Saturday, 21 August 2010

Borderland


I have slipped over the border on the basis of a tip-off, leaving Nelson’s county behind as I cross the river south of Thetford. A friend told me that he had heard them the other night as he drove along the road, windows down because of the sultry conditions. What he had heard was the stridulating song of the Great Green Bush Cricket, one of our most impressive insects. Adult Great Green Bush Crickets are chunky beasts, 4cm long in body and both large and loud enough to be worth a special trip over the border into Suffolk.

This particular colony is well known, close to the road and just across the river from the county boundary. Knowing they are here is one thing because, despite their size, they are not the easiest of creatures to spot. Despite the proximity of the road, there is something gentle and welcoming about this spot; the presence of a heron that lifts slowly out of the shallow water upon my approach and the controlled flight of hawker dragonflies. Beyond the small area of mown grass, no doubt maintained by the Environment Agency to retain access to the small weir, there is a wall of bracken which reaches to head height. It is in here that the crickets will be positioned, away from prying eyes and difficult to reach. I will have to be content with listening to their stridulations, not dissimilar to the more familiar Roesel’s Bush Crickets that stridulate outside work. Even this early in the afternoon there are one or two individuals in song and between the passing cars I can listen and marvel at such a cleverly constructed sound.

These are southern creatures, arriving here after the passing of the last glaciation they have been slow to spread north, highlighting their dependence on warm summers. Most populations are coastal and the species is distinctly local inland. They do not occur much further north than this and so they remain a tantalising colonist, not quite on my patch. Wasteground such as this, dominated with thistles and bracken, meets their needs and this scruffy patch provides ideal habitat.

I venture under the road bridge, working my way along the narrow ledge that sports the old remains of Otter spraints – a sure sign that they are doing well on the river and have ventured upstream from more familiar sites a mile or so distant. The cover on the other side of the road is less suitable, more heavily shaded and I soon head back under the bridge into the warmth of the fading sun to listen to the crickets for one last time. I should return one evening, torch in hand, to see if I can spot them.

Friday, 20 August 2010

Them ruddy ducks!


Conservation can be a brutal business and there are times when sensible, sound and necessary actions require practitioners to implement uncomfortable management options. Nowhere has this been more evident than in the case of the Ruddy Duck. This North American species was first introduced to Britain over half a century ago. Originally held within waterfowl collections, the duck escaped and became established as a breeding species more widely across Britain. By the start of 2000 there were estimated to be some 6,000 Ruddy Ducks living wild in Britain.

The main problem with these ducks was that they did not remain here but instead ranged more widely across Europe and, from the early 1990s, they began to turn up in Spain. Spain is home to the White-headed Duck, a species that is very closely related to the Ruddy Duck and one that has been developing naturally because it is reproductively isolated from its cousin over the water. The newly arrived Ruddy Ducks were found to hybridise with the native White-headed Ducks. If this were allowed to continue then in all likelihood it would lead to the extinction of the White-headed Duck.

Following a great deal of research work, and many discussions, a decision was taken to eradicate the population of Ruddy Ducks living in Britain. Not everyone welcomed this process and there has been a fair amount of bad feeling in some quarters. In some cases the arguments against eradication have been well-intentioned and well-researched; in others they have been ill-informed. The process, however, looks as if it is nearing its end; the latest count suggests that there could be as few as 200 Ruddy Duck left, with many of these associated with traditional sites towards which the eradication work will remain targeted into 2011.

It is a shame that conservation practitioners have been forced to take this action. It is, after all, a consequence of human activities that the Ruddy Duck was brought to Britain in the first place. It is our fault that it escaped and our fault that its presence threatens another species. I know that some readers might argue that if the two ‘species’ can interbreed then they are not really two different species. Such an argument is an oversimplification, since it fails to understand that without our na├»ve meddling these two species would have remained reproductively isolated because of their geographical separation. Over time they would have become further isolated, as mating behaviours diverged and genetic compatibility declined.

That conservation practitioners must sometimes eradicate a species from an area into which it has been introduced, is never an easy option. It is a sad consequence of the wider damage we humans continue to inflict upon the world.

Thursday, 19 August 2010

A silvery tree-top dance


A friend recently told me of a White-letter Hairstreak butterfly that had appeared in her Thetford garden. The butterfly, which spent a few minutes on some climbing beans, soon disappeared but the proximity of the garden to a site where the butterfly had once occurred hinted at its origins. A trip to the site in near perfect weather revealed the presence of at least one other individual and provided welcome news that the colony is still in existence.

The chances are that you may never of heard of the White-letter Hairstreak. It is one of our more enigmatic butterfly species, spending most of its life in and around the canopy of an elm tree. Given the tremendous damage that Dutch Elm Disease did to our hedgerow elms, together with the butterfly’s lifestyle, it is easy to see why this species is so rarely seen. It seems certain that there are many White-letter Hairstreak colonies that go unrecorded and even butterfly enthusiasts tend to just visit the best-known local colonies.

This butterfly derives its name from the white hairline markings set against the pale brown underwings. The upperside of the wings is almost never seen, not least because the butterfly sits with its wings folded. Watching the White-letter Hairstreak is best done with a pair of binoculars and, when in active flight, the silvery form of the butterfly can be seen to tumble and circle its way around the treetops. Rarely moving any distance from the elms with which it associates, your chances of getting a close view are not good. There are some places and times where White-letter Hairstreaks descend from the treetops to nectar on thistles or other flowers but they only seem to do this when honeydew is in short supply. Honeydew is the sugary substance produced by feeding aphids; it collects on the surface of leaves and this means that butterfly does not normally have to leave the tree in order to feed. In fact, the entire lifecycle is acted out at canopy level. Courtship, mating and egg-laying all take place high off the ground, with the resulting caterpillars feeding, growing and then pupating within the elm’s luxuriant growth.

Despite the huge impact that disease had on the elm population, the hairstreak has survived well in many of its former haunts. One reason for this may be that the species of elm preferred by this butterfly (the Wych Elm) was less severely affected by Dutch Elm Disease than other species of elm. An additional factor may well be the changing climate, the warmer conditions allowing this butterfly to expand its range northwards. East Anglia was one of the former strongholds so it is worth checking out your local elms.

Wednesday, 18 August 2010

The lure of Fennel


The fennel that dominates the small bed outside of our kitchen window is alive with insect life. To be honest this is the main reason why I have not moved it elsewhere, tolerating its scruffy domineering form because of the fascination I derive from a few minutes stood watching the many and varied insects that arrive to feast on its juices. At the moment it is the small yellow and black forms of hoverflies that catch my eye, so great is their number. This sudden influx suggests that these are immigrants, newly arrived from continental Europe and part of a wave of immigration that has also delivered the Silver-Y moths that emerge as soon as darkness falls.

Hoverflies have always struck me as interesting insects and, importantly, a group which it is possible to tackle because of the relatively small number of British species (roughly 270) and the relative ease by which most can be identified. Just as there is diversity in their adult forms, with some excellent bee mimics and others strongly reminiscent of certain solitary wasps, so there is diversity in their pupal forms. Some spend their pupal stage in tree sap, some in decaying vegetation and others in water or even dung! I didn’t say they were pleasant, merely interesting.

Of course, it is not just hoverflies that are attracted to the fennel. There are many other small flies, most belonging to families of flies that I have never been brave enough to tackle, plus various beetles, including many familiar ladybirds and soldier beetles. A walk around the rest of the garden soon reveals that the fennel is the main draw at the moment, with the very dry conditions of earlier in the year having greatly reduced nectaring opportunities elsewhere. Fennel has a deep tap root, allowing it to survive well in such dry conditions and, incidentally, making it rather persistent once established.

The attractiveness of the fennel has an obvious parallel away from the garden. Walk along a quiet Norfolk lane or explore a bit of waste ground and you will encounter other plants from the same family as fennel. These other umbellifers also do well for insects, with soldier beetles in particular a common sight feeding on the tiny flower heads. I would imagine that many of these visiting insects are rather short-tongued and that this is why they visit these smaller flowers.

Although fennel is a familiar culinary herb, sometimes used as an ornamental in borders, it has also become established beyond the garden gate. Its Mediterranean origins explain why the Romans brought it to Britain and also why, outside of gardens, it is largely restricted to southern parts of Britain.

Tuesday, 17 August 2010

Old gravel pit a welcome stopover


Over recent weeks there has been a pleasant inevitability to my weekly visits to the old gravel workings. Each week, as I approach the shallow fringes of one particular pool, I invariably see the white-flash of a Green Sandpiper flicker out low across the water and away. On some days there may be two or even three of these delightful little birds feeding together. Watching them jink away, all white rump and dark body, they are reminiscent of oversized House Martins. These sandpipers are most likely passage birds, already working their way south on an autumn migration that will take them to a wintering area that extends from western Europe, down around the Mediterranean Basin and into sub-Saharan Africa. Some do overwinter here, often returning to the same favoured spots, and I have come across them on occasion at that time of the year.

The birds that I have been watching recently will have come from breeding grounds that stretch across the boreal forest zone, north to the edge of the Arctic Circle and south to those countries bordering the Baltic. Breeding does occur in Britain but it is a very rare event and largely restricted to the North of Scotland. Unusually for a wader, Green Sandpipers do not nest on the ground but instead make use of old pigeon nests and squirrel dreys. This might explain their breeding season preference for coniferous forests dominated by spruce or pine and with access to small water bodies.

Like certain other species using these northern breeding grounds, the autumn migration starts early. In fact the Green Sandpiper is probably the first wader to be on the move come autumn, with the first returning birds reaching Britain in mid-June. Peak numbers do not appear until July and then the passage continues through into late September. These early arriving birds will be adults, most likely females who have left their unfledged young in the care of their mate. By late July or early August, the first of the juveniles have reached Britain, stopping to feed on freshwater lagoons and old gravel-pits with unvegetated muddy fringes. Later in the year, when we are probably looking at birds that are going to overwinter here, the birds become more solitary in habits, often moving away from still water sites to those where the water is in motion. Presumably this is linked to the better feeding opportunities available on rivers, streams and watercress beds during the winter months, although it is worth noting that the birds will return to lagoons and gravel pits each evening, when they retire to roost. The presence of these delightful birds alerts me to the approaching autumn and a season of change.

Monday, 16 August 2010

A stately bird returns


The news that at least four pairs of Spoonbills have bred successfully in North Norfolk this summer is extremely exciting. Although not completely unexpected, with increasing numbers of birds now recorded annually and with successful breeding having taken place elsewhere in the country, it is still staggering to think that this is the largest breeding colony seen in Britain for more than 300 years. Reliable information on the former status of the species within Norfolk is rather hard to come by but it seems certain that Spoonbills once bred at Claxton, Reedham and Cantley, probably up until the mid-seventeenth Century. The loss of coastal lagoons to land reclamation may have been one reason for their disappearance from the county’s breeding avifauna.

These elegant and distinctive birds add a taste of the exotic to some of our shallow coastal pools, especially at this time of the year, when many immature birds are moving away from their breeding colonies. The characteristic spoon-shaped bill, which gives the bird its name, is held slightly open when feeding. By sweeping the bill from side to side the bird can filter out invertebrates, small fish and other prey. This method of feeding requires shallow water, of a fairly even depth, and with a bottom of mud, silt or fine sand. This is why the best places to see these birds within the county are the coastal lagoons at Cley, Titchwell and Salthouse.

The presence of our expanding population has its origins in the successful Dutch colonies, which have also been increasing over recent years. This increase, also witnessed in the Spanish population, is in contrast to the significant declines seen in other parts of Europe, notably Russia and Austria. Spoonbills are migratory in habits, retreating south to wintering grounds located across West Africa, and they tend to leave our shores during late August and September. They are also surprisingly mobile birds, moving between different feeding sites on a daily basis and with immature birds moving between breeding colonies and wide spatial scales. For example, an individual that was ringed as a chick in a Dutch colony in May 1988, was later seen in France in September of that year, then at a breeding colony in Italy in May 1991, before turning up at Hickling in August 1992.

It seems likely that the Spoonbill population in Britain has reached the point where it can now consolidate its toehold into more widespread colonisation. It will be following in the footsteps of another recent colonist, namely the Little Egret, and there is every chance that it will become an equally familiar sight around the Norfolk coast over the years ahead. It will be a truly welcome return for this stately bird.