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Introduction
As part of the JMBB program, 34 breeding birds species are monitored in
the Wadden Sea, of which 26 are presented here with overall and national
trends (the other species are too rare to allow trend calculations). Trends
are shown for (1) the Wadden Sea as a whole, (2) The Netherlands (3) the
federal states of Niedersachsen/Hamburg (Germany), (4) the federal state of
Schleswig-Holstein (Germany) and (5) Denmark, see the page ‘Counting sites’
for an overview of counting sites.
Data and methods
For each year, data on rare and colonial birds are summarized for 56 census
regions in the international Wadden Sea. Trend calculations are based on the
totals of these census regions within each country or the Wadden Sea as a
whole. For common species, numbers are summarised for 103 representative
sample sites. Again, trends are calculated at country-level or for the whole
international Wadden Sea. On few occasions where a sample plot was not
counted in a certain year, data are imputed by the commonly used TRIM
package (Trends and Indices in Monitoring data; Pannekoek & van Strien,
1999). Furthermore, TRIM was used to calculate trends. Trends are tested
with a Wald-test for significance at P = 0.05, and presented as an index,
where 1996 is set at 100. Thus, all indices show population changes relative
to 1996. For presentation of the monitoring data, a standardized trend
classification is used (similar to that in migratory birds):
|
Trend
classification |
Trend
description |
Population
change |
|
++ |
strong increase |
sign. increase
of >5% per year |
|
+ |
moderate
increase |
sign. increase
of <5% per year |
|
0 |
stable |
no significant
population change |
|
- |
moderate
decrease |
sign. decrease
of <5% per year |
|
-- |
strong decrease |
sign. decrease
of >5% per year |
|
? |
uncertain |
no reliable
trend classification possible (mostly due to strong
fluctuations) |
Trends are either presented for the whole period that
counts have been carried out (i.e. since 1991) or for the last ten years.
This allows a comparison of long term and short term trends.
Acknowledgements
Fieldwork for breeding birds is carried out by a large number of
people, including staff from NGOs and conservation agencies, local
governmental bodies, volunteer bird watchers and professional bird
counters. Current organisation and co-ordination for Denmark is done
by the National Environmental Research Institute/University of Arhus
(Kalø/Arhus), for Schleswig-Holstein by the National Park Agency
‘Schleswig-Holsteinisches Wattenmeer’ (Tönning), for Niedersachsen
and Hamburg by the National Park Administration ‘Niedersächsisches
Wattenmeer’ (Wilhelmshaven) and in The Netherlands by SOVON Dutch
Centre for Field Ornithology (Nijmegen), commissioned by the
Ministry of Agriculture, Nature and Food Quality.
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