Guanotrophy: Waterbirds Pay for Using Resources at Their Wintering Habitats

Abstract

Nutrients present in the guano of the aquatic birds might alter the water quality and nutrient loading in the wetland ecosystem. We recorded the changes in waterbird abundance for two consecutive wintering seasons, October–March (2018–2019 and 2019–2020), in four wetlands of Bankura and Purulia district, West Bengal, India, on Central Asian and East Asian-Australasian Flyways. The monthly variation in the water parameters, along with total guano and nutrient loadings by waterbirds, were evaluated during the study. Waterbird species varied from 37 to 61 in these wetlands. Guano loading in the study tenure ranged from 50.2 to 2979.1 kg month−1, depending on the wetland resources and the abundance of waterbird species. In most cases, total guano loading showed significant positive correlations with total N and P loading and, consequently, NO3 and PO4 concentrations in water. In all four wetlands, guano and nutrients added by herbivorous waterbirds were significantly higher than carnivorous and omnivorous waterbirds due to the much higher abundance of herbivorous waterbirds. Linear regression analyses showed that the abundance of the wintering waterbird community significantly impacted the nitrate and phosphate availability in most of the sites. Sustainable management of these wetlands depends on the delicate balance of guanotrophic nutrient enrichment and habitat fitness to attract migratory waterbirds.