PhD: Using past archives to constrain baselines in avian biodiversity

Although birds number ~11,000 species today, 40% are in population decline, with 20% of species identified as at risk of extinction. Broadly, it is expected that ongoing climatic and environmental changes will result in a loss of avian biodiversity and a polewards shift in their geographic distributions, with large-bodied species thought to be at greatest risk of extinction. However, such forecasts are based entirely on very recent records. Even data from the last 500 years show that the present day represents a heavily filtered avian registry, with the extinction of >160 bird species in that time, including iconic forms such as the dodo and passenger pigeon. Current distributional ranges therefore likely reflect substantial anthropogenic disturbances, limiting the applicability of present-day data for forecasting. As such, our concepts of baselines of avian biodiversity, including extinction rate and selectivity, are severely distorted by the narrow temporal lens through which they are viewed.

The emerging field of conservation palaeobiology utilizes the fossil record to provide the only empirical data on long-term interactions between biodiversity, climate, and human impacts. This rich archive preserves information on past avian geographic distributions and climates different from those in the present day, including time intervals characterised by climatic conditions potentially analogous to near-future scenarios. Perhaps most importantly, it enables us to decouple the distorting effects of human influence on biodiversity, providing our only evidence of ‘normal’ extinction rate dynamics. The disappearance of vertebrate species in many regions over the last 50,000 years is coincident with the arrival and modelled population growth of prehistoric modern humans. Many of the species that went extinct over this interval (including birds) were the largest members of their respective families, but it remains unclear whether size selectivity has been a consistent factor structuring avian extinctions prior to human influence, or if this pattern is primarily attributable to human-driven extinctions, as appears to be the case for mammals. Were long-term climatic fluctuations the main driver of avian extinction patterns prior to human impacts? How much avian ecomorphological diversity have we already lost?

Using and contributing to The Paleobiology Database, this project will harness the rich fossil and zooarchaeological record of birds to understand how past avian extinctions were affected by long-term climatic changes over the last few million years (Plio-Pleistocene), and, more recently, by prehistoric human impacts. The PhD student will produce the first sampling-standardized regional baselines for avian biodiversity estimates prior to human impacts and before globalisation. Combined with collecting ecomorphological data (e.g. body size proxies) from avian fossils, this will enable the identification of unevenness in past extinctions across different taxonomic groups, ecomorphological categories, and geographical regions. The PhD student will also quantify how much ecomorphological diversity has been lost during this time interval. This project will produce results that have implications for the past, present, and future of avian biodiversity. It will also dovetail with the recently developed IUCN Green Status of Species, which incorporates longer-term species trajectories to measure recovery against historical baselines.