The audiovisual experience of observing birds in cities provides numerous benefits
to residents, but their diversity is endangered by urbanization. Although the magnitude
of the surface urban heat island effect (hereafter SUHI) has grown in recent years,
its impact on bird diversity has not been adequately investigated. Here, we calculate
the SUHI in 336 Chinese cities and we document the implications of the SUHI for avian
species richness and functional diversity during the 2001, 2011, and 2019 breeding
and non-breeding seasons. We predict that the SUHI will result in greater species
richness and functional diversity in urban areas during the non-breeding season, especially
for cities located within colder regions of China where the SUHI is more likely to
relax thermoregulatory costs and reduce the propensity of some species to migrate.
We predict that the SUHI will result in decreased species richness and functional
diversity during the breeding season due to increased physiological stress, especially
for cities located within warmer regions of China. Our findings showed that the SUHI
was associated with lower species richness and lower functional diversity of birds
in urban areas compared to suburban areas during both the breeding and non-breeding
seasons. These results suggest that the SUHI induced birds to avoid urban areas or
to move to cooler suburban areas during both the breeding and non-breeding seasons.
This effect persisted irrespective of a city's size or geographical location. Our
findings suggest that the SUHI is degrading bird diversity in Chinese cities.
