Factors Influencing Occurrence and Species Richness of Heronries in the Wetlands of Tamil Nadu, India

Wetland dependent tree nesting colonial waterbirds select wetlands that enhance breeding opportunities to increase their reproductive fitness. From conservation standpoint, identifying these wetlands that support heronries is essential. The state of Tamil Nadu in southern India has high number of wetlands, both natural and human-made encompassing diverse and heterogenous habitats.. Factors determining the occurrence of heronries among the wetlands in Tamil Nadu were assessed. Furthermore, variation in species richness of colonial nesting waterbirds among the identified heronries was evaluated. Binomial regression framework was used to quantify spatial occurrence of heronries among wetlands and Poisson regression to evaluate variation in species richness of colonial nesting waterbirds among heronries. A total of 106 wetlands were surveyed, of which 50 harboured heronries. Nineteen species of colonial nesting waterbirds were recorded belonging to six families. Among the wetlands, distance from human settlement, extent of disturbance level, desilting of the wetland, and the extent of tree cover explained the spatial occurrence of heronries. The probability of heronry occurrence was higher in the wetlands farther from human settlement, with lower human disturbance, with high extent of tree cover and desilted. Tree-nesting colonial waterbirds species richness was higher in wetlands with larger nesting area, higher heterogeneity of tree species, and at relatively lower elevation sites.