Summary1. Agri-environment schemes (AES) are the main European policy response to biodiversity loss caused by agricultural intensification. Maximizing their effectiveness is a key policy challenge. Monitoring is essential to inform adaptation and improvement of schemes over time, and to understand how measures may need to vary across a species' range. 2. We measured changes in breeding abundance of a severely declining bird, the corn bunting Emberiza calandra, in response to AES in Scotland over 7 years and 71 farms. Two AES were monitored, one with general management for farmland birds, and one with targeted, adaptive management for corn buntings. We use these data to estimate the proportion of the population that AES must influence to halt the overall decline. 3. Corn buntings increased by 5AE6% per annum on farms in the targeted AES, showed no significant change on farms in the general AES, and declined by 14AE5% per annum on farms outside AES. 4. In arable-dominated areas, AES management that increased food availability reversed population declines. However, where a high proportion of corn buntings nested in grasslands, an additional AES option that delayed mowing was essential to achieving population increase. 5. Results suggest that approximately 72% of the corn bunting population in mainland Scotland must receive targeted AES management to halt the current decline. In 2009, only 24% was targeted in this way. 6. Synthesis and applications. AES measures are capable of reversing corn bunting declines in Scotland, and the same measures are likely to benefit a wide range of other taxa too, but require geographical targeting and flexibility to adapt and improve management options, backed by expert advice. Targeted AES provision to the required level for corn buntings will cost approximately £120 000 per annum, with 500-600 ha under appropriate management. This is 0AE02% of annual subsidies paid to Scottish farmers, and 0AE5% of land in the remaining mainland range of the corn bunting. These outcomes illustrate the value of AES monitoring studies to assess scheme effectiveness, identify improvements, and determine the scale of implementation required for reversing species declines.

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1. The decline of farmland birds across Europe is a well-documented case of biodiversity loss, and despite land stewardship supported by funding from agrienvironment schemes (AES), the negative trends have not yet been reversed. 2. To investigate the contribution of AES towards farmland bird conservation, we compared abundance of five farmland bird species across 13 years and 53 farms (158 farm years = AES, 72 farm years = non AES) in Northeastern Scotland (UK), a region with relatively mixed farmland. 3. Between 2003 and 2015, on both AES and control farms, skylark (Alauda arvensis) showed a nonsignificant decline, and tree sparrow (Passer montanus) and yellowhammer (Emberiza citrinella) nonsignificant increases, whereas reed bunting (Emberiza schoeniclus) and linnet (Carduelis cannabina) populations remained relatively stable.4. We did not detect a significant association between AES and avian abundance or population trends for any of these species, but there were positive associations with some AES management options. 5. Possible explanations for the lack of a significant AES-bird abundance association include poor uptake of the best AES options for farmland birds, suboptimal implementation, spill-over effects from AES onto control farms, and the relatively good state of farmland habitats outwith AES in Northeastern Scotland.6. Synthesis and applications. We documented a weak effect size of participation in agrienvironment schemes on farmland bird abundance. We therefore recommend future monitoring studies be designed after consulting a power analysis. Among different land management options, we found that species-rich grasslands, water margins, and wetland creation enhanced breeding bird abundance, highlighting the importance of relatively undisturbed herbaceous or grassland vegetation for farmland conservation. K E Y W O R D Sagriculture, agri-environment schemes, farmland birds, low-intensity farmland, multimembership, offset, passerine, spatial statistics This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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The UK population of Corn Buntings Emberiza calandra declined by 86% between 1967 and 2003 (Baillie et al. 2006), and the species is on the Birds of Conservation Concern red list, and is a priority species in the UK Biodiversity Action Plan (Gregory et al. 2002). It is also listed as a species of unfavourable conservation status at a European scale, due to widespread decline across the continent (BirdLife International 2004). In Scotland, Corn Buntings were common and widespread at the start of the 1900s almost everwhere that cereals were grown (Donald et al. 1994, Holloway 1996), but there are now perhaps as few as 800 territorial males (RSPB unpubl. data). Most of these are concentrated in the mixed and arable farming areas of the eastern lowlands, from Moray and Aberdeenshire in the north to Angus and Fife in the south, and, increasingly, the distribution is fragmented in each of these areas. Other populations persist in the Outer Hebrides, Inverness-shire, and Dumfries and Galloway, but all are declining (Wilson et al. 2007b). Agri-environment measures likely to benefit Corn Buntings have been available through the Scottish Executive's Rural Stewardship Scheme (RSS) since 2001 (SEERAD 2003). The scheme includes options likely to increase seed and grain food over winter and to offer improved habitat for nesting and for rearing nestlings (Table 1). However, entry to the RSS is competitive and, at least initially, funding constraints limited the number of farmers taking part. For this reason, in 2001, the Royal Society for the Protection of Birds (RSPB), with support from Scottish Natural Heritage and assistance from the Farming and Wildlife Advisory Group, introduced the Farmland Bird Lifeline (FBL), an intervention project targeted at Corn Buntings on farms within the core of the species' range