Thursday, 30 April 2009

In awe of snakes

The other week I visited the garden of Dave Shearing to take part in some filming we were doing to promote a new survey of garden reptiles and amphibians. The garden was a wildlife haven, a formal area stocked with bird feeders and then a gate through into open woodland complete with nestboxes, wildlife pond and corrugated tin plates. The tin provided shelter for Grass Snakes and Slow-worms, both of which proved to be present in the garden in good numbers.

With a careful approach and lifting of the tin it was possible to take a close look at these two less commonly encountered creatures. While some of the snakes made a swift retreat into one of the many woodpiles that dotted the garden, others remained and seemed just as inquisitive about us as we were of them. By being able to watch the snakes in this way I was really impressed by the range of adaptations they displayed.

Snakes are not unique amongst the reptiles in being limbless but this feature does form the cornerstone of their anatomy. The long thin body places constraints on its internal structure and many of the internal organs are highly modified (or absent - most snakes have just a single functional lung). Many organs are elongated and paired organs are often arranged one behind the other, rather than side-by-side; the left kidney, for example, sits behind the right. Each of the vertebrae (and there are usually between 160 and 400 of these) has a pair of ribs attached to it. The ribs themselves articulate and can be swung forward, allowing the snake to flatten out its body to soak up more of the sun’s warmth (I often see Adders doing this) or to allow the passage of a large prey item down the digestive tract. The skull is also adapted to aid the passage of large prey, the two lower jaws not joined at the chin and allowing them to move independently of one another as well as pull apart. This is why even some of the smaller individuals we watched could have tackled an adult frog.

The survey of garden reptiles and amphibians is being organised by the British Trust for Ornithology, Froglife and the Herpetological Conservation Trust. The researchers want to find out which factors influence whether or not particular species of reptile and amphibian will use a garden. As such, they want to hear from anybody who has a garden, regardless of whether or not it contains any reptiles or amphibians. A free survey pack and identification chart can be requested by calling the BTO, by emailing or by writing to Reptile Survey, BTO, The Nunnery, Thetford, Norfolk, IP24 2PU.

Wednesday, 29 April 2009

Woodlarks abound

The sky is dark and brooding, almost autumnal in nature, and the strength of the wind makes me feel that I may have chanced my luck in coming out this morning. The weather forecast predicted that the overnight rain would have pushed through soon after first light and I’m rather hoping that the scatter of raindrops on the car windscreen are the end, not the beginning, of a belt of showers.

The moody sky suits the open landscape of these Surrey heaths; their open vistas are spared the horizon-shortening banks of conifers that spoil so much of my native Breckland, hemming me in and compartmentalising so much of the landscape. Many of the Surrey heathlands have been shaped by the military and have only recently been taken on as nature reserves. They remain open; a mixture of sandy soils sloping down to wetter ground, abundant pools and (in summer) a multitude of dragonflies and damp-loving plants. The cloud and wind combine to deliver a chill and I am glad to be on the move, striding across the boardwalk towards the higher ground ahead. Despite the weather there are a few birds singing, the melancholy fluty whistle of Curlew, the ever-present Wren and a distant snatch of Woodlark. It is the Woodlarks that I have come to see, even though they are a familiar bird at home in Norfolk. Here, on Thursley Common, they are doing well, with a good number of breeding territories spread across the ground.

I can see that the bank of cloud is slipping away to the southeast and the brightening sky brings much-needed warmth, stirring not only my spirits but prompting other birds to start singing. Finding some higher ground I stand in the sunshine and watch one of the Woodlarks perched, as they so often do, in a suitable tree. Singing from a Silver Birch, one of many that seem to have lost their tops, the Woodlark is beautifully lit in the spring sunshine and it fills the telescope’s field of view. Smaller than a Skylark, this species is noticeably short-tailed and has a strongly patterned head. In addition to this, there is the diagnostic ‘pale-dark-pale’ panel on the edge of the closed wing.

I’m soon watching other individuals, some singing and others foraging on the ground amongst the heather. The common was damaged by fire two summers ago and many of the trees remain blackened. Woodlark numbers have increased over recent years, no doubt contributing to the numbers on show this morning. While I see them almost daily in Norfolk at this time of the year, I never see them in these numbers, nor in such striking surroundings. It was worth chancing my luck with the weather.

Tuesday, 28 April 2009

Shades of purple

Spring brings with it the greening of the land, as increasing day length and warming temperatures stimulate new growth. In with the green are welcome splashes of colour, the first of the year’s flowers providing early nectar for newly emerged insects. Alongside the shouty yellow of Lesser Celandine, there are the softer purple tones of Red Dead-nettle and Ground-ivy. I have always liked the soft purples of these small springtime flowers, perhaps because they are understated, perhaps because you have to get down on your hands and knees to really appreciate them. Both Red Dead-nettle and Ground-ivy are overlooked plants, often regarded as weeds within the garden by those who do not appreciate their aesthetic or wildlife value. This is a real shame, not least because Ground-ivy (in particular) was once a well-regarded plant.

Take a closer look at Ground-ivy and you will see that it is a softly-hairy plant, with blunt-tipped, kidney-shaped leaves, each of which is strongly toothed. The flowers are pale violet colour (sometimes almost pink) with delicate purple spotting. The plant sets very little in the way of seed but instead spreads vegetatively through the rapid growth of its creeping stems. This habit earned it the local name of ‘blue runner’ now seemingly no longer in use. Although it is common and widespread, the plant appears to be increasing within woodland habitats, particularly in southern Britain. It is thought that this a consequence of expanding deer populations, whose preferential grazing on more palatable herbs has favoured the bitter-tasting Ground-ivy.

It is this bitter taste that has seen Ground-ivy used in tonic herbal teas and, occasionally, in salads. The early Anglo Saxons, who used it to clarify their beers, made greater use of the plant. Added to a brew, the plant improved flavour, extended the time over which a beer could be kept and also improved its clarity. The practice of using Ground-ivy in this manner continued up until the reign of Henry VIII, at which time it was replaced in this role by the Hop, a cultivar of which was introduced into Britain during the 16th Century specifically for this purpose. The beer was referred to as ‘gill-ale’, derived from one of the English names for the plant; another name for the plant, associated with the brewing of beer, was ‘ale-hoof’.

There appear to have been a number of other local uses for the plant. It was used as a stuffing at Easter for a leg of pork in Shropshire and, elsewhere in Europe, the leaves were eaten by French peasants during autumn, when their flavour was further strengthened by the presence of brown galls formed by a small gall wasp.

Monday, 27 April 2009

A spring passage of LIttle Gulls

It is easy to see why the lake at Livermere is such a magnet for visiting waterfowl and waders. Situated in an open expanse of agricultural land it is an obvious feature for any bird passing over the borderlands of west Suffolk. The lake can be particularly productive during April and May and has already turned up trumps this spring, with a sizeable passage of Little Gulls noted on April 6th.

Varying numbers of Little Gulls had been reported from other inland waterbodies that morning, including the nearby lakes at Lackford, and I was certain that I would see some at Livermere. What did surprise me, however, was the number of individuals present, with several dozen birds passing through en route to breeding grounds in Finland, northern Russia and the Baltic States.

Almost immediately upon arriving at the lake I raised my binoculars and picked out the delicate dancing forms of the Little Gulls, swooping and darting about in a tern-like fashion to pick food from the water’s surface. By comparison, the more familiar Black-headed Gulls that were also present seemed almost cumbersome in their movements, less agile on the wing and with a greater tendency to bicker among themselves. Some of the older Little Gulls showed a dark underwing, a character that becomes more prominent with age and which can usefully be used when picking the birds out from among other gulls. In with the second-year and adult plumaged birds were a number of first-years, sporting a black tail band and bold black ‘W’ pattern extending across the wings and back. This is another useful feature that can be used in the field. Mind you, the general feel of these birds is very different from other gull species and they are pretty easy to spot once you know what you are looking for. Little Gulls are dainty birds. With a wingspan some 20-30% shorter than seen in Black-headed Gull, they are the smallest of the World’s gulls. This goes some way to explaining their tern-like jizz and the light, almost dancing, flight. Unlike terns, however, they show quite rounded wings, a feature that is further accentuated by the pale tips to the longest of their flight feathers.

An inland movement of this size is unusual but not unprecedented and, since 1994, there has been a tendency for increased numbers to pass through our region on spring passage. Individuals also appear on the coast at this time of the year, and Titchwell is a favoured site a little later into Spring, regularly attracting a couple of dozen birds. In 2007, Little Gulls made a nesting attempt at Titchwell, only the fifth British record. Who knows what might happen this year?

Saturday, 4 April 2009

Water bugs

There are some water bugs that are familiar to just about anyone who has ever been pond-dipping. Included among these are the pond skaters and water boatman that make use of the surface tension to eek out a living. However, there are all sorts of other weird and wonderful invertebrates that can be found in our ponds, rivers and streams; some can even be found in cattle troughs. All you need is a net, a white plastic tray in which to sort through your haul and a decent hand lens. Armed with such kit you should be able to turn up something of interest in all but the coldest weather. Even now, so early in the year there is plenty to be found.

Late winter or early spring is actually quite a good time to go looking for corixid bugs, some of which look quite similar to the more familiar water boatman, though they typically swim the other way up. As a group they can be regarded as being highly successful, with representatives found from Iceland to New Zealand and from ice-bound pools to hot springs and even the saline waters of estuaries. They are mainly herbivorous and feed on algae collected from the bottom of weedy ponds, slow river backwaters and dykes.

One of the most commonly encountered species around here is a bug called Corixa punctata, which also goes by the rather unimaginative English name of the Common Corixid. The first adults of the year emerge in mid-July and overwinter in the adult form. Mating takes place in January or February and soon after this the males die, leaving the females to lay their eggs over the few remaining weeks that they have left. The eggs are laid in small batches, each batch being attached to the stem or leaf of an aquatic plant. As the females approach the end of their all too brief lives, so the number of eggs laid diminishes, the females using up the resources they have left.

If you ever go to the trouble of catching or keeping Corixa punctata you’ll soon discover two interesting things about it. First, like many other water bugs it is endowed with a pair of stink glands from which the bug can release a noxious substance to deter would-be predators; the smell is really rather unpleasant. The other interesting feature is that these small creatures communicate by stridulating, making a characteristic ‘zip-zip-zip’ sound that can be heard over several metres. They do this by rubbing a special patch of short hairs on their front leg against a resonant part of the head. Having them do this in an aquarium can be rather unnerving, as you cannot easily tell where the noise is coming from.

Friday, 3 April 2009

a glorious morning for butterflies

The first of the spring’s butterflies is always a welcome sign; not the Peacock disturbed from its winter slumbers in the woodpile or the Small Tortoiseshell that has spent the winter in the cool of the spare room but one that has truly emerged from hibernation, brought to life by the rising daytime temperatures. The other morning, venturing into a different part of the forest to check out some ponds marked on the large scale map, I found not one but many butterflies on the wing, each one making the most of the early springtime warmth. All bar one of the two dozen or so individuals that I encountered in a little under two hours was a Brimstone, invariably a brightly coloured male, sulphurous yellow in colour.

That these individuals are on the wing so early in the year stems from the fact that they have chosen to overwinter as adults, fattening up on autumn nectar before finding somewhere suitable to pass the winter; in the case of the Brimstone the site will often be deep within an evergreen shrub. Just a handful of our butterflies overwinter as adults. Along with the Brimstone, Small Tortoiseshell and Peacock there are the Comma, Red Admiral and Large Tortoiseshell, the latter now effectively extinct as a resident. Other species pass the winter as caterpillars, eggs or as pupae, with each species overwintering at the same stage each year. There is an exception to this rule in the form of the Speckled Wood, which may pass the winter as either a caterpillar or a pupa depending upon late summer temperatures and their impact on larval development times.

The Brimstone has the longest adult lifespan of any British butterfly and individuals on the wing now may have emerged from their pupal stage early last July, and they may continue on the wing through into this June or even July. The brightly coloured males emerge from hibernation before the females (hence my seeing almost entirely males the other morning) and they can be wide ranging in their habits. Over the coming weeks the males will meet and court the pale coloured females, initiating what the great lepidopterist and illustrator F. W. Frohawk described so beautifully as ‘a prolonged dalliance flight in the sunshine’. The eggs will be laid towards the end of May, each one deposited singly on the underside of Buckthorn or Alder Buckthorn leaves.

It is an encouraging sign to see so many on the wing and equally reassuring to hear of other reports from across the county charting the emergence of other species. This might suggest that the cold weather has had little impact on their overwintering success, a good omen for the coming season.

Thursday, 2 April 2009

The first migrants arrive

The first of our summer visitors have arrived and over the coming weeks their numbers will increase as others join them for the northern summer and the bounty of invertebrate food that it provides. Over the last few days there have been reports of Swallows, Wheatears and, more widely, Chiffchaffs from across the county.

The predictable and annual journeys made by many of our breeding bird species have always fascinated me, as they have done many generations of naturalists before me. Now, with an extensive literature published on the subject of migration and new technologies available to us with which to track the movements of birds, we have a great (though not complete) understanding of how and why they undertake such incredible journeys. For some species it is easy to see the driving forces behind migration – a summer bounty of invertebrates for insectivorous birds that are then forced south as the bounty vanishes with the approach of winter. But what about those birds that eat seeds? Why do some of them (for example the Turtle Dove) migrate when close relatives remain in one place (either here in Europe or elsewhere, in Africa)? Perhaps this is part of the attraction; that we don’t have all of the answers, that there is more to learn.

The arrival of the first migrants brings with it a need to recall temporarily forgotten songs and calls, all-important if I am to identify the newly arrived songsters. Some are easy and never truly lost, perhaps helped by the onomatopoeic nature of their names. Foremost amongst these is the Chiffchaff, a small ‘leaf warbler’ which is one of the first migrants to reach us each spring and whose ‘chiff-chaff’ song can be heard in woodland and well-wooded farmland. Many of the first Chiffchaffs to arrive appear to be associated with damper habitats, perhaps because this is where the first of the season’s insects are to be found. Later into the month and there will be a half a dozen or so singing Chiffchaffs in the birch scrub that dominates some of the more open areas of plantation woodland through which I walk each morning, but right now I am still waiting for my first.

The Chiffchaff is one of three related species (it is joined by Willow Warbler and Wood Warbler) that show certain similarities in appearance but which have very different songs. While the two smaller species (Chiffchaff and Willow Warbler) may be encountered pretty much anywhere within the county, the later arriving Wood Warbler is a rare visitor, its distribution now largely restricted to the oak woods of western Britain. The Wood Warbler’s song is a spring highlight for me but then so is my first Chiffchaff.

Wednesday, 1 April 2009

The eye of the day

My recollections of childhood always associate the familiar daisy with the dizzy days of high summer, sprawled on the lawn with a book or engaged in idle conversation with friends on the short turf of a school playing field. I think that it is because of the strength of this association within the brief but vivid memories of childhood, that I am always a little surprised to see daisies in flower now, at the transition from winter into spring. Yet the association of the daisy Bellis perennis with spring is one that is enshrined in folk tradition. An old country saying, of which there are several variants, has it that spring has not truly arrived until you can cover seven daisy flowers with your foot; in some parts of the country the figure is nine not seven, in others it is 12.

Writing in Flora Britannica, Richard Mabey reflects that there is scarcely a day during the year when there is not a daisy in flower somewhere within the country, something he further supports by drawing upon the journal of John Clare, the poet. Clare, writing in 1824, notes how he collected a handful of daisies in full bloom on Christmas Day.

The daisy is one of our most familiar flowers and is probably one that any child, no matter how removed from nature, would recognise and could quite possibly name. Yet it is an unassuming plant; the flowers, while botanically complex, appear structurally simple and it never attains a size that might intrude upon the gaze of the casual observer, glancing across the short green turf of a formal lawn. Each flower, with its bright yellow central disc around which are arranged the white petals, stands on a stalk just four inches or less in height, emerging from a rosette of flat and fuzzy leaves. Being small has its advantages but the plant is easily out competed by taller species and so does best where grazing or lack of nutrients favours a short sward.

It is thought that the name ‘daisy’ derives from the Anglo-Saxon ‘daeges-eage’ – the ‘eye of day’, a name suggestive of the opening of the flowers at dawn and their closure again at the end of the day. The petals that close about the golden orb at the day’s end feature in folklore, most commonly in a form of divination whereby a young girl wanting to know if her love is requited will pluck the petals one by one with the words ‘he loves me, he loves me not’. This too, holds childhood memories of a bashful youth and childhood games that broke down the barriers between the fair girls and us boys.