Effects of heat stress and green cover on urban birds in the megacity of Bengaluru.

Cities, despite being responsible for the loss of habitat as they grow, are also an important refugium for biodiversity. Many urban areas in the tropical areas of the global south are rich in biodiversity and are also undergoing climate warming and heat island impacts. Eliciting support from policy and decision makers for sustaining the habitats for birds in cities may depend on how conservation of bird habitats is linked to the new emphasis on ecosystem services, including heat stress mitigation. The megacity of Bengaluru has over 350 species of birds that are found in diverse habitats that include urban forests, large institutional campuses, gardens, and parks. Based on existing literature, we a priori predicted that parts of the city with higher levels of heat will have lower bird presences and parts with higher green cover are likely to support higher presences of birds, while allowing for some birds to prefer open habitats with less greenness. We tested hypotheses on the role of green cover and heat stress on bird occurrence using an informed Bayesian regression approach. We summarized the information and uncertainty on the direction of the slope of the two covariates as hyper priors as inputs to the regression. We used satellite data on heat stress as a proxy for urban heat islands and climate warming effects, and green cover (Normalized Difference Vegetation Index [NDVI]), to test their effects on spatially explicit occurrences of urban birds. We found that all birds responded negatively to the hotter parts of the city, but the effects of green cover varied (negative, neutral and positive) with species identity (Pseudo-R 0.13-0.36). This could partially be due to the preference for open spaces or dependence on anthropogenic food sources for foraging by these species. We mapped heat islands, cooling potential, and the bird diversity of green spaces in Bengaluru to identify areas of conservation value that also help mitigate heat stress for citizens. Going forward, these results can help us answer nuanced species-level responses and their vulnerability to the impacts of climate change and foster support for conservation of bird habitats in Bengaluru.