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Case Study: Dstl Porton Down
A three year study of butterfly populations using newly established arable field margins at Dstl (Defence Science and Technology Laboratory, part of the Ministry of Defence) Porton Down indicates that rapid and sustained utilisation of this habitat was achieved, not only by ‘farmland’ butterflies, but also by less common species including BAP species.
An initial survey of 111 arable field boundaries carried out in 2005, prior to margins being sown, recorded a total of 211 butterflies of 14 different species. Only one BAP species was recorded, the Small Heath.
Field margins were sown in 2005/06 and comprised mixtures to benefit butterflies, small mammals and other invertebrates, wild birds and game birds.
In 2006, during the first year of margin establishment, 202 margins were surveyed. A very dramatic increase in butterfly populations led to 6980 butterflies of 26 species being recorded. Exceptional weather during June and July, when the survey was undertaken, enabled the value of margins to be fully expressed. Of the 2 BAP species recorded in 2006 the Small Heath was present on every margin and a singleton Small Blue was seen.
The survey was repeated in 2007 during less advantageous summer weather. A total of 144 margins were examined in May, June, July and August and 1415 butterflies of 24 species were recorded. The development of populations on margins had progressed with, despite the weather, species such as Marbled White increasing in number. Excitingly BAP species had been augmented by the appearance of Dingy Skippers and Marsh Fritillaries in May and Grizzled Skippers in June. The presence of the Marsh Fritillaries on an arable margin was totally unexpected and led to the discovery of a new population at Porton Down.
This exercise has shown what can be achieved for farmland butterflies, including some BAP species. Further developments will include the establishment of larval foodplants in margins and, most importantly, the dissemination of this success to other landowners in the vicinity to increase the establishment of favourable habitat within the farmed landscape.
