Saturday, 22 September 2007

Take time to watch the little things

The other afternoon I took a break from tiling the kitchen floor to make the most of the now weakening late summer sun. Sitting on the wooden bench in our garden I was able to spend some time watching various insects going about their business. Large numbers of harlequin ladybirds, at various stages of development, could be seen on the fence, the pot plants and on the large buddleia that drapes over from the garden next door. The harlequins have obviously had a good season, their numbers are well up on last year and I fear that it won’t be long before some of these unwelcome aliens seek shelter in the house. Not only are they known to bite but they also stain upholstery and can gather in very large numbers around windows!

My attention was caught, however, not by the ladybirds but by the behaviour of a wasp. Flying along the fence, just below the top, I thought that it was about to become ensnared in one of the many spiders’ webs that litter the fence panels. Instead of becoming the victim, the wasp began to act as if it was actively seeking out the owners of the webs. Passing by one particular web, the wasp suddenly veered towards its centre, where a tiny piece of brown leaf hung like a spider. The wasp seemed to hover just off the leaf as if trying to work out if this was a spider or some other object. Its curiosity satisfied, the wasp moved off. It was then that I noticed that the wasp was quite deliberately quartering the fence panel, actively checking out each web in turn. This gave me the very definite impression that the wasp was hunting. This is something that I have not witnessed before, nor read about in the literature. Wasps feed on a range of foodstuffs, including other insects, and so perhaps I should not be surprised to see one hunting in this fashion.

Seeing this wasp, and being able to observe an element of its behaviour, made me appreciate just how much interesting life there is within my own, very ordinary, garden. There is something about watching insects that is special. Perhaps it is because they are so small and that you have to watch very carefully to see what they are actually doing. Watching carefully means that you are putting more effort into your observations and, consequently, getting a more rewarding experience from them. Of course, you can apply the same level of detail to watching larger organisms, like birds, but this often seems unnecessary and you can end up rather taking them for granted. Perhaps this is why insects are so fascinating.

Friday, 21 September 2007

Good news for garden birds

There has been some good news for garden birds of late; news that has, to some extent, slipped by unnoticed because attention has been focussed on more glamorous species. This is the addition of several garden birds, most notably dunnock, starling and house sparrow, to the Government’s list of species to receive priority conservation action. Known as the BAP list, where BAP stands for Biodiversity Action Plan, the list is one of a number of different tools that the Government uses to help it determine the best ways in which to deliver its conservation action within the UK. Periodic reviews of the status of each of our plants, animals and habitats, enable experts to assess which species are in greatest need of support. Central to this review process are the data collected through long-term monitoring schemes, each charting the changing fortunes of our wildlife.

Some 26 bird species were already on the list (following the first BAP review, carried out in 1995) and to these have been added a further 33. The inclusion of house sparrow and starling is particularly welcome; house sparrow numbers have declined dramatically over recent decades and our breeding population is now less than half what it was back in the 1970s. A similarly alarming decline has hit both our breeding and wintering populations of starling. That two species, so closely associated with Man, should be in such difficulties gives us fair warning of our impact on the environment around us. The reasons for their declines are not fully understood and their inclusion on the BAP list should help to direct more resources towards identifying the underlying causes. Once these have been identified, conservationists can set about trying to halt and, ultimately, reverse the declines.

A number of other species that frequent gardens were already on the original BAP list and it is interesting to see how being on the list has helped their status. In some cases, such as for song thrush, inclusion on the BAP list has prompted a great deal of research and this has seen a recovery in numbers in recent years – evidence that the system works. However, for certain other species more clearly needs to be done. The decline in bullfinch has continued, despite inclusion, but we now have a much clearer understanding of why the species is having such a tough time. One of the most important aspects of inclusion on the list is the establishment of a number of key targets. By using targets, it is possible to determine whether the resulting conservation action has been successful. It also provides a focus for the researchers, something to aim for and something by which they can measure their success.

Thursday, 20 September 2007

The antics of young crows

I never tire of watching the antics of young birds and over the past few weeks have been delighted by the presence of a family party of crows. Although overlooked by many, and persecuted by others, the carrion crow (to give the bird its full name) is a resourceful, emblematic and adaptable bird, with a wide range that stretches from Ireland and Portugal in the west to China in the east.

Our local pair, nesting high in a tree on the edge of a narrow finger of woodland, has three youngsters. Over past weeks the parent birds followed a tireless routine of bringing food to the nest and seeing off potential predators. Now their role has changed; their young charges mobile and keen to explore the expanding world around them. The impression they give off is one of precocious teenagers, trying out new things and then running to mum went it all goes wrong. The parents seem resigned to the demands forced upon them but remain vigilant to potential threats. New objects attract particular attention, as one of my colleagues noted the other day. He watched one of the young crows investigating a hedgehog. Each time the crow approached, the hedgehog rolled into a ball and remained still. The crow seemed puzzled, then lost interest; the hedgehog unrolled itself and started to go about its business again. Now moving, the hedgehog attracted the crow’s attention and the game of stop/start repeated itself. Although this inquisitive behaviour may sometimes land the crow in trouble, it is an important component of learning, preparing the young bird for adulthood and helping to make the species so successful.

It can sometimes be difficult to distinguish between crows and rooks, since both share the general impression of a large black bird. There is an old country saying which runs “if tha’s a rook ‘tis a crow and if thems crows tis rooks.” This alludes to the different social systems of the two species, with the highly social and colonial nesting rook likely to be seen in large groups. Carrion crows, on the other hand, are typically seen singly or, as at this time of the year, in small family parties. There are structural differences too; carrion crow has a heavy black bill, which appears more blunt at its tip than that of the rook. The rook has a steeper forehead, a bill that tapers along its entire length and shaggy feathering on its thighs. Over the coming weeks both birds may come together, as they collect in huge winter roosts which draw in birds from large parts of the region, a feature so beautifully described by the author Mark Cocker in his new book ‘Crow Country’.

Wednesday, 19 September 2007

Bats make the most of late summer insects

Our local bats seem to have been busy of late. Each evening, just as dusk starts to settle over the town, two or sometimes three bats can be seen, each silhouetted against the last of evening’s light. There are two species that make use of our garden, something confirmed through chance encounters with individuals perched on walls or, in one case, caught in a mist net set for roosting thrushes. By far the commoner species is one of the pipistrelles, most likely the soprano pipistrelle. Up until just a few years ago it was thought that there was just one species of pipistrelle in Britain, then it was discovered that this one species was in fact two. One of these, the pygmy pipistrelle, tends to occur in smaller colonies in more rural areas, while the other, the soprano pipistrelle, forms larger colonies and often roosts in houses. In 2001, a third species, Nathusius’ pipistrelle, was found apparently breeding in east Norfolk. It’s presence was revealed by Susan Parsons who had picked up the species’ social calls on a bat detector used to monitor the colony of barbastelle bats at Paston Barns.

The other species using my garden is the brown long-eared bat, a highly distinctive species within the county; its close relative, the grey long-eared bat, is restricted to a small area in the extreme south of England. As their name suggests, long-eared bats can be distinguished from all other British species by their enormous ears, which are joined at their inner bases. These ears are used by the bat to pick up “reflections” which bounce back from objects caught in the bat’s weak echolocation pulses. Brown long-eared bats are leaf gleaners, typically hunting in lightly wooded areas and taking moths and other insects from the surface of leaves. The tall sycamore in our neighbour’s garden appears to form part of the hunting beat used by one or more of these bats, and they can be seeing making relatively slow passes around the tree. The flight of the local pipistrelles has a more frantic feel about it.

I have encountered brown long-eared bats on and off over the years. The species had both a breeding colony, some 40 to 60 strong, and a winter hibernaculum at Wolterton Hall in north Norfolk, where I used to live. In the summer moths, the breeding females and their young occupied the attic space above the old stable block, while in winter they were to be found in the cellars under the hall – where temperatures were buffered against outside ambient fluctuations. Nowadays, I only tend to see one close-up when it perches on the sheltered wall of my side passage to dismember a moth. 

Tuesday, 18 September 2007

Dark bush Crickets

There was a stillness to the morning, a calm that had draped itself over the river, delivering an almost soporific quality to the air. The river flowed with a gentle ease, reflecting the lack of rain over recent days, as it murmured its way quietly downstream. Only the steady chirps of dark bush crickets broke the silence. These calls, with their resonant quality, had a tropical feel to them, something enhanced by the slightly humid air of this mild early morning. Every bush or piece of waterside vegetation seemed to host several crickets; each one was sat squarely like a little toad, squat in posture and dark brown in colouration. The short chirping call was an advertisement, directed at a potential mate.

I had come down through the meadows to collect two crayfish traps, set the previous evening. As I moved through the vegetation I could smell the umbellifers and that strange aroma that I have come to associate with wet meadows. It is an almost acrid scent, slightly unpleasant and vaguely reminiscent of a public lavatory, but with an underlying sweetness. I remember how the short-tailed voles, that I used to live-trap as part of a study into their ecology, also had this scent and how it clung to my clothes after early morning rounds of my traps. Did the voles acquire the scent through their diet or because they lived within the pungent vegetation? I am sure a botanist could tell me its source and the chemical nature behind it.

The two traps are packed with crayfish, despite being in the water for only a dozen hours, and it is clear that this section of the river still supports a very large population of signal crayfish. I have commented before upon the problems that this introduced species has caused, wrecking river banks, reducing fish populations and eliminating our own native species of crayfish. Although I am trapping these signal crayfish in order to monitor their numbers, and to test the effectiveness of different types of trap, I am not allowed to release them back into the river. Instead, they must be killed and so end up in a pot, cooked and then served with a garlic mayonnaise or forming the centrepiece of a pasta dish.

As I trudge back to the car with my bucket of crayfish, I become aware of another cricket calling. This is Roesel’s bush cricket, a large species with a distinctive high-pitched call. It sounds like a softly running fishing reel, of the old-fashioned style used for fly-fishing, and is one of the first sounds to disappear through the hearing loss than comes with age. I am glad that it is still part of my morning soundscape.

Monday, 17 September 2007

A hissing beetle

I was surprised and, to tell the truth, a little unnerved by the loud hissing sound generated by the small black beetle that I had just picked up. It was as if there was some kind of deep-rooted instinct to pull back from any creature that hisses at you; some evolutionary impulse, derived from ancestors exposed to the harsh realities of living alongside more dangerous animals than this small beetle. I knew what the beetle was, knew that it was harmless and yet I felt a momentary flash of fear. Why was this? That such a reaction was provoked, despite my knowledge of this beetle, might seem to suggest that this irrational response is inherited and not simply a behaviour learnt during childhood – nature winning out over nurture. However, things are not as clear-cut as this. Experiments using young, wild-born monkeys suggest that a fear of snakes is learned by watching how other group and family members react. A monkey that is shown a video of another monkey reacting to a snake, learns to fear snakes itself but, manipulate the video to replace the snake used in the experiment with a flower and a na├»ve monkey (that has never seen a flower) does not suddenly learn to fear flowers. This, and similar experiments, demonstrate that monkeys learn to fear some objects (e.g. snakes, spiders and water) more readily than they learn to fear other, typically less threatening, objects. So, there may well be a genetic influence at work here as well.

The beetle in question goes by the name of Cychrus caraboides – it has no English name and specialises in feeding upon snails. The hissing sound, subtle though it is, is presumably a measure deployed to warn off potential predators. A similar approach is adopted by a wide range of other insects and, indeed, by a number of vertebrates. Great tits, for example, will hiss if disturbed on their nest and it has been suggested that these birds, and a number of other cavity-nesting species, hiss to give the impression to a potential predator that there is a snake in the cavity and not just a defenceless feathered meal. In other species, notably snakes, the hissing is a warning which is backed up by a venomous bite. Because of this, and because of the underlying threat implied by the act of hissing, other, harmless, creatures have been able to use hissing as a form of deception – making out that they are dangerous when in fact they are not. Although I had nothing to fear from this beetle, I must admit to holding on to it for a rather shorter time than I would otherwise have done!