Supranational species indices are combined in multispecies indicators. These are produced for groups of species according to their main habitat types. To produce precise indicators with small standard errors, it is important to include as many bird species as possible. The rationale behind the construction of composite indicators is that each species is seen as a replicate that may respond in the same way to environmental drivers as the other species and repeats 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 this species was already used in previous versions of the indicators, whether better data can be expected in the near future 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 trend of the indicator. For more details on the tool and statistical procedure please check Soldaat et al. (2017).
For some species the available time series started later than first year. In such cases, the multispecies index has been calculated using the chaining method (e.g. Marchant et al., 1990; Ter Braak et al., 1994) that 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 with species trends and indices, the interannual consistency of the indicators is examined: new versions are compared with previous ones. In case any inconsistency is found, we investigate whether this is caused by improvements in the data (e.g. improved national data sets, longer time series, new countries contributing their data) or by a computation error.
Indicators are produced for common farmland birds, common forest birds and all common birds. We developed the PECBMS European species classification to classify the bird species.
The indicators are produced for Europe, EU, but also for four European regions (Central & East Europe, North Europe, South Europe, West Europe) and for two EU regions (Old and New EU).
The regional indicators are produced in two versions: one according to the PECBMS European species classification and one according to the regional classification system, which may differ a little.
For list and graphs of the indicators produced, see the latest update of European indicators.