A new study of bird biodiversity in China provides one of the first continental-scale snapshots of how human cities shape the diversity and geographic distribution of birds, especially of threatened species that face habitat loss.
The results, based on 20 years of observations of birds in Chinese urban centers, show that hotspots of many threatened birds overlap with urbanized areas. However, the study showed that green infrastructure initiatives within cities could improve bird diversity, at least on the local scale.
The results could guide governments' efforts to reverse the decline in biodiversity that has taken place in many urban areas — a key step to protecting ecosystems and achieving sustainable development goals.
The new paper was published in the December 9 issue of Science Advances.
"We provided the first analysis of the impacts of urbanization on spatial variation and species similarity of bird diversity distribution at the continental scale in the Global South," said Yonglong Lu, a research professor at Xiamen University in Fujian, China, who was involved in the study.
How the Planet's Newest Ecosystem Shapes Bird Populations
Cities have become the planet's newest type of ecosystem. Urban centers are typically linked to pollution and environmental damage, but buildings and other structures can offer habitats not only for humans but also for rodents, insects, and several types of birds.
However, many other animals and plants have struggled in the face of urbanization. The growth of cities threatens many native species with the loss of their preferred habitats, leaving them at risk of decline and even extinction.
The rapid spread of cities over the past two centuries has had a major impact on the diversity and range of birds in particular. Species such as pigeons that can adapt to urban environments have thrived, while native species with narrower ranges must contend with the fragmentation and pollution of their habitats.
Governmental organizations have made it a point to study and maintain biodiversity, which is vital to the health and maintenance of ecosystems. In 1992, 150 governments committed to reduce biodiversity loss through the Convention on Biological Diversity, with the convention's COP15 conference currently taking place in Montreal, Canada.
However, studying how cities and their associated human activities impact the biodiversity of birds near urban areas has proved challenging for researchers, Lu explained.
"Birds are an important indicator of urban ecological status and are among the key animals that survive in the urban environment," he said. "Our understanding of the relationships between urbanization and biodiversity remains insufficient, especially in the Global South."
He added that studies in developing countries have been held back by a lack of long-term spatial and temporal data on bird distributions, partly due to a lack of infrastructure that can monitor biodiversity in large cities.
Human Activities and Cities Constrain Threatened Birds
Lu, along with Bin Sun, a researcher at Xiamen University and lead author of the new study, and colleagues set out to capture the impact of urbanization on bird distribution in China, which is the fastest-urbanizing country in the world.
The researchers first aimed to get a detailed picture of bird populations and movements in the country. They combed through data from three sources: the China Bird Watching Record Center, the birdwatching app eBird, and the Global Biodiversity Information Facility.
After parsing these data sources, Lu's team eventually gathered a bounty of observational data on bird movements from 2000 to 2020. They then harnessed various models of species distributions to simulate how birds might be distributed across China based on the observational data.
The models probed how night lighting, the building of impervious surfaces such as rooftops, and other human activities affected bird populations. The team also simulated how these activities might affect the distribution of China's threatened bird species, which are concentrated in coastal regions like Shanghai and Tianjin.
They discovered that hotspots of threatened bird species substantially overlapped with urbanized areas, especially in China's eastern prefectures. For example, the growth of impervious surfaces was highest in hotspots for threatened birds such as the Yangtze River Delta.
These hotspots also overlapped with the growth of areas affected by nighttime lighting. Artificial lights can disrupt bird behavior and cause nocturnal migratory birds to fly into buildings, often with fatal results.
Overall, just 3.9% of these birds' preferred land was present in urban areas. Lu's team therefore concluded that ongoing urbanization and the growth of human activities has increasingly constrained the habitat ranges of threatened birds.
The data also showed that the composition of birds was less diverse in urbanized regions in China. However, cities such as Beijing and Guangzhou that scored higher on indices of urban green infrastructure and urban vegetation maintained higher bird diversity than surrounding cities.
The team further studied the effects of green infrastructure on bird diversity and found something unexpected. Although including green infrastructure boosted bird diversity in the immediate area of the city, it also made bird populations more similar across cities on the regional scale.
This finding suggests that green infrastructure in cities can protect local bird diversity but may also reduce larger-scale biodiversity between regions, Lu said.
"Ultimately, highly homogeneous urban environments may have little effect on the restoration of bird diversity from the global perspective," he added.
How Cities Can Still Maintain Bird Biodiversity
Despite this last discovery, the scientists believe their work will help inform how authorities in China and other countries approach maintaining diversity and protecting threatened birds.
For example, many of the threatened birds examined in the study seek wetlands as their preferred land cover type. Therefore, Lu suggested that stakeholders should prioritize strengthening the protection and restoration of wetlands as cities continue to grow.
Secondly, the scientists say that biodiversity conservation strategies should emphasize coordination between local and global conservation objectives. Conservation efforts should focus on strengthening the protection of native species and those with narrow ranges, which are more vulnerable to the effects of urbanization and human activities.
"In addition, we would like to emphasize that urbanization effects can mostly be reversed by ecosystem conservation and restoration measures," Lu added. His team cites several regions in China that have managed to preserve bird diversity by establishing protected areas in nonurbanized regions of city clusters.
One notable example is the city of Yancheng, whose Tiaozini wetland was declared a World Natural Heritage site in 2019. Thanks to these conservation efforts, Yancheng has become a node for bird biodiversity in the Yangtze River Delta.