Threatened and extinct island endemic birds of the world: Distribution, threats and functional diversity

Abstract

Aim The world's islands support disproportionate levels of endemic avian biodiversity despite suffering numerous extinctions. While intensive recent research has focused on island bird conservation or extinction, few global syntheses have considered these factors together from the perspective of morphological trait diversity. Here, we provide a global summary of the status and ecology of extant and extinct island birds, the threats they face and the implications of species loss for island functional diversity. Location Global. Taxon Birds. Methods We provide a review of the literature on threatened and extinct island birds, with a particular focus on global studies that have incorporated functional diversity. Alongside this, we analyse IUCN Red List data in relation to distribution, threats and taxonomy. Using null models and functional hypervolumes, in combination with morphological trait data, we assess the functional diversity represented by threatened and extinct island endemic birds. Results and main conclusions We find that almost half of all island endemic birds extant in 1500 CE are currently either extinct or threatened with extinction, with the majority of threatened extant species having declining population trends. We also found evidence of 66 island endemic subspecies extinctions. The primary threats to extant island endemic birds currently are agriculture, biological resource use, and invasive species. While there is overlap between the hotspots of threatened and extinct island endemics birds, there are some notable differences, including the Philippines and Indonesia, which support a substantial number of threatened species but have no recorded post‐1500 CE bird extinctions. Traits associated with threatened island endemic birds are large body mass, flightlessness, aquatic predator, omnivorous and vertivorous trophic niches, marine habitat affinity, and, paradoxically, higher dispersal ability. Critically, we find that threatened endemics (i) occupy distinct areas of beak morphospace, and (ii) represent substantial unique areas of the overall functional space of island endemics. We caution that the loss of threatened species may have severe effects on the ecological functions birds provide on islands.

Trait diversity metrics can perform well with highly incomplete datasets

“…All trait values were log 10 transformed and standardised. While we aimed to use all available data, after initial exploration we removed the four species of kiwis (Apterygidae) recognised in the BirdTree phylogeny (Jetz et al, 2012) as they were extreme outliers with respect to morphological traits (see Supplementary Information section 1, Matthews et al, 2022). The final master dataset included data for 9579 bird species.…”

“…AVONET (Tobias et al, 2022) is available for use under the creative commons licence (CC BY 4.0) and can be accessed at: https://figshare.com/s/b990722d72a26b5bfead. BirdTree phylogenetic and taxonomic data can accessed at: https://birdtree.org/.…”

“…Using the AVONET dataset of avian morphological traits (Tobias et al, 2022), we investigated the impact of data missingness and bias in estimates of trait richness and trait divergence. In this analysis, we followed the BirdTree taxonomy and phylogeny (Jetz et al, 2012).…”

“…For example, while 80% of plant species are represented in the largest plant trait dataset (the TRY database) (Kattge et al, 2020), only 17% of species have data for 10 or more traits (Tobias et al, 2022), less than 1% had complete data across the six fundamental traits that were used to characterize the global spectrum of plant form and function (Díaz et al, 2016), and this percentage goes down to 0.1% when fine-root traits are also considered . Etard et al (2020) found that mean trait completeness across seven ecological traits was only 47% for amphibians and 46% for reptiles.…”

“…Etard et al (2020) found that a mean of 89% of mammals and 84% of birds were represented (across seven ecological traits). A recent release of a new dataset, AVONET, sees 95-99% of bird species represented (with some variation by trait and taxonomy) for 11 morphological traits (Tobias et al, 2022) with ecological and geographical data also available for most species. However, even when a small proportion of species are missing data, the available information may not be representative of the true diversity (González-Suárez et al, 2012).…”