Friday, 14 July 2017

Oak Topping and Sallow Searching

As a birthday present work colleagues thoughtfully bought vouchers for me to go on a purple emperor butterfly safari at Knepp. Despite several previous attempts I have not seen a purple emperor.

Male purple emperor. Photo: Martin Landy

What makes Knepp landscape so special? It is part of a re-wilding experiment. In 2004 internal farm fences were removed and fallow deer, longhorn cattle, Tamworth pigs introduced at low stocking densities and allowed to graze where they will. So in a way an undirected conservation project, just wait and see what happens. This has developed under the influence of Frans Vera whose theory was that the wild wood was not continuous cover but much more of a savannah like landscape of extensive open and interconnected glades maintained by grazing animals surrounded by scrub and high forest. The livestock is in commercial meat production but I suspect the real commercial add-on is the development of several types of wildlife safaris, honesty box shop and campsite.

This particular safari was lead by the duo Matthew Oats, National Trust, and Neil Hulme, Sussex Butterfly Conservation, both great observes of butterfly behaviour. We were also joined by Frans Vera who was pleased to show us regenerating oaks protected from grazing long horn cattle by a mantle of surrounding thorny shrubs, and Charlie Burrell, 10th Baronet of Knepp, the land owner

“Did anybody really have to leave at 3pm?” was the first question as these were great enthusiasts and the emperors will fly until the early evening if warm enough. Matthew Oats was later checked out by a purple emperor whilst having an open air bath at Knepp’s campsite. Re-wilding was not about the species but human reconnection with nature.  

What has happen with this re-wilding experiment? The numerous small fields lined with hedgerows containing majestic oaks have been invaded with sallows. This is a perfect habitat for the purple emperors.  

Purple emperor egg on sallow. Photo: Martin Lan

The adults can look brown, purple or blue depending on the angle of light and sometimes look like they have different coloured wings. The butterflies do not visit flowers but feed on aphid honey dew and sap weeps on old oak trees. The males claim the top of the trees as their territory and have dog fights with other males over poll position there. This is described as oak topping.  

In poll position on an oak. Photo: Martin Landy

They also can be seen diving down to search the sallow, usually in the morning, for the much more elusive recently emerged empress who will be looking for potential egg laying sites on the sallow.

Matthew has been a purple emperor enthusiast for many years. In 1975 he found about 130 emperors in a whole season across many sites. On 21st June at Knepp this year he recorded 148 in one day! A  British record. Matthew now finds purple emperor numbers beyond his imagination. The view of the purple emperor has changed from a butterfly of deep woods to one of a much broader environment of hedgerows with sallows. The butterfly has been squeezed by human activity especially against sallows but is now bouncing back.
As we walked around on the tour Matthew notched butterfly count on his forearm and reached an agreeable count of 56, with only about 4 recorded as female.  

Matthew Oats keeping a tally. Photo : P. Loughnane

The bolder white banding of the female gives her away.

Purple emperor female. Photo : Martin Landy

We stopped several times to view purple hairstreak butterflies flying around the oak canopy with Neil being particularly enamoured by them only to be rebuked by Matthew to “stop hairstreaking’’. Despite the emperors flying 15 metres above us in the oak canopy, being large butterflies (wing span range male to female: 75-84mm) they were still easily seen, with the finest views of the males is when they are  searching the sallows beneath the oaks. The best view of all was an empress perched at 2 metres.

At Knepp there are safaris of general interest and specialist ones with top conservators such as Dave Coulson on bees and Ted Green on ancient trees. Well worth a visit and a substantial picnic half way through the full day tour. You will come back enthused!

Paul Loughnane

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