Saturday, 23 August 2008

Stinking Willie

Over recent weeks the blocks of forest clearfell have been carpeted with the bright golden yellow of ragwort, not just a few plants scattered here and there, but many thousands of them. This striking spread of late summer colour, which practically glows against the backdrop of dark conifers, is a welcome sight for me, but for many landowners the ragwort is a far less welcome plant. Those who keep horses may spend many hours pulling this agricultural ‘weed’ from paddocks and pastures, hoping to spare their animals from the irreversible cirrhosis of the liver that comes from eating quantities of the plant. Interestingly, while horses and other grazing animals normally avoid eating the flowering stems, they will take it when it has died and dried out; presumably they are unable to identify the risk it poses once it has lost its characteristic colour. Curiously, sheep appear to be immune to its effects and may even relish it.

The general antipathy directed towards the ragwort can be seen in many of its local names, from ‘mare’s fart’ in Cheshire to ‘stinking Willie’ in Scotland. The latter name is a reference to the Duke of Cumberland, whose victory at the Battle of Cullodon Moor earned him the nickname of ‘butcher’. It is reported that ragwort was spread around by his troops during their campaign. Another local Scottish name for the plant is ‘wee-bo’, meaning ‘little devil’. It is clear from such names, and indeed from the reaction of friends and colleagues to the plant, that it is an unwelcome part of our arable flora. Yet, I have always associated ragwort with the cinnabar moth, whose striking black and yellow caterpillars feast upon its foliage.

Ragwort is known as ‘St. James’s herb’ in certain other countries and even here in Britain the same association has been made (through the alternative name of St. James’s wort’). This association may stem from the fact that the plant is in flower on St. James’s Day (25th July) or, alternatively, it may have something to do with the plant being used to treat the sores and ulcers which afflicted pilgrims visiting the shrine of St. James in Santiago de Compostela (Spain). There are also references in old herbals of the plant being used as a treatment for gout, sciatica rheumatism – in each case the green leaves being used as a poultice. The ragwort has even become a national flower – the ‘cushag’ of the Isle of Man.

It is easy to dismiss the ragwort as a troublesome and unwanted neighbour. However, this ignores the long interplay between Man and plant, with the plant acting variously as weed, poisoner and healer. For me, such associations add to its fascination.

Friday, 22 August 2008

Eyes and ears for bats

Returning from the office the other evening, I stopped on the Nun’s Bridges to scan the river. It was not quite dark and there was always the possibility that I might spot one of the local Otters. Needless to say, my luck was out and no dark shape was to be seen cutting it’s way across the surface of the slow-moving waterbody. However, other mammals were abroad and I was soon entranced, watching the dancing silhouettes of a dozen or so bats as they hawked for insects low above the water. This small cloud of tiny, delicate mammals, ‘chattered’ away as they circled too and fro to snatch midges and other small flies.

The chattering calls, whose intense high-pitched pulses I can still just about pick up with my hearing, are used to target prey and derive from a technique known as echolocation. This is really a highly developed form of sonar, the bat sending out short pulses of intense sound and then monitoring the returning echo with its sophisticated hearing to build up a ‘map’ of its surroundings. Although many people are bewildered by the apparent complexity of bat echolocation, to the bat it is just another component of its sensory armoury – much like how we might view our sense of sight or taste. Bats make and hear sounds in the same way as most mammals; the echolocation pulses are generated in the larynx and the resulting echoes are picked up by their ears. Admittedly, the larynx of a bat is proportionally bigger than our own, relative to body size, because the call has to carry a great deal of energy in order to produce a useful echo. Most bats emit the echolocation call through their mouth but there are species, like the horseshoe bats, where the sound is emitted through the nose.

Because the echolocation calls of bats often differ in their core frequency, it is possible to identify the different species by the pattern of the call and the frequencies over which it occurs. For example, the calls of Daubenton’s Bat start at about 85kHz and drop to about 32kHz, with a peak in intensity around 45kHz. Simple bat detectors, which convert the inaudible calls to a frequency we can hear, can help you split bats into rough groups but more complex detectors, coupled with computer software, are needed to separate the calls of species which are similar in their outputs.

The size and behaviour of the bats hawking over the river suggested that these were one of our pipistrelle species, although there may well have been a Daubenton’s Bat or two in with them. I will have to bring my bat detector down to the river in order to find out.

Thursday, 21 August 2008

Have moth trap, will travel

You know how it is when you go away for the weekend; the list of things that you need to pack. In addition to the essential clothes and toiletries I often take my moth-trap, dozens of small sample pots and various field guides to Britain’s moths. I know that I am not alone in this behaviour and there is a growing army of moth enthusiasts who not only run traps at home each evening but also seem hard to separate from their trap when they go away. Much like birdwatching, one of the joys of moth trapping is seeing something new and, since different moths live in different habitats or different parts of the country, it is easy to see the appeal of running your trap somewhere completely different.

A moth trap works by drawing moths in towards a bright light, normally a mercury vapour lamp, which produces light of a different wavelength to that of standard household bulbs. Any moths which collide with the bulb, are stunned very briefly and drop into a collecting box below. This box has a narrow entrance, so escape is difficult, and the moths soon settle amongst the pile of egg boxes added to the box to give them some cover. Early the next morning, the moth-trapper can rise from his or her slumber and check the contents of the box. Depending upon location, time of year and weather conditions the trap can contain just a few moths or it can contain thousands. After logging what has been caught the moths are released to continue with their lives.

Last weekend my trap accompanied me to my parent’s garden on the edge of a market town among the oak and beech woodlands of the Surrey/Sussex border, where a very different suite of moths from those present in my small urban garden are to be found. Sure enough, come morning there were just in excess of 170 moths in the trap of several dozen different species. Among these were common and widespread species, like Large Yellow Underwing, Brimstone and the Dunbar, but there were many others that I don’t tend to catch at home. These included my first ever Maiden’s Blush (no mischievous smirks please) and Small Phoenix, not to mention two rather stunning black and white moths known as Black Arches. I never cease to be amazed by the sheer diversity of moths, the combination of shapes, sizes and colours. Most casual observers, encountering the more familiar moth species, will be completely unaware of just how beautiful many of our moths our. If you have never seen the results of a moth-trapping session then I urge you to go along to a local moth-trapping evening. You will not be disappointed.

Wednesday, 20 August 2008

A fortunate find

The Slow-worm is one of those creatures which I rarely stumble across these days, perhaps because it spends the greater part of the year hiding underground or in deep cover. Being ‘cold-blooded’ the Slow-worm tends to thermoregulate by keeping its body in contact with warm surfaces. While our three snakes tend to bask out in the open, the Slow-worm will often warm itself by settling under a piece of tin or other refuse that absorbs the sun’s warmth. Of course, it is with the snakes that the Slow-worm is sometimes confused; despite its cylindrical body and absence of external legs, the Slow-worm is not a snake but a harmless ‘legless’ lizard. Unfortunately, ignorant householders, panicked by the ‘snake-like’ appearance, may soon dispatch any Slow-worm that turns up in their garden. This is not only bad for the Slow-worm but also for the gardener, because Slow-worms eat good numbers of common garden pests, like slugs. Slow-worms differ from snakes in having a visible eyelid and smooth body scales. In addition, the cylindrical body shape is uniform along most of its length, whereas in a snake there is a clear narrowing behind the head to produce a discernable ‘neck’.

Hibernation ends in March and throughout the spring adult Slow-worms indulge in breeding. Mating is a fairly aggressive affair, with the adult males grabbing and holding females by their head. The resulting young are ‘born’ in September or October, hatching from their eggs almost immediately they are laid, giving the appearance of live birth. These young Slow-worms are just eight or nine centimetres in length and have the colour of newly minted metal. As adults they become a shiny metallic grey-brown, like well-aged bronze, often with thin longitudinal stripes of chocolate brown. Some of the older males are adorned by a pattern of pale blue spots, scattered along their head and flanks.

My most recent Slow-worm encounter happened just the other week and was unusual in that the lizard was out in the open, part way across a gravel track. I normally encounter them when turning over sheets of corrugated tin or refuse on areas of rough grassland or heathland. This particular individual had clearly shed its tail at some point in the past, either lost during courtship or shed to distract a would-be predator. The tail is physically shed (as opposed to being pulled off) by the lizard, muscular contractions pulling apart the tail at a point of fracture within the vertebrae. Once shed, the tail will flex and spasm for several seconds, sufficient distraction for the lizard itself to slip away. I managed to take a few photographs and then the Slow-worm was gone, disappearing into thick cover.

Tuesday, 19 August 2008

A shimmering carpet of blue

The chalk escarpments of southern England are a second home for me; their steep slopes providing vantage points from which to take in that ‘green and pleasant land’ triumphalised in Blake’s poem ‘And did those feet in ancient time’, better known as the hymn “Jerusalem’. I grew up here, in the verdant growth of the heavily wooded Surrey Weald, with the chalk downs rising to the south and framing my youthful years.

I return to the woods and downs fairly often, particularly so at this time of the year when the chalk escarpments have an added draw, alive as they are with a shimmering carpet of blue butterflies. Many of the remaining chalk grasslands around Winchester support good numbers of chalkland butterflies, some of which will have been on the wing much earlier in the year, but for sheer numbers it is the August mix of Chalkhill Blues and Silver-spotted Skippers that is most impressive. The steep slope at Old Winchester Hill, edging the Meon Valley, had a peak count of 1,000 plus Chalkhill Blues last year – a poor comparison though when compared with the 6,800 seen flying together back in 2006. The short turf of a chalk sward, rich in flowers and invertebrate life, is a good backdrop against which to watch the male blues as they drift back and forth across the turf in search of a receptive female. The skippers are less leisurely in their flight, whizzing around to nectar at flowers, challenge rivals and to seek out a mate. The short sward is important for the blues because these particular butterflies spend much of the year living within the nests of ants and the success of the ants themselves is heavily influenced by temperature. A hot, south facing-slope provides just the right amount of warmth for the ants but if the vegetation gets too tall, it shades out the ant nests and the required temperature cannot be maintained.

Of course we have our own band of chalk here in East Anglia, skirting the western fringes of Norfolk and cutting south through Cambridgeshire and Hertfordshire. I’ve written before of the Chalkhill Blues at Therfield Heath, just west of Royston, explaining how the small population at this site was once much bigger, drawing in collectors because of the incredible variation present within the butterflies themselves. However, these days the numbers here are insignificant when compared with the spectacle of the Hampshire downs and the hundreds or thousands of blues that can be seen on the wing together.

If you are ever in Hampshire during late July or early August make an effort to visit some chalk downland; you won’t be disappointed.

Monday, 18 August 2008

A chance encounter

The vast regimented ranks of plantation forest can seem lifeless for much of the year; dark and foreboding they stand in silence, with barely the whisper of a birdcall to stir them from apparent slumber. To some extent this all changes in summer, as countless Goldcrests and Coal Tits broadcast their thin, territorial songs from high in the canopy. Later in the summer, there are even more signs of activity, as small family parties of tits, leaf warblers and finches move throughout the plantations in search of feeding opportunities. Such flocks are commonly encountered, mobile though they are, and on occasion the path of a mixed flock may follow your own; your walk accompanied by a small chorus of soft tweets, churrs and weeps.

A two-hour walk around the woods at Middle Harling the other morning brought several encounters of this nature, with the soft flutterings of a Long-tailed Tit flock the first welcome diversion from the low monotone buzz of many flies and midges. Later in the walk it was a very different sound that caught my attention. In a shelterbelt on the edge of an area of clearfell I chanced across a young Long-eared Owl, potentially taking its first wing-beats towards full independence. While it may have left the nest several weeks ago it could still have been dependent upon its parents for much of its small mammal or small bird diet.

Throughout the various stages of their lives Long-eared Owls make some of my favourite sounds. As nestlings they make a short ‘pssee’ call which, although not much to write home about when uttered by a single chick, has a wonderful jingling quality (like jingling small coins in your pocket) when several chicks call together. Then, later in life, there is the food begging call of older youngsters, notably those that have left the nest. This is best described by thinking of the sound made by an un-oiled hinge. It was this call that first alerted me to the bird, difficult to see well as it sat in thick cover.

It has been a couple of years since I last saw a young Long-eared Owl so it is good to know that pairs are still breeding in the forest. The Long-eared Owl is one of those species about which we know surprisingly little, largely because they are widely but thinly distributed, fairly secretive in habits and predominantly nocturnal in activity. The most recent estimate suggests that there are somewhere between 600 and 2,000 pairs in England, breeding in coniferous plantations, mature hedgerows and shelterbelts. Numbers are known to fluctuate from year to year because of variations in prey availability and may be swelled in winter by the arrival of migrants from further north.