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Distribution and habitat associations of the critically endangered bird species of São Tomé Island (Gulf of Guinea)

  • RICARDO F. DE LIMA (a1) (a2), HUGO SAMPAIO (a3), JONATHON C. DUNN (a4), GABRIEL CABINDA (a2), RICARDO FONSECA (a2), GABRIEL OQUIONGO (a2), JOEL OQUIONGO (a2), SEDNEY SAMBA (a2), ARISTIDES SANTANA (a2), ESTEVÃO SOARES (a2) (a5), LEONEL VIEGAS (a2) (a5), ALICE WARD-FRANCIS (a6), LUÍS T. COSTA (a3), JORGE M. PALMEIRIM (a1) and GRAEME M. BUCHANAN (a6)...
Summary

São Tomé holds 20 endemic bird species, including the little known and ‘Critically Endangered’ Dwarf Olive Ibis Bostrychia bocagei, São Tomé Fiscal Lanius newtoni and São Tomé Grosbeak Neospiza concolor. We conducted a systematic survey of the core forest area, performing 1,680 point counts and compiling occasional observations, which enabled the identification of new areas of occurrence for the target species. MaxEnt distribution modelling suggested that the ibis and fiscal have roughly half of the potential area of occurrence that had been assumed (127 and 117 km2, respectively), while it more than doubled that of the grosbeak (187 km2). The south-west central region of the island, most of which is included in the São Tomé Obô Natural Park, has the highest potential for the Critically Endangered birds. We confirmed the association of all target species with native forest. The ibis preferred high tree density, while the fiscal selected low tree density and intermediate altitudes. Despite very restricted ranges, population sizes seem to be larger than previously assumed. These results suggest that the fiscal and grosbeak might be better classified as ‘Endangered’, while the ibis should maintain its status under different criteria, due to a very restricted range during the breeding season. This work provides vital ecological knowledge to support conservation action focusing on these species and their habitats, highlighting the need to improve the effectiveness of the São Tomé Obô Natural Park in protecting its unique biodiversity.

São Tomé alberga 20 espécies endémicas de aves, incluindo a Galinhola Bostrychia bocagei, o Picanço Lanius newtoni e o Anjoló Neospiza concolor, todos pouco conhecidos e em perigo crítico. Prospectámos sistematicamente o bloco central de floresta, realizando 1680 pontos de contagem e compilando observações ocasionais, que permitiram identificar novas áreas de ocorrência para as espécies alvo. A modelação de distribuição usando MaxEnt sugere que a galinhola e o picanço têm aproximadamente metade da área potencial de ocorrência que havia sido assumida (127 e 117 km2, respectivamente), enquanto que mais que duplicou a do anjoló (187 km2). A região centro e sudoeste da ilha, maioritariamente incluída no Parque Natural do Obô de São Tomé, tem o potencial mais elevado para as aves criticamente ameaçadas. Confirmámos a associação de todas as espécies alvo com a floresta nativa. A galinhola prefere densidades arbóreas elevadas, enquanto que o picanço selecciona densidades arbóreas baixas e altitudes intermédias. Apesar das distribuições muito restritas, os tamanhos populacionais aparentam ser maiores do que assumido anteriormente. Estes resultados sugerem que o picanço e o anjoló poderão ser melhor classificados como em perigo, enquanto que a galinhola deverá manter o seu estatuto, sob critérios distintos, devido à distribuição muito restrita durante a época reprodutora. Este trabalho esclarece alguns aspectos ecológicos cruciais para fundamentar acções de conservação focadas nestas espécies e nos seus habitats, sublinhando a necessidade de melhorar a eficácia do Parque Natural do Obô de São Tomé para proteger a sua biodiversidade única.

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*Author for correspondence; e-mail: rfaustinol@gmail.com
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