In a recent study published in “Science of the Total Environment,” scientists at Cornell’s Lab of Ornithology and Zhejiang University found that the surface urban heat island effect had implications on bird diversity in China, causing them to migrate from urban to suburban areas in the 336 Chinese cities studied.
“The urban heat island effect occurs when urban areas become ‘islands’ of higher temperatures which occurs when they have little green vegetation and abundant heat-retaining surfaces such as asphalt, concrete or steel,” said Frank La Sorte, senior research associate at the Lab of Ornithology and one of the authors on the paper.
During the 2001, 2011 and 2019 breeding and non-breeding seasons of studied avian species, bird species diversity saw a substantial decline in observed areas with higher heat island effects.
The study found that many bird species were leaving urban areas in favor of the surrounding suburban areas, consequently impacting bird breeding and foraging, resulting in decreased species diversity during both the birds’ breeding and non-breeding seasons.
The non-breeding season, though typically cooler than the breeding season, still observed a decrease in diversity similar to breeding season — an unexpected finding.
La Sorte explained that researchers expected that the urban heat island effect would lower bird diversity in cities during the summer breeding season, and would increase the winter nonbreeding season. Thus, the fact that bird diversity still decreased even during the typically cooler nonbreeding season was unexpected, LaSorte said.
Quantifying the results, the study found that, overall, a one degree Celsius increase in temperature between urban and suburban areas was associated with 0.291 fewer species on average during the nonbreeding season and 0.132 fewer species on average during the breeding season, according to La Sorte.
Expansion of urban areas, both in size and density, may have growing implications on bird diversity across the globe over time. “As urban areas become hotter, birds’ abilities to maintain normal body temperatures will become more challenging, increasing physiological stress”, explained La Sorte. “Over the long term, this could result in population declines [of birds],” he said.
Though the study was limited to China, a country with a high level of urbanization, the findings are applicable to metropolitan areas across the globe that contain structures promoting heat absorption and retention, according to La Sorte.
“As the climate continues to rise, these effects will likely be exacerbated as urban temperatures continue to increase,” LaSorte said.
Emma Arboleda can be reached at [email protected].