waders and their estuarine food supplies - Vlaams Instituut voor de ...

That science is making progress, may clearly be illustrated
with the growth of our knowledge about
watlers. or shmebirds. and their food supply, the
macrozoobenthos living in the intertidal mud and
sandflats. Forty years ago, the exciting phenomenon of
the massive wader flocks passing through the Wadden
Sea was appreciated but not quantified, nor were the
migratory pathways known in detail. Now we know
where the waders breed, where they winter and how
many millions stage in the Wadden Sea. thanks to the
many people who have been catching and counting
birds the last decades. Also die year-to-year variation
in their food supply is known, as well as the factors
causing these fluctuations, thanks to the NIOZ. in particular
the perseverance ol Jan Beukema who started in
1964 a biannual sampling programme of the macrozoobenthos
in the western part of the Wadden Sea. The
annual number of scientific papers reflects this explosion
of our knowledge in this field of research, as visualised
with the frequency distribution of cited papers in
the list of references.
Do we not know enough about the Wadden Sea?
For scientists, this is an illogical question, because
-._ sea
INTRODUCTION
iiiii
1930-39 1940-49 1950-59 1960-69 1970-79 1980-89 1990-96
Frequency distribution of cited papers in lis* of references.
11
there is no limit to the sky The mosl profitable research
strategy must be a comparison between the
well-studied Wadden Sea and less-studied estuarine
systems elsewhere and. indeed, expeditions to West
Africa and elsewhere during the last 15 years, in which
many workers from the Wadden Sea took part, resulted
m the mosl interesting papers. Clearly, these papers
would not have been written without the knowledge
built up during many years of research in the Wadden
Sea. Yet it remains of importance to continue research
in the Wadden Sea, and not only to monitor the annual
fluctuations in animal life, because several fundamental
questions have still not been answered. The question
whether the population of birds using the intertidal
Hals is limited by their food supply, has been a leading
question in most of the bird research in the Wadden
Sea. The tendency of *waderologists' in the Wadden
Sea. but also elsewhere, to focus on the problem of the
carrying capacity is not surprising, because the bird
species depending on the tidal zone, have recently lost
a substantial part of their feeding area in Europe and
Asia. Does the loss of refuelling stations during migration
and the decreasing surface area of their overwintering
grounds negatively affect the size of the bird
populations'.' The question is simple, but appears to be
extremely difficult to answer. Therefore, the best strategy
is to break down the main question into many
small, more or less answerable, questions. Most of the
papers collected in this thesis deal with these derived
questions. To what extent the solution of the isolated
questions contributes to the overall problem will help
to define the research needs of the coming years.
Our research has focused in detail on the relationships
between three waders. Oystercatcher. Curlew and
Knot, and their food supply. On the tidal flats along the
Frisian coast, we built hides on towers from which the
feeding birds could be observed at short distance.