Fortunes Of The Sussex Duke In 2012

The following article is the 'Species Champion' summary for Duke of Burgundy, reproduced from the Sussex Butterfly Report 2012 - Issue 5, Spring 2013. How did the butterfly do on your patch?

In line with most of our species, the Duke of Burgundy had a difficult time in 2012, courtesy of the Great British weather. In the last couple of issues it has been very satisfying to publish bar charts demonstrating year-on-year increases in the Sussex population of this nationally threatened species. We hope to do this again in the years ahead, but this season was all about damage limitation. Thankfully, all remaining ‘Duke’ sites in Sussex are under active management and in good condition, a situation which will soften the impact of the extremes in weather experienced this year. Despite the significant drop in the number of butterflies recorded on most sites, abundance figures remain higher than for many years prior to 2010 (total 2012 count = 360).

In most locations we saw a reduction of between 50% and 75% on 2011 totals, although one or two sites remained virtually unscathed. The one area that gives genuine cause for concern is in the far west of Sussex, close to the Hampshire border. Although the relentlessly poor weather severely restricted surveying opportunities, no butterflies were seen at either Harting Down or Treyford Hill. It will be very important to assess the situation here as a matter of urgency in 2013. Looking at the bigger picture, it will be surprising if at least one or two of the last remaining UK colonies, of which there are approximately 90, has not been lost; in some parts of the country the entire flight season was conducted under grey skies.

The first male was seen at Heyshott Escarpment on 22nd April, but it would be another 5 days before the second appeared in a wood near Arundel. This slow, faltering start was typical of all our spring species this year. It was not until the third week of May that the Sussex population peaked, as the majority of individuals held back from emergence, in anticipation of better weather. Butterflies can delay the completion of their life-cycle in this manner for up to three weeks or more, but by doing so they suffer a significantly increased mortality rate. As the point of no return is reached, desiccation becomes a major factor, and the total number of healthy adults produced will fall.

On the cooler, north-facing slopes ‘Dukes’ were still emerging during the last week of May and a timely spell of much better weather will have saved the local population from potentially much worse. The last survey this year, conducted on 29th May, recorded 57 specimens over 4 different locations, so the butterfly probably persisted until mid June.

One of the many different factors which influence the Duke of Burgundy population from year to year is larval survival rate. In some years the species suffers particularly badly at this stage of the life-cycle, through droughting of the Primula food-plants; droughting was not a problem during the summer of 2012!   

With all of the ongoing habitat management work for this species across West Sussex, I am optimistic that ‘the Duke’ will make a rapid recovery from this downturn in its fortunes. As always, thanks are extended to those who provide such tireless support in conserving this species, most notably the South Downs National Park Authority, Murray Downland Trust, Norfolk Estate, West Dean Estate and other local landowners.





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