Don't dismiss flies

If you ignore the cold and rather wet weather that greeted the Bank Holiday weekend, it would be fair to say we have had a rather pleasant spring with some unseasonable warmth. This period of warmth drew out a whole range of insects, from holly blue butterflies and scurrying ground beetles to industrious bumblebees. Various species of fly have also been on the wing, some of which have tended to enter the house and terrorise one of our two dogs. The dog in question, an eight-year old springer spaniel, was stung by a wasp when she was a puppy. Since then, she has taken a dislike to anything that flies around emitting a buzzing sound; you can always tell when there is a fly in the house by the way in which the dog looks nervously over her shoulder.

It is very easy to just dismiss these flies as all being the same but there are actually a great many different species, all showing slightly different lifestyles. For example, while some species lay eggs, others give birth to live young, a process known as viviparism. When we tend to think of flies we often have in mind the bluebottle, famously punned by the Goon Show, but there are many others with which we share our houses and gardens. Something of the revulsion that many direct towards the bluebottle can be seen in its Latin name ‘Calliphora vomitoria’, a reference to our fears that it can spread disease. Since the female bluebottle will enter houses and seek out exposed fish and meat for egg-laying (having done the same outside on decaying flesh or excrement) it is easy to determine the pathway by which a disease might reach us. The male bluebottle has more pleasant habits, and is more likely to be seen visiting flowers, particularly umbellifers, for nectar.

Another fly that is often seen in our houses is the common house-fly (Musca domestica). This species has proved its adaptability by establishing itself across the globe, living alongside Man and laying its eggs in our rubbish and excrement. Amazingly, the 900 or so eggs that each female lays can hatch within eight or nine hours, the whole life cycle being completed in as little as two weeks. Equally familiar is the greenbottle, one of a number of very similar looking flies with a blue-green or emerald-green colouration. This particular species is very variable in size, the result of how nutrient-rich is the medium in which it hatched. Unlike the bluebottle and house-fly, the greenbottle rarely ventures into houses, preferring instead to forage and reproduce outside. So, next time that you see a fly, don’t just dismiss it.

Red-footed falcons grace our skies

It has been a rather good spring for Norfolk’s birdwatchers. For me, it started with the Black Lark at Winterton, only the third record for Britain and a truly stunning bird. The series of weather systems conspired to draw in a series of birds that would normally pass to the east of our shores, making for some excellent birdwatching. The presence of a number of Red-footed Falcons is typical of this pattern. These small falcons (noticeably smaller than a Kestrel) are long distance migrants that breed from eastern Europe east to Mongolia. Some 30,000 pairs are thought to breed in Europe but virtually all of these do so in Russia and just a handful of individuals is encountered here in a typical year. This year, however, has proved to be exceptional, with individuals reported from across the country and with two birds (a male and a female) present over several days at Hockwold Washes (just outside the county boundary).

Red-footed Falcons undertake what is known as a loop migration. During the autumn they take an easterly route south from their breeding grounds and down through the eastern end of the Mediterranean and into Africa. The wintering grounds themselves are in southern Africa and many thousands of individuals may gather together where food is abundant. The spring migration follows a more westerly route which brings them back into western Europe, with birds reaching Britain in varying numbers depending upon the prevailing weather conditions. Many of the birds to reach the westernmost parts of Europe are younger birds, perhaps suggesting that either these take a more westerly route or they are less experienced in navigating home. The timing of the annual migration, coupled with the loop it takes, means that Red-footed Falcons are most likely to be encountered in Norfolk from late April to early June.

Red-footed Falcons are fairly distinctive; the plumage of adult males is a mix of different shades of grey and black, save for the undertail feathers which, like the feet, are red. Females show a slate grey back, wings and tail, with darker barring running across it, the underside a beautiful rufous buff. The female bird at Hockwold was distant but even so, still showed the generally pale head which contrasted with the grey upperparts and buff underparts. In flight, Red-footed Falcons can seem quite compact, shorter winged than a Hobby and noticeably smaller than a Kestrel. Like a Kestrel, the red-foot may hover into the wind, before dropping down onto prey. However, it may also hunt like a Hobby, making a direct approach to take an insect or (very occasionally) a small bird. They will even hop about on the ground to take insects.
 

Dragonflies need your help

There have been a few chilly mornings down on the fen over recent days; the air crisp but the clear blue sky heralding what will be a warm day ahead. Here and there on the lush growth are the fragile forms of dragonflies and damselflies, the first of this season’s new generation, struggling to warm up before they can venture forth. These primitive forms seem sluggish at this time of day but once their bodies are up to temperature they will become the insect masters of the air, voracious predators with a formidable reputation.

Roosting overnight in the vegetation has clear advantages, not least the avoidance of most predators. However, the limp bodies of many dozens of damselflies hang contorted in the webs of a myriad of spiders. A closer inspection reveals these to be Azure Damselflies. The emergence of these tiny creatures must represent a seasonal bounty for the spiders. Elsewhere on the fen, along one of the more sheltered rides, are Hairy Dragonflies, a species of early spring and one of the first to be on the wing. The males have fine white down on the top of their thorax, between the huge eyes and the powerful wings. These are robust creatures, the males actively patrolling low over the vegetation.

Seeing these dragonflies is all the more important this summer because the British Dragonfly Society has just launched a new National Dragonfly Atlas. Fieldwork will continue over the next five years with the aim of building up a picture of how our various species of dragonfly and damselfly are doing. It is fair to say that a new atlas is urgently needed. Changes in the quality of wetland habitats, coupled with global warming, mean that we really need a new stock take of these wonderful creatures. Several new species have established themselves here since the last atlas and others have declined in number, maybe by more than we realise. The beauty of the new atlas is that anybody can get involved. This means that any records that you can collect of dragonflies can be fed into the atlas. All you need to do is record which species you saw, when and where you saw it and then submit this, together with your contact details, to the British Dragonfly Society (www.dragonflysoc.org.uk). Of course you need to be able to identify which species you saw. If this is something that you are unable to do, then simply take a photograph of the dragonfly and send this in with the other details. Experts at the society will be able to identify it for you and then add the record to the atlas. Now where did I put my notebook?

The swifts are back!

The Swifts are back! The so-called ‘frog-gapers’ and ‘international mobsters’ described so perfectly by the late Ted Hughes in his children’s poem ‘Swifts’. It is the twenty-sixth of April, half a month earlier than the date which opens the poem but even this is a week or so behind when I would normally expect to first see them. In his opening verse Hughes describes how the swifts ‘materialise at the tip of a long scream…’ There is none of this youthful brashness for my first arrivals, two swifts silently marking their gentle arcs high above me in the sky. Are these the swifts that will breed in town or are they merely loitering to feed as they move slowly towards more northerly breeding sites? Over the coming days I expect to see them in greater numbers. Finally, their arrival confirmed, they will become a feature of my daily routine, catching my gaze in the evenings as they dash past my study window and into the nest site above.

The fact that the swifts return each summer never ceases to fill me with wonder, more so than when I hear my first willow warbler or cuckoo. There is something otherworldly about them, only landing to breed, they belong to the sky and not the ground. Their wheeling flights exhilarate because of the effortless ease with which they carve across great chunks of space. And yet they will be here for such a brief spell, just 16 weeks, before continuing their seemingly everlasting journey around the earth.

Distance seems to have little meaning to swifts. While breeding here, they may forage as far afield as Germany, tracking clockwise around low-pressure systems to seek those areas with the greatest abundance of their aerial prey. Immature birds (some immature swifts will not breed until their fourth year) undertake the same migrational journeys as the adults, arriving here to seek out vacant nest sites, planning for breeding seasons to come. During this period it is thought that young swifts remain entirely on the wing. This makes that first flight from the nest seem like a very big leap of faith.

The return of these denizens of the sky is reassuring and I do not know how I would feel if they failed to appear. Over the coming weeks I may become less aware of their presence, accepting them completely into the daily pattern of life as an ever-present backdrop to my day. But, come the end of the summer, I will notice that they have gone ­– the terrible feeling that something is missing. The process of loss and return is a balance of emotions, an affirmation that, as Hughes notes, ‘the globe’s still working’.

Early butterflies

The warmth of recent days has triggered the first real wave of spring butterflies. Most of the species on the wing at the moment, notably peacock, comma, brimstone and small tortoiseshell, will have spent the winter as adults, hibernating in some suitable crevice, garden shed or evergreen bush. All these early season butterflies will be seeking out suitable nectaring opportunities. Those that have overwintered as adults will have to replenish energy reserves spent getting though the long cold winter months. As such, many will range widely, seeking out nectaring opportunities with flights that may well bring them into your garden. This is one reason why gardens with spring-flowering plants are particularly beneficial to butterflies, and indeed to other insects (such as bumblebees) on the wing at this time of the year.

Butterflies do not take nectar from just any old flower but actively select those that offer the best returns. We are not just talking about the amount of nectar on offer but have also to consider the amount of energy that a butterfly has to expend in getting that nectar. Each nectar-producing flower is a bit like a petrol pump but one which a visiting butterfly will typically drain on each visit. It takes time for the fuel pump to be refilled so a butterfly does not want to be visiting a pump that has been recently emptied by another visitor. The amount of nectar left in the pump is known as the standing crop and the size of the standing crop will depend on how quickly the flower produces nectar and when it was last emptied. Flowers in which the nectar is held at the end of a long tube (known as the corolla) tend to have higher standing crops because only long-tongued visitors can access them. Flowers with short corollas can be accessed by most insects, including those with short tongues, and so tend to have smaller standing crops available.

What does this mean for our visiting butterflies? Well, those butterflies which are large in size and which therefore expend more energy just getting around, will seek out flowers with the biggest standing crop. Fortunately they can access these because of their long tongues (tongue length has been found to correlate well with body size and wing loading). Such long-tongued species also prefer to forage on plants where the flowers are clumped together rather than spaced apart. This is why you see red admirals, small tortoiseshells and peacocks feeding so readily on Buddleja davidii later in the year, while shorter-tongued species (typically smaller in size and with lower flight costs) can afford to visit solitary flowers, like bramble and dandelion, with the risk of reduced standing crops.

The pipit descending

It is at this time of the year that my morning walks are accompanied by a fine serenade, delivered from on high by the delightful tree pipit. This is another of our summer migrants, arriving here in mid-April to breed in semi-open habitats. Although there are several pairs breeding in that part of the forest where I make my steady morning circuit, one particular bird has a territory which is clearly bisected by one of the forest rides that I use. This fortunate fact means that I often receive my own personal performance, the bird rising silently from a favoured perch, climbing into the air rapidly before cresting above my head. It is then that the song begins, a clear and far reaching set of phrases that intensify as the bird slowly descends back to earth. Each descent is slowed by the way in which the bird fans its tail and holds its wings above its tiny body. Legs dangling, the bird is like a miniature parachutist dropping back to ground. It is a fantastic display and I feel privileged to witness it.

I do not meet this display every morning, for on some days the pipit remains perched, still singing to proclaim ownership of his territory but the song lacks the intensity heard when delivered on the wing. Casual observers often dismiss the tree pipit, the apparent trickiness in separating the bird from the other pipit species brings with it a reluctance to accept that it is anything other than a little brown bird. And while the plumage may lack the showy brashness seen in certain other species, there is a subtle beauty to its markings that triggers a deep sense of appreciation in me.

The forest holds significant numbers of breeding tree pipits but they are also found in areas of woodland edge and scrubby downland across other parts of the county (though not in the uplands). It is the combination of sparse open ground for foraging and trees for song posts that is needed by the tree pipit. The nest will be a shallow depression on the ground, usually hidden in low cover. For a summer migrant the breeding season is surprisingly protracted, the first eggs will have already been laid and the last young won’t fledge until August. The display flight is at its most noticeable early in the season but even when the birds are engaged in feeding young, they will still be there sitting sentinel on the young pines, pumping their tails downwards in a wagtail like fashion. All the while they will be adding to the delight of my early morning walks, another player in the forest’s summer pageant.

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.