Why do the national farmland bird indicators of PECBMS differ from the national farmland bird indicators used in my country?
The national farmland bird indicators produced by PECBMS to contribute to EU´s Structural Indicators and Indicators of Sustainable Development, are based on PECBMS European species classification. Countries however also produce their own bird indicators, designed for other policy purposes. For example, EU countries produce farmland bird indicators for EC Regulation on Rural Development Plans (No 1698/2005). Such national indicators can be based on a species classification system developed for that particular purpose and can therefore, in some cases, differ a bit from those on the Eurostat website. When interpreting an indicator, one should always pay attention to the purpose for which it is designed.
Learn more about PECBMS European species classification in Methods, chapter 3., Multispecies indicators.
Check national farmland bird indicators produced by PECBMS on the Eurostat website.
The indicator values in early years are different between indicator updates. Does it mean that the indicator is not robust and credible?
These differences arise because the species population indices at national and supranational levels are recalculated each year again for the full time series. In addition, as national schemes increase their capacities to analyze old data (e.g. data not computerized before), new data from early years become available in some cases and this can influence the index values too. When index values change, the multispecies indicator values also change. These changes are however small and they are of minor importance because the interpretation of indicator values should focus on long-term trends.
Learn more in Methods, chapter 2. Supranational species indices and trends.
Read more about interpretation of indicators in the next question “What exactly does the multispecies bird indicator tell us about changes in bird diversity?“
How sensitive is the indicator to population changes in one or a few species?
The indicator uses the logarithm of the indices of species, and taking the logarithm usually dampens the effect of changes in one or a few species on the indicator substantially. Also criteria used for decision whether a species is to be included in an indicator are aimed to prevent too much effect of a single species on it. Nevertheless, if the indicator would contain only a handful of species, population changes in one or a few species may affect the indicator considerably. It is possible – and useful – to test statistically whether the change in the indicator is only based on one or a few deviating species or reflects an overall change of the group.
Learn more in Methods, chapter 4. Quality control.
Some countries produce their own bird indicators. Are these indicators similar to the PECBMS indicators?
Not necessarily. Apart from indicators produced under coordination of PECBMS, countries produce their own wild bird indicators according to specific national needs (e.g. national legislation). Links to some national indicators also can be found on the PECBMS web site. They may deviate slightly from PECBMS indicators because of different methods of species selection and classification, computation procedure etc., that are tailored to the specific national purpose.
Learn more about national monitoring schemes in Europe in the country reports or about types of indicators that PECBMS produce in Methods, in chapter 3. Multispecies indicators.
See also related question “Why do the national farmland bird indicators of PECBMS differ from the national farmland bird indicators used in my country?“
How sensitive are the indicators to changes in species selection?
Changes in the list of species that contribute to an indicator may affect that indicator. We improved the species classification procedure and finally based it on bio-geographical regions. That has led inevitably to changes in the species lists.
The farmland bird indicator (especially when statistically smoothed) has always shown the same message, i.e. a dramatic decline of farmland birds in Europe, regardless of the species classification used. It appears to be robust and less sensitive to changes in species lists. The index of common forest birds shows a higher sensitivity to changes in species lists, probably linked to the fact that forest habitats are much more diverse and different driving forces operate at a national or regional scale. This requires a further study.
To make the indicators less sensitive to changes in species composition, we include as many species in the indicators as possible. Furthermore, criteria used for species selection and classification for the indicators are chosen so as to prevent too much influence of one or a few species.
Learn more about PECBMS species habitat classification in Methods, chapter 3, Box Species selection and classification or in chapter 2, in Box Data checks.
See also related question “How did PECBMS classify the species that are characteristic for each habitat type?“
Is the classification of species to be included in the (farmland) bird indicator similar across countries?
Yes, it is. PECBMS uses one and the same European species classification to produce indicators for Europe, EU, and European regions. Furthermore, PECBMS provides Eurostat with national versions of the Farmland Bird Indicator as parts of EU´s Structural Indicators and Indicators of Sustainable Development. These national farmland bird indicators also are based on this PECBMS European species classification. Since some bird species are missing in some countries, some of these national farmland bird indicators are based on a sub-set of species from the pool of European farmland birds. See also the next question.
Apart from indicators produced by PECBMS, countries produce their own national indicators for their national purposes, e.g. driven by national legislation and policy. These nationally produced indicators are not centrally coordinated and may deviate with respect to species selection, computation procedure etc.
Learn more about PECBMS species habitat classification in Methods, chapter 3, Box Species selection and classification or about national monitoring schemes in Europe in country reports or about European indicators on the Eurostat website.
Which criteria are used to include a particular species in an indicator or not? E.g. why is Picoides tridactylus not included in the forest bird indicator?
Whether species are included in PECBMS indicators depends on
- species classification (i.e. whether a species has been selected for a given type of indicator,
- species data quality, and
- species data availability.
As a consequence, some suitable species are excluded because they are not properly monitored. There is however ongoing effort to increase data availability, using for example data from species specific monitoring schemes in European countries next to generic breeding bird monitoring schemes.
See more in Methods, chapter 3, Box Species selection and classification or chapter 4. Quality control.
How did PECBMS classify the species that are characteristic for each habitat type? Has there been any change in this procedure since the start?
So far, three versions of PECBMS European species classification have been produced and used. The first set of European indicators was based on European trends of 47 common bird species, classified according to the expertise of the national coordinators of monitoring schemes and other experts who met at the PECBMS workshop in Prague in 2002. For the second set of European indicators, based on an enlarged species sample, the classification was improved. It was based on a publication by Tucker & Evans (1997), describing habitats and their importance for birds in Europe. Since 2007, when the third set of European indices and indicators was produced, data on more than 100 species are used and the species classification is based on assessments within bio-geographical regions in Europe.
See more in Methods, chapter 3, Box Species selection and classification.
Is it possible that early years results are biased towards western Europe, as monitoring schemes started later in many other countries?
This may indeed be true. However, we have examined this issue recently and so far did not find any such bias. For instance, data on farmland bird trends in Europe from independent sources showed that PECBMS data correctly described the decline of farmland birds in 1980s across Europe (Voříšek et al., 2010).
Nevertheless, PECBMS results that are suspected to be biased in this way are labeled as such in all outputs. The potential effect of such suspicious species indices on supranational indices is also routinely examined and suspicious data are abolished.
So far, there is no other option than to use a hierarchical procedure to impute missing values in European regions.
Learn more in Methods, chapter 2.2. Combining national data into supranational outputs or chapter 4. Quality control.
See PECBMS results in details in special reports on European trends and indicators.
National indices are weighted when combined according to national population size estimates (from European Red List of Birds, BirdLife International 2015), but the quality of population estimates is very different between countries. Does it mean that weights are based on incorrect values?
Information on population size published by BirdLife International 2015 is the best source of information in Europe that is available. The data have been used in several studies, published in high profile scientific journals (e.g. Donald et al., 2007). There are indeed differences in the quality of information between countries, but the population estimates are robust and to obtain extra guarantees we asked the national coordinators to judge these estimates.