Wednesday, 30 April 2008

Origami with leaves

Things have really started to green up over the last few days; the vibrant fresh greens of new growth add a sense of life to a previously dull canvas. Look closely and you will see that there is a clear succession to much of this greening. Trees in particular provide an opportunity to spot which species come into leaf first and which are more sluggish. Over the last few days the rowan in my garden has come into leaf, while the hazel is only just bursting through from its buds. The buds of beech on the other hand, remain firmly sealed, the leaves inside yet to put in appearance.

Many of the newly emerged leaves clearly have quite a bit of growing still to do; look at those of horse chestnut for instance, miniature versions of their final form. On the other hand, the beech leaves will emerge almost fully-formed, raising the question of just how they can be packed into such a small bud. It seems that the key to this trick lies in the way in which the new leaves are folded. Researchers have discovered that the angle between the mid-rib of the leaf and the lateral veins that emerge from it determines how the leaf will unfold. This angles varies between different tree species, ranging from 10 degrees to almost 90; the bigger the angle the more compactly a leaf can be folded and, hence, crammed into a smaller bud. However, this space-saving option comes at a price, since the larger the angle the more slowly the leaf expands. Beech has an angle of roughly 40 degrees (ranging from 50 near the stalk to 30 near the tip), allowing it to expand to its full area that much more rapidly. This strategy lies behind the long leaf buds that you see on beech, each containing a virtually fully-formed leaf, folded ready for rapid deployment.

That we know all this is down to work carried out by a team of scientists working in Japan. They have spent time studying the mechanics of leaf emergence, even using paper to replicate the nature of the unfolding process. An understanding of the principles of leaf emergence and, in particular, how you cram a large flat object into a much smaller three dimensional space, has value elsewhere in science by highlighting how we might overcome particular design problems. This area of science is known as biomimetics and has been used to look to nature for solutions to design issues relating to as wide a range of subjects as folding tents through to deploying the solar panels of satellites and other space-craft. The mechanics of nature are something that we can all learn from.

Tuesday, 29 April 2008

A songster from the east

I spent part of the weekend (the dry part) manning the British Trust for Ornithology stand at a wildlife event in north London. The event, held annually in the Lea Valley, took place at a disused water treatment works, the old filter beds now managed to provide a range of habitats for wildlife.  As the sun shone, small parties of sand martins bounced low over the filter beds, feeding on the many small flies that were readily available, while the first of the summer’s reed warblers rattled out their songs.

The highlight, however, came from one of our more secretive summer visitors – the lesser whitethroat. Throughout the day, two of these delightful little birds issued short bursts of rattling song from the deep cover of the many tumbling brambles. Lesser whitethroats are warblers, closely related to the blackcap, garden warbler and whitethroat. Unlike their cousins, these lesser whitethroats will not have arrived from the south but will, instead, have travelled in from eastern Africa and the eastern end of the Mediterranean. They are one of very few of our summer migrants to winter in Eritrea, Ethiopia, Chad and the Sudan. This choice of wintering location has spared them some of the problems caused by the Sahel drought (which hit Whitethroats and other species wintering in West Africa) but, while they have fared well long-term, things have been more difficult of late.

The lesser whitethroat can be admired for being one of our most attractively marked warblers; however, it is rarely seen well. While newly arrived males may sing from obvious song-posts it is not long before they switch to singing from deep cover. The males arrive during the second half of April, followed a week or so later by the females. The adults are highly site faithful, most returning to the site at which they bred the previous year and even the young return to the same general area. The adults pair up quickly and get down to the business of making a nest and laying their clutch of four to six eggs. The nest itself is usually placed in bramble or hawthorn, low to the ground and extremely well-hidden. As the breeding attempt progresses so the amount of song diminishes; if you hear a lesser whitethroat singing well in June then this is likely to be an unpaired male. It seems that just as soon as the breeding season has started then it is over, with most lesser whitethroats departing in August, heading southeast towards the wintering range. Researchers have found that the birds build up enough fat reserves to see them reach northern Italy (some 770km away) where they make a stopover before making the final hop to Africa.

Monday, 28 April 2008

Dancing with newts

I often make a visit to the forest’s drinking pools during early spring. These small ponds, uncovered and man-made, draw down siskins, crossbills and other birds during dry periods. One particular pool is home to a breeding population of smooth newts. This is our most widespread and abundant newt and it is the one that you are most likely to encounter within Norfolk. The closely related palmate newt prefers more acidic ponds and is only known from two sites within the county.

Over the years I have spent a bit of time watching smooth newts, both in the field and by housing them temporarily in a tank, observing their behaviour and their fascinating courtship dance. Smooth newts have a terrestrial phase, which extends from mid-summer in the adult newts through to February or March the following year. During the first warmer days of spring the adults emerge from their overwintering sites and return to the breeding ponds.

Male smooth newts first attract the interest of a prospective mate by blocking her way. If the female is receptive she will turn to face the male, stimulating him to initiate a long and rather frenetic courtship display. There are three components to this display, the first of which is the quiver. This sees the male face the female before vibrating his tail rapidly against his own body. The second, known as the wave, involves the male turning side on to show off his breeding colours and crest to best effect. The final component is a violent tail movement known as the whip. All three actions can be seen in a typical courtship, although the female may break off the engagement at any point should she determine that the male is unsuitable. A receptive female will follow the male as he moves away still displaying, before touching his tail. This intimate contact causes the male to release a package of sperm, known as a spermatophore, which the female then collects as she passes over it. Males usually outnumber females in the breeding ponds and competition for a mate can be fierce, with some males resorting to underhand tactics in order to secure a mating. These males watch the courtship displays going on around them and then cut in at the appropriate moment. They do this by touching the other male’s tail, causing him to release his package of sperm, before leading the female away elsewhere with their own dance.

The presence of immature newts in the drinking pool shows that breeding took place successfully last year. With their external gills these individuals have yet to undergo metamorphosis, a sign that they were hatched late last summer. Here’s to a good season this year.

Saturday, 5 April 2008

Bug-eyed monster

There is a rather frightening bug-eyed monster lurking just outside of my back door. With strong biting mouthparts and huge forward-facing eyes, this monster is beautifully adapted for hunting prey, actively seeking out victims with a quick darting lunge. Fortunately, for me, it is only a few millimetres in length and, consequently, would only be truly frightening if I happened to be of similar size!

The creature in question is a ground beetle known as Notiophilus biguttatus. Unfortunately, like many of its kind, it lacks an English name (though ‘Common Springtail Stalker’ has been suggested). As the name implies, this is a not uncommon species, found across a range of habitats (including gardens), where it specialises in feeding on springtails, mites and other small animals. Springtails are the favoured prey though; these are those tiny wingless insects that exist in huge numbers within leaf litter, where they feed on fungi and decaying plant material. As their name suggests, springtails have a rather useful adaptation, an organ known as the furcula. This is held, clicked into place beneath the body. If danger threatens, the catch is slipped and the furcula slams down into the ground propelling the tiny creature up into the air and away from immediate danger. The only downsides of this strategy are that the springtail has no control over where it lands and that the furcula takes a little while to reset before it can be used again.

I am fortunate in having a stereo-microscope that enables me to take a detailed and close-up look at such small organisms. At times-forty magnification, the brutal power of the common springtail stalker can be see. The compound eyes dominate the front of the face, ideally adapted to detect movement and to determine the distance between the beetle and its prey. Between these eyes are a series of furrows, the exoskeleton of the beetle rippling up in a pattern characteristic of the species; there are seven other British species of springtail stalker, each typically with a different pattern of furrows. Then there are the biting mouthparts, able to slice through the soft-bodied springtails once caught. Behind the head and thorax is the abdomen; like other ground beetles this is covered with a pair of hardened wing-cases, though unlike many other beetles, the species is actually flightless. The whole body is carried on three pairs of jointed legs, able to propel the beetle across the ground with an astonishing turn of speed. Seen without magnification this beetle may easily be dismissed as an ant scurrying across the ground. However, invest in a magnifying glass and take a closer look. You will soon discover that it is something of a jungle out there.

Friday, 4 April 2008

Butterflies emerge as sun shines

The brimstone is one of the earliest butterflies to be seen on the wing. As I write, a bright sulphur yellow male is making the most of the early warmth, seeking out nectar sources in the garden. Despite its bright colouration the brimstone is often overlooked, perhaps because it is on the wing so early in the year, relegating it to a lower tier in terms of familiarity. The species is one of just a handful of butterflies to spend the winter in their adult form, along with comma, peacock and small tortoiseshell (from the common species) and large tortoiseshell and Camberwell beauty (from the rare visitors). To these can be added red admiral, a species now able to overwinter here successfully because of our increasingly mild winters. Resembling a dying ivy leaf, the brimstone is ideally camouflaged to spend the winter tucked away in thick vegetation; only venturing out once sufficient warmth is felt. Too early an arousal can be disastrous, with the limited fat reserves quickly depleted if energy is expended in a fruitless search for nectar that is not yet available.

Alongside the bright yellow males, whose colouration is thought by some to have given rise to the word ‘butterfly’, female brimstones may also be seen on the wing. Their colouration is a pale yellow green, reminiscent of the primroses that are in flower at the same time. These adults will remain on the wing through into June, possibly even early July, mating and then laying their eggs singly on buckthorn or alder buckthorn, the favoured food plants of their caterpillars. Unlike certain other species, which form distinct colonies, brimstones range widely and females will travel considerable distances in order to find suitable sites for egg-laying. The generation of adults that emerges from these eggs may be on the wing from late July or early August and will remain on the wing as the warmth of summer begins to fade through into autumn. This means that, successful hibernation allowing, some of these adults will reach 11 months of age, making the brimstone one of our longest-lived butterflies. Because it overwinters as an adult, the brimstone has to spend many hours in late summer nectaring, laying down the fat reserves that will get it through the winter ahead. Watch one feeding in your garden and you will quickly notice that it is able to utilise those flowers with particularly deep nectarines, like buddleia, teasel and runner bean.

So, while this butterfly may be seen on the wing in every month of the year, it is only really now, during early spring, that we tend to notice them; a real shame for such a spectacular insect.

Thursday, 3 April 2008

A floral tradition

It is, perhaps, rather unsurprising that so many of our spring flowers have a strong history of folklore associated with them. After the long, drab days of winter, the first splash of colour would be especially welcome and it is relatively easy to see how such folklore could develop. The primrose, for example, is widely regarded as a token of spring, its delicate pale yellow flowers used to decorate churches over Easter. Primrose flowers were also picked for use in the preparation of ‘Pasche Eggs’, another tradition associated with Easter. The word ‘Pasche’ is an archaic word for Passover or Easter. The primrose blooms were wrapped around the egg, along with ivy leaves, onion peelings, gorse flowers and the petals of lesser celandine. The egg was then hard-boiled before being eaten on Easter Monday.

Lesser celandine itself, another early bloom, was used in the treatment of haemorrhoids, not because of proven medicinal qualities but because its knobbly tubers actually resembled the haemorrhoids they were used to treat. Early herbalists believed that treatments for particular ailments could be found in the plants or other materials that most resembled the condition, almost as if they carried a visual signpost as to their designated use.

Much of this kind of folklore is of mixed origin, some more ancient than others. Early folklore associated with the primrose has it that the brown marks in the centre of the primrose flower are the rust marks left behind when St. Peter mislaid the keys to heaven. Not all associations were positive, even for the same plant. As a corollary with the fertility associated with spring, the primrose became part of superstitious folklore relating to hens. In Suffolk in particular, it was considered unlucky to bring a posy of less than 13 primrose blooms into the house. Since 13 was considered to be the size of a standard clutch of eggs, bringing in fewer blooms than this was thought to lower the productivity of the family hens. Bringing a single primrose bloom into the house was deemed even unluckier and malicious neighbours would sometimes give a small child a single primrose to take home, hoping this would bring bad fortune onto the child’s family.

A far more recent piece of primrose folklore is ‘Primrose Day’ (19th April). On this day, primroses are placed on the statue of Disraeli at Westminster Abbey. Disraeli’s favourite flower was the primrose and Queen Victoria often sent bunches to him. Following his death, in 1881, Sir George Birdwood suggested that Disraeli be remembered through a Primrose Day, a tradition that continues. Whatever the associations, I am just glad to see the soft yellow tones of primroses adorning our woods in spring.

Wednesday, 2 April 2008


This is rook country; a late Easter break has brought me to the undulating pasturelands and woodlots of Dorset, where the green of spring is a week or more in advance of that in Norfolk. The still bare trees that crowd the narrow lanes are topped with the nests of rooks, upturned cones of sticks collected from nearby or stolen from the unguarded nests of neighbouring pairs. Many nests, though, have rooks in attendance, dressed in funereal black and with bone white bills. These are splendid birds; their ragged loose-winged forms rise effortlessly from the trees in the brisk wind, sweeping away to feed on the slowly warming turf. Others attend to unfortunate creatures that have been killed by traffic, scavenging much-needed protein from road-kill badgers and rabbits. A closer view in the strengthening sunshine reveals a plumage that is not simply black, but is instead dressed with a wonderful mix of bronze, blues and purples, reminiscent of the way in which oil on water separates out into a kaleidoscope of colours.

It is the social cohesion of the rookery that, to me, provides a real sense of the vitality of spring, more so than the sight of newborn lambs or a woodland alive with the sound of the first chiffchaffs. The sound of a rookery at dawn is something else, providing a bustling sense of the activity that is taking place within this vibrant community. Yet, most English rookeries contain fewer than 50 nests and only a handful have been recorded with more than three hundred nests. A few really big rookeries have been recorded in the past, notably on large Scottish estates where, for example, some 2,274 nests were noted at the Haddo House rookery near Aberdeen in the 1970s. The trend, certainly within England, seems to be towards smaller and smaller rookeries, perhaps a reflection of food availability, loss of suitable nesting trees or increased levels of disturbance.

Levels of activity vary throughout the day and, indeed, also change as the breeding season progresses. During the period of nest construction, raiding parties, composed primarily of young birds, attempt to steal twigs from unguarded nests. For this reason, breeding females will typically guard the nest while their mate seeks out suitable twigs. Only when the lining of the nest begins, is the female confident enough to join the male in collecting material. Once the nest is complete the female will initiate egg-laying, typically producing between two and six eggs which she will then incubate alone over the coming weeks. As the season progresses, so the expanding leaf cover hides the rookery from prying eyes, halting our glimpse on the busy collective lifestyle of these enigmatic birds.

Tuesday, 1 April 2008

Little Owl

As I lifted my gaze from the ground I became aware of a round, pale-brown object bouncing its way towards me through the air. As it approached it gained height, its buoyant flight taking it up and over my head into the mature oak by which I was standing. Turning around to follow its trajectory I was greeted by the piercing yellow rimmed stare of an adult little owl, now perched on one of the thick lower limbs of this majestic tree. This was my first little owl of the year and, perhaps surprisingly, the first seen here at Kilverstone.

Despite its familiarity, the little owl is not a native of the county but established itself here as a result of deliberate introductions carried out some 140 years ago. The first attempts to introduce this delightful owl into England took place in 1842, when individuals collected from Italy were released into Walton Park, Yorkshire. This release, and several other early attempts, failed to establish the species but two successful introductions did take place in the 1870s, one to Edenbridge in Kent and one near Oundle in Northamptonshire. By 1925 the species was established across most of its current British range, including Norfolk.

Although most active from dusk through to dawn, little owls can often be seen during the daytime, perched in a tree or, occasionally, seen in flight. At this time of the year they are well into their breeding season and many local pairs will have already initiated egg laying. Vocal activity over recent weeks will have reflected this upsurge in breeding behaviour, with male little owls proclaiming ownership of their territories through a ‘hooo-oo hooo-oo’ call, answered by the female through a series of short shrieks and yelps. The little owl has quite an impressive vocal repertoire and, in addition to the territory calls, a plaintive ‘kiew kiew’ call may often be heard. The breeding pair will spend increasing amounts of time around the chosen nest site, the male demonstrating its suitability to his mate and also presenting her with choice items of prey. These behaviours serve to cement the pair bond and strengthen the association with the nest site.

To many people the little owl is a welcome addition to our avifauna and, even though introduced, we should be concerned by the decline in numbers seen over the last 50 or so years. Loss of nesting sites and a fall in populations of favoured prey are behind the decline. Equally worrying is that a similar pattern can be seen elsewhere in Europe, in countries to which the species is native, and it is for this reason that the little owl has been flagged as being of conservation concern.