Birds
Tropical bird diversity drops sharply in cities
A global study reveals that equatorial cities lose far more avian species than northern settlements, disrupting an ancient biodiversity pattern.
Reported by Phys.org · · 1 min read
Urban development across the globe is eroding an ancient biological trend that concentrates wildlife variety near the equator, according to research conducted by scientists at McGill University. The investigation indicates that cities constructed in equatorial regions experience a considerably greater drop in avian variety than urban centers located in higher latitudes.
Appearing in the journal PNAS, the proceedings of the National Academy of Sciences, the investigation examined records covering over 10,000 avian species across five continents. By evaluating community sightings cataloged through Cornell University's eBird platform, investigators partitioned the globe into square-kilometer blocks, retaining locations where data captured at least 95 percent of local variety.
Researchers categorized these sections into urban, suburban, or natural zones depending on resident density and landscape disruption. The resulting comparisons revealed that equatorial cities lost an average of 42 percent of their bird species relative to nearby wild areas. Across the entire planet, the average metropolitan decline stood at 32 percent, while settlements situated at 65 degrees latitude saw only a 12 percent reduction.
Study authors explained that this pronounced disparity stems from two distinct factors. Modern cities throughout the tropics often feature more aggressive development, while native tropical birds typically possess a diminished capacity to tolerate environmental disruption compared to their northern counterparts.
Senior author Anna Hargreaves observed that the gradual increase in variety toward the equator has persisted across tens of thousands of years, making its current unraveling particularly striking. However, lead investigator Jory Griffith and colleagues noted that metropolitan zones retaining abundant plant cover, alongside suburban tracts, suffered milder losses. Preserving vegetated refuges within city layouts could provide a practical method for birds to share habitats with growing human populations.
Following these findings, the scientific group plans to explore how shifting urban avian diversity influences critical ecological relationships, including pollination and predation dynamics within city borders.
