Ecological factors play a major part in species abundance in an ecosystem, particularly abiotic factors as well as the biotic factors determine the abundance and diversity species of a habitat. Wetlands are among the most diverse and productive ecosystems in the world, that provide a home to a unique collection of birds found nowhere else. A damaging heavy rainfall, accompanied with strong gusty winds, struck Thalawathugoda, Sri Jayawardenepura Kotte of Sri Lanka on 9th December 2017, affecting the area severely with floods and other damages. Storm disturbances such as this provide a unique and rare chance to study how the impact affected wildlife species. I investigated the short-term effects heavy rain and strong winds on the abundance of wetland bird species of Diyasaru wetland park, due to the gap of knowledge found in short-term effects of storm disturbances on bird abundance and diversity of wetlands. With survey data of collected on five consecutive days before and after the heavy rainfall and strong winds, the total bird abundance was calculated, and the results presented that after abundance was lower than abundance before the storm. However, considering the species for each species showed a mixed abundance response, suggesting disturbance in abiotic and biotic factors of the wetland affected each species differently. Overall, a change in the abundance of birds after the storm was found.
Ecological factors account for species abundance in an ecosystem, particularly the abiotic factors rainfall, temperature, habitat area, latitude, and altitude; which can cause a change in abundance of species in an ecosystem. The biotic factors, for example, vegetation types also play a part in determining the abundance and diversity of species of an ecosystem (Stroud et al., 2015). Many studies have shown a high ratio relationship between ecological factors and species abundance (Brown,1984; Knutson & Klass,1997; Tejeda?Cruz & Sutherland,2005).
Sri Lanka is a country in the tropical zone of the globe where wildlife is affected by monsoonal storms and many other storms. It is also a country with many different ecosystems, such as lowland rainforests, Montane forests (example: Tropical and Subtropical moist broadleaf forest); Dry-zone dry evergreen forests (example: evergreen forests and thorny scrubs spread in flat lands); Deccan thorn scrub forests (example: tropical thorn shrubs and dry deciduous trees); Rivers and streams (freshwater ecosystems); West and South Indian shelf (example: Marine ecosystem) and Wet zone (example : wetlands, estuaries, and many other freshwater ecosystems) (World Atlas,2018). Among all these magnificent ecosystems wetlands hold special place due to its unique biodiversity.
A wetland is an interface between land and water (Association of State Wetland Managers, 2015), they are important as they amidst of most prolific ecosystem in the world, equivalent to rainforests and coral reefs (Environmental Protection Agency, 2013). Among the ecological services are wetlands act as sinks for stormwater drainage (Mitsch & Gosselink, 2000) and provide a home to a monumental variety of species that visit wetlands. Atmospheric conditions, study of land, its features and migration and abundance of water help to resolve the flora and fauna that inhabit each swamp ecosystem and therefore, wetlands depend heavily on precipitation to maintain biotic and abiotic factors such as mud/soil, rocks, peat, sunlight, plant litter and hydrology, temperature respectively. Wetlands also responsible for an inherent aspect for the watershed.
By maintaining shallow water, tremendous levels of nutrients and primary productivity wetlands provide an optimal environment for the development of primary consumers. Many fish, amphibians, mammals and birds, especially in their breeding seasons, depend on wetlands for their shelter, nutrition and water (Environmental Protection Agency, 2013). Therefore, the extreme rainfall and strong winds cause a shift in biological communities in wetlands (Pandit & Qadri, 1990).
River ecologists define disturbance as drought or floods with realistic comparisons among repetitions, locations, and watercourses (Poff and Ward, 1989; Resh et al, 1988). In flooding wetlands, large volumes of precipitous moving water with shear forces which suspended sediments, and redistributed the bottom materials, removed vegetation (e.g., microscopic algae to macrophytes), snagged and debris streambeds and maimed, killed and displaced all forms of biota (Lakes,2000). Floods decrease the level of food supply and primary productivity of the ecosystem by causing sediment deposition and habitat destruction (Pandit & Qadri, 1990). In turn, this affects the rest of the food web via the fish and amphibians that consume the aquatic plants and occupy the habitat. These changes cause a loss of populations of aquatic birds (Association of State Wetland Managers,2015). Floods could be predictable or unpredictable (Poff, 1992) and could vary from high water events, which entrained fine sediments and moved patches of streambeds to infrequent disastrous events. (Costa and O’Connor, 1995).
The strong gusty wind that accompanied the heavy rainfall further destroyed the tall vegetation by uprooting them, damaging the public goods such as information boards, bridges, boardwalks, pathways, birdwatch hideouts, and bird watch tower. There are many factors that influenced the storm damage to structures: Storm surge, Wind direction, waves, velocity, and building quality. Moreover, the effects of waves, storm surge, and wind usually interact in a nonlinear way that might vary with the vegetation and local topography (Howes et al., 2010; Wamsley et al.,2010) and affect many species abundance and distribution of the ecosystem affected.
Therefore, I chose to investigate on this topic due to the gap of scientific knowledge found on short-term effects of storm disturbances on bird abundance and diversity of wetlands which could aid in the long-term development of wetland ecosystem and conservation of wetland birds. In this scientific study, I propose a hypothesis that there is a difference in the abundance of birds before and after the storm. The aim of this report is to analyse the effects of the heavy rainfall and strong winds on the wetland bird abundance of Diyasaru wetland park in Sri Jayawardenepura Kotte, Sri Lanka (Figure 1) and discuss the management resource strategies for the Wetland Park and mitigation of resource damage due to the store and finally, take the outcome of this research to aid in management and possible future recommendations to further improving the Wetland Park. Hence, my reason for selecting this wetland park as my study site, because it is known as a diversified wetland by bird enthusiast of Sri Lanka (Lockwood, 2018) and since it is not officially opened this research project will be novel and provide useful information for the wetland park management and development.