Spatial assemblage of shorebirds (Aves: Charadriiformes) in an altered wetland of the southern coast of Sri Lanka

Abstract

The coastal wetlands along the southern coast of Sri Lanka are home to a diverse array of shorebirds thriving in their natural habitats, classified under the order Charadriiformes. This study examines the impact of land cover changes within the Kalametiya Sanctuary, situated on the southern coast, on the diversity, distribution, and habitat utilization of migrant and breeding resident shorebirds. Three distinct habitat types were selected within the study area: grassland, lagoon, and mixed mangroves. Employing Geographic Information System (GIS) data the land cover changes of these habitats from 2002 to 2023 were analyzed using satellite imagery. Results indicated a substantial decrease in lagoon habitat area by 70% and grassland habitat by 30%, while mixed mangrove habitat saw an increase of >90%. These changes were attributed to anthropogenic interventions and natural events such as the 2004 Tsunami. To determine the shorebird assemblages within the study area thriving in these changing habitats, surveys were conducted from May 2022 to April 2023 at 30 fixed point-count stations along transects in the selected habitat types. A total of 25 shorebird species belonging to six families were recorded. Notable among these were the globally ‘Near Threatened’ species such as the Black-tailed Godwit Limosa limosa and the Great Thick-knee Esacus recurvirostris, alongside nationally threatened species including Kentish Plover Charadrius alexandrinus, Gull-billed Tern Gelochelidon nilotica, and Common Tern Sterna hirundo species. The mixed-mangrove habitat exhibited the highest shorebird abundance, with 19 species recorded, surpassing the 13 and 11 species recorded in the grassland and lagoon habitats, respectively. Additionally, both grassland and mixed-mangrove habitats demonstrated similar diversity indices and shared more species in common (Shannon’s diversity index [H] = 2.17; Jaccard Similarity Index = 0.45) compared to the lagoon habitat (H = 2.09). Despite the notable decline in lagoon habitat cover, during the present study, it was observed that the overall shorebird populations have been sustained within grassland and mixed-mangrove habitats utilized for their feeding and nesting. Additionally, over-summering migratory shorebirds were observed utilizing these habitats. Hence, the Kalametiya sanctuary serves as a unique setting to study the ecological resilience of migratory and breeding resident shorebirds amidst human interventions. This research provides valuable insights for biodiversity conservation and habitat management in the face of human-induced alterations within ecosystems located especially along migratory pathways of shorebird species. Both grassland and mixed-mangrove habitats exhibited similar diversity indices and shared more species (Shannon’s diversity index [H] = 2.17; Jaccard Similarity Index = 0.45) compared to the lagoon habitat (H = 2.09). Despite the significant decline in lagoon habitat cover, this study observed that overall shorebird populations have been sustained within the grassland and mixed-mangrove habitats, which they use for feeding and nesting. Additionally, over-summering migratory shorebirds were observed utilizing these habitats. Thus, the Kalametiya sanctuary serves as a unique setting for studying the ecological resilience of migratory and breeding resident shorebirds amidst human interventions. This research offers valuable insights for biodiversity conservation and habitat management, particularly in ecosystems along migratory pathways of shorebird species, in the face of human-induced alterations.