Nature 2004 August

Stop, Look and Listen – Nature is evolving all around us

Looking back to June, despite memories of a disrupted Wimbledon fortnight, rainfall at 34mm (1.3in) was significantly less than June last year. We were blessed with warm weather during early June including 30.6°C on the 8th. (Cambridge at 31.5°C just beat us to be hot-spot for the UK.) The unsettled weather in the second half of the month, which resulted in the familiar power cuts, spilled over into July, with short, sharp downpours producing cool days and chilly night-time temperatures (4.5°C). Indeed as I pen this, St Swithin’s Day (15th July) is just a few days off. Last month I commented on English folklore expressions. The well-known rhyme about St Swithin as you may know goes:-

“St Swithin’s Day, if it does rain; Full forty days, it will remain;
St Swithin’s Day, if it be fair; For forty days, t’will rain no more.”

St Swithun (as it is should be spelt) was the Saxon Bishop of Winchester in the 10th century. On his deathbed, so the story goes, he declared he wanted to be buried outside, where he would be trodden and rained on. The monks initially acceded to his wish but the on 15th July 971 they were interring his remains in a shrine in the cathedral, at which point the heavens opened and a heavy rainstorm ensued. The legend has it this occurred again on the next anniversary leading to the rhyme we recite today. Maybe by the time you read this the latter part of July will have been a washout. I doubt it somehow though as the odds are very much stacked against it. Met Office records suggest it has never occurred since records began, so the survival of this lore for over 1000 years must say something about our preoccupation with the weather.

Out and about in August are some of our more highly evolved and spectacular insects. First on this list are the dragonflies which can be distinguished from their cousins the fluttering damselflies, by their larger size and fast and purposeful flight. Despite the lack of streams and rivers high up in the Chilterns there are sufficient ponds around us, where the nymphs develop over two years before metamorphosing into adults, to support a healthy population of both insects. Dragonflies are territorial and aggressive hunters often encountered patrolling hedgerows and gardens on the lookout for prey. Hence the name ‘hawker’ given to larger (up to 4in) species which can fly at up to 30mph but live only a month or so. Although harmless to us, they possess strong jaws that can be heard clicking as they buzz you, which are capable of grabbing other large invertebrates on the wing, including smaller dragonflies. Those displaying the most colouration are usually the males and the green and blue bodies are the result of light refraction or iridescence.

 

Another group of highly evolved insects making their presence known these months are the grasshoppers and crickets. As a rough guide, to tell them apart the grasshoppers have short antennae whilst crickets have long, whip-like ones. But first you have to find them, so listen out for the sounds. Although not foolproof, the short intermittent chirp heard in the daytime is more often a grasshopper, while the longer chirring sound coming from the hedgerows, particularly during warm evenings, is probably one of the many bush-crickets. Only the males make these sounds or ‘stridulations’ by scraping their toothed legs along their wings (grasshoppers) or wing against wing (crickets).

 

August and September also provide an abundance of fruit and seed for many garden birds. This is essential for the young born this year and to build up the fat supplies of all so they have a better chance of surviving the winter. I predict, from the type of weather we have experienced over the past 12 months, a better than average crop of wild fruit, both hedgerow berries and apples, etc, this year. But many of our commoner garden birds also rely on the ‘spent flowers’ of perennials and shrubs in our backyard prairies. For example, each variety of our native finches (green-, gold-, bull-, and chaffinch as well as the sparrow and siskin) has evolved a different-shaped beak and has become specialised in extracting particular seeds. So to give them a chance to take there fill and do you a favour at the same time by removing insects harboured lower down on stems and leaves, try to desist from dead-heading for as long as possible.

 

All the birds and insects I have selected this month are excellent examples of specialisation within the animal kingdom and how, over many millions of years they have evolved and diversified through survival of the fittest. In fact it was a study of finches’ beaks (in the Galapagos) by Charles Darwin, which as you may know led to explanation of this phenomenon and caused a stir amongst the creationists of the time when, in 1859, On The Origin of Species was first published. Previous to this the belief had been that the earth had been created in 4004BC. This enlightenment also enabled understanding about the fossil record, including how dragonflies like those we can see today could be found in carboniferous rock over 300 million years ago.

So to enjoy the sights and sounds of some more marvellous examples of natural selection my suggestion for a walk this month is to take to the ‘high ground’. The open farmland of St Leonards / Buckland Common as well as along the ‘mountain’ in Hawridge (see local history walks – www.cholesbury.com) are excellent opportunities to listen out for skylarks. The trend towards more intensively grown summer cereals has taken its toll on the skylark in recent years. However, in these parts because the variable soil conditions produce some more sparsely cropping areas in fields this may be encouraging better survival rates amongst the fledglings. If out for early morning or late evening walks also look and listen out for noisy flocks of sand or house martins which congregate in late August, before their annual migration to Africa and ahead of their close relatives the swifts and swallows.