Category Archives: Questions & Answers

Question 3.2

The supra-national species indices and the multispecies indicators are based on adding national results. Is this justified, as the borders between countries are artificial?


Of course, birds have nothing to do with country boundaries and bird populations should be considered as a whole across Europe. That is exactly what we do by weighing the national species indices on base of the national population size estimates (from European Red List of Birds, BirdLife International 2015). This procedure warrants that each individual bird counted gets the same weight in the trends and indices, whether it lives in one country or another.

See more in Methods, chapter 2. Supranational species indices and trends.

Question 3.1

Does PECBMS check the quality of the national data collected, and how?


Yes, the PECBMS coordination unit thoroughly checks the national data, apart from quality control performed by coordinators of national monitoring schemes. We check the parameters that accompany each species index and that allow us to detect suspicious data, especially data with a low precision or with potential bias. If the data are inconsistent or if we suspect that their quality is low, such data are not used for the computation of supranational indices and trends and multispecies indicators. Also, at each data update, we compare the newly computed national indices and trends, as well as the supranational indices and trends and the multispecies indicators, with the previous ones and check for consistency.

See more in Methods, chapter 4. Quality control

Question 2.4

Is it possible that plots have been sampled in a non-random fashion at the start of the national monitoring schemes – because observers tended to count at sites with a high species richness and abundance of birds – biasing the results for the first years?


A non-random selection of plots has indeed occurred in some cases, but in these cases the plots once chosen were consistently monitored during following years. When new, randomly chosen plots were added to the initial plots, we imputed missing values for these newly added plots in earlier years, thereby preventing any bias.

See more in Methods, chapter 1, Box Selection of sample plots and Box Missing values I.

Question 1.4

It is impossible to count all birds present at a site during a visit, as not all birds are observed. How does this affect the results?


This does not affect the results. PECBMS focuses on changes in bird populations, not on absolute numbers. The only requirement is that numbers can be compared between years. Standardized field methods have been adopted in each country to assure that no systematic changes in observation effort are occurring.

See more in Methods, chapter 1.1 Counting birds.

Question 4.1

What species habitat classification is used for PECBMS data?


The PECBMS currently uses two versions of species habitat classification at the moment: single European species habitat classification and BioGeo regional species habitat classification.

This species habitat classification for main habitat types (farmland, forest and other) has been developed using improved procedure accepted at the PEBCMS workshop in Prague in 2005.

BioGeo regional species habitat classification is based on the expertise of regional coordinators, who were responsible for the production of regional species lists in cooperation with all relevant experts within their regions. Distinguished regions were: ´Continental´, ´Atlantic´, ´Mediterranean´, and ´Boreal´. Within these regions, coordinators classified each species for main habitat types (farmland, forest and other). BioGeo regional species habitat classification for each region is specified in the table, columns ´Continental´, ´Atlantic´, ´Mediterranean´, and ´Boreal´.

Single European species habitat classification is been created as a combination of the BioGeo regional habitat characteristics of each species into the general species habitat classification unified for the whole Europe. For this general, single European classification, a species was assigned to a particular habitat category if:

  • at least two regions provided their classification and all providing regions agreed, or
  • only one region (minority) classified a species differently than the others.

In some cases a species classification was provided by one region only, but if the species was concentrated in that region and didn´t occur elsewhere in Europe, the species BioGeo regional classification was accepted as single European too. If regional classifications differed completely, a species was generally considered as ´other species´.

The latest single European species habitat classification is defined in the table, column ´Europe´.

Detailed information is provided in the Methods section, chapter 3, Box Species selection and classification.

Questions & Answers

Compiled by Petr Voříšek, Arco Van Strien, Willy Van Strien, Jana Škorpilová, Ian Burfield and Richard D. Gregory

Updated on 11 November 2017

In a form of questions and answers, this section aims to help understanding methods of data collation and analysis within the Pan-European Common Bird Monitoring Scheme. The section is complementary to the section Methods. We expect the Questions and Answers will be updated on regular basis and appreciate suggestions for improvements or completely new questions on methods of production and interpretation of supranational species population trends and indicators. Please send comments and suggestions to Petr Voříšek, the PECBMS coordinator,

1. National data sources, field work

2. National species trends and indices (some questions apply to the supranational level too)

3. Supranational species trends and indices (some questions apply to multispecies indicators too)

4. Multispecies indicators: species selection and classification

5. Multispecies indicators: production

6. Multispecies indicators: interpretation

7. References


Question 2.2

What is BirdSTATs, how does it work, where can it be obtained?


BirdSTATs is a tool that facilitates the use of TRIM and makes it possible to run TRIM automatically and in batch mode. In other words, BirdSTATs runs TRIM for many data at once, making the production of trends and indices faster and more effective.

BirdSTATs is capable of importing different kinds of count data, enables stratification of count sites and selection of subsets of count data, and produces standardized TRIM input and command files. It collects the output of the batched TRIM runs in a convenient and standardized format (database tables) and standard TRIM output files as well.

BirdSTATs is an open source Microsoft Access database and can be downloaded from the EBCC website.

Question 6.7

What is the evidence that the changes reported in farmland birds are due to agricultural change?


There are multiple strands or evidence both correlational and experimental that point to changes in agricultural practices as the primary, but not the only, cause of farmland bird declines in Europe (for full review and supporting literature see: Wilson et al., 2009). One strand of evidence comes from detailed studies of individual birds species, some carried out over many years that have pin-pointed agricultural change, sometimes with other factors, as a major cause of population decline and range contraction. Farmland birds in this category include Grey Partridge Perdix perdix, Stone Curlew Burhinus oedicnemus, Corncrake Crex crex, Lapwing Vanellus vanellus, Turtle Dove Streptopelia turtur, Skylark Alauda arvensis, Whinchat Saxicola rubetra, Cirl Bunting Emberiza cirlus and Corn Bunting Miliaria calandra, to name a few where research has been carried out by a number of different organisations. In each case, specific changes in agricultural operations or practice have been identified as the main cause of decline (Wilson et al., 2009).
To take an example, Hole et al. (2002) worked on the House Sparrow Passer domesticus, whose populations have declined sharply in Western Europe in recent decades. They used a combination of field experimentation, genetic analysis and demographic data to show that a reduction in winter food supply caused by agricultural intensification was probably the principal explanation for the widespread local extinctions of rural House Sparrow populations in southern England.
In a wider study, Chamberlain et al. (2000) examined changes in agriculture through time (1962-95) quantitatively for 31 variables representing crop areas, livestock numbers, fertilizer application, grass production and pesticide use in England and Wales. The period 1970-88 saw most intensification, characterized by increases in the area of oilseed rape, autumn-sown cereals, and the use of pesticides and inorganic fertilizers. Spring-sown cereals, bare fallow and root crops declined. Indices of relative population change between 1962 and 1996 were determined for 29 bird species over the same area. The ordinations of agricultural change and bird population change matched each other with a time lag in the response of birds. The authors conclude that large shifts in agricultural management are a plausible explanation for the declines in farmland bird populations.
Donald et al. (2001) showed that population declines and range contractions of farmland birds 1970-1990 were significantly greater in countries with more intensive agriculture, and significantly higher in the European Union than in former communist countries. Cereal yield alone explained over 30% of the variation in population trends. The results strongly suggest that recent trends in agriculture have had deleterious and measurable effects on bird populations on a continental scale. Donald et al. (2006) went of to show that of the 58 species classed by an independent assessment as being primarily birds of farmland, 41 showed negative overall mean trends across Europe in 1990-2000, 19 of them significant. There was a significant negative correlation between mean national trends of all farmland species and indices of national agricultural intensity. This relationship strengthened when the 19 declining species were considered alone, and was not apparent when only non-declining species were considered. Population trends of terrestrial non-farmland bird species over the same period were unrelated to agricultural intensity. The results support earlier evidence that population trends of farmland birds across Europe can be predicted from gross national agricultural statistics.
There are many other peer-reviewed studies from the UK (Aebischer et al., 2000; Vickery et al., 2004) and across Europe that have explored links between birds and agriculture, as well as alternative drivers of population trends. Although the individual bird species, bird communities and farming systems vary across Europe, change in agricultural systems is the predominant and recurrent factor implicated in population declines of breeding birds (see more info on the website of online BOU conference proceedings, Lowland farmland birds III).
A final compelling strand of evidence comes from cases where limiting factors on farmland have been identified and practical remedies put in place to bring about the recovery of bird populations. Individual bird species in this category include stone curlew, corncrake, skylark, and cirl bunting in the UK. The RSPB´s Hope Farm in Cambridgeshire shows how wildlife friendly measures can bring about the rapid recovery of farmland birds and in this case increase farm profits at the same time.

Question 6.4

Is there any evidence that birds are good indicators for biodiversity as a whole? Do population trends of birds reflect trends in other taxa?


To a certain extent, they do, at least for farmland. Studies in Europe have shown that many vertebrate, insect and plant species of farmland have declined in parallel, whereas only a few species have increased, and these changes are thought to be driven by agricultural intensification and specialization (see table 5 in Gregory et al., 2005). So it is reasonable to assume that trends in bird populations mirror those in other taxa, at least in farmland.
On the other hand, no single metric is likely to adequately describe changes in biodiversity as a whole and the bird trends cannot be straightforwardly generalized to biodiversity. PECBMS recommends further work to explore the correspondence of across-taxa trends, and encourages the production of some other indicators as well, such as the butterfly indicator that has already been produced (see more on EEA website).