Trend of breeding birds: trend assessment
Description
This table provides an overview of the trends of all native bird species breeding regularly in the Netherlands for which a reliable national trend can be calculated. This table also contains the (geographical) average trend of all species listed in this table. Trends are shown over a period from 1990 or from the year after 1990 on which reliable counts of the species in question are available. Trends have also been shown over the last 12 years.
The national trend of breeding birds is based on different types of sample counts whose data are combined. The basis of the census is territorial mapping at measuring points of approximately 50-200 ha, where breeding pair territories are determined by repeated visits of the measuring points during the breeding season. However, there are also additional methods for species for which this method is less or not suitable, e.g. point counts for urban birds.
The trends are shown in this table according to the trend classification. This is determined over a series of years using the annual indices of the species. Year-on-year indices have a wide margin of confidence, which makes it impossible to directly conclude whether a species has increased or decreased significantly. Whether the population of a species has increased or decreased is therefore calculated separately over the whole series of years and the most recent period of 12 years. The increase or decrease is then classified as strong if the average annual change is greater than 5 % or moderate if the change may also be less than 5 %. If no increase or decrease can be demonstrated but the average annual change is less or equal to 5 %, it shall be assessed as stable. If no increase or decrease can be demonstrated and the trend cannot be considered stable, it is classified as uncertain. Indices per year are shown in a separate table (see paragraph 3. Links to relevant tables and articles).
Status of the figures:
New counting data is available each year, which is processed in the (re)calculation of trends. These added annual figures and any follow-up of counting data from previous years may change trend classifications in the event of updates. This may be the case in particular for the trend classification over the last 12 years, as the period for which the calculation takes place shifts.
Amendments as of 4 November 2022
Trend classifications of 2021 have been added.
The trend calculations used improved population data on breeding birds in the 2018 bird atlas (see paragraph 3). These have led to redeployment of sub-areas of the Netherlands and changes in the weighting of the counting results in those areas. This weighting is used to correct differences in sample density in the sub-areas. Although index values of a large part of the species have changed to a greater extent than usual in an update, this has little impact on the trend classifications in this table.
Amendments as of 10 November 2021:
Trend classifications of the year 2019 and 2020 have been added.
Seven additional species (European Canary, Grass Singer, Houtsnip, Kleinst Waterhoen, Cranevogel, Oehoe and Witwangstern) have been included, because their counts now yield reliable trends.
When will there be new figures?
The table is updated annually. The next update will be released in October 2022.
Resources
| Name |
Format |
Description |
Link |
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0 |
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https://opendata.cbs.nl/statline/#/CBS/nl/dataset/84563NED/table |
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23 |
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https://opendata.cbs.nl/statline/#/CBS/nl/dataset/84563NED/table |