Waders were counted monthly for six years at the three high tide roosts which are normally used by more than 50% of the waders in the Firth of Thames. The annual cycle of wader numbers is shown for all waders and selected species. The data are used to "correct" wader count data and demonstrate that such "correction" changes apparent population trends. Timing of future bi-annual wader censuses can be improved to maximise counts and/or to minimise variability.