Saturday, 21 July 2012

Tough times for butterflies

This summer’s appalling weather, with its low temperatures, heavy rainfall and strong winds, may well be causing problems for many of our butterflies. Temperature can influence the time that it takes for a butterfly larva or pupa to develop, or reduce the activity of adults that need to find a mate or lay eggs. Of course, there is still much of the summer to go and we might find that as the weather picks up so do our butterflies.

The impression that you get of just how well a particular species is doing is very much shaped by where you live, which habitats you visit and when. Just because I have not seen many butterflies on the wing during my visits to local sites does not necessarily mean they are doing badly everyway. This is why we need the efforts of scientists, operating monitoring schemes in association with ‘citizen scientists.’ The changing fortunes of our butterflies, for example, are monitored through schemes like the BTO Garden BirdWatch (which records garden butterflies on a weekly bases throughout the year) and Butterfly Conservation’s annual Big Butterfly Count (

Last year over 30,000 people took part in the Big Butterfly Count, which runs from 14 July – 5 August, and it would be great to see even more people involved this year. The survey is simple – a 15 minute count of the butterflies seen in a sunny place – and provides information on the more familiar and widespread species. For those species of a more restricted distribution, perhaps because they have more specialised habitat requirements, or which are more difficult to identify, there are other schemes. These typically involve fewer people and use more complex methods but they provide robust and essential results, generating a long-term measure of the changing fortunes of our butterfly species.

By recording butterflies in the same way from one week to the next, or from one year to another, provides a standardised measure of change, something that allows objective conclusions to be drawn about how particular species are doing. Some of the changes revealed may be the result of natural processes, perhaps a run of poor weather or an abundance of butterfly predators or parasites, while others may be the result of habitat or climate change driven by our activities.

In order to establish the effectiveness of conservation efforts we need to be able to say with confidence whether or not a species is responding favourable and the way to do this is by systematic monitoring. This is why the work of organisations like Butterfly Conservation and the BTO is so important. Since both organisations represent a partnership with volunteer surveyors, it is easy to see the valuable roles that you and I, as individuals, can play.

Friday, 20 July 2012

On silent wings

I have fond memories of late summer afternoons spent counting and identifying plants on a piece of wet meadow in north Norfolk. On some days I would watch the barn owl quartering the meadow around me, on the wing early because of rain the night before or because there were hungry chicks to feed in the nearby barn. Every now and then the barn owl would pass within a few feet of me while I sat motionless and intent on some plant or other. The thing that still strikes me about these close encounters was the silence of the owl as it drifted by.

The silent flight of the barn owl is something that many have commented upon. When you compare the flight of the barn owl with a bird like a pigeon – which, incidentally, is about the same weight – the difference is striking. How the owl manages to minimise the noise that it makes while flying is all down to some clever adaptations in its wing feathers.

The first of these can be seen with the naked eye if you examine the leading edge of the wing closely; you would need a bird in the hand to do this. The outer flight feather (a primary) and the smaller feather that covers its base (a primary covert) is modified into a comb-like structure which is comprised of a series of gently curving serrations. These are formed from the feather barbs, their modified structure very different to the barbs found on the other flight feathers. Research suggests that the serrations alter the flow of air over the wing and reduce the amount of wing noise.

A second adaptation can be seen on the trailing edge of the flight feathers. Here the barbs are loose, producing a softer fringe to the feather and again reducing the amount of wind noise. The final adaptation, the downy nature of the upper surfaces of the flight feathers, serves a similar purpose. Measurements of flight noise across a range of bird species show that barn owl flight does not generate the frequencies of ultra-sonic noise that are a feature of other birds. This is important for a predator of small mammals which have hearing that is especially sensitive in the ultra-sonic range. There is another advantage of this adaptation for the barn owl, in that it locates much of its prey by ear. Small mammal squeaks, together with the sound of them moving through vegetation, would be lost to the owl if it drowned them out with noisy flight. For a bird like a pigeon there is no selection pressure in favour of silent flight, so it is only in the small mammal-eating owls that we find this adaptation.

Thursday, 19 July 2012

Plume moths

The other morning a delicate moth appeared on the kitchen window. No doubt it had entered the previous evening when the windows were flung open to draw in the cool air of dusk. The resting posture of this moth, the wings folded to a narrow horizontal, held at right angles to the body and reminiscent of a small crucifix, showed this to be a plume moth. Rather than the species that I normally encountered, this was different and more strongly marked. A quick check of my moth book confirmed it to be a beautiful plume, Amblyptilia acanthadactyla, a common species of gardens, woodland and rough ground. The larvae of this moth feed on various plants, including mints, cranesbills and hedge woundwort.

There are forty-four species of plume moth in the family Pterophoridae, plus another (the Many-plumed Moth) in the family Alucitidae. The latter, a particularly common species that is often attracted to light, is encountered in the house on an almost weekly basis throughout the summer and occasionally found hibernating in the shed during early winter.

The Pterophorid plume moths rest on long legs, that lift the moth away from the surface on which they are sat. The narrow wings vary from a flat and uniform beige through to a beautiful mix of rich ochres, yellows and browns. Some appear solid and brittle, all sharp edges and rigid lines, while others (such as the white plume moth) are softer in their appearance, with feathered trailing edges to the wings. The appearance of narrow wings is an illusion, created by the wings being folded or even rolled when at rest.

While the beautiful plume is something of a generalist when it comes to its choice of larval foodplant, many of the species are associated with just one or two foodplants. In many cases the moth takes its common name from the foodplant, as is the case with the goldenrod, yarrow and tansy plumes. Perhaps the most unusual choice of foodplant, however, goes to the sundew plume, its larvae feeding on round-leaved sundew. Not only does round-leaved sundew feed on insects but it also has something of a limited distribution within the moth’s English range – round-leaved sundew is more widely distributed in the north west of Scotland where this moth has yet to be discovered.  Sundew plume feeds on the leaves, developing seeds and flowers of the sundew.

Seeing this moth reminds me of the variety of insect life that occurs in the garden and highlights the diversity of form that is there to be seen. The beautiful plume is a moth that doesn’t look like a moth but, to my mind at least, it is certainly worthy of closer examination.

Wednesday, 18 July 2012

Rain boosts lush vegetation

The mix of sunshine and showers that has been a steady feature of the summer has benefited many plants. The meadows, woodland rides and patches of urban green-space have developed unchecked into thick swards, green and lush. In places, umbellifers have reached up beyond head height to stand sentinel over a sward dotted with the soft purple touches of thistle and the dusty grey smudges of flowering nettles.

Associated with those patches of rank grassland that sit on the dampest ground – everything seems damp underfoot at the moment – is a strong and sweetly bitter scent. It is a smell that I know well from my days of working in wet meadows but something I have never tied down to a particular plant. Curiously, on muggy summer mornings the scent was also associated with the voles that I used to handle as part of a project looking at small mammals and barn owls on a North Norfolk estate. The voles were caught in live traps and I often pondered how they picked the scent up from the vegetation – it was, after all, a very different smell from that which I would normally associate with a small mammal.

Many of the dense swards to have grown up over recent weeks have become impenetrable, a tangle of cleavers having grown through other vegetation and binding it together. This has created little patches to which we humans no longer have access. Areas where dogs were exercised earlier in the year are now left to the myriad of plant feeding insects, the foraging shrews and voles and the occasional nesting whitethroat.

While these areas are rich in wildlife I have heard complaints from some of the passers-by who suggest that they look untidy. The aesthetics of a manicured piece of amenity grassland seem, for many of us, to be more important than the wildlife value that comes with leaving the grass to develop into a richer and more varied sward. You see the same thing in the countryside, where intensive pasture with its fertilisers and other inputs becomes the definition of a green and pleasant land, while neighbouring rough grassland, less vividly coloured, is regarding as unkempt, weedy and of little value.

When I am passing one of the urban green-spaces and happen to see the council’s hired mower team nearby I shudder, wondering if today is the day that they will ‘tame’ the sward, cutting it back and cutting back the opportunities for the creatures that have made it their home over recent weeks. I don’t know, but maybe the council has become more enlightened, the locals more accepting and willing to give nature a chance under its own terms instead of ours.

Tuesday, 17 July 2012

The wind

It is not so much the rain of June and early July that has caused the problems for our reed warbler project but the wind. The seemingly relentless run of windy days that hit during the second half of June tipped the contents from nests as the reeds bent and shifted. Weekly visits to the reed bed revealed an all too familiar picture; nests that had eggs or young chicks were now empty or gone altogether.

Reed warblers are, however, robust birds and quick to replace a nest with eggs that has been lost. In fact, some of the nests that disappear (leaving behind the tiny marker tape placed beneath the nest) are dismantled by the birds themselves, the material reused for the new nest placed just a few feet away. It was during our first field season that we first noticed this tendency to dismantle a failed nest and on occasion it caught us out. During that first season we only marked the location of a nest with a piece of tape placed on the track that we used to move through the beds. The nest itself would be unmarked but located within a few feet and easy enough to spot. Sometimes, however, you would arrive at the tape, recall the location of the nest and then adopt a puzzled expression at either your failure to refind it or to find that it had moved by a few feet. The addition of that second piece of tape leaves no doubt that a nest has been dismantled and moved.

Those nests placed in the most sheltered parts of the reed beds seem to have done alright, the birds rearing their young to fledging before probably making a second breeding attempt. Others may have lost their clutch to a cuckoo, the cuckoo chick typically hatching first and quickly jettisoning its hosts’ eggs over the side of the nest. The cuckoo chicks have not had it all their own way though, the windy conditions have taken their toll on them as well. So far, just one of the cuckoo chicks has fledged, others have only just hatched and others were lost to the weather.

Working so closely alongside these birds generates a degree of affection and you feel for the reed warbler pair in whose nest you spot a cuckoo egg. You know that this breeding attempt will be a failure for the warblers but the sadness is countered by the hope that a young cuckoo will fledge. After all, it is the cuckoo that is in decline while the reed warbler remains one of the few African migrants that seems to be flourishing. Lets hope the weather gives them both a fair crack over what is left of the season. 

Monday, 16 July 2012

A dance of beauty

It is late afternoon and the muggy conditions cast a sultry feel. The shade on the river provides some comfort and I stand and watch the river from the stone bridge that marks an ancient crossing point. The water is running clear again after the rain of earlier in the week and the waterweed ripples in the slowly moving current. Towards the bank, where a shaft of sunlight cuts through the shadow cast by the bank-side trees, a school of small fish dance and glint just below the surface. I have seen pike here and suspect that the small fish face an ever-present threat.

A movement catches my eye, as from the shadows emerges the jewelled blue of a banded demoiselle, the county’s most stunning damselfly. This species favours slow moving rivers and the male is easily recognised by wing band of brilliant blue. Only the male beautiful demoiselle is more stunning but, alas, it does not occur this far east. The male banded demoiselle has a blue body, dark legs and robust, paddle-shaped wings. The female is emerald green, her wings with a pale green hue but sporting no band.

This male is not alone; arcing out across the water he dances around another male that has just appeared from under the bridge. The two protagonists circle each other, seemingly displaying with a fluttering flight that is reminiscent of a butterfly. Even though there is no contact between them, I lose sight of which was the original male but assume it is the one that has looped back to the shadows from where it first emerged.

Alone among the British damselflies, it is only in our two demoiselles that courtship behaviour has been confirmed, the male responding to the presence of a female with a simple display in which he raises his abdomen and opens his wings. If she is receptive to these advances she will communicate this by alighting near the male. He will then perform an aerial dance in front of her, first moving backwards and forwards and then from side to side. If the female remains receptive then he will approach and land, perching on her wing tips and then climbing slowly down onto her abdomen. It is then that he takes a grip on her to adopt the characteristic ‘tandem position’, something that you may well have observed in other damselflies.

These damselflies are a thing of beauty, so delicate that it is difficult to equate them with the squat larvae hauled from the silty root masses of waterside vegetation. The adults make a forlorn sight when you come across them on the nearby road, a life extinguished that should have been dancing jewel-like above the river.

Sunday, 15 July 2012

A buzz in the kitchen

It is only when I spotted her, perched as she was on the frame of the window, that I understood why one of the dogs was so unsettled. Stung by a wasp as a puppy, she now had an aversion to anything large that buzzed, especially inside the house, and this particular buzzy thing was one of Britain's biggest hoverflies.

Volucella zonaria is spectacular. Mimicking a hornet, and not far off in size, you can appreciate the alarm that this harmless insect might generate in those fooled by its vespine mimicry. She was fairly docile and easily potted for release outside, where I took a couple of reference shots as she sat on a hosta. In both pictures you can see the chestnut-coloured segments at the front of the abdomen which, together with the larger size, separate zonaria from the related inanis.

Volucella zonaria female by Mike Toms
Volucella zonaria by Mike Toms

Volucella zonaria female by Mike Toms
Volucella zonaria by Mike Toms