Friday, 30 June 2006

Have you spotted a Great Spot?

Today sees the launch of a new national survey of great spotted woodpeckers. A collaboration between the British Trust for Ornithology (BTO) and BBC Radio 4’s new nature series ‘Shared Earth’, the survey aims to find out how great spotted woodpeckers use gardens during the summer months. Results from the BTO’s year-round Garden BirdWatch scheme have revealed that great spotted woodpeckers increase their use of gardens from the end of June through into early August. This ties in with a period during which newly fledged woodpeckers are seen to visit garden bird feeding stations alongside their parents. The team running the project want to establish which types of food are used and the extent to which visits to gardens are driven by the nature of surrounding habitat. As a woodland species, the great spotted woodpecker is most likely to use gardens close to woodland but the team want to find out how far the birds will go to make use of the food provided by garden birdwatchers.

The survey also aims to find out more about one of the less pleasant aspects of great spotted woodpecker behaviour, that of nest predation. These woodpeckers are known to drill their way into wooden nestboxes to predate young tits but it is not known how widespread this behaviour is. When you think of nest predation you tend to think of cats, magpies and rats, rather than woodpeckers, so it may come as something of a surprise to some readers to discover that these striking birds don’t just feed on insects taken from dead wood. In fact, they also eat a lot of seeds (particularly of pine and spruce).

Adult male and female great spotted woodpeckers are readily distinguishable. The male has a small patch of bright red at the back of his head and a larger area of red underneath his tail. The female also has this patch of red under her tail but lacks the patch on the back of her head. Young birds can be separated from adults by the red cap covering the top of the head and by the fact that the area of red under the tail is rather pale, almost washed out.

If you have woodpeckers breeding close by then you may find them putting in an appearance in your garden over the coming weeks, providing you with an opportunity to contribute to the project. The survey itself is web-based and will be accessible from today through until August and can be accessed from The Radio 4 ‘Shared Earth’ programme is being broadcast at 3pm today and has more information on this project and on other projects that should help get you out and about in the countryside.

Thursday, 29 June 2006

Shieldbugs raise a stink

Many readers will be familiar with the shieldbugs, a group of large and distinctive insects encountered during early summer and autumn. Most shieldbugs can be identified on sight but, with only a handful of the largest and most common species having English names, we know rather less about their distribution and status than we might. Adult shieldbugs will often remain still when approached, only flying off with a loud buzz of wings as a last resort. Such bold behaviour, unusual in an insect, comes from an ability to produce a pungent smell from strategically positioned stink glands.

In shieldbugs, the forewings are hardened in their front half and membranous in their back half. This characteristic feature gives rise to the name Heteroptera (different wings), used to describe these and a number of related insects. The forewings overlap to form a diagonal cross at the front of which a shield-shaped triangle is formed, which gives these bugs their name. A second characteristic feature is the four-jointed beak, known as a rostrum, with which the bugs can ingest fluids (either from plants or other insects). When not in use the beak is folded away underneath the body. Most shieldbugs spend the winter as adults, emerging in spring to mate and lay eggs. Mating is a somewhat protracted affair, with male and female paired end to end for up to three and a half days. The eggs are laid in clusters and, in all but one species, left alone to develop. The barrel-shaped eggs change colour as they mature and as hatching approaches you can see the eyes through the shell. A temporary projection at the back of the head allows the young nymph to push its way out of the shell and into the wider world. In one species, the female sits over her eggs and newly hatched nymphs to protect them from predators. This behaviour has been known about for more than 200 years and gives the species its name ­– parent bug. 

Other shieldbugs with English names tend to be named after the plant species upon which their young feed. Hence the hawthorn shieldbug is most commonly associated with hawthorn, the birch shieldbug with birch and the gorse shieldbug with gorse. Named after its appearance rather than its choice of foodplant, the green shieldbug is probably the most familiar species, though it is not our only green coloured shieldbug. This species can sometimes be found in gardens on ornamental shrubs or runner beans. As a group, shieldbugs are well worth study. Large, approachable and easy to identify, ideally with the help of Roger Hawkins’ Shieldbugs of Surrey (published by Surrey Wildlife Trust), they are well worth the effort.

Wednesday, 28 June 2006

Unexpected visitor raises a question or two

It came as something of a shock the other morning to discover a toad sat in the middle of the kitchen floor sporting a look of passive acquiescence. I was still bleary-eyed, roused from sleep by two dogs intent on their morning walk, and there it was, sat on the carpet, raising the question of how it had made its Houdini-like appearance in my kitchen. Needless to say the dogs were decidedly non-plussed, having developed a grudging respect for toads at a young age. Anything that can inflate itself and exude an unpleasant chemical when approached by an overly-inquisitive puppy soon earns respect. I picked up the toad and deposited it in the garden. The toad was a youngster, not a toadlet but a two-inch long juvenile from last year. I suspect that it had clambered up the pipe that links the outlet from the washing machine to the outside drain but while this answered the question of how it had got into the kitchen it did raise the question of where it had come from.

Like our other amphibian species, the common toad is dependent upon water for breeding but at other times of the year it can be found in gardens, woodland and even grassland. Research into the ecology of the common toad has revealed that individuals typically overwinter within a 1,000 metres or so of their breeding pond. Since our small wildlife pond only ever has frogspawn, it seems likely that there is a suitable breeding pond nearby, and that this individual came from there. Toads favour larger-sized ponds than frogs, with an optimal size being about 1,000 square metres, with plenty of marginal cover. They also seem to prefer ponds containing fish, perhaps because fish find their tadpoles unpalatable but will feed on the newt and frog tadpoles with which the toads compete. Deliberate attempts to introduce common toads into garden ponds invariably fail so competition with other amphibians may not be the only reason why we see adult toads in our gardens but not breeding in our ponds.

There is an interesting footnote to this episode. Last year, our new neighbours were figuring how to convert a rather large and overly deep pond into something more wildlife friendly. The previous owner had dug the pond in the expectation of populating it with carp but never did. He only managed to fill it with water just prior selling the house. Before the pond could be adapted several strings of toad spawn appeared followed by a number of tadpoles. With no vegetation within the pond these soon perished and that was that. Perhaps a new and bigger wildlife pond might tempt them to breed again.

Tuesday, 27 June 2006

Parenthood takes its toll

Our cock blackbird and his mate are looking a bit frayed around the edges, perhaps unsurprising now that they are on their third nesting attempt. The first attempt took place several weeks ago and was successful, with two fledglings harassing their father for food with plaintive begging calls. A second nesting attempt was initiated by frenetic nest building activity in a small holly bush growing against my neighbour’s wall. The female seemed to take great delight in pulling apart one of my wall-mounted baskets to find suitable fibres with which to line the nest. The two birds were dutiful parents and it was not long before they were again busy feeding growing chicks. Then, one evening and with much agitation, they appear to have lost their chicks to one of the many neighbourhood cats. The nest, it seems, was easily accessible and there was nothing that the parents could do. Two days later and the female was doing her best to finish off my wall-mounted basket, showering the ground with soil. She might as well have nested in it! In the event, she built a new nest deep within the climbing rose that sprawls across the timber arch by our pond. At least this site should be safe from the cats. The first of her three (possibly four) eggs was laid nine days ago and she is now busy incubating, her tail or head just visible – depending upon how she is sitting.

Throughout all this the pair have been rather endearing, following us around the garden and full of optimistic expectation that our gardening activities will reveal some tasty morsel or other. The hen is more trusting than her mate and will often approach within a foot or so when I am planting or weeding. His contribution to our general enjoyment comes in the form of a serenade, delivered at various times throughout the day from the top of the shed or next door’s apple tree. The rich blend of notes provides a wonderful backdrop to a warm summer evening or a gentle introduction to a new day. While his song may have the crisp signature of a smart concert musician, his appearance is becoming more unkempt by the day. Fatherhood, it seems, takes a heavy toll on your appearance. The underlying reason for the state of his plumage, in particular his body feathers, is that this third breeding attempt is cutting into his annual moult. Over the next few weeks he will replace his feathers in a regimented order, renewing worn and damaged ones and gaining a smart new appearance. The hen too will need to moult but right now she has other things on her mind.

Monday, 26 June 2006

Trust works to secure Swallowtail's future

The reserve at Wheatfen Broad is well worth a visit at this time of the year. Situated between Surlingham and the River Yare, the area is used as a spillway during the winter to reduce the risk of flooding in Norwich. In late June it is alive with the bird and insect life attracted to the mixture of carr woodland, fen and reedbed. The cottage at Wheatfen Broad was home to Ted Ellis (the great naturalist and broadcaster) for forty years and the reserve itself is now managed by the Ted Ellis Trust, in memory of his achievements.

The reserve is also home to the swallowtail butterfly, one of our rarest and most spectacular species. The native race, britannicus, with its striking cream, black and blue markings, occurs only around the Norfolk Broads, where it can be observed on the wing from late May through to mid-July. The adults tend to fly on hot, cloud-free days, searching for potential mates and (in the case of the females) suitable sites for egg-laying. Like many of our butterfly species, the swallowtail caterpillar is associated with one particular food plant. In this case it is milk-parsley, a native species favouring tall-herb fens and which, like the swallowtail, now has a much-reduced distribution centred on the Broads. Swallowtail eggs tend to be laid on prominent plants, either those that stand clear above the surrounding vegetation or those positioned on the edge of paths cut through the fen. The eggs, which darken as they mature, are surprisingly easy to find – it’s just a case of checking the most likely plants. The tiny caterpillars initially resemble bird droppings but, after the second of several moults, they adopt a conspicuous green, black and orange colouration – a warning to potential predators of their unpalatable nature.

Swallowtails can be seen at a number of our broadland nature reserves, including Strumpshaw, Hickling, Catfield Fen and Wheatfen and genetic studies have shown that there is good interchange between the various populations. A detailed understanding of the habitat requirements of the swallowtail has allowed the development of habitat management regimes sensitive to the needs of both the butterfly and its food plant. Management of sedge fens on a three-year rotation allows milk-parsley to flourish, bolstering swallowtail populations and helping to secure the long-term future of this species. However, there are other risks that need to be taken into account, including any lowering of the water table, pollution of ground water by nitrates or phosphates and scrub invasion. Thanks to the efforts of the Ted Ellis Trust, Wheatfen seems secure from these threats for now. Let us hope that this wonderful butterfly continues to thrive.

Saturday, 3 June 2006

Enigmatic falcon graces our skies

When asked to name their favourite bird of prey, many birdwatchers will answer “peregrine falcon”. No doubt they are impressed by the size and power of this aerial hunter. However, for me the peregrine is something of a brute and lacks the grace and enigmatic beauty of the smaller hobby, a migrant raptor that breeds here and winters in Africa. Although arrivals usually begin in May, many individuals will only now be reaching our shores. As a breeding bird, the hobby is elusive and tends to be under-recorded, with the sighting of a single bird being the most typical encounter during the summer months. At this time of the year, however, newly arrived individuals may gather together to feed over insect-rich wetlands and along river corridors. Hickling Broad, Catfield Fen, Strumpshaw and the Hockwold Washes are sites where half a dozen or more individuals may be seen feeding on insects, caught and eaten in flight. Large beetles, dragonflies and butterflies are favoured, most often taken on still warm days. The hobby will also take small birds and is well-known for its ability to catch swallows, martins and swifts on the wing. Given the manoeuvrability of these species, it is no surprise that the hobby is a true master of the air. The long tail and long curve of the wings provide the power and dexterity needed to catch such agile prey. Avian prey is most important when there are hungry young to feed.

It is hard to gauge just how many pairs of hobby breed within Norfolk. There are certainly a number of pairs around Breckland, nesting in the abandoned crow nests that can be found in the taller pines so characteristic of Breckland field boundaries. There are also pairs within Thetford Forest, the Stanford Training Area and around the Broads. The most recent estimate suggests that there are between 10 and 20 pairs breeding annually within the county. Favoured breeding territories tend to be used from one year to the next, although the birds may not, necessarily, use the same nest.

The hobby population seems to have faired well over recent decades and there has been a marked increase in the size of the East Anglian breeding population. During the Nineteenth Century, egg collectors and gamekeepers persecuted the species quite heavily, but conditions are now more favourable. It has been suggested that the increase has been driven by the flooding of old gravel workings and the associated boom in dragonfly populations but this may only be part of the story. Bans on the use of harmful pesticides and recent global warming may also have had a part to play. Whatever the reason, it is us birdwatchers who are reaping the benefits. 

Friday, 2 June 2006

Murder, sleaze and Swallows

If, like me, you have a bit of a soft spot when it comes to the swallow, you might find it best to skip today’s ‘In the Countryside’, especially if you wish to maintain your unblemished image of this quintessential summer visitor. If you choose to read on, then I must warn you that you are about discover that not all is as it seems in the apparently harmonious world of the swallow. You see, even though the swallow is outwardly monogamous, the private life of this long-distance traveller is sufficiently full of sleaze to find favour with your average tabloid hack. Although most pairs will generally remain together for the breeding season, and often for life, a short lifespan means that there is a high turnover of partners and quite a few unpaired individuals looking for a mate.

Unpaired males will visit the nests of other swallows and associate with paired females. It is thought that they do this to become the most likely candidate for new mate should the established pair divorce or the male of the pair die. Females make such visits less frequently but will do so if their own nesting attempt has failed. Rather than wait for an existing pair to divorce, a male may sometimes help things along a bit by killing an entire brood of nestlings. A female whose brood has been killed in this way will be more likely to divorce her mate, since he will have failed in his duty as guardian. This leaves her free and more receptive the attentions of the unpaired male who committed the killing. Although infanticide may be a beneficial strategy for an unpaired male, the incidence of such behaviour is not that high. In one study, infanticide was recorded in under 5% of cases and there are records of individuals who practice infanticide in one year but not another. While such behaviour may be abhorrent to us, in the cut and thrust of nature it is just one of the strategies employed in an attempt to pass on genes to future generations. Interestingly, paired Swallows exhibit a number of behaviours to reduce the risk of losing a brood to infanticide. The first, and simplest, of these is nest guarding. Paired males that spend more time at their nest suffer lower levels of infanticide than males which show poor nest attendance. There is even the possibility that females may act to reduce the risk of infanticide through mating promiscuously with other males. If a male believes that he has fathered some of the young in a nest he will be less likely to kill them. Will you ever look at swallows in the same way again?

Thursday, 1 June 2006

Difficult times for Grizzled Skipper

The recent run of wet and windy days has proved to be frustrating, not least because the only decent weather seems to arrive when I am stuck at work and not when I wish to be out and about looking at butterflies. The other day it all got a bit too much for me and I ventured out in less than favourable conditions to see if I could catch up with a grizzled skipper. This species is one of our smaller and less obvious butterflies and has had a hold on me since I first attended a workshop on it several years ago. Although formerly widely distributed across England and parts of Wales, a substantial decline has left the grizzled skipper in a precarious position in Norfolk, restricted to a handful of colonies, a pattern repeated across much of its former range. This means that you have to work hard to get good views and photographs of this rather understated species.

Grizzled Skipper, by Mike Toms

I made the short drive across to Foulden Common, usually my first port of call when looking for this species. If I find them on the wing here, it gives me the confidence to move on to other, more difficult, sites. The weather was predominantly overcast but occasional breaks in the cloud allowed the warmth of the sun to burst through. Even if no other butterflies appeared to be on the wing, this gave me hope. In the event I need not have worried, for within ten minutes of arriving at the common, I had connected with my first grizzled skipper.

In order to find them, you have to cover a lot of ground, walking slowly forwards and scanning the short turf to see what you flush before you. Often, the small brown lepidopteran that flies up and away turns out to be one of the day-flying moths, typically a mother shipton or latticed heath but every now and then it will be a grizzled skipper. When I first started watching them, I used to have to catch an individual to be sure of identification but now I can identify them in flight and have worked out a way to approach them. Once flushed, the important thing is to watch where the butterfly lands, then approach to within about ten feet. Then it is a case of getting down on your hands and knees and making a slow approach. By doing this I usually manage to take up a position within a foot or so of the butterfly, ideal for macro photography. The dull conditions of the other day proved ideal for getting close and I managed to get some of my best ever shots and to overcome my frustration with the weather.