Hydrological Conditions Drive Colonial Waterbird Breeding Dynamics in Monsoon‐Dependent Wetlands of Southern India

ABSTRACT

Wetland ecosystems are highly sensitive to environmental variability, but the relative importance of hydrological and climatic drivers of colonial waterbird breeding is poorly understood in landscapes that depend on the tropical monsoon. We investigated the influence of wetland inundation and climatic conditions on the occurrence of nesting, colony abundance and species richness of colonial nesting waterbirds across nine wetlands in Tamil Nadu, India, over three breeding seasons (2022–2023 to 2024–2025). Breeding responses were quantified through systematic field surveys and related to wetland water extent derived from Sentinel‐2 imagery and climatic variables obtained from the ERA5 reanalysis dataset. We measured the effects of water extent, temperature, precipitation and wind speed with generalised linear mixed models. A total of 16 colonial nesting waterbird species were recorded. Environmental conditions during the 30‐day period preceding surveys consistently provided the strongest explanation of breeding responses. Water extent emerged as the dominant predictor of nesting occurrence, colony abundance and species richness. The nesting probability increased significantly with water extent ( β  = 1.732, p  < 0.001), whereas colony abundance ( β  = 0.612, p  < 0.001) and species richness ( β  = 0.275, p  < 0.001) increased with greater inundation. Maximum temperature negatively affected colony abundance and species richness, whereas precipitation had weaker negative effects and wind speed had no significant effect. Our findings indicate that the main driver of colonial waterbird breeding dynamics in monsoon‐dependent wetlands is wetland inundation, while climatic factors exert secondary effects on colony performance and diversity. Securing suitable hydrological conditions will be essential to the conservation of colonial waterbird populations in the face of increasing climatic variability.