Vegetation structure as a key determinant of habitat use and abundance of the endemic Pemba Green Pigeon Treron pembaensis on Pemba Island, Tanzania

Abstract

The Pemba Green Pigeon Treron pembaensis, a frugivorous species endemic to Pemba Island, Tanzania, listed as Vulnerable on the IUCN Red List, is increasingly threatened by habitat loss due to anthropogenic pressures. Although the Pemba Green Pigeon is adapted to forest habitats, limited knowledge exists on how vegetation variables influence its abundance. To establish the relationship between the Pemba Green Pigeon and vegetation parameters, we used the point count method, which overlapped with vegetation sampling across 44 nested quadrats (20 × 20 m) with subplots (2 × 5 m) for young trees. At each vegetation sampling location, we counted Pemba Green Pigeons seen and heard, and assessed tree height, diameter at breast height, canopy cover, tree density and the density of feeding and perching plant species. The density of Pemba Green Pigeons was significantly higher inside the forest than outside the forest. Overall, 20% of the recorded plant species were used as feeding (nine species) and perching trees (three species). Five previously undocumented feeding plant species were identified: Ficus sur, Sorindeia madagascariensis, Syzygium cumini, Syzygium guineense and Chrysalidocarpus pembeanus. Pemba Green Pigeon abundance correlated positively with diameter at breast height, canopy cover, tree density, tree height, and perching and feeding plant availability, suggesting that structurally complex, diverse habitats enhance its survival by providing food and protection. This study highlights the need to conserve native forest structures, particularly including mature trees, which provide essential feeding, perching and roosting sites to sustain a viable population of this vulnerable and endemic species.