Supranational species indices are combined in multispecies indicators (PECBMS Wild Bird Indices). These are produced for groups of species according to their main habitat types. To produce precise indicators with small standard errors, including as many bird species as possible, is important. The rationale behind composite indicators is that we consider each species as a replicate that may respond in the same way to environmental drivers as the other species and repeat the same signal.
After the supranational species indices have been produced; species are checked for their suitability to be included in the indicators. If a species trend (i.e. multiplicative trend) is classified as ‘uncertain’ AND if the index value is > 200% or < 5%, data are considered doubtful, and the species index and data quality are examined in detail. The decision to exclude such a species from an indicator depends on whether the species was already used in previous versions of the indicators, whether we expect better data shortly and whether index fluctuation is believed to be caused either by poor data or by other reasons linked to methodology.
To produce multispecies indicators, we used an indicator tool (MSI tool) developed in Statistics Netherlands. The tool produces the same outputs as in the previous updates of the indicators and also the smoothed values with confidence intervals and the trend of the indicator. For more details on the tool and statistical procedure, please check Soldaat et al. (2017) and further reading.
The available time series started later than the first year for some species. In such cases, we calculate the multispecies index using the chaining method (e.g. Marchant et al., 1990; Ter Braak et al., 1994). This method is incorporated in the indicator tool, assuming that the average change in all other species of the indicator reflects the changes of the focal species during the period that is missing.
As in the case of the species trends and indices, we examine the indicators’ interannual consistency: we compare new versions with previous ones. In case any inconsistency is found, we investigate whether improvements in the data cause this (e.g. improved national data sets, longer time series, new countries contributing their data) or by a computation error.
We produce the indicators for farmland, forest, and all birds. For this reason, we developed the PECBMS European species classification to classify the bird species.
We produce the indicators for Europe, the EU, four European regions (Central & East Europe, North Europe, South Europe, West Europe) and two EU regions (Old and New EU).
Due to Brexit in February 2020, we calculate all EU bird indicators by excluding data from the United Kingdom. We removed the UK data from the whole time series to create the indicators without the country that is no longer considered a part of the EU. EU indicator calculation without the UK was done for the first time in 2022 update (the 2021 update was based on data until 2019 when the UK was still an EU Member State). Starting 2024 update, we only present all EU indicators calculated without the United Kingdom data.
All indicators are produced using the PECBMS European single species habitat classification (Box Species selection and classification).
See the latest update of European indicators for lists and graphs of the indicators produced.