Blog post by Prof Richard Gregory, Head of Species Monitoring and Research, RSPB Centre for Conservation Science and Centre for Biodiversity & Environment Research, University College London 

Farmland wildlife is threatened right across Europe and the plight of specialist birds has been the subject of detailed research and growing understanding. While the problem and threats to wildlife may be complex, the solution, or at least part of the solution, might be simple according to new research published in Scientific Reports.

We know that farmland bird populations have declined across Europe in recent decades driven by agriculture policy linked to the EU’s Common Agricultural Policy (CAP). The European Farmland Bird Index, the FBI, for example has fallen by nearly 60% since 1980, considerably more than for bird populations living in other habitats and that picture of loss is mirrored across the EU (see figure). The Iberian Peninsula is a case in point that is home to an amazing variety and concentration of farmland birds, many typical of cereal Steppe habitats, including iconic, threatened and declining species, such as the Great and Little Bustards.

Graph: Temporal trend in populations of common and widespread birds in Europe. 

Policy change under the CAP was designed to maximize crop yield and revenue and bring food security, but that has led to a rapid increase of inputs and agrarian operations, which in turn have led to the loss of environmental heterogeneity and driven biodiversity loss. At the field scale, the habitat has become much less hospitable for wildlife, and at landscape scale, this has meant a simplification and homogenization of the land through the loss of non-cultivated elements (e.g. ponds, field margins, hedges, fallow and wasteland), further reducing habitat availability for nesting and feeding birds. The face of European farmland has changed considerably in the last few decades and there is less space for nature.

In their new paper, Traba and Morales use the area of fallow land in Spain as a measure of this landscape-scale agriculture intensification. Fallow land being the cultivated land that is not seeded for one or more growing seasons, including semi-natural grasslands and pastures that will eventually be ploughed for a new crop cycle. Adequately managed, fallows are one of the most important habitats for wildlife, and particularly for farmland birds, due to the high diversity and abundance of food resources that they provide such as weeds, seeds, and invertebrates, as well as vegetation cover for foraging or nesting. The authors argue that fallows have been crucial for the maintenance of farmland biodiversity in Mediterranean countries, and that is likely to be true right across Europe.

Photo: Little Bustards are among the amazing of farmland birds in the Iberian Peninsula. By Francesco Veronesi

Using unique data from the National Survey on Agrarian Surfaces of the Spanish Ministry of Agriculture, Fisheries and Food, the authors were able to demonstrate a significant loss of fallow land area since 2002 (figure: Fallows: −16.1%, Old Fallows: −41.8%).  Such land use data are surprising rare and so this paper is the first of its kind to link changes in habitat area to changes in bird populations; lots of other work has shown birds prefer fallow or set-aside land and live there at higher densities and are more productive in those habitats. The other notable feature in the figure is a big drop in the amount of fallow when the EU removed an obligation on farmers to keep 10% of their land in fallow or set-aside (from 2008). Certainly, the loss of this set-aside land in the UK at this time is thought to have had a very considerable negative effect on our farmland wildlife.

Graph: Temporal trend in the surface occupied by fallow land in Spain (2002–2017). The linear regression line is shown in blue, and 95% Confidence Intervals in grey (linear regression: adjusted R2 = 0.800; p < 0.0001).

The authors were then able to show, using bird data from the Spanish national bird monitoring programme (the ‘SACRE’ Program which has operated since 1998 and was established with assistance of the RSPB), that the annual rate of change in fallow land was correlated significantly with (A) rate of change in the numbers of Little Bustard – a quintessential bird of cereal-Steppe, as well as with (B) a Spanish Farmland Bird Index, and (C) with a specially constructed Spanish Cereal Bird Index (Figure).

Relationship between species and fallow land annual change in Spain between 2002 and 2017. (ALittle bustard (adjusted R2 = 0.761; p < 0.00001). (B) Farmland birds (adjusted R2 = 0.644; p < 0.001). (C) Cereal birds (adjusted R2 = 0.668; p < 0.001). Linear regression lines are shown in blue, and 95% Confidence Intervals in grey.

So, there is a nation-wide statistical correlation between the temporal trend in the amount of a habitat type linked to extensive agriculture, that is fallow land, and the population trends of different groups of farmland birds, including a declining fallow specialist. The authors interpret these results to suggest causation between the loss of fallows and the loss of bird populations, and there is a body of additional evidence to support their view. They go on to recommend that in the upcoming CAP discussions any new EU agri-environmental schemes should mandate the maintenance of fallow land as a condition on farmers receiving income support. Moreover, they suggest a return to the magic number of 10% as an obligatory amount of land to be left as fallow on each farm (and to restore the conditions prior to 2008).  They also recommend a reduction in field-level intensification of farming, with the aim of reducing agro-chemical inputs, and demand more ambitious regulations to address all levels of the food production chain, from the farmer to the consumer.

Photo: The Iberian Peninsula is home to an amazing variety and concentration of farmland birds, many typical of cereal Steppe habitats, including iconic, threatened and declining species. Picture from Picón, Ciudad Real by Carles Carboneras.

This sentiment would be shared by many conservationists, including the RSPB, and several different studies and analyses come back to this magic number of around 10% of farmed land being dedicated to bird-friendly measures to allow the recovery of farmland birds, and likely other wildlife.  While the evidence is incomplete, we believe that if 10% of farmed land was set-aside and managed for wildlife, fallows being an important component of the mix required, this would help turn around the fortunes of many threatened and declining species across Europe.

There are however important caveats with this study and the first is that it is a simple correlation and does not demonstrate causation. The authors are careful to explain that much has changed in Spain over the same period too; pesticide and fertiliser use appears to have increased, no-till farming with high herbicide weed control has increased, and more and more land is given over to irrigated woody crops, in the form of olive groves and vineyards. In addition, the authors were not able to assess the quality of the fallow land, which is likely to be crucial for farmland birds and other wildlife, nor did they look at the influence of weather or other land use covariates in their models or consider time-lagged effects. 

In this respect, we must be cautious of a single simple correlation and yet the simplicity of this study is also a strength and their recommendation to bring back an EU obligation under a revised CAP to devote 10% of farmland to wildlife-friendly measures makes a great deal of sense and would be well supported by science-led practitioners and conservationists. The magic number is 10%.

Traba, J. & Morales M.B. (2019) The decline of farmland birds in Spain is strongly associated to the loss of fallowland. Scientific Reports 9, 9473, https://doi.org/10.1038/s41598-019-45854-0.

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