European species indices and indicators 2007: Data and computation procedure in details

Data and computation
Countries contributing with their data.

The data come from 20 countries: Ireland, UK, Netherlands, Denmark, Sweden, Finland, Estonia, Latvia, Poland, Czech Republic, Hungary, Austria, Germany, Belgium, France, Spain, Portugal, Italy. Data from Estonia are old data from the first PECBMS attempt to produce European indices and cover limited number of species and time period (until 2000). Data from Belgium come from two regional monitoring schemes in Wallonia and Brussels resp. Data from former West Germany was treated separately from the data from former East Germany. Countries within the same group (region) used for calculation regional and European indices (see also below) are in the same colour.

Country/region Region (group of countries) First year Last year
Austria WE 1998 2005
Belgium-Brussels1) WE 1992 2005
Belgium-Wallonia1) WE 1990 2005
Czech Republic CEE 1982 2005
Denmark WE 1976 2005
Estonia 2) CEE 1983 2000
Finland NE 1983 2005
France 3) SE 1989 2005
Germany East 4) CEE 1991 2005
Germany West 4) WE 1989 2005
Hungary CEE 1999 2005
Italy SE 2000 2005
Latvia CEE 1995 2005
Netherlands WE 1990 2005
Norway NE 1995 2005
Poland CEE 2000 2005
Portugal SE 2004 2005
Republic of Ireland WE 1998 2005
Spain SE 1996 2005
Sweden NE 1975 2005
Switzerland WE 1999 2005
United Kingdom WE 1966 2005

WE – West Europe
NE – North Europe
SE – South Europe
CEE – Central & East Europe
First year – first year of data time series in a country/region
Last year – last year of data time series in a country/region
Time series for individual species from national schemes could be shorter in few cases.
1) Data for Belgium were combined from Wallonia and Brussels
2) Old data covering limited number of species and time period
3) Data in France come from two schemes, old and new one, data from both schemes were combined.
4) Data for Germany were combined from schemes in former East and West Germany.

In order to estimate missing values in countries with shorter time series with TRIM (a process analogical to production of indices at national level) we made groups of countries where we expect similar changes in bird trends. Thus we avoid e.g. estimating missing values in south European country using data from the North. Then, yearly totals for missing years for countries within a group were estimated.
Weighting factor for each country and species was calculated as population size (geometric mean of population minimum and maximum provided by Birds in Europe 2 (BirdLife International 2004) divided by estimated (model) scheme year total for the same years.
Combined year totals and their standard errors for whole group were then calculated using weighting factors.

Overview of computation steps incl. groups of countries:

Data quality control
National data on species trends were checked using criteria:
1. Data should be available from countries which host at least 50 % of ‚PECBMS European‘ population of a species. ‘PECBMS Europe’ – countries included in our definition of Europe for assesment of abundant and widespread species. Includes countries which contribute actively by data provision or are supposed to provide data by 2010. These are: Austria, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Italy, Latvia, Lithuania, Netherlands, Norway, Poland, Portugal, Republic of Ireland, Romania, Slovakia, Spain, Sweden, Switzerland, United Kingdom.
However, some parts of countries (states) listed above were not used and their population not considered in the assesment. These are: Faroe Islands and Greenland, Svalbard, Azores, Madeira, Canary Islands, Gibraltar.
2. Ratio of national population size estimates (E) and scheme year total (T) and should not be < 1 or too high.
Despite several species were excluded from an analysis using these criteria, European index of some species could not be estimated because of poor data. Such species were excluded as well.
The computation was done using automation system developed by the Statistics Netherlands, but several species were selected randomly for checks of results – indices of these species were calculated by hands using exactly the same procedure and outputs of both computations were compared.

European and regional species were checked for their use for production of indicators too. If a species index is classified as ‚uncertain‘* AND index value is >>>> 200% or <<<< 5 %, then the species index and data quality was examined in details. This criteria was considered as indicative, final decision taken (i.e. species to be potentially excluded from an indicator) considers also whether a species was used already in previous versions of the indicators, whether better data can be expected in near future and whether index fluctuation is believed to be caused either by poor data or by reasons not linked directly to habitat quality. This rather conservative approach is used in order to prevent bigger influence of subjective decision.
Three species were excluded at European level: Dendrocopos medius, Sylvia nisoria and Passer hispaniolensis. The same assessment was done for all versions of indicators produced.
Similarly as in case of species indices, the indicators were produced automation system provided by the Statistics Netherlands and also by hands and outputs were compared.

* 1)Trend classification

The multiplicative overall slope estimate (trend value) in TRIM is converted into one of the following categories. The category depends on the overall slope as well as its 95% confidence interval (= slope +/- 1.96 times the standard error of the slope).

  • Strong increase - increase significantly more than 5% per year (5% would mean a doubling in abundance within 15 years). Criterion: lower limit of confidence interval > 1.05.

  • Moderate increase - significant increase, but not significantly more than 5% per year. Criterion: 1.00 < lower limit of confidence interval < 1.05.

  • Stable - no significant increase or decline, and most probable trends are less than 5% per year. Criterion: confidence interval encloses 1.00 but lower limit > 0.95 and upper limit < 1.05.

  • Uncertain - no significant increase or decline, and unlikely trends are less than 5% per year. Criterion: confidence interval encloses 1.00 but lower limit < 0.95 or upper limit > 1.05.

  • Moderate decline - significant decline, but not significantly more than 5% per year. Criterion: 0.95 < upper limit of confidence interval < 1.00.

  • Steep decline - decline significantly more than 5% per year (5% would mean a halving in abundance within 15 years). Criterion: upper limit of confidence interval < 0.95.


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