The diversity-area relationship for waterbird communities in small artificial reservoirs over winter

Abstract. In the middle of the 20th century, artificial reservoirs were created in Crimea due to a lack of freshwater resources. The nearest important hotspot for waterbirds is more than 100 km from these reservoirs. The five reservoirs are differently sized, and their water levels vary in response to regional climatic conditions and ice formation during winter. In this study, we investigate the bird communities of these small reservoirs using long-term waterbird surveys. Data were collected over 18 observation sessions on the five reservoirs in the winters of 2009-2021, with observations from the Simferopolske reservoirs grouped into two clusters for 2009-2014 and 2015-2021. Waterbird species richness was moderate, ranging between three and 19 species, including two considered threatened. Mallard (Anas platyrhynchos), Caspian gull (Larus cachinnans) and common gull (Larus canus) contributed significantly to dissimilarities between observations, with numbers of common gull decreasing significantly in relation to average January temperature and precipitation. Fisher's alpha diversity and Caspian gull number showed negative relationships with water surface area. We suggest that such negative relationships between area and diversity can be observed during cold waves when species are forced to migrate in search of more favourable conditions, leading to increased diversity in small areas.