This indicator measures changes in populations of characteristic farmland bird species. The relative change (index) in the number of pairs is measured based on field surveys. According to our estimates, monitoring will allow us to follow long-term population trends, as monitoring is carried out on a large number of plots (110 plots in the period 2008–2016). These surveys are mostly carried out by local volunteers close to their homes. If there is no data for a certain year, it can be replaced with the data from a relevant statistical model.

In order to determine the Slovenian farmland bird index (SFBI), monitoring of widespread bird species has been carried out for 9 years (2007 was a pilot year with approximately half as many plots) and trends can be calculated for the period 2008–2016. The Slovenian farmland bird index improved slightly in 2016 (by 3.6%), as well as the indices of generalists, meadow and hedge species. This does not necessarily indicate an improvement in the trend – it may just reflect the short-term fluctuation of populations. In 2016, the value of the composite index for 29 indicator farmland bird species was 75.4 +/-2.7. In the same year, the value of the composite index of meadow species was 62.5 +/- 4.4, which was 0.7% higher than in 2015. The trend of Slovenian farmland bird species is showing a moderate decline for the period 2008–2016. Population trends in 16 out of 29 species are showing a decline, while the populations of 8 out of 29 species are stable or increasing. (Kmecl & Figelj, 2016).

A recently published Pan-European study of trends of farmland bird species showed that the impact of agri-environmental payments in Europe has been positive, but not enough to halt negative impacts of other factors; intensification of agriculture negatively affects the populations of farmland birds regardless of their migration strategy (Gamero et al., 2016).

Conclusions as regards the growth or decline of a population must always be based on long-term (at least several years) trends. In interpreting these trends, we cannot eliminate other impacts on farmland bird species, such as climate change, epidemics, outbreaks and conditions on wintering grounds. All these (potential) impacts can occur as simultaneous and intertwining factors along with the intensification of agriculture. Nevertheless, there is highly prevailing evidence that changes in agricultural practices (especially towards greater intensity) are a key factor in declining farmland bird species populations. Scientific publications on this impact are available for the entire territory of Europe, while evidence for other impacts is considerably less abundant. A good overview is given in Wilson et al., 2009.

The trend in meadow bird species in Slovenia is slightly worse than that for farmland bird species (index 62.5 for the period 2008–2016, a trend of moderate decline). One of the probable causes, at least in some areas, is the decline of the surface area covered in meadows. In some places, the decline has been extensive, e.g. on the Ljubljana Marshes. Reasons for such declines differ, from conversion to arable fields in plain areas, to expanding forests in mountainous and karst areas and urbanisation, which causes the disappearance of meadows through the construction of roads and buildings. A number of species also feels the impact of mowing intensification and meadow management, e.g. early mowing, intensive manure application and intensive grazing on the Ljubljana Marshes (Vukelič, 2009). For example, disappearing meadows are the main cause of the declining populations of the red-backed shrike (Lanius collurio) in Šturmovci (northeastern Slovenia).

On the other hand, a favourable impact of flooding and, consequently, more extensive farming on meadow bird species has been observed on the Ljubljana Marshes (Tome, 2002), where extensive meadows are of crucial importance for the survival of the corncrake Crex crex (Božič, 2005). According to a survey conducted in 2016, 46.3% of corncrake broods were destroyed on the Ljubljana Marshes due to early mowing, while the percentage on the Planina Polje was an alarming 76%. In the case of corncrake, meadows that are otherwise their favourable nesting environment have turned out to be an ecological trap when floods occur during the breeding period. Therefore, it would be necessary to expand appropriate grass-covered areas to higher grounds on the Ljubljana Marshes. Corncrake-friendly agri-environment-climate operations (humid extensively managed meadows [VTR] and litter-producing stands [STE] payments in Slovenia) are probably effective, but participation is far too low as they are not financially stimulative (Božič & Jančar, 2016). A considerable reduction of extensively managed meadows has also been observed in the Goričko region (Trčak et al., 2012).

The trends of indicator species in the Slovenian agricultural landscape are as follows (Kmecl & Figelj, 2016):

(1)
Uncertain trend (5 species)
northern lapwing, stock dove, hoopoe, western yellow wagtail, corn bunting;

(2)

Moderate decline (9 species)
crested lark, woodlark, marsh warbler, common whitethroat, red-backed shrike, common starling, Eurasian tree sparrow, yellowhammer, cirl bunting;

(3)

Steep decline (7 species)
European turtle dove, Eurasian skylark, tree pipit, whinchat, European stonechat, European serin, linnet;

(4)

Moderate increase (2 species)
barn swallow, common redstart;

(5)

Stable trend (6 species)
common kestrel, common wood pigeon, Eurasian wryneck, European green woodpecker, common nightingale, European goldfinch.

Long-term trends in the European PECBMS scheme have been calculated since 1980, the latest report (up until 2014) for Europe showed a 57% decline in populations of farmland bird species in the period 1980–2014. For the European Union as a whole, the decline was 58%, while for new EU Member States, the decline was 46% (EBCC 2016). Regionally, the decline of common farmland species for Central and Eastern Europe was 54% (1982–2014), while it was lower (34%) for Southern Europe (1989–2014) (EBCC 2016a).

Bird species trends are available for some neighbouring or nearby countries. Currently, the Austrian FBI for the period 1998–2015 is 64.3%, while trends are similar as in Slovenia for a surprising number of species. The entire trend of the Austrian index, as well as its absolute value, is similar to that of Slovenia. With 2008 as the baseline, the Austrian farmland bird index was 73.5 for 2014 and 80.9 for 2015. The Slovenian farmland bird index was 71.8 in 2015 and 75.4 in 2016.

The total Italian farmland bird species index for the period 2000–2014 was approximately 83 (a decline of approximately 17%). In Italy, typical species of the agricultural landscape are in decline; for example, the Eurasian skylark, red-backed shrike, marsh warbler, European stonechat and Eurasian wryneck. The growth of the population of ortolan bunting, which is in decline and critically endangered in Slovenia, is surprising.

Generally, negative population trends of farmland bird species are caused by the intensification of agriculture (Donald et al. 2001). Index results also reveal that the efficiency and/or extent of the agri-environment-climate measures within the Rural Development Programme are probably insufficient. This phenomenon has been known to occur throughout Europe. While European nature protection policy (Natura, agri-environment-climate measures) is effective, it cannot halt the negative effects of agriculture intensification.