Working group members compiled the global dataset for birds in 54 cities and for plants in 110 cities. The majority of urban bird and plant species they found are native, they write, and cities even support populations of 36 threatened bird and 65 threatened plant species.
But across the study, cities supported about 92 percent fewer bird species and 75 percent fewer native plant species than expected for similar undeveloped lands, a “substantial decline” that is best explained by human-built features such as land cover and city age. The working group found that cities with more natural habitats support more bird and plant species and experience fewer species losses as the city grows.
The most common “cosmopolitan” bird species, occurring in more than 80 percent of cities, were the rock pigeon, house sparrow, starling and barn swallow. Among plants, 11 species including annual meadow grass occur in more than 90 percent of cities.
One of Warren’s co-leaders and the paper’s lead author, Myla F.J. Aronson of Rutgers, points out that “while urbanization has caused cities to lose large numbers of plants and animals, the good news is that cities still retain endemic native species, which opens the door for new policies on regional and global biodiversity conservation.”