Fluctuations in Avian Distribution and Diversity in Anavilundawa Ramsar Sanctuary

Many of the seasonal water bodies in Sri Lanka harbour substantial numbers of aquatic birds. Local aggregation of water fowl during communal roosting and colonial breeding results in substantial inputs of nutrients into aquatic systems and can alter fresh water aquatic systems. The present study calculated the density and species richness of true aquatic bird and aquatic associated bird species in Anavilundawa Sanctuary (Ramsar Site) from July 2007 to July 2008 using the point count method. In Anavilundawa reservoir, the number of true aquatic bird species was higher (40.49 ± 1.251 birds ha-1) than the number of aquatic associated bird species (3.40 ± 0.437 birds ha-1). Amongst true aquatic birds recorded in the study area, Anastomus oscitans (Asian openbill) was the most abundant species (137.43 ± 7.246 birds ha-1). Further, Asian openbill inhabited only the Anavilundawa reservoir for nesting and breeding. Density and species richness of birds were the highest during rainy season when migratory species also arrived at the site. During the rainy season; the highest bird density was recorded in tree-covered habitats (11.72 ± 1.683 birds ha-1) followed by shallow open water habitats (2.05 ± 0.724 birds ha-1) and grass covered habitats (1.84 ± 0.579 birds ha-1). The lowest bird density was recorded in deep open water habitats (0.40 ± 0.263 birds ha-1). During the dry season when the migratory species left the area a few resident species have engaged in nesting activities. During the dry season too, the highest bird density was recorded in tree covered habitats (1.57 ± 0.497 birds ha-1) followed by grass covered habitats (0.99 ± 0.317 birds ha-1) and shallow open water habitats (0.63 ± 0.374 birds ha-1). Red-wattled Lapwing was the most abundant aquatic associated species recorded (2.05 ± 1.137 birds ha-1). The result also showed that true aquatic birds have the highest species diversity i.e., Shannon’s index (N1 = 2.233), species richness i.e., Margalf’s index (R1 = 2.015), Menhinick’s index (R2 = 0.782) and species evenness (E = 0.899) which were much higher compared to aquatic associated birds. It is concluded that Anawilundawa Sanctuary has retained its potential as an important ecosystem for avifauna despite human mediated disturbances.