Islands’ Biodiversity Network, and coordinated from the island of São Tomé. This email network continued to operate in order to disseminate news about biodiversity research and conservation as well as to get all the participants together in forwarding their contributions.