Hydro-ecological relations in the Delta Waters

of birds and this: immediately stresses the internatianal importance M
the Delta. Criteria have been agreed upon intsrnatiooally to &press
the importance of a wetland area CSzijj, 1972): if more than 1% of a
population (either 20 000 waders or 10 000 ducks) r-ularly occurs, the
area is considered to be of international importance. In the Delta area
the numbers of /+l species exceed these criteria.
Figure 4 Proportion of the tetal number of waterbirda in the Delta
occurring in each of the basins. (Vmordelta (M);
Westerschelde (WS); Oasterschelde (OS) ; Krammer-Volkerak (KV) ;
Grevelingen Meer (GM) ; Veerse Meer (W); Haringvliet (HV);
Bollands Diep (BD) ; Biesboseh (BB))
The bir& are not evenly spread over the whole Delta area. In Figure 4
the relative importance of each basin is given (expressed ss the
percentage the total number of birds in each basin represent$ of the
ove~all total number in the Delta). The oatstanding importance of the
Ooster- and Westerschelde is very clear. With less than 50% af the
total vetland area they accmmodate 67% ef the birds of Khe whole Delta
area. KQV this distribution is related to rood supply will be analyzed
in the fallowing bections.