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Context. Habitat loss is a global problem and in Fiji >50% of the land area once covered by forests has been converted to grasslands and agricultural land. About 99% of Fiji's endemic biodiversity and 80% of the land bird species have been identified as forest species. Aims. In this study, we compare forest and grassland sites and test for consistency in avian diversity, abundance, foraging guild, and distribution status (endemic, native, introduced to Fiji) over a 5-year period (2016-2020). Methods. We surveyed bird communities using the point count method with a 100 m radius and 7-min observation period per site. Key results. A one-way analysis of similarities (ANOSIM) analysis showed significant differences in species composition and bird abundance between the forested habitats and grassland habitats. A general linear model test showed significant differences in foraging guild composition and distribution status between forested and grassland habitats. There were no significant differences between the three forested sites (primary montane forest, secondary old-growth forest, old-growth mahogany plantations with regenerating native species), while grassland sites had stronger annual change in species composition. Implications. Forest cover, irrespective of whether these forests are of primary or secondary nature, therefore plays an important role in maintaining the native and endemic land bird species and other biodiversity in oceanic island ecosystems such as Viti Levu Island, Fiji. [ABSTRACT FROM AUTHOR]

Expert knowledge is widely used for assessing the conservation status of little-known species. Pterocymbium oceanicum is a large, emergent tree endemic to Fiji. Experts classified the species as 'Critically Endangered' (IUCN Red List) in 2016 and estimated the population size at <250 mature individuals with the largest subpopulation consisting of a single stand of 100 individuals. We surveyed this stand and counted 133 individuals, which validated the expert estimate. However, we discovered an additional three stands nearby, increasing the total subpopulation size to 433 individuals. Therefore, the expert estimate reliably and conservatively estimated population size but missed important information. Field surveys suggest that P. oceanicum has a narrow ecological niche as a long-lived early pioneer at mid-elevations (400–800 m) in seasonally dry forests, one of Fiji's most degraded ecosystems. The introduced African Tulip Tree, Spathodea campanulata , is invading the sampled subpopulation and shares the characteristics of being a large, fast-growing and early successional tree. Therefore, the narrow niche of P. oceanicum may now be threatened by S. campanulata. Our study highlights that expert knowledge can provide valuable information about threatened species but also has limitations. IUCN Red List assessments based solely on expert assessments should therefore be cautiously interpreted. The invasion by S. campanulata poses a serious threat to P. oceanicum and needs to be carefully monitored, with the impacts of S. campanulata on the establishment and growth of P. oceanicum requiring urgent investigation. Pterocymbium oceanicum is a large, emergent tree endemic to Fiji that was classified as 'Critically Endangered' (IUCN Red List) based on expert knowledge. Our field survey quadruples the known size of the largest subpopulation by discovering three previously unknown stands, highlighting the value and limitations of expert knowledge for conservation assessments. Furthermore, we found that the species has a narrow ecological niche and is potentially threatened by the invading African Tulip Tree, Spathodea campanulata , which should be carefully monitored. [ABSTRACT FROM AUTHOR]