The aim of WeBS Alerts is to raise awareness of decreases in numbers that give particular concern to conservationists.
For Special Protection Areas, the suite of species considered has been derived from Stroud et al. (2001). However, as the data suitable for the Alerts process may be restricted to the winter months species that are cited as qualifying in a SPA due to important passage numbers may not feature in the Alerts. Often, in particular for larger sites, it may be possible to assess the trends of additional species for which the site is not considered important. However, these species / site combinations are not considered as part of the standard WeBS Alerts process.
In the case of SSSIs, sites have often been designated for their "general waterbird interest" without specific information regarding the species composition being readily available. Consequently, species for SSSI assessment were selected on the basis that they were either listed specifically within the valid citation or are likely to be a component of an undefined assemblage, such as 'wintering waterfowl' listed in the citation. Their listing by WeBS-Alerts does not necessarily mean that they are legaly notified interests. The species included may be revised in future in response to consultation.
This Alerts report provides interpretation of the trends in over-wintering numbers of over 40 common and widespread waterbird species that occur in constituent countries of the United Kingdom.
The report is based on data to 2010/11, and therefore reports Alerts status as of 2009/10 for wetland sites of national importance for non-breeding waterbirds. These sites form part of the SPA (Special Protection Area) and SSSI (Site of Special Scientific Interest) networks. Results for the aggregated SPA suite, Great Britain and the constituent countries of the UK are also included in this report.
The WeBS Alerts System fits smoothed trends to annual WeBS indices. Proportional changes in the smoothed index value over short- (5-year), medium- (10-year) and long- (25-year) term are calculated, and for all SPAs the time-frame relating to the period since designation. Declines of between 25% and 50% trigger Medium Alerts and declines of greater than 50% trigger High Alerts. Although they generally do not promote discussion within the context of this report, increases of 33% and 100% (values necessary to return numbers to their former size following declines of 25% and 50% respectively) are also identified.
Each account lists the species for which the given site is important and gives details of High- and Medium-Alerts that have been triggered. Figures and tables are provided that allow site trends to be compared with regional and national trends.