One of the main aims of the waterfowl counts in Sweden and internationally has been to follow the population development for wintering waterfowl species. As it is not possible toperform country-wide total counts annually the efforts have been concentrated to survey a numberr of representative sites to be able to calculate annual indices. As many species leave Sweden for the winter, ta September count was introduced nationally in 1973.
From the start of the counts, indices have been calculated as chain indices by pairwise comparisions of the totals counted on a number of sites in two consecutive years. Starting with the season 2013/14 this was changed and the indices are now calcujlated according to the TRIM-method.
Example of trend figure. The graphs show yearly indices for European Wigeon for September (Sept) and January (Jan), respectively. Summary statistics are shown for the entire time period covered by the trend line. For each of the periods the following is shown (from left to right): mean annual number of observed individuals; mean annual rate of change in per cent; statistical support for the trend (NS: not significant *: p<0.05, ** p<0.01, *** p<0.001).
September and Midwinter indices for the different species are found by following the links below.