Saturday, 25 August 2007

Disease may benefit nesting birds

A walk through Thetford Forest gives the impression that you are in a huge monoculture; the ranks of immense, silver-grey trunked conifers stretch away into their dark, unwelcoming distance.  Yet there is some sort of diversity here. Where the stands of conifers run alongside a road there is a thin veneer of deciduous trees, oak and beech, planted perhaps to give passers-by the impression that the woodland is natural. Within the acres of plantation woodland itself, there are stands of different age, collectively providing a varied micro-habitat for birds, animals and plants. While the younger-aged stands support important species, like nightjar and woodlark, mature stands provide nesting sites for crows, long-eared owl and goshawk. There is even some degree of diversity to the types of conifers that have been planted and this can also have an effect on which bird and animal species are present.

Two of the most significant pines in the forest are the Scot’s pine, which has not been a native in England for some 4,000 years, and the Corsican pine, a species that is commonly planted on dry, sandy soils across southern England. The Scot’s pine is a familiar part of the Breckland landscape, its twisted forms often present in the exposed hedgerows and shelterbelts. Many of these were planted during the enclosures of the 19th Century, as they were thought to be a better choice on such light soils than the more traditional hazel or hawthorn.

If you were to map the distribution of crow and bird of prey nests within the forest, you would most likely see a preference for nesting in Scot’s pine over Corsican. This is because of the different shape of the two trees, that of the Scot’s pine being better suited for supporting the nests of crows. Crows prefer to nest slightly down from the top of the tree, generally on a strong limb or in a stout fork against the trunk. Since a new nest is built each year, the old nests become available for those birds of prey, like hobby, that tend not to make their own nest. Over the next few years we will see a change in the types of conifers being planted within the forest. This follows an outbreak of red band needle blight disease. In Britain, the disease is caused by a fungus called Dothistroma septosporum, which has hit Corsican pines across a wide area. A moratorium on the planting of Corsican pine will be in place for at least the next five years, while research into the disease is carried out. Consequently, we are likely to see more Scot’s pine, larch and sitka spruce being planted, which should benefit future generations of crows.

Friday, 24 August 2007

Musical crickets

August is a good month in which to look for crickets and grasshoppers. After hatching earlier in the year, many species will by now have passed through a succession of nymphal instars to reach adulthood. From the rank grass outside the entrance to work, the drawn-out, high-pitched songs of male roesel’s bush crickets mix with shorter bursts from field grasshoppers. These bursts of noise are invariably the result of stridulation – the rubbing of one body part against another to make a sound. In the case of the bush crickets, modified forewings are used to produce the sound, which is then amplified by a further modification of the wing. In grasshoppers, the sound is produced by modifications to the hind legs – namely a series of stridulating pegs – which are rubbed against the most prominent veins of the flexed forewings. Some observers refer to the songs as ‘chirps’ but this can be somewhat misleading. Strictly speaking, each song is comprised of a number of syllables, with each syllable representing one complete upstroke and one complete downstroke (think of a violinist). A series of these syllables may be strung together and are then referred to as an ‘echeme’. Hence, a field grasshopper will produce an echeme of 9 syllables length, lasting some 0.2 of a second. Interestingly, the oak bush cricket lacks the wing modifications seen in its relatives and so does not stridulate. Instead it produces a drumming sound by tapping its hind legs against whatever it happens to be perched upon.

The oak bush cricket is rather unusual in two other respects; it is the only British cricket to be almost entirely carnivorous, feeding on a wide range of other insect species, and it is our only completely arboreal species. Oak bush crickets are sometimes attracted to light and the species may be found indoors or even appear in moth traps. This may explain why this small bush cricket is so often encountered across the southern section of Britain.

Another cricket that has been much in evidence in recent days is the speckled bush cricket. This is a larger beast, reaching up to nearly two centimetres in length, which can be found in its adult form from August through into November. A large female, with her beautiful, scimitar shaped ovipositor, was on our grape vine the other day; a pale green colour – with tiny dark spots – she was difficult to pick out on the leaves, reinforcing her unobtrusive nature. Despite her larger size, she is largely vegetarian in habits; a trait which could have explained the damage to the vine that had appeared within the last week. Still, I would happily tolerate this, knowing that such a fine insect was in residence.

Thursday, 23 August 2007

Birdwatchers flock to Bird Fair

One of the beauties of birdwatching is that it can be either a solitary or sociable hobby, depending upon the mood that takes you. There are times when I seek out the attachment with nature that comes from birdwatching alone on my local patch or on one of the quieter stretches along the Norfolk coast. I can watch a bird, undisturbed by the comments of others, and really appreciate its character. At other times, I enjoy the comradeship and happy banter that is derived from the company of other birders, seeking out some rarity or combining a spot of birdwatching with a pub lunch or cake-filled visit to a tearoom.

The social side of birdwatching was brought home to me over the weekend, while working at the British BirdWatching Fair, held annually at Rutland Water. This event, the biggest of its kind in Britain (and quite probably Europe), brings together birdwatchers from across the continent. Many come to feast on the multitude of stands selling and promoting everything from binoculars and books, to birdwatching holidays and bird conservation. Others delight in the opportunity to listen to talks or to question ornithological experts on bird identification and behaviour. It is also a place to meet old friends, many of whom I only see at the bird fair, and to make the acquaintance of others who, like me, delight in watching and studying birds and other wildlife.

There is always a real buzz about the place and most visitors must come away from the fair pumped full of enthusiasm for their hobby. For me, in my role as the organiser of the BTO/CJ Garden BirdWatch, it is meeting those who participate in my survey that most inspires me. They are a diverse crowd; a mix of armchair birdwatchers – who only occasionally venture out to watch birds on nature reserves, keen birders – who dash around the country in search of rarities, and those in between, all watching birds to va rying degrees. There is one commonality though; all of these people enthuse about their garden birds. They delight in relating stories of chance encounters or in detailing observations on unusual bird behaviour that they have witnessed in their garden. Most of these garden birdwatchers get as much from witnessing the commonplace – the blackbirds, robins and finches – as they do from seeing something more unusual. To me, this emphasises the tremendous appeal of birds and of birdwatching itself. It is a hobby that is accessible to anyone and this must be why it draws in such a diverse following of acolytes. You can pick your own level, involve yourself as little or as much as you choose and that has to be a good thing.

Wednesday, 22 August 2007


There has been a noticeable chill in the air over recent mornings, the overnight drop in temperature sufficient to cast a heavy dew. The tall vegetation that flanks the forest rides hangs seed heads bowed by the weight of the dew upon them and tiny droplets of water glisten in the first of the sun’s rays. The gossamer of a thousand spiders is draped over the vegetation like the silken threads of an untidy seamstress. Here and there a whole web, radiating out to points of firm anchorage, is stretched and contorted, pulled down by the weight of dew that coats its every thread.

Is autumn upon us? It seems too early, yet there are the tell-tale signs that summer is moving towards its end. The screaming parties of swifts have left, deserting the rows of terraced housing and those few that remain have fallen silent as they make their lonely arcs across the sky. Small numbers of house martins are beginning to drift southward and swallows will soon be gathering on the overhead wires. The woods hold a scent of fungi, their fruiting bodies erupting through the surface to fling their tiny spores onto the strengthening winds. Reports of sandpipers and whimbrel herald the arrival of the first autumn passage migrants; with breeding finished they are free to move south.

I welcome this slow change, the steady transition between seasons, as nature turns through another part of her annual cycle. The lush, verdant growth of early summer is being replaced by mature browns as plants begin to shift their resources, either drawing back within themselves to fuel the spurt of growth that will come next year, or packing seeds that will soon be dispersed by a procession of unwitting accomplices. This process of renewal fascinates me; I like the idea of drawing back within myself as the months of light and warmth pass, hoarding those experiences gathered throughout spring and summer in readiness for the winter ahead. By doing so I hope to remain in touch with the ebb and flow of the seasons, accepting the pattern of the natural world around me and not blinkered to the narrow view, offered by a world in which we can divorce ourselves from the seasons through artificial lights and gas-fired central heating.

This is why these first crisp mornings that hint at autumn are so invigorating. My senses are alert to the changes in temperature and light, to the scents and behaviour of plants and animals and I feel closer to the world around me. In some subtle way we are all influenced by the changing of the seasons; we should acknowledge this and celebrate these periods of transition, as one season passes into another.

Tuesday, 21 August 2007

Chalk-hill Blues benefit from careful management

As I head southwest down the A11 and onto the A505 so I leave the acidic, sandy Breckland soils behind and cross onto the underlying chalk. Much of the chalk grassland has been lost to agriculture and the remnants are restricted to the steeper slopes of the chalk escarpment and to areas of favourable land-use, such as horseracing and golf. I am heading to the chalk grassland to search out the chalkhill blue, a butterfly that is on the wing in August. Instead of stopping near Newmarket to view colonies on the Devil’s Dyke and Fleam Dyke, I am travelling further afield to a colony on Therfield Heath, just to the west of Royston. My reason for visiting this particular colony lies in its history; Therfield famously attracted butterfly collectors from across Britain, each drawn by the lure of the varied colour forms of the butterfly to be found on the heath. Most of our butterflies are known to exhibit unusual colour forms from time to time, known as aberrations, but the chalkhill blue is noted for having more forms than is typical. The large population at Therfield Heath numbered many thousands and early last century the heath would have been inundated with collectors, each seeking that elusive aberration to add to their collection. One particular aberration, known as semi-syngrapha, in which the normally brown-coloured female has blue wings typical of the male, was the main target of the collectors.

Sadly, the pressure of collecting, coupled with changes in land management – notably the cessation of grazing by sheep, resulted in a dramatic decline in numbers and the population of chalkhill blues fell to dangerously low levels. These were restricted to the tiny pockets of suitable chalk grassland that remained, some only a few square metres in size. Fortunately, thanks to the efforts of local volunteers with an interest in the butterfly, the population was saved from extinction and since 1989 the number of chalkhill blues has increased. I wanted to see the results of this work and pay homage to the volunteers’ efforts by visiting the heath to photograph the butterfly.

One unusual aspect of the heath is the presence of a golf course, many fairways and greens of which are perched precipitously on the chalk escarpment. It is a large site and I thought that it might prove difficult to locate the discrete colonies. However, it did not take long to find the blues, the males actively quartering the vegetation in search of females that remained hidden below. These were delightful butterflies and seeing a dozen together made me wonder how it must have been to witness hundreds on the wing when the population was at its peak

Monday, 20 August 2007

Quail much in evidence

Barely bigger than a skylark, the quail has the distinction of being our smallest gamebird; it is also our only migratory one. The presence of this diminutive delicacy is usually only revealed upon hearing the sharp three-note call of the male. I, like many other birdwatchers, use the phrase ‘wet-my-lips’ as a mnemonic, as it almost exactly describes the pattern of this call. The call itself is often repeated several times by the male and, since it is far-carrying, it is tempting to use it to locate the bird. Unfortunately, such are the ventriloquial properties of the call that this is a fruitless exercise. Over the past couple of weeks there have been a number of calling birds reported from the west of the county, associated with arable land on that swathe of chalk running from north to south down through Norfolk. Because quail are able to reproduce at three months of age, it is possible that some of the birds calling now are young from breeding attempts that took place further south earlier in the year. Research suggests that there are two components to the British breeding population, with some birds arriving in May and others, including these young birds, reaching us later in the summer.

It may seem surprising that the quail, belonging to a group of species not necessarily known for their powers of flight, should be such a mobile migrant. The species has a huge breeding range, extending east from Britain across Europe and into central Asia, and south through the Mediterranean and down across Africa. Normally a scarce breeder in Britain, in some years much larger numbers appear. Although the exact reasons for these periodic influxes are unknown, it is thought that they may be linked with good breeding seasons in Iberia and North Africa, producing more young birds that move north.

The quail was almost certainly more common historically in Britain than it is now and it appears, as do many other birds, on the lists of species taken for the table. Interestingly, some ancient Greek writers describe the flesh of the quail as being unwholesome, suggesting that this results from the quail’s eating poisonous plants, like hellebore. Having never tried quail (nor likely to, as a vegetarian) I cannot comment on its flavour. Aside from when on migration, it would appear to have been a difficult species to catch, what with the ventriloquial qualities of the song and its tendency to hide in long vegetation. Chaucer alludes to this in ‘The Clerkes Tale’, where he uses the quail as a simile to describe how well someone hides. It is a good job, then, that birdwatchers can appreciate the quail simply by hearing its call.