Friday 19 October 2012

High Flying Painted Lady Travels Well

We may not have been seeing many butterflies around Atholl for a good few weeks now but they are still managing to make the press (if not the major headlines). There are several stories in the news today covering the publication of a scientific study that has discovered exactly what happens to Painted Lady butterflies (Vanessa cardui) over the winter.

Painted lady (Vanessa cardui). Image rights: Butterfly Conservation

The previous, collective best guess of the scientific community was that many of the individuals that migrate to Britain in the summer couldn't make it back to warmer climes when the weather arrived and so ended up dying here. However, this newly published study based on survey data from 2009 shows that they do in fact manage to migrate back to the desert edges of Northern Africa, the Middle East, and central Asia. It's just that they have been flying too high for us to notice them previously. Using a combination of "citizen science" in the form of 60,000 volunteers in 66 European countries and islands to record of sightings of the elusive butterflies' autumn migration and a radar station in Hampshire, capable of detecting and tracking individual objects as small as an aphid at a range of 1.2 kilometers  the science team discovered that the Painted lady has been soaring away at altitudes of 500 metres (half a kilometer). This is impressive flying for a small insect, and it also enables the butterfly to travel at speeds of up to 30 kilometers per hour when the wind is favorable, enabling them to keep well ahead of the advance of winter, which only advances around 16-24 kilometers per day.

Comparisons have been made with the epic migration of the Monarch butterfly in America that travels 2,000 miles across the continent each year. The really spectacular thing about the Painted Lady though, is that not only do they travel intercontinentally, crossing oceans, but they take up to 6 generations (all born in a single year!) to travel to their summer feeding grounds in the UK and then back to 'over-winter' in the equatorial regions. All in all, a staggering round trip of 9,000 miles. The butterflies are constantly on the move, looking for new food sources and eventually places to lay their eggs so that the next generation can continue the journey.

It's amazing to think that these visitors we get up here each year are part of a nomadic tradition, reaching Scotland as the turning point of the outward leg of their annual journey, before their offspring carry on the journey and eventually return home for the whole trip to start again with a whole new series of butterfly generations.

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