Habitat Preference of Lesser Whistling Ducks (Dendrocygna javanica) in Selected Wetlands within Colombo Ramsar Wetland City

Abstract

Lesser Whistling Ducks (LWD) (Dendrocygna javanica) mostly occur in flocks and inhabit lakes, ponds and marshes within freshwater wetlands. They feed mainly on plants taken from water (seed, shoots, tuber and leaves), vertebrates (fishes) and invertebrates (mollusks and worms). In this study, habitat preference of LWD in five selected wetlands in Colombo Ramsar Wetland City (CRWC); Beddagana Wetland Park (BWP), Diyasaru Park (DP), Heen Ela Marsh (HEM), Thalangama Marsh (TM) and Kimbulawala Wetland (KW) was studied from May 2021 to April 2022 as wetlands in urban areas act as the last resort for many resident and migratory bird species and play a major role in the assemblage and conservation of water birds. Habitats present in the selected wetlands were categorized as open water body, floating vegetation, trees, grassland, paddy field, shrubs, bare land. Percentage cover of each habitat type at each sampling site were estimated using quadrat method. LWD were surveyed using line transects of 100m in length, laid in each selected study site to cover representative habitats and observations were made up to 30m towards either side of each transect. Sampling was done in three time slots of the day, morning, mid-day and evening. Floating vegetation, open water body and grassland were the preferred habitat types of D. javanica in BWP, DP, HEM and TM. LWD were not recorded in KW. Floating vegetation (54.97%) was the most preferred habitat by LWD in each study site followed by open water body (24.70%) and grassland (15.82%) habitat types. Eicchornia crassipes (Common water hyacinth) and Salvinia molesta (Giant salvinia) were their most preferred floating vegetation type. Higher abundance of LWD was recorded in TM (83.22%) followed by DP (9.17%), BWP (4.16%) and HEM (3.45%). TM which had higher abundance of LWD had higher floating vegetation coverage (28%) and was rich with E. crassipes and S. molesta. Present study revealed that, LWD mostly used E. crassipes and S. molesta as their main foraging and resting sites. Management of invasive alien species have been undertaken in Colombo wetlands and as E. crassipes and S. molesta are alien species they are currently being removed. Therefore, outright removal of E. crassipes and S. molesta may not be suitable and a monitored removal program that will conserve this habitat type should be implemented in order to conserve the habitats preferred by LWD in CRWC. 

Keywords: Lesser whistling ducks, Wetlands, Habitat preference