Final report for the determination of the Slovenian Farmland Bird Index

The Farmland Bird Index is listed as one of the indicators of the state of biodiversity and the impact of agricultural policy in the Rural Development Programme(RDP) of the Republic of Slovenia for the 2014-2020 period and in the Slovenian 2023-2027 CAP Strategic Plan.

This report presents the monitoring results of common bird species used to determine the Slovenian Farmland Bird Index from 2008 to 2023. It summarises the main monitoring results and the census results of target species in each year. The report also provides a short professional interpretation of the census results, including the degree of reliability of the numerical estimate and compliance with the census protocol. The field method is a standard transect inventory in two bands.

The analysis of indices and trends of the species was done with a package rtrim in the programme. Rtrim data analysis uses models based on the Poisson regression. The multiplicative total trend for individual bird species is categorised by the programme based on slope criteria and confidence interval. The indicator (composite index) was calculated as the geometric average of the indices of indicator types.

The composite index's trend, its annual standard error and the differences between the trends of species groups were calculated using a Monte Carlo simulation. To compare trends, the species were divided into generalists and farmland birds. The latter were further divided into meadow and non-meadow species, as well as migratory and non-migratory species.

According to the calculated trends, the indicator species for the year 2008-2023 are classified into four groups: strong decrease (2): skylark, turtle dove; moderate decrease (15): cirl bunting, starling, tree sparrow, woodlark, nightingale, crested lark, yellowhammer, stonechat, common whitethroat, northern lapwing, serin, linnet, tree pipit, marsh warbler, whinchat; stable (4): green woodpecker, wryneck, corn bunting, red-backed shrike; moderate increase (8): stock dove, hoopoe, wood pigeon, goldfinch, common redstart, yellow wagtail, barn swallow, common kestrel.

The Slovenian Farmland Bird Index for 2023 is 75.7%, which is 2.1 % more than in 2022. The index has been stable for the last nine years but one has to be careful with the interpretation of this trend. Short-term trends can be a consequence of weather and climate conditions (unusually mild winters), conditions on the wintering grounds (illegal killing) and other factors. We could see this trend (especially if it continues in the following years) as a positive turn towards the improvement of farmland biodiversity. The overall trend for the 2008-2023 period is still a moderate decline and shows a substantial decrease in population. The current result doesn't necessarily indicate a better long-term trend. National agri-environmental measures (nature conservation and organic farming) do have some positive impact on the Farmland Bird Index, however, their impact is not strong enough.