Trend of breeding birds: indices

This table gives an overview of the trends of all native bird species regularly in the Netherlands for which reliable national trends can be calculated. This table also contains the (metric) average trend of all species listed in this table. Trends have been shown 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 counted only from a later year and/or species that have increased very strongly. The first year of counting was chosen as the base year with index=100.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, with territories of breeding pairs being determined by repeated visits of the measuring points in the breeding season. However, there are also additional methods for species for which this method is less or unsuitable, e.g. point counts for urban birds. Trends are shown in this table in indices per year. However, indices per year have a broad margin of reliability, which makes it impossible to conclude whether the population of a species has increased or decreased significantly. Therefore, whether there is an increase or decrease is calculated separately over the entire 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 more than 5 % or moderate if the change can 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 presented in a separate table (see paragraph 3. Links to relevant tables and articles). Status of the figures: Every year, new counting data are made available that are processed in the (re-)calculation of trends. The added annual figures and possible subsequent delivery of counting data in combination with the analytical method used may vary slightly in the case of recalculation, thus in particular changing the figures for the last 3 years. Due to the outbreak of foot-and-mouth disease in 2001, too little breeding bird data were collected in that year to be able to calculate reliable indices. For this year, the averages of 2000 and 2002 are shown. Changes as of 10 November 2021: Index values of the year 2019 and 2020 have been added. Seven additional species (European Canary, Graszanger, Houtsnip, Kleinst Waterhoen, Cranevogel, Oehoe and Witwangstern) have been included, as the counts of these now yield reliable trends. Changes as of 26 June 2020: Index values of the year 2018 have been added. By recalculating indexes with all data from 1990 onwards, indexes in other years may differ slightly from the previous version of this table. The data of the Great Yellow Mercury Tail and the great Canadian goose have been mistakenly exchanged. Because the large Canadian goose is an exoot in the Netherlands, it should not be mentioned in the table ‘trend of Dutch breeding birds’ and has therefore been removed from the list. The large yellow mercury tail, on the other hand, is now included. When are new figures coming? The table is updated annually. The next update will be released in October 2022.