It’s not called the “African Galapagos” for nothing. The island of São Tomé, off the west coast of central Africa, is truly one of a kind. For a start, it has a remarkable level of endemism for such a small island: 17 of its 50 bird species are confined to that island alone.
It is also unusual in that it has no recorded human-driven bird extinctions – yet.
The island’s rugged landscape has protected its bird population from human influence, but this has proven a double-edged sword, making it difficult to survey the island. And it does need to be surveyed.
Because, as every conservationist knows, knowledge is power. We can’t conserve a species unless we know where they live, which habitats they prefer, what’s threatening them and how many (or how few) there are.
What we do know is this. Among the island’s 17 endemic bird species, nine are classed as globally threatened, with three listed as Critically Endangered on the IUCN Red List: the Newton’s Fiscal Lanius newtoni, São Tomé Grosbeak Crithagra concolor and Dwarf Olive Ibis Bostrychia bocagei. These three species formed the focus of an intrepid survey to discover more about the secretive forests of this island.
Prior to the survey, the Newton’s Fiscal and São Tomé Grosbeak were assumed to have a population of fewer than 50 individuals. The Newton’s Fiscal in particular was hardly ever sighted: often, only its distant calls revealed it was still there. The Dwarf Olive Ibis fared somewhat better in terms of population size, but loses out by being the only one targeted by hunters.
And hunters aren’t the only problem. Most of São Tomé’s birds live in its forests – but these are being encroached upon by human activity. Records show that the island used to be entirely covered in forest, but over half of it has been cleared, mostly for crops such as cocoa, coffee and oil palm. Invasive species, such as feral pigs or the Quinine plant Cinchona ledgeriana, have also irrevocably changed the landscape. São Tomé Obô Natural Park, the home of most of the island’s endemic species, offers protection from some of these threats, but not all.
Torrential rain, mountainous escarpments and venomous snakes made the landscape hard to traverse
And so, in 2016, a team of intrepid conservationists including SPEA (BirdLife in Portugal) and the RSPB (BirdLife in the UK) set out to survey the island. It wasn’t easy. Surveyors faced a range of challenges: despite the small size of the island, torrential rain, mountainous escarpments of up to 2,000m and venomous snakes made the landscape hard to traverse.
Ricardo de Lima, lead author of the study, describes the experience: “It was very intense. We had a large team on the ground, sometimes camping in the forest for over a week, carrying tents, food and equipment on our backs, and moving camp almost every night.”
But it was worth it, with the results shedding a new light on these mysterious birds.
The findings were revealing and unexpected, presenting both good and bad news, and showing just how much scientists hadn’t realised about the ecology of these species – and of the forests as a whole. On one hand, all three species were discovered in previously unknown areas, and the São Tomé Grosbeak’s range was found to be more than twice the size of what had previously been assumed. On the other hand, the home ranges of the Newton’s Fiscal and the Dwarf Olive Ibis were only half the size previously estimated.
Despite these restricted ranges, the population sizes of all three birds are most likely to be larger than what had been assumed. In particular, surveyors noticed that the sightings of São Tomé Grosbeak varied wildly between seasons, implying that the scarcity of sightings outside the breeding season might be due to its shyness, and not necessarily due to a very low population size. This has merited suggestions that the Newton’s Fiscal and São Tomé Grosbeak be downlisted to Endangered in the near future. However, the Dwarf Olive Ibis’ limited breeding range, coupled with the ongoing hunting pressure, keeps it in the Critically Endangered category.
Overall, the three birds’ home ranges fell mainly within the São Tomé Obô Natural Park – good news, in that conserving the park will conserve the birds. But sadly, it isn’t that simple. Dwarf Olive Ibis were found to concentrate themselves around the south-west of the park – which, unfortunately, is one of the most accessible areas, being targeted for development. A 30 km2 palm oil plantation has recently been introduced, and the area is under even greater danger from the proposal of a large hydroelectric dam. This, on top of the Ibis’ other problems, means this species looks like the conservation priority in the coming years.
All three species were found to prefer native forest – so, similarly, keeping this habitat untouched is the best way to conserve these birds. But how best to go about it?
A safe home
The next step of the study will be to determine how invasive species such as the Mona Monkey Cercopithecus mona, African Civet Civettictis civetta and Black Rat Rattus rattus are impacting our three focal birds. And does the Quinine plant, for example, interfere with the birds’ hunting by obstructing the forest understory? In addition to invasive species, the impact of local communities collecting forest products such as timber and charcoal also needs to be assessed.
One thing’s for certain – the future of these fascinating species depends on the São Tomé Obô Natural Park being managed effectively. But although the area is legally recognised, enforcement is currently weak due to staff and logistical limitations – and those need money.
“If this precious and unique biodiversity is to be protected, we need to focus on finding the funds for a rigorous enforcement and surveillance programme, to make sure the park’s restrictions are honoured,” says Ricardo.
São Tomé Island has had no anthropogenic extinctions so far. Let’s keep it that way.