Land cover and socioeconomic factors explain avian diversity in a tropical megacity

Abstract

Factors driving urban biodiversity remain poorly documented in the rapidly growing tropical cities. We investigated the drivers of bird diversity in Dhaka city, located in Bangladesh, South Asia. Using existing sources, we compiled a bird checklist of the city. Next, we conducted point-count surveys of birds across its urban areas. Using field survey data, we investigated urban land cover and socioeconomic effects on resident bird species richness and abundance by applying linear regression modeling. Additionally, we performed path analyses for an in-depth understanding of direct and indirect relationships between selected urban land covers and socioeconomic variables and bird diversity. Our linear regression model assessment indicated that land cover is significantly shaping resident bird richness, whereas bird abundance is influenced by the combined effect of land cover and socioeconomic factors. Specifically, an increasing proportion of imperviousness was causing low bird richness, whereas bird abundance increased in areas with high habitat heterogeneity and proximity to parks but decreased with rising poverty (one of the major socioeconomic issues in Dhaka). Causal path analysis revealed that socioeconomic status, directly as well as indirectly mediated by urban land cover factors, affects bird diversity. Most importantly, it confirmed the greater significance of the direct negative effect of imperviousness on bird richness and of poverty on bird abundance in urban areas. This, in turn, suggests that bird diversity is favored by heterogeneous habitats and in wealthier neighborhoods. Nevertheless, overall bird diversity in Dhaka city was largely made up of generalist species of low conservation concern; species of the omnivore feeding guild and with ubiquitous habitat preferences were the most abundant. Our results represent the first step toward understanding drivers of biodiversity patterns across urban areas of tropical megacities within South Asia and contribute to a solid basis for urban biodiversity planning in the region.

Keywords

• bird
• conservation
• imperviousness
• poverty
• south asia
• urbanization