Long-term changes in population and diversity of the wintering waterbirds in the wetlands and southern coast of the Caspian Sea

In this study, trends in population and species diversity of wintering waterbirds in the south Caspian Sea region, based on mid-winter censuses of waterbirds over a thirty-year period from 1988 to 2017, have been studied. The trends in population and the ecological indicators of biodiversity were respectively calculated using the RTRIM statistical package (TRends and Indices for Monitoring Data in R software) and the software SDR-IV (Species Diversity and Richness). Results showed that the average number of waterbirds in the whole Caspian region for the last thirty years was 947,853±71,073 with a range of 326.281-1.934,226 individuals. The share of Mazandaran province alone was more than the other two provinces during the study period. The total number of waterbirds recorded increased in 2004 and then formed a stable trend. Calculation of the statistical trend of changes over the 30 years in the waterbirds population size of the south Caspian region indicated a slight increase with a slope of 3.3% per year, but over the last ten years, the population has gradually declined, showing a 2.7% decrease over this latter period. The results for species diversity indices (Shannon-Wiener and Simpson D), species richness (Margalf and Minhinick), and species evenness (Pielou and Simpson E) confirmed that high values ​​of species diversity and richness and low values ​​of species evenness indices during the period of 2004-2009 were basically due to the increase in the number of species recorded and conducting more accurate censuses backed by a comprehensive census program and the participation of foreign birdwatchers. The results of this study can play a practical role in informing the ecological management of the wetlands and southern coast of the Caspian Sea.