GULF OF GUINEA CONSERVATION GROUP

GULF OF GUINEA ISLANDS' BIODIVERSITY NETWORK


Threats to the avifauna of São Tomé e Príncipe

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1.Habitat Alteration

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.

Lowland forest

 

São Tomé Fiscal Shrike

Lowland primary forest is essential for this species

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

 

São Tomé Giant Weaver - a secondary habitat specialist

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 minimising 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.

Mangroves

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.

2. Hunting

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 ro├ža 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 for 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.

5. Tourism

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 minimised by ensuring responsible behaviour 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. Introduced 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.

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