How cows are helping one of Britain's rarest butterflies

How cows are helping one of Britain's rarest butterfliesTo play this video you need to enable JavaScript in your browser.This video can not be playedFigure caption, How volunteers help one of Britain's rarest butterfliesByTomos MorganWales correspondentPublished1 hour agoWith its brilliant orange wings and black markings, the high brown fritillary butterfly was once widespread in Wales and England.But now it's one of the rarest of all British butterflies, with it numbers declining by 62% since 1970.One reason is its incredibly specific requirements to survive."They are the pickiest," says Paul Dunn, who for more than 30 years has been working hard among the bracken of the Alun Valley at Old Castle Down, in the Vale of Glamorgan, to revive the butterfly's fortunes.And now, the volunteers have enlisted the help of a far more common animal, by allowing cows to graze on the site.Image source, Paul DunnImage caption, Butterfly Conservation says there has been a dramatic decline in numbers of high brown fritillaries since the 1950s"Almost everywhere else in Britain it's dying out and yet here we seem to be hanging on and doing very well. It's very positive," he said.High browns need a delicate combination of bracken and common dog violet."Traditionally bracken was used as animal bedding, but less and less people use it now they can get straw," says Richard Smith, who has been with Paul since the start, in 1993.Too much bracken inhibits the growth of the dog violet, the food source for the caterpillars. But the plants also serves another purpose."It hasn't been able to adapt its life cycle away from this need from a certain temperature on the ground. The cutting of the bracken is essential."Image source, Paul DunnImage caption, Just enough bracken... but not too muchWhen this coarse fern is trimmed it is "litter", the dead leaves on the floor that create a warmer ecosystem underneath which...