Saturday, 20 September 2008

Very rare visitor reaches Kelling

The arrival of a Particoloured Bat at Kelling last Saturday caused something of a stir among local naturalists. This is just the third record of this northern European species in Norfolk and the first since one was found in a wood yard at Great Yarmouth in August 1968. On that occasion the bat was thought to have arrived with a load of timber imported from the Baltic but the most recent arrival appears to have been unaided, with the bat reported flying in off the sea. Fortunately, the bat made use of an old pillbox on the beach and so Steve Gantlet of Birding World magazine was able to snap a brief photograph as it roosted.

There have been at least 23 confirmed records of this migratory species since 1980 and it is now recorded almost annually from somewhere in Britain, with Shetland and various North Sea oil and gas installations hosting the bulk of the records. However, it has been recorded as far west as Plymouth, Wiltshire and the Isle of Wight. Although recorded in all months of the year except February, most of the records come in spring or autumn, hinting at the migratory nature of the movements that may bring this bat to our shores. The normal breeding range is from the Alps and the Balkans in the south, Norway and Germany in the west and then up through Russia and east to the Pacific coast. Records from Britain, France and the Netherlands are therefore of migrants that have strayed west of their normal migration routes.

It may seem odd to think of a bat migrating, especially when you consider that most of our bat species survive the winter by entering hibernation. However, the more northerly populations of Particoloured Bat face harsh winter conditions and so are forced to move south or southwest of their breeding range to find somewhere more suitable for wintering. Movements of several hundred kilometres are typical, but there is a record of one moving some 1,780km, a staggering movement for such a small and seemingly delicate creature.

With a covering of long dark fur, tipped with silver-grey, this handsome bat has the appearance of being frosted. The fur of the underside is a bright creamy white, which contrasts with the darker upper surface. In flight the wings appear narrow and pointed, and these features equip this bat with a fast and manoeuvrable flight, ideal for catching small flies in open spaces. It is these flies that make up the bulk of its diet.

Although very much still a vagrant to our shores, it is interesting to note the scatter of summertime records which may just suggest that this bat could colonise Britain.

Friday, 19 September 2008

Buzzards drift by

Last weekend saw an influx of Honey Buzzards into the county. These rather unusual birds of prey are very rare breeders within Britain but larger numbers may sometimes pass through on their autumn migration. Although the numbers reported over the weekend suggest a sizeable arrival, no doubt driven by prevailing easterly winds pushing the birds west of their normal migration route, it is unlikely to match the influx seen in 2000, when between 500 and 1,500 birds were thought to have drifted over. The Honey Buzzard is a long distance migrant, breeding predominantly in Russia, eastern Scandinavia, Germany and France (with fewer than 100 pairs breeding in Britain). Arriving here from late April, the birds face a short breeding season before setting off south again to the wintering grounds in the tropical woodlands that lay to the south of the Sahara. Unusually for a bird of prey, the staple food items are the larval stages of wasps and bees, obtained as the birds break open the nests of these social insects.

Adult Honey Buzzards depart from the breeding grounds some two weeks earlier than the young and migrating individuals are normally seen singly; that is, unless you happen to be watching at one of the main points where birds gather to make a crossing of the Mediterranean. At Gibraltar, many hundreds may be seen together, utilising thermals to gain the height needed to make their gliding flight over the sea.

Picking out and identifying migrating Honey Buzzards is not straightforward. Similar in size to the more familiar Buzzard (itself now fairly well established within the county), the Honey Buzzard shows a great deal of variation in its plumage. As such, you have to place greater emphasis on the structural characteristics of the bird rather than expecting to see clearly-patterned underparts. The wings of a Honey Buzzard are proportionally longer and narrower than seen in Buzzard and are held horizontally, or even slightly dipped, when in gliding flight. Watch a gliding Buzzard and you will see that it invariably holds its wings in a shallow ‘V’. Another useful feature is the head which, in Honey Buzzard, appears small in relation to the size of bird. I have heard the head referred to as being rather ‘cuckoo-like’ and this is a pretty fair description of both its size and the way it protrudes so prominently. Young Honey Buzzards show a greater degree of variation in their plumage than adults. Dick Forsman, a leading expert on raptors, reckons that juvenile Honey Buzzards are probably the most often misidentified birds of prey in Europe. As such, you can see why you need to be pretty sure of what you have seen before calling one in.

Thursday, 18 September 2008

Late arrivals face a tough time

Judging by the number of young Hedgehogs seen over the last couple of weeks, it seems likely that they bred somewhere in the grounds at work. Arriving back at the office late after an evening lecture, I have been greeted by several of these delightful little creatures, each helping to control the slugs and snails at large in the new wildlife-friendly garden. However, the sight or one of more of these youngsters out and about in daylight is less welcome. Normally nocturnal, Hedgehogs are only seen abroad during daylight hours when food is in short supply. As such, it seems that these youngsters will face an uphill struggle to put on the fat reserves that they need to get through the coming winter.

Hedgehogs show two main peaks in the birth of their young. Most are born in June but those from late litters can be born as late as August or even September. Given that the young do not gain their independence until they are some four to six weeks of age, it seems that these youngsters are from a late litter. Born blind in a breeding nest, they would have developed a set of white spines soon after birth; their eyes would have opened at roughly two weeks of age and by this stage they would already be capable of rolling into a ball as a defence against would-be predators. While the young from early litters should have little difficulty in reaching adult size prior to hibernation in late October or November, late-emerging youngsters may remain active through into December.

Fattening up in readiness for hibernation involves the deposition of white fat just under the skin and around the viscera. In addition, brown fat is also deposited and this plays an important role in starting the body up again when the time comes to emerge from hibernation. The magic weight for a Hedgehog is roughly 450g because individuals that fail to attain this weight before entering hibernation rarely survive the winter. The majority of young from the late litters end up entering hibernation at subadult size and so are unlikely to survive. Given the visual appeal of these mammals, and with a worrying decline in their population, it is easy to see why many of these underweight individuals are helped through the provision of some meaty pet food or taken to Hedgehog rescue centres as winter approaches. Foraging Hedgehogs can range over a sizeable area so I would not be surprised if some of those around here are getting a helping hand from some of the nearby households. I shall have to see how they fair over the next few weeks.

Wednesday, 17 September 2008

Catching up with the migrants

It was an early start, leaving well before dawn in order to be in place as the sun came up. Travelling up the A11 towards Norwich and passing through a series of heavy showers made the early start seem all the more ridiculous but as we approached the east coast our mood brightened, mirroring the clearing skies. By the time we reached the dunes at Winterton the weather conditions were just about perfect for picking up on the visible migration likely to be taking place, as small birds passed south on their autumn journey.

Watching visible migration can be an unpredictable pastime; earlier in the week there had been big ‘falls’ of birds much further north and we were uncertain as to our chances of catching up with good numbers of birds this far south. However, things can change and the weather conditions over western Europe were such that there should have been some good birds on the move. This unpredictability can both add to the excitement of this form of birdwatching (who knows what might turn up) and prove frustrating (with few birds passing over). It also involves a lot of standing in one spot and scanning the sky, scanning to pick out the small specks passing over and straining to hear a diagnostic call.

It did turn out to be a quiet morning, with only small numbers of birds passing overhead; a few finches, the odd wagtail and a single Tree Pipit. There were also a few Rooks, arriving singly from the east. Since we could not see the shore from our position it was not clear if these were migrant birds, arriving from the Continent, or local birds that had been feeding along the tide line. Then there was the Sparrowhawk, working its way along the dunes. Again, this could have been a passage bird, newly arrived, or it could have been a local, like us hoping to connect with some migrants. After an hour or so of watching it became clear that we should turn our attention to the bushes and shrubs that lined the back of the dune system. Here, sheltered, below the low cliff-top gardens were feeding and roosting opportunities for migrants that may have arrived the previous night. Working our way slowly south, we soon turned up a rewarding mix of birds, many of which were migrants. As well as Willow Wabler and Chiffchaff, there were Blackcap, Whitethroat and even Siskin. Spotted Flycatcher and Pied Flycatcher could be seen in the same field of view through the telescope and, in such good light, we were rewarded with a fantastic morning of birdwatching. We’ll be back again over the coming weeks to see what else we can pick up.

Tuesday, 16 September 2008

A place on your table?

The combination of warmth and rain over recent weeks has triggered a mass of fungal fruiting bodies to emerge across the countryside. Fairy rings of mushrooms dot many of the grassland swards around here and little groups of toadstalls adorn decaying stumps or cluster around the root balls of still living trees. Some of these fruiting bodies would make a tasty meal but knowing which requires a degree of skill and understanding. Over the years I have sampled a number of different fungi; from the meaty textured Cep through to the delicate flesh of the Parasol Mushroom and the butter-greedy Giant Puff-ball. However, my real interest remains in the natural history of these organisms rather than in their culinary value.

In particular, I have always been interested as to why some species are highly poisonous while others (even closely related ones) remain entirely edible (and rather tasty). For example, one of our most dangerous species, the Death Cap, contains a cocktail of poisons that not only interferes with some of our body’s most fundamental processes but also actively targets cell nuclei in the liver and kidneys. Death comes after a week and the species is responsible for 93% of all fungi-related poisonings in Europe; yet despite this, slugs, maggots and Rabbits all seemingly eat this toadstall with impunity. Is it a chance of chemistry that has made the Death Cap so deadly to us?

The Death Cap belongs to a wider group of fungi known as the Amanita and this group (of which we have roughly 30 species) contains toadstalls with some wonderful names. Along with the familiar Fly Agaric, there are the Panther, the Blusher, the Destroying Angel and the aptly-named Fool’s Mushroom. While some Amanita are edible (for example, Caesar’s Mushroom – which has been prized since Roman times) most are inedible and a few are deadly. Several species are considered edible after thorough cooking. The toxins of the Blusher, which attack red blood cells and cause a form of anaemia, are broken down by parboiling. The same is true of the toxins contained in the Grisette and Tawny Grisette, two species that were formally thought of as being edible without the need for cooking! The Amanita are fairly easy to identify as a distinct group because they share a number of common features that can be seen in the field. Separation of certain species within the group is, however, less easy. This is another reason why the comments made by one famous mycologist in describing these toadstalls are best followed. He noted that this is a group of fungi ‘to which it is better to devote a purely botanical interest than to give them a place on your table.’

Monday, 15 September 2008

The silent hunter

I have sometimes heard the Barn Owl referred to as ‘the silent hunter’, a particularly apt description for what is one of our most engaging birds. Many years ago I undertook a study into the habitat associations of various small mammals, the favoured prey of the old white owl, and this involved spending many hours on my knees measuring and sampling grassland habitats. The study area was part of the hunting range of a pair of Barn Owls and in some years the birds were joined by a neighbouring pair as they hunted over the ground. The birds were often to be seen quartering back and forth across the meadow, their slow flight designed to help them detect small mammals in the sward below. Every now and then one of the owls would fly right over my prostrate form, the bird completely silent as it passed within three or four feet of me. I guess that I was such a regular feature on the meadow that they had come to accept me as part of the landscape.

Silent flight is obviously important for this active hunter, allowing a close approach to the mice, voles and shrews that form the bulk of its diet. The silent flight also increases the effectiveness of the owl’s already exceptional hearing, reducing any unnecessary noise that might interfere with its efforts to secure prey. If you have ever handled a Barn Owl then you will know just how soft the plumage is, beautifully contoured to cut down on drag as the bird moves through the air. The individual wing feathers also show modifications to help reduce noise. Each of the primary feathers has a fine comb-like fringe along its leading edge and a velvety texture to its upper surface. Collectively, these features reduce turbulence as air rushes across the surface of the wing, which means less resistance and less noise in flight. The wings themselves are broad and fairly long, enabling the owl to perform its buoyant flight with surprisingly little expenditure of energy.

With the fieldwork finished I no longer see Barn Owls on such a regular basis and close encounters are now a ‘red-letter day’. However, there are a few breeding pairs in this south-western corner of the county and I still get a real buzz from seeing them. Just the other morning, a very pale individual (probably a male) was quartering a wet meadow near the village of West Stow. As it moved across the field, periodically dropping down to snatch at some hidden prey item, I felt very tempted to hunker down in the vegetation to see if it would make a close approach.