The dynamics underlying avian extinction trajectories forecast a wave of extinctions

The global loss of avian functional and phylogenetic diversity from anthropogenic extinctions

Humans have been driving a global erosion of species richness for millennia, but the consequences of past extinctions for other dimensions of biodiversity-functional and phylogenetic diversity-are poorly understood. In this work, we show that, since the Late Pleistocene, the extinction of 610 bird species has caused a disproportionate loss of the global avian functional space along with ~3 billion years of unique evolutionary history. For island endemics, proportional losses have been even greater. Projected future extinctions of more than 1000 species over the next two centuries will incur further substantial reductions in functional and phylogenetic diversity. These results highlight the severe consequences of the ongoing biodiversity crisis and the urgent need to identify the ecological functions being lost through extinction.

Global shortfalls in documented actions to conserve biodiversity

Threatened species are by definition species that are in need of assistance. In the absence of suitable conservation interventions, they are likely to disappear soon1. There is limited understanding of how and where conservation interventions are applied globally, or how well they work2,3. Here, using information from the International Union for Conservation of Nature Red List and other global databases, we find that for species at risk from three of the biggest drivers of biodiversity loss-habitat loss, overexploitation for international trade and invasive species4-many appear to lack the appropriate types of conservation interventions. Indeed, although there has been substantial recent expansion of the protected area network, we still find that 91% of threatened species have insufficient representation of their habitats within protected areas. Conservation interventions are not implemented uniformly across different taxa and regions and, even when present, have infrequently led to substantial improvements in the status of species. For 58% of the world's threatened terrestrial species, we find conservation interventions to be notably insufficient or absent. We cannot determine whether such species are truly neglected, or whether efforts to recover them are not included in major conservation databases. If they are indeed neglected, the outlook for many of the world's threatened species is grim without more and better targeted action.

Global conservation status of the jawed vertebrate Tree of Life

Human-driven extinction threatens entire lineages across the Tree of Life. Here we assess the conservation status of jawed vertebrate evolutionary history, using three policy-relevant approaches. First, we calculate an index of threat to overall evolutionary history, showing that we expect to lose 86-150 billion years (11-19%) of jawed vertebrate evolutionary history over the next 50-500 years. Second, we rank jawed vertebrate species by their EDGE scores to identify the highest priorities for species-focused conservation of evolutionary history, finding that chondrichthyans, ray-finned fish and testudines rank highest of all jawed vertebrates. Third, we assess the conservation status of jawed vertebrate families. We found that species within monotypic families are more likely to be threatened and more likely to be in decline than other species. We provide a baseline for the status of families at risk of extinction to catalyse conservation action. This work continues a trend of highlighting neglected groups-such as testudines, crocodylians, amphibians and chondrichthyans-as conservation priorities from a phylogenetic perspective.

Urban tolerance does not protect against population decline in North American birds

Population declines of organisms are widespread and severe, but some species' populations have remained stable, or even increased. The reasons some species are less vulnerable to population decline than others are not well understood. Species that tolerate urban environments often have a broader environmental tolerance, which, along with their ability to tolerate one of the most human-modified habitats (i.e. cities), might allow them to persist in the face of diverse anthropogenic challenges. Here, we examined the relationship between urban tolerance and annual population trajectories for 397 North American bird species. Surprisingly, we found that urban tolerance was unrelated to species' population trajectories. The lack of a relationship between urban tolerance and population trajectories may reflect other factors driving population declines independent of urban tolerance, challenges that are amplified in cities (e.g. climate warming, disease), and other human impacts (e.g. conservation efforts, broad-scale land-use changes) that have benefitted some urban-avoidant species. Overall, our results illustrate that urban tolerance does not protect species against population decline.

Undiscovered bird extinctions obscure the true magnitude of human-driven extinction waves

Birds are among the best-studied animal groups, but their prehistoric diversity is poorly known due to low fossilization potential. Hence, while many human-driven bird extinctions (i.e., extinctions caused directly by human activities such as hunting, as well as indirectly through human-associated impacts such as land use change, fire, and the introduction of invasive species) have been recorded, the true number is likely much larger. Here, by combining recorded extinctions with model estimates based on the completeness of the fossil record, we suggest that at least ~1300-1500 bird species (~12% of the total) have gone extinct since the Late Pleistocene, with 55% of these extinctions undiscovered (not yet discovered or left no trace). We estimate that the Pacific accounts for 61% of total bird extinctions. Bird extinction rate varied through time with an intense episode ~1300 CE, which likely represents the largest human-driven vertebrate extinction wave ever, and a rate 80 (60-95) times the background extinction rate. Thus, humans have already driven more than one in nine bird species to extinction, with likely severe, and potentially irreversible, ecological and evolutionary consequences.

Genetic Load and Adaptive Potential of a Recovered Avian Species that Narrowly Avoided Extinction

High genetic diversity is a good predictor of long-term population viability, yet some species persevere despite having low genetic diversity. Here we study the genomic erosion of the Seychelles paradise flycatcher (Terpsiphone corvina), a species that narrowly avoided extinction after having declined to 28 individuals in the 1960s. The species recovered unassisted to over 250 individuals in the 1990s and was downlisted from Critically Endangered to Vulnerable in the International Union for the Conservation of Nature Red List in 2020. By comparing historical, prebottleneck (130+ years old) and modern genomes, we uncovered a 10-fold loss of genetic diversity. Highly deleterious mutations were partly purged during the bottleneck, but mildly deleterious mutations accumulated. The genome shows signs of historical inbreeding during the bottleneck in the 1960s, but low levels of recent inbreeding after demographic recovery. Computer simulations suggest that the species long-term small Ne reduced the masked genetic load and made the species more resilient to inbreeding and extinction. However, the reduction in genetic diversity due to the chronically small Ne and the severe bottleneck is likely to have reduced the species adaptive potential to face environmental change, which together with a higher load, compromises its long-term population viability. Thus, small ancestral Ne offers short-term bottleneck resilience but hampers long-term adaptability to environmental shifts. In light of rapid global rates of population decline, our work shows that species can continue to suffer the effect of their decline even after recovery, highlighting the importance of considering genomic erosion and computer modeling in conservation assessments.

Extinct in the wild: The precarious state of Earth's most threatened group of species

Extinct in the Wild (EW) species are placed at the highest risk of extinction under the International Union for Conservation of Nature Red List, but the extent and variation in this risk have never been evaluated. Harnessing global databases of ex situ animal and plant holdings, we report on the perilous state of EW species. Most EW animal species-already compromised by their small number of founders-are maintained at population sizes far below the thresholds necessary to ensure demographic security. Most EW plant species depend on live propagation by a small number of botanic gardens, with a minority secured at seed bank institutions. Both extinctions and recoveries are possible fates for EW species. We urgently call for international effort to enable the latter.

The EDGE2 protocol: Advancing the prioritisation of Evolutionarily Distinct and Globally Endangered species for practical conservation action

The conservation of evolutionary history has been linked to increased benefits for humanity and can be captured by phylogenetic diversity (PD). The Evolutionarily Distinct and Globally Endangered (EDGE) metric has, since 2007, been used to prioritise threatened species for practical conservation that embody large amounts of evolutionary history. While there have been important research advances since 2007, they have not been adopted in practice because of a lack of consensus in the conservation community. Here, building from an interdisciplinary workshop to update the existing EDGE approach, we present an "EDGE2" protocol that draws on a decade of research and innovation to develop an improved, consistent methodology for prioritising species conservation efforts. Key advances include methods for dealing with uncertainty and accounting for the extinction risk of closely related species. We describe EDGE2 in terms of distinct components to facilitate future revisions to its constituent parts without needing to reconsider the whole. We illustrate EDGE2 by applying it to the world's mammals. As we approach a crossroads for global biodiversity policy, this Consensus View shows how collaboration between academic and applied conservation biologists can guide effective and practical priority-setting to conserve biodiversity.

Integrated index-based assessment reveals long-term conservation progress in implementation of Convention on Biological Diversity

The Convention on Biological Diversity (CBD) has launched two long-term, target-based conservation Strategic Plans in the past two decades. We compiled an index-based assessment framework to evaluate target achievements of the CBD using long-term indicators. The CBD Index is steadily increasing, with the Goal Indices for biodiversity mainstreaming, protection, and supporting mechanisms all improving over time. While the State and Pressure Indices continue to deteriorate coupled with human population and economic development, their changing rates have slowed down, most likely because of the constantly growing conservation efforts as revealed by the Response Index. The first quantitative assessment of the CBD’s long-term performance may provide critical science-based evidence for continuing commitments to developing and implementing a new Post-2020 Global Biodiversity Framework. We also call for enhanced efforts to address the emerging challenges in achieving the 2050 Vision for Biodiversity and the adoption of a rapid assessment framework to track future progress.

Revisiting species and areas of interest for conserving global mammalian phylogenetic diversity

Various prioritisation strategies have been developed to cope with accelerating biodiversity loss and limited conservation resources. These strategies could become more engaging for decision-makers if they reflected the positive effects conservation can have on future projected biodiversity, by targeting net positive outcomes in future projected biodiversity, rather than reflecting the negative consequences of further biodiversity losses only. Hoping to inform the post-2020 biodiversity framework, we here apply this approach of targeting net positive outcomes in future projected biodiversity to phylogenetic diversity (PD) to re-identify species and areas of interest for conserving global mammalian PD. We identify priority species/areas as those whose protection would maximise gains in future projected PD. We also identify loss-significant species/areas as those whose/where extinction(s) would maximise losses in future projected PD. We show that our priority species/areas differ from loss-significant species/areas. While our priority species are mostly similar to those identified by the EDGE of Existence Programme, our priority areas generally differ from previously-identified ones for global mammal conservation. We further highlight that these newly-identified species/areas of interest currently lack protection and offer some guidance for their future management.

Dark extinction: the problem of unknown historical extinctions

The extinction of species before they are discovered and named (dark extinction, DE) is widely inferred as a significant part of species loss in the 'pre-taxonomic' period (approx. 1500-1800 CE) and, to some extent, in the 'taxonomic period' (approx. 1800-present) as well. The discovery of oceanic islands and other pristine habitats by European navigators and the consequent introduction of destructive mammals, such as rats and goats, started a process of anthropogenic extinction. Much ecosystem change happened before systematic scientific recording, so has led to DE. Statistical methods are available to robustly estimate DE in the 'taxonomic period'. For the 'pre-taxonomic period', simple extrapolation can be used. The application of these techniques to world birds, for example, suggests that approximately 56 DEs occurred in the 'taxonomic period' (1800-present) and approximately 180 in the 'pre-taxonomic period' (1500-1800). Targeting collection activities in extinction hotspots, to make sure organisms are represented in collections before their extinction, is one way of reducing the number of extinct species without a physical record (providing that collection efforts do not themselves contribute to species extinction).

Generation lengths of the world's birds and their implications for extinction risk

Birds have been comprehensively assessed on the International Union for Conservation of Nature (IUCN) Red List more times than any other taxonomic group. However, to date, generation lengths have not been systematically estimated to scale population trends when undertaking assessments, as required by the criteria of the IUCN Red List. We compiled information from major databases of published life-history and trait data for all birds and imputed missing life-history data as a function of species traits with generalized linear mixed models. Generation lengths were derived for all species, based on our modeled values of age at first breeding, maximum longevity, and annual adult survival. The resulting generation lengths varied from 1.42 to 27.87 years (median 2.99). Most species (61%) had generation lengths <3.33 years, meaning that the period of 3 generations-over which population declines are assessed under criterion A-was <10 years, which is the value used for IUCN Red List assessments of species with short generation times. For these species, our trait-informed estimates of generation length suggested that 10 years is a robust precautionary value for threat assessment. In other cases, however, for whole families, genera, or individual species, generation length had a substantial impact on their estimated extinction risk, resulting in higher extinction risk in long-lived species than in short-lived species. Although our approach effectively addressed data gaps, generation lengths for some species may have been underestimated due to a paucity of life-history data. Overall, our results will strengthen future extinction-risk assessments and augment key databases of avian life-history and trait data.

The past and future human impact on mammalian diversity

To understand the current biodiversity crisis, it is crucial to determine how humans have affected biodiversity in the past. However, the extent of human involvement in species extinctions from the Late Pleistocene onward remains contentious. Here, we apply Bayesian models to the fossil record to estimate how mammalian extinction rates have changed over the past 126,000 years, inferring specific times of rate increases. We specifically test the hypothesis of human-caused extinctions by using posterior predictive methods. We find that human population size is able to predict past extinctions with 96% accuracy. Predictors based on past climate, in contrast, perform no better than expected by chance, suggesting that climate had a negligible impact on global mammal extinctions. Based on current trends, we predict for the near future a rate escalation of unprecedented magnitude. Our results provide a comprehensive assessment of the human impact on past and predicted future extinctions of mammals.

Roads as a contributor to landscape-scale variation in bird communities

Roads and their traffic can affect wildlife over large areas and, in regions with dense road networks, may influence a high proportion of the ecological landscape. We assess the abundance of 75 bird species in relation to roads across Great Britain. Of these, 77% vary significantly in abundance with increasing road exposure, just over half negatively so. The effect distances of these negative associations average 700 m from a road, covering over 70% of Great Britain and over 40% of the total area of terrestrial protected sites. Species with smaller national populations generally have lower relative abundance with increasing road exposure, whereas the opposite is true for more common species. Smaller-bodied and migratory species are also more negatively associated with road exposure. By creating environmental conditions that benefit generally common species at the expense of others, road networks may echo other anthropogenic disturbances in bringing about large-scale simplification of avian communities.