Global survey of urban birds and plants find more diversity than expected

The largest analysis to date of the effect of urbanization on bird and plant species diversity worldwide has found that despite human influences many cities retain high numbers of native species and are far from barren environments.

Urban ecologist Paige Warren of the University of Massachusetts Amherst, co-leader of a 24-member research working group at the University of California Santa Barbara's National Center for Ecological Analysis and Synthesis (NCEAS), said that they were able to build the largest database to date from the largest number of cities, more than 140 on every continent except Antarctica.

She said looking at what drives the number of species found, we see that human factors are more influential than region or where the city is located, for example.

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.

The study has been published in Proceedings of the Royal Society B.