Hydro-ecological relations in the Delta Waters

measure affecting food supply or available feeding area will reduce the
population of tkse species (e.g. waders in the Oosterschelde). Far
other species the relircion between density and food supply is lese
oboioys and other variables confeuding this relation are discussed.
The influence of reduced food supply or available habitat m these
species is less easy to pre&tct, although the birds will certainly not
benefit from these. Beyond doubt, disturbance has a negative effect
on all species. I£ the international importance of the Delta area for
waterbirds is to be preseraed, this aspect should receive much
attention from the manager. It is very important! to inform the public
about the imeortance of the area fOr birds and their need for rest.
Canalizing people by means of hides or observation places might be one
part of the salntion. It reduces disturbance and the good observation
possibilities may enhance a positive attitude towards the habitat and
its inhabitants. Additionally the accessibility of certain sites should
be sestricted. Man's impact on the habitat, hg means of dredging.
pollution, etc., should be minimized so that naturally functioning
ecesrystem might be' created or preserved.
These few examples imply that management of the Delta area should he
based on a sound ecological knowledge, but in order to understand the
ecology Of a species much detailed research bas to be done and a
general pattmn, as presented in tbls paper, is amly a first step.
The data presented in this paper have been collected by a large umber
of people. Their help was invaluable. E. Wijken and S. BublE provided
a stimulating enviromeat in Gent, and Rijkswaterstaat. Tidal Waters
Division and Directorate Zeeland not only provided the funds necessary
for the research, but were also very interested fm the results and
wed to use chem in the management of wetlands.