Extinction Risk In Birds Research Articles

Correlates of avian extinction timing around the world since 1500 CE

Avian extinctions have been relatively well documented in modern history, and in the past millennia, more bird species are known to have gone extinct than species in any other vertebrate class. We examined the biological correlates of extinction timing among 216 bird species that recently were either observed to go extinct or disappeared since 1500 CE, performing a novel analysis for examining the extinction trends of birds by modelling traits against the number of years since present day during which species have been extinct. We analyzed a broad range of traits and characteristics that have previously been associated with extinction and extinction risk in birds and compared the effects of these traits simultaneously against one another. In order to provide a more comprehensive and robust assessment of trait-based drivers of global bird loss in comparison to prior studies, we included extinct species recognized by any of the three major avian taxonomies as well those birds that lack recent confirmed sightings and are at least functionally extinct. We found that insular, flightless, larger-bodied, ecologically specialized species, as well as those with high aspect ratio wings, were likely to go extinct earlier in time. Besides identifying the key locations and time periods over the past five centuries where birds have gone extinct, and highlighting specific extinction-prone taxonomic groups, we provide a complete and unified dataset of traits used in this study that helps address the lack of extensive public data on modern extinct species.

Biological Correlates of Extinction Risk in Resident Philippine Avifauna

The majority of the world’s biodiversity occurs in the tropics, but human actions in these regions have precipitated an extinction crisis due to habitat degradation, overexploitation, and climate change. Understanding which ecological, biogeographical, and life-history traits predict extinction risk is critical for conserving species. The Philippines is a hotspot of biodiversity and endemism, but it is a region that also suffers from an extremely high level of deforestation, habitat degradation, and wildlife exploitation. We investigated the biological correlates of extinction risk based on the IUCN Red List threat status among resident Philippine birds using a broad range of ecological, biogeographical, and life history traits previously identified as correlates of extinction risk in birds. We found strong support across competing models for endemism, narrower elevational ranges, high forest dependency, and larger body size as correlates significantly associated with extinction risk. Additionally, we compared observed threat status with threat status fitted by our model, finding fourteen species that are not currently recognized by the IUCN Red List as threatened that may be more threatened than currently believed and therefore warrant heightened conservation focus, and predicted threat statuses for the four Philippine Data Deficient bird species. We also assessed species described in recent taxonomic splits that are recognized by BirdLife International, finding 12 species that have a fitted threat status more severe than their IUCN-designated ones. Our findings provide a framework for avian conservation efforts to identify birds with specific biological correlates that increase a species’ vulnerability to extinction both in the Philippine Archipelago and elsewhere on other tropical islands.

Behavioural plasticity is associated with reduced extinction risk in birds.

Behavioural plasticity is believed to reduce species vulnerability to extinction, yet global evidence supporting this hypothesis is lacking. We address this gap by quantifying the extent to which birds are observed behaving in novel ways to obtain food in the wild; based on a unique dataset of >3,800 novel behaviours, we show that species with a higher propensity to innovate are at a lower risk of global extinction and are more likely to have increasing or stable populations than less innovative birds. These results mainly reflect a higher tolerance of innovative species to habitat destruction, the main threat for birds.

The dynamics underlying avian extinction trajectories forecast a wave of extinctions.

Population decline is a process, yet estimates of current extinction rates often consider just the final step of that process by counting numbers of species lost in historical times. This neglects the increased extinction risk that affects a large proportion of species, and consequently underestimates the effective extinction rate. Here, we model observed trajectories through IUCN Red List extinction risk categories for all bird species globally over 28 years, and estimate an overall effective extinction rate of 2.17 × 10-4/species/year. This is six times higher than the rate of outright extinction since 1500, as a consequence of the large number of species whose status is deteriorating. We very conservatively estimate that global conservation efforts have reduced the effective extinction rate by 40%, but mostly through preventing critically endangered species from going extinct rather than by preventing species at low risk from moving into higher-risk categories. Our findings suggest that extinction risk in birds is accumulating much more than previously appreciated, but would be even greater without conservation efforts.

Loss of forest intactness elevates global extinction risk in birds

AbstractOnly around a third of the world's remaining forest cover survives in the form of Intact Forest Landscapes (IFL), and that proportion is declining. Loss of intactness could impact on biodiversity in many ways but the relationship between intactness and extinction risk has not been quantified. We created Extent of Suitable Habitat (ESH) maps for all the world's forest‐dependent birds and intersected them with an independently derived IFL layer. We also estimate the proportion of the total global range‐rarity of forest‐dependent birds that is captured by IFL. The majority of forest‐dependent bird species are now confined largely or entirely to be degraded, disturbed, or fragmented (non‐IFL) forests. Furthermore, only 22.5% of global hotspots of range‐rarity for forest‐dependent birds are found within intact forests. We find a very strong positive relationship between the global extinction risk of forest‐dependent birds and the proportion of forest within their ESH that is no longer intact. This effect was independent of overall range size and phylogeny. There was also a tendency for extinction risk to be higher in species that lost more intactness in their forest ESHs between 2000 and 2016. Restoring intactness to forest landscapes will reduce global extinction risk in forest‐dependent birds.

Colour polymorphism is associated with lower extinction risk in birds.

Colour polymorphisms have played a major role in enhancing current understanding of how selection and demography can impact phenotypes. Because different morphs often display alternative strategies and exploit alternative ecological niches, colour polymorphism can be expected to promote adaptability to environmental changes. However, whether and how it could influence populations' and species' response to global changes remains debated. To address this question, we built an up-to-date and complete database on avian colour polymorphism based on the examination of available data from all 10,394 extant bird species. We distinguished between true polymorphism (where different genetically determined morphs co-occur in sympatry within the same population) and geographic variation (parapatric or allopatric colour variation), because these two patterns of variation are expected to have different consequences on populations' persistence. Using the IUCN red list, we then showed that polymorphic bird species are at lesser risk of extinction than nonpolymorphic ones, after controlling for a range of factors such as geographic range size, habitat breadth, life history, and phylogeny. This appears consistent with the idea that high genetic diversity and/or the existence of alternative strategies in polymorphic species promotes the ability to adaptively respond to changing environmental conditions. In contrast, polymorphic species were not less vulnerable than nonpolymorphic ones to specific drivers of extinction such as habitat alteration, direct exploitation, climate change, and invasive species. Thus, our results suggest that colour polymorphism acts as a buffer against environmental changes, although further studies are now needed to understand the underlying mechanisms. Developing accurate quantitative indices of sensitivity to specific threats is likely a key step towards a better understanding of species response to environmental changes.

Elevational distribution and extinction risk in birds.

Mountainous regions are hotspots of terrestrial biodiversity. Unlike islands, which have been the focus of extensive research on extinction dynamics, fewer studies have examined mountain ranges even though they face increasing threats from human pressures – notably habitat conversion and climate change. Limits to the taxonomic and geographical extent and resolution of previously available information have precluded an explicit assessment of the relative role of elevational distribution in determining extinction risk. We use a new global species-level avian database to quantify the influence of elevational distribution (range, maximum and midpoint) on extinction risk in birds at the global scale. We also tested this relationship within biogeographic realms, higher taxonomic levels, and across phylogenetic contrasts. Potential confounding variables (i.e. phylogenetic, distributional, morphological, life history and niche breadth) were also tested and controlled for. We show that the three measures of elevational distribution are strong negative predictors of avian extinction risk, with elevational range comparable and complementary to that of geographical range size. Extinction risk was also found to be positively associated with body weight, development and adult survival, but negatively associated with reproduction and niche breadth. The robust and consistent findings from this study demonstrate the importance of elevational distribution as a key driver of variation in extinction dynamics in birds. Our results also highlight elevational distribution as a missing criterion in current schemes for quantifying extinction risk and setting species conservation priorities in birds. Further research is recommended to test for generality across non-avian taxa, which will require an advance in our knowledge of species’ current elevational ranges and increased efforts to digitise and centralise such data.

Behavioural flexibility predicts species richness in birds, but not extinction risk

The number of species varies greatly among taxa. In birds, for example, the parvorder Passerida contains 3556 species while the Odontophorida contains only six species. This uneven distribution of species among bird groups is not a consequence of random branching patterns and therefore warrants an explanation. According to the behavioural drive hypothesis, behavioural innovation coupled with social transmission of the new skill to other members of the population may lead to accelerated rates of evolution, and could therefore account for differences in species richness. In this paper, we test the behavioural drive hypothesis by examining the link between behavioural flexibility and the number of species per taxon. We estimate flexibility with relative brain size and feeding innovation rate and predict that both will be positively associated with the number of species per taxon. Since the number of species at any given time results from a balance between speciation and extinction rates, we also examine the link between flexibility and the number of species threatened with extinction. We predict that the two flexibility correlates will be negatively associated with the number of species at risk. In simple regressions, both flexibility correlates were significantly associated with species number per taxon. However, only innovation rate remained in the final model. Relative brain weight dropped out of the multiple regression due to its association with innovation rate. Relative brain weight, innovation rate and species number per taxon were all significantly correlated with the number of threatened species in the simple regression, but only the latter remained significant in the final model. The same results were obtained on independent contrasts, indicating that behavioural flexibility predicts richness but not extinction risk in birds. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Ecological basis of extinction risk in birds: habitat loss versus human persecution and introduced predators.

Understanding the ecological mechanisms that underlie extinction is fundamental to conservation. It is well established that not all taxa are equally vulnerable to extinction, but the reasons for these differences are poorly understood. This may be, in part, because different taxa are threatened by different mechanisms. Theoretically, sources of extinction risk that perturb the balance between fecundity and longevity, such as human persecution and introduced predators, should be particularly hazardous for taxa that have slow rates of population growth. In contrast, sources of extinction risk that reduce niche availability, such as habitat loss, should represent a particular threat to taxa that are ecologically specialized. Here we test these predictions by using a phylogenetic comparative method and a database on 95 families of birds. As theory predicts, extinction risk incurred through persecution and introduced predators is associated with large body size and long generation time but is not associated with degree of specialization, whereas extinction risk incurred through habitat loss is associated with habitat specialization and small body size but not with generation time. These results demonstrate the importance of considering separately the multiple mechanisms that underlie contemporary patterns of extinction. They also reveal why it has previously proven so difficult to identify simple ecological correlates of overall extinction risk.

Effects of Human Activity on Global Extinction Risk

Both natural and anthropogenic factors are important in determining a species’ risk of extinction. Little work has been done, however, to quantify the magnitude of current anthropogenic influences on the extinction process. The purpose of this study is to determine the extent to which measures of the intensity of human activity are related to the global variability of two measures of species’ susceptibility to extinction. We observed six indices of human activities in 90 countries, and we tested their relationships to the proportion of threatened bird and mammal species in each country, as well as to mammalian population density. After correcting for area effects, latitudinal diversity gradients, and body size (for population density), 28 to 50% of the remaining variation was statistically attributable to anthropogenic variables. Different measures of anthropogenic influence were most closely related to extinction risk in birds and mammals. Human population density was the variable most closely related to the proportion of threatened bird species per country, whereas per capita GNP was more important for mammal species. Mammalian population density strongly correlates with the extent of protected area per country. Contrary to suggestions in earlier literature, our work does not support the hypothesis that habitat loss is a prime contributor to species loss because frequencies of threatened birds and mammals are not closely related to patterns of land use.