Biodiversity Survey

Guy Parker from Wychwood Biodiversity shares the results of the third annual biodiversity survey of Southill Solar Farm.

The following is an extract of the recent Biodiversity Survey Report presented to the board of directors. A copy of the full report is available to download here.

Since 2016, Southill has adopted an ambitious plan for biodiversity enhancement, and in the past year the site has undergone further habitat creation, including the sowing of a limestone wild flower meadow in the south field, the sowing of a small area of traditional grazing in the north of the site and the re-sowing of the pollinator mix and the winter bird seed mix.


At Southill, the number of botanical species has risen from 39 in 2016 to 57 in 2017 to 65 in 2019, largely due to the creation of new grassland habitats, the establishment of a wild bird seed mix and the persistence of a wide range of common agricultural herbs and grasses. The proportion of bare soil (23%) has fallen from 35% in 2017 as the new habitats in the field margins and mid-field establish.

The field margins were sown with tussock grassland and wild flowers the previous year. The north field remains as a reverted wheat crop which hosted 4 pairs of breeding skylarks again in 2018. This phased sowing of the south and north fields has allowed the skylarks that flourish on this site to continue to breed here.

Small tortoiseshell butterflies were observed in the field margins

Small tortoiseshell butterflies were observed in the field margins

Butterflies and Bumblebees

For butterflies and bumblebees, a small number of common species were observed at relatively high abundance, with the encounter rate for both groups having increased annually since 2016. The greatest abundance of butterflies occurred in the old wild flower meadow, whereas bumblebees were observed in the greatest abundance in the newly sown wild flower meadow to the south, and the reverted wheat crop to the north of the site.

The increase in butterflies in the field margins is likely to reflect the increase in wild flowers in this field area, due to the majority of field margins having been re-sown wild a wild flower rich seed mix in 2016. These wild flowers provide a variety of nectar sources for butterflies to feed upon.

Breeding birds

In total, 67 species of bird were recorded during 3 surveys conducted during the breeding season by professional bird surveyor Tony Powell. Of these, 27 species were listed as birds of conservation concern (BOCC) for the UK. The red listed dunnock, linnet, marsh tit, meadow pipit, redwing, skylark and starling were noted on site this year.

Although 67 species of bird were observed on Southill, a high diversity, this is slightly lower than observed during 2016. This decrease may be related to the large-scale habitat clearance undertaken by Network Rail along the rail embankment adjacent to the site.

However, at the time of writing, no other solar farm surveyed by the Wychwood Biodiversity team comes close to this species number. The high number of bird species is in part due to the range of habitats within and surrounding Southill, including:

  • mature hedges which provide excellent nesting habitat for a wide range of species, including chaffinches, chiffchaffs, dunnocks, house sparrows, wrens, robins, blue tits and great tits;

  • the large open field area across the majority of the site which is suitable for foraging meadow pipits, linnets and yellowhammers, and breeding skylarks;

  • the rail embankment to the western boundary of the site which is dense with scrub of different ages and provides excellent foraging and breeding habitat for a wide variety of breeding birds; and

  • the stream and associated scrub which is suitable for warblers.

What’s next?

As of summer 2018, most of the Biodiversity Management Plani (BMP) activities had been undertaken and others are planned for implementation soon. Below are the BMP activities which are recommended for 2019:

  • Commencing sheep grazing between August and March within the solar farm;

  • Monitoring the site for problems with annual and perennial weeds, especially in the newly sown north meadow and the pollinator mix. Taking action to re-sow problem areas in the Autumn if physical weed control is not sufficient;

  • Re-sowing access track used by rail contractors to access the riverside during 2018;

  • Over-sowing areas of the solar farm grassland with wild flowers;

  • Maintaining existing hedge and scrub whips and keeping them weed-free;

  • Installing bird and bat boxes around the site’s perimeter; and

  • Planting an arc of scrub in the south western corner of the solar farm, within the field margin.