I-WeBS Count Unit Definition Inventory (CUDI) 

In most instances, the accurate definition of the count units used is of fundamental importance for the interpretation of the waterfowl count data. The precise location and extent of count units are the two most important attributes which are necessary for the appropriate use of data collected through I-WeBS. This inventory is essential if the maximum benefit is to be gained from I-WeBS counts.
The importance of such information in the collection, interpretation and application of I-WeBS data can be illustrated in the following examples:

• When the counter for an I-WeBS site changes it is important that the new counter uses exactly the same area covered previously. This ensures, for example, that changes in the number of birds are genuine rather than an artefact of covering a different area. This is particularly important when counting a sector of a large site to ensure that double-counting does not occur and that birds are not missed.
• Monitoring within designated sites, such as SPAs, requires that information be available specific to the area contained within the site boundary. As site designations are often based in whole or in part on the numbers of waterfowl occurring within the site, it is essential that information is available on the exact area important for birds – otherwise there is the risk that designated site boundaries may not encompass all the most important areas.
• The evaluation of the relative importance of sites invariably requires count information from specific areas. Such information is increasingly used when sites come under pressure from developmental threats. It is, again, essential that the area from which individual counts are defined is known.

Count area definitions

I-WeBS defines a 'site' as a discrete, meaningful area for waterfowl, in which movements occur frequently but are distinct from adjacent sites in that movements are more occasional. For counting purposes, a large site may be divided into smaller areas termed 'subsites'. These are typically sites which can be practicably counted by one person in a reasonable time and/or sites with distinctly different habitat characteristics to that of other parts of a larger site (e.g. a brackish lake adjacent to a large estuary). The term 'count unit' is the general term used to describe sites and subsites.
 

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