Conservation monitoring of a polluted urban river: an occupancy modeling study of birds in the Yamuna of Delhi

Abstract

Given that ecological knowledge of large urban river systems is extremely sparse due to logistics and accessibility an occupancy modeling study was conducted on the resident birds of Delhi. River Yamuna passing through Delhi is a refuge for several resident and migratory species of birds but its water quality has been deteriorating due to ever growing population, contributing most of its pollution load in the urban center. The objectives of this study were 1) to determine whether the occupancy of common waterbirds varied between differential polluted sections of the river, 2) to better understand the associations between habitat variables and use of the river habitat by common waterbirds and 3) to identify whether any species or groups of species could be useful as indicators for habitat quality. The occupancy parameter Ψ was estimated for 17 common resident species among 68 species, recorded from 176 sampling locations during 2018, on the banks of river. Species occupancy was estimated as a function of habitat variables such as physico-chemical characteristic of water, solid waste, percent area of surface and emergent vegetation and human disturbance at each sampling site. The results suggest that Little Grebe (Tachybaptus ruficollis), Grey Heron (Ardea cinerea), Grey-headed Swamphen (Porphyrio poliocephalus), Eurasian Coot (Fulica atra), Common Moorhen (Gallinuala chloropus), Purple Heron (Ardea purpurea) and Little Cormorant (Microcarbo niger) are negatively associated with the Total Dissolved Solute (TDS). Interestingly, occupancy of Black-winged Stilt (Himantopus himantopus) is negatively associated with pH but positively with solid waste strongly suggesting its preference for the polluted sections of the river, possibly due to the increased availability of food. For river Yamuna, estimates of Ψ for various birds forms a baseline to study future trends. This study also indicates that species like Black-winged Stilt, can serve as an indicator of contaminated water bodies. The challenges posed by increasing urbanization and pollution to riparian bird habitats in urban areas can be effectively dealt with by incorporating such ecological knowledge with habitat restoration and conservation efforts.