New study reveals that autumn-sown ‘green manure’ can support breeding Corn Buntings while delivering improved soil health and other benefits for farmers
A new study published today shows that sowing a green manure seed mix in autumn can provide safe places for Corn Buntings to nest while improving soil condition on farms.
RSPB Scotland is now calling on the Scottish Government to include autumn-sown green manure in future agri-environment schemes as soon as possible.
Once widespread across the UK, Corn Buntings have suffered huge declines particularly in East Scotland where numbers plummeted by 83% between 1989 and 2007. This earnt them the unfortunate accolade of being one of Scotland’s fastest declining species. Work by farmers in Fife and Angus has dramatically improved the fortunes of this bird there. By growing wild bird seed mix, farmers have provided the three key things Corn Buntings need: seed for food in winter; insects to feed their chicks in spring; and, safe nesting sites.
However, in NE Scotland reversing declines in numbers has been harder as the main challenge is safe nesting sites. In this part of Scotland Corn Buntings tend to favour nesting in grass silage fields and because they nest late and on the ground this puts nests at risk of being destroyed at egg or chick stage when fields are mown, typically in June.
There is an existing Agri-Environment-Climate Scheme (AECS) option that pays farmers to delay mowing until August. This significantly improves Corn Bunting breeding success but the quality of forage is significantly reduced by mowing this late and therefore it is not a popular option for farmers to choose. This trial study, on six farms in north east Aberdeenshire between 2021 and 2023, has shown that autumn-sown green manure crops might be another option.
Corn Bunting nest survival was 60% in the trial plots which was similar to nearby cereal fields (70%) and far greater than in nearby grass (silage) fields where survival was just 25%.
In parts of the NE of Scotland silage fields may act like a trap. Corn Buntings are attracted in to them in May and June to nest, but then around the time eggs are hatching and nearly always before chicks can fly, the fields are mown. Previous research showed not mowing until 1 August is effective at increasing nest survival sufficiently to halt declines and agri-environment payments have been available for this since 2008. However, because the quality of forage harvested declines with later cutting, the uptake of this option has been low. Therefore, an additional option that works for more farmers is badly needed if we are to halt and reverse declines in this once common species; the trial shows autumn-sown green manure could be just that option. It should supplement the delayed mowing option and be made available for farmers in a targeted way, in Corn Bunting breeding areas that lack safe nesting habitats during May and June.”
Green manure crops are an increasingly popular agri-environment scheme option for farmers across the UK. Grown in rotation, they can dramatically reduce dependence on manufactured fertilisers and help alleviate soil compaction, erosion and water pollution.
These crops include clovers, vetches and phacelia which all provide a rich source of pollen and nectar for pollinating and predatory insects too. Such insects can provide additional benefits to farmers via the pollination of crops and pest control.
In Scotland’s Agri-Environment Climate Scheme, the uptake of a spring-sown green manure option has been high, suggesting an autumn-sown option would also be popular. Providing the autumn-sown option was left in place until at least the 15 August, it would have the added benefit of also providing safe nesting sites for one of Scotland’s most threatened birds.