Loss and degradation of natural habitats and direct overexploitation of many species are cited as the key threats to avian biodiversity. Climate change is identified as an emerging driver of bird population declines.
"We are now witnessing the first signs of a new wave of extinctions of continentally distributed bird species," says lead author Alexander Lees, senior lecturer at Manchester Metropolitan University in the United Kingdom and also a research associate at the Cornell Lab of Ornithology. "Avian diversity peaks globally in the tropics and it is there that we also find the highest number of threatened species."
The study says approximately 48% of existing bird species worldwide are known or suspected to be undergoing population declines. Populations are stable for 39% of species. Only 6% are showing increasing population trends, and the status of 7% is still unknown. The study authors reviewed changes in avian biodiversity using data from the International Union for Conservation of Nature's "Red List" to reveal population changes among the world's 11,000 bird species.
The findings mirror the results of a seminal 2019 study which determined that nearly 3 billion breeding birds have been lost during the past 50 years across the United States and Canada. The lead author of that study is also an author on this global status report.
"After documenting the loss of nearly 3 billion birds in North America alone, it was dismaying to see the same patterns of population declines and extinction occurring globally," says conservation scientist Ken Rosenberg from the Cornell Lab, now retired. "Because birds are highly visible and sensitive indicators of environmental health, we know their loss signals a much wider loss of biodiversity and threats to human health and well-being."
Despite their findings, study authors say there is hope for avian conservation efforts, but transformative change is needed.
"The fate of bird populations is strongly dependent on stopping the loss and degradation of habitats," says Lees. "That is often driven by demand for resources. We need to better consider how commodity flows can contribute to biodiversity loss and try to reduce the human footprint on the natural world."
"Fortunately, the global network of bird conservation organizations taking part in this study have the tools to prevent further loss of bird species and abundance," adds Rosenberg. "From land protection to policies supporting sustainable resource-use, it all depends on the will of governments and of society to live side by side with nature on our shared planet."
Information is key, and study authors point out that the growth of public participation in bird monitoring and the advent of easy-to-use tools, such as the Cornell Lab's eBird database, make continental-scale breeding bird surveys, distribution atlases, and abundance models possible and help inform conservation efforts.