Capital ponds: Site-level habitat heterogeneity and management interventions at ponds regulate high landscape-scale bird diversity across a mega-city

Abstract

Mega-cities of the global south are (in)famous for their size and human populations with little information on their ability to conserve urban biodiversity. Creating new habitats in such cities is untenable but retaining persisting small habitat patches such as ponds (wetlands ≤5 ha) is potentially practical to secure urban wildlife refugia. Studies on biodiversity of urban ponds in tropical cities are lacking because of assumptions that they are degraded. We explored characteristics of, and bird diversity at, ponds in the National Capital Territory of Delhi, India – an area predicted to become part of the world's most populous urban region – to understand the relative importance of commonly measured site-level and landscape-scale variables, including ongoing management interventions, on bird diversity. Ponds were rare (0.5% of area) and had varying levels of degradation. Management interventions created idiosyncratic conditions but ponds still supported 37% of Delhi's bird species. Site-level variables had effects magnitudes higher relative to landscape-scale variables on bird abundance and species richness. Neither total bird abundance nor species richness was influenced strongly by landscape-scale variables (built-up area, pond proximity, extent of wetlands). Instead, bird abundance increased with pond size and greater shoreline heterogeneity, and species richness increased with greater shoreline heterogeneity and presence of islands but decreased with increase in management interventions. Birds at Delhi's ponds were influenced by some drivers of biodiversity common to other locations, but local management regimes imposed novel conditions. Contrary to assumptions sparse remnant habitats in crowded mega-cities can provide disproportionately high advantages towards boosting urban biodiversity and meeting multiple conservation goals.