Heath Fritillary conservation on Exmoor

23/09/2006 00:00:00 In the early 1980s the Heath Fritillary butterfly was on the verge of extinction. Only a handful of small colonies in East Kent and the Tamar valley in Cornwall remained. The future was bleak and the butterfly was given protected status under the 1981 Wildlife and Countryside Act. A breakthrough came with the discovery of a large population on National Trust land on East Exmoor. On 25 June it will be 25 years since this momentous discovery on Exmoor. Since then the Heath Fritillary has been on a roller coaster ride of population crashes and recoveries, often weather induced.

On 25 June this year you will be very lucky if you see a Heath Fritillary at Exmoor. The fair weather we experienced during April means they will have emerged earlier and finished earlier.

Shortly after the discovery in June 1982 Dr. Martin Warren, now Chief Executive of the charity Butterfly Conservation, organised a survey to ascertain the extent of the Heath Fritillary on Exmoor. The results were encouraging and showed a significant population. He said: ‘This discovery was one of the two great British butterfly discoveries of the 20th Century. The Heath Fritillary was then our most endangered butterfly and we were thrilled to find further colonies in a totally new region.’

Further surveys in 1989 found a total of 29 colonies on Exmoor, many of them large and most on National Trust land. These surveys also brought to light some more intriguing developments for the Heath Fritillary. Previously it was thought of as woodland and wood edge meadow butterfly, but the surveys showed it had started to breed on common cow-wheat which is an annual and is semi- parasitic on the roots of bilberry. This meant that conservationists had to start from scratch and learn this new ecology. Population collapse
During the early 1990s the Exmoor colonies took a downward plunge and suffered a huge collapse. By 1999, 14 of the 29 colonies were lost and by 2004, another eight had gone leaving the Heath Fritillary in a perilous position. This devastating collapse coincided with a decline of grazing, particularly cattle grazing, and a drop in burning on the moor.

In a bid to reverse this downward trend a partnership was formed between the National Trust and Butterfly Conservation. In March 2000, the National Trust burnt a large area of bracken which had developed over a former main breeding area (Bin Combe) - and then sprayed off the live bracken regrowth that July. This had dramatic results and Heath Fritillary conditions instantly improved.

To make sure that this was the right approach large experimental plots were set up on National Trust land at Halse Combe where a large colony was lost. With the help of Butterfly Conservation different techniques were trailed to see which produced the most benefits for the Heath Fritillary. The results showed that burning and then spraying off works better than others such as burning and cutting.

Following this restoration method means the Heath Fritillary has returned to Bin Combe and is thriving again. Currently conservation work is focused on finding a more sustainable solution than relying on herbicide to take back the vegetation.

Matthew Oates, butterfly expert at The National Trust, comments, ‘Burning, cutting and spraying with a bracken herbicide has rescued the butterfly. Last year there were an estimated 10,000 adults at one former breeding site. But these are emergency restoration techniques. We now need to find more environmentally-friendly and sustainable solutions.’

The Heath Fritillary flies from late May to late June, with numbers usually peaking mid June. The most visually stunning location for the Heath Fritillary is the slopes of Dunkery Beacon, the highest point of Exmoor.