Analyses of trends in wintering waterbird numbers were carried out using IWC data from 847 of the 1,078 sites as only those sites which had been counted in at least two winters over the 1966– 2008 period were included. A log-linear Poisson regression analysis was used to estimate the missing data using the TRIM software (Statistic Netherlands version 3.52, PANNEKOEK & Van STRIEN 2005).