To attain international importance and thus protection as a Ramsar site or as a Special Protection Area (SPA), a wetland site must either regularly support at least 20,000 waterbirds or seabirds, or 1 percent of the individuals of a population of a species or subspecies of waterbird.

Essential to the management of any wild bird population is an understanding of the relationship of the organism with its environment and particularly the processes that affect the demographics of the species.

The Alerts System provides a standardised technique with which to monitor changes in the population sizes of wintering waterbirds in the UK over a range of spatial scales and time periods, using data collected as part of the Wetland Bird Survey (WeBS).