RICHARD WILLIAMSON: Butterflies are our coalmine canaries in changing climate

An orange-tip butterfly feeding on a cowslip flower
An orange-tip butterfly feeding on a cowslip flower

BACK in 1976, 50 of us butterfly buffs started recording those lovely insects every week to see what was happening to their numbers.

Today there are more than 1,000 people doing it. Most work in the National Parks.

Twenty of them record in the South Downs NP.

From Cape Wrath to the Lizard, we pick the best day of each week from the first day of April to the last week of September, walking exactly the same set route at exactly the same slow pace, noting every butterfly within a three-metre distance all around. It is a pretty accurate nationwide sample.

I shall start my 38th recording year this week as usual at Kingley Vale.

My wife did the recording for West Dean Woods for 30 years, but recently handed over to Mike Bridger and his wife.

Annual reports funded by nine major UK conservation bodies from Natural England to the charity Butterfly Conservation tell the world what we have found over the past third of a century for the 59 species that regularly occur over the country.

Here are some results from the latest – 2011 – report.

Orange-tips had their best year ever.

This was largely due to the perfect weather two years ago when March was warm and dry, April temperatures reached 24 degrees C and much of May was warm. My photograph shows a male feeding on a cowslip.

A total of 22 species showed their earliest emergent date and another ten their second earliest. Orange-tips and green hairstreaks were three weeks earlier than the year before. But then the weather declined and 2011 actually turned out to be 18th-best out of 36 years of records. So, bang in the middle.

The main concern is the long-term slide of several species in decline. Among these are the high-brown fritillary and, most surprisingly, the once-common small tortoiseshell.

Back in 1964 I can remember small torts swarming on buddleia in Chichester’s West Street near the junction with St John’s Road (by the old cinema) when I counted 240 feeding together and more in front of the chapel in St John’s Road itself.

My results for Kingley Vale combining all species show a regular graph of highs and lows in a seven-year flow that looks like a hospital heart graph.

The UK ‘heart graph’ is roughly similar. Around 17 million recorded butterflies have gone into that data, in a quarter-of-a-million site visits.

Butterflies, having rapid life cycles, being highly sensitive to environmental conditions and climate changes, are very suitable indicators to us of how healthy our world remains (equivalent to the canaries down coalmines in the old days).

With the projected five new ‘Birminghams’ by 2050, how will the countryside look to our descendants? We must keep farmland free to produce food, but will national parks become unable to sustain the onslaught of millions more human feet?

The Butterfly Monitoring Scheme (UKBMS) will continue to show what we are doing to our habitat. Check it out on its website.

Meanwhile, I will of course, be reporting here news on my patch as the season progresses.