Blog post by Dr Allan Perkins, Senior Conservation Scientist, RSPB Centre for Conservation Science
A new study, recently published in the Journal of Applied Ecology, looks at the population responses of farmland bird species to agri‐environment schemes and land management options in north-eastern Scotland.
Background
Over the past three decades, agri-environment schemes (AES) have been the main policy tool for addressing population declines of farmland birds across Europe. Many studies have assessed the effectiveness of AES, revealing mixed results.
In the UK, population recovery of rare and range-restricted species such as corncrakes, stone curlews and cirl buntings is strongly linked to the provision of evidence-based management solutions through AES that are targeted in the right places and backed by sound conservation advice. For common and widespread species, however, the effectiveness of schemes appears to be more variable, and may depend to some extent on the intensity of the farming system.
Reed bunting Image by Mick Richards (rspb-images.com)
Intensive farming tends to create simpler landscapes with little habitat variation, and the provision of ‘beneficial’ habitats through AES may have a bigger impact on bird populations here than in less intensive and more diverse landscapes. With growing evidence for the importance of landscape heterogeneity in moderating AES effectiveness, but relatively poor knowledge of AES performance in complex landscapes with diverse crop regimes, we investigated long-term AES performance in a low-intensity mixed farming landscape in Scotland.
The study...
Using data collected by the RSPB’s Centre for Conservation Science as part of studies on corn buntings, we compared breeding population sizes and trends of five farmland passerines between farms participating in AES and those not. We studied 53 lowland farms in Northeastern Scotland between 2003 and 2015, focusing on yellowhammers, reed buntings, tree sparrows, linnets and skylarks. In contrast to some parts of the UK, these species are still common and widespread on lowland farmland in eastern Scotland.
Here mixed farming predominates, creating a mosaic of arable and grass fields interspersed by non-farmed habitats such as mosses and small-scale woodlands. Barley is the most common arable crop, and most of it is sown in the spring, meaning lots of seed-rich stubbles is retained over the winter. Arable and grassland management also tends to be less intensive than in other parts of the UK such as southern Scotland and England.
Yellowhammer. Image by Gergana Daskalova.
The University of Edinburgh carried out data analyses, including the novel application of a multi-membership model to determine associations with specific AES management interventions.
Our findings...
Overall, there were no significant changes in breeding populations amongst the five study species, but there were indications of declines for skylarks and increases for tree sparrows and yellowhammers. Population trends didn’t differ between farms that participated in AES and “control” farms not in schemes.
Our lack of detection of a significant association between AES and avian abundance or population trends could have been due to a lack of additionality of AES in complex landscapes, increases on conventional farms due to spill-over effects from AES farms, land-use legacy on farms that dropped out of schemes, and/or poor selection and implementation of AES management options. Nevertheless, within AES, there were specific land management options that appeared to be beneficial for some species.
We found positive associations between the provision of species-rich grasslands, water margins and wetland habitats and breeding abundance of yellowhammer and reed bunting, highlighting the importance of undisturbed herbaceous or grassland vegetation as nesting or foraging habitats for these species during the breeding season.
Conclusions...
Although the study found few significant associations between AES management and farmland bird abundance or trends, the apparent increases in yellowhammers and tree sparrows, and stability of linnet and reed bunting populations across our study sites is encouraging, especially as declines continue in other UK regions. Greater resource provision (food and nesting habitat) in the more diverse and less intensive mixed farming landscapes that characterise our study area is a likely explanation.
AES have probably played a crucial supporting role, but the high mobility of birds between seasons makes this difficult to prove. For example, birds breeding on control farms may well utilise winter food resources on neighbouring AES farms, particularly during harsh conditions when flocks using AES ‘wild bird cover’ crops can be spectacular.
Intriguingly, one species that tends to shun such crops is the skylark – the only one of our study species that appeared to decline, with numbers falling sharply in our study and the national Breeding Bird Survey following two consecutive cold snowy winters in 2009–11. Skylarks are ground-feeders that favour open fields, making them particularly vulnerable to prolonged periods of heavy frosts or snow that locks up their food resource, forcing hazardous movements to warmer climes.
Typical lowland mixed farmland in Aberdeenshire, Northeastern Scotland. Image by Allan Perkins.
AES are most effective when farm- and field-scale targeting of key management interventions is aimed at individual species, as demonstrated for corn buntings in eastern Scotland whose numbers in some areas have doubled since targeted AES began. In the present study, none of the five species were targeted individually by AES interventions, although several management options are designed to benefit farmland birds generally.
Our findings suggest that where AES are targeted at breeding yellowhammers or reed buntings, they should provide patches of undisturbed herbaceous or grassland vegetation via management options such as species-rich grasslands, small-scale wetlands or well-vegetated ditches.
AES ‘Water Margin’ option, providing undisturbed herbaceous vegetation used by nesting reed buntings and yellowhammers. Image by Allan Perkins.
And finally...
A special thanks to Gergana Daskalova, the incredibly dedicated student who transformed an unused RSPB dataset into her undergraduate dissertation, a British Ecological Society (BES) conference presentation, and now a manuscript published in a high quality journal. A fantastic achievement for an early career scientist who, through her current PhD and future work, will go on to publish many more papers – thank you Gergana!
For more on our science, check out the RSPB Centre for Conservation Science web pages.