Trend of breeding birds: indices

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 displayed from 1990 onwards or from the year after 1990 on which reliable counts of the species in question are available. The year 1990 is in most cases the base year with index = 100. Another base year occurs in species that are only counted from a later year and/or species that have increased very strongly in number. 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 in indexes per year. However, year-on-year indices have a broad margin of confidence, so it is not possible to conclude simply whether the population of a species has increased or decreased significantly. Whether there is an increase or decrease 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 assessed as uncertain. Due to limitations in StatLine, these trend assessments cannot be displayed in the same table as the indices. They are therefore 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 subsequent delivery of counting data in combination with the method of analysis used allow the figures to vary slightly when recalculated, in particular the figures of the last 3 years. Due to the outbreak of foot-and-mouth disease in 2001, insufficient breeding bird data were collected in that year to be able to calculate reliable indices. For the year 2001, the averages for 2000 and 2002 are therefore shown. Amendments as of 4 November 2022 Index values of 2021 have been added. Index values of a large part of the species have changed to a greater extent than usual in an update to this table. This is due to the availability of improved population data of 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. Amendments as of 10 November 2021: Index values 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 2023.