Saturday, 12 November 2011

A daylight owl

It has been something of a remarkable autumn, with fantastic numbers of Short-eared Owls arriving in the county from breeding grounds further north. Many of these birds are likely to have made a substantial sea crossing; setting out from Scandinavian breeding grounds their arrival ‘in off the sea’ charted by birdwatchers all along the Norfolk coast. This autumn, there was a report of fifty of these stunning birds arriving at Titchwell in a single day, very much a red-letter occasion for the owl enthusiast.

Short-eared Owls are generally recorded arriving from mid-September onwards, with numbers peaking during October and a few stragglers arriving into the beginning of December. Some will remain on the coast, haunting the grazing marshes, but others move further inland to the fens or the riverside marshes at places like Halvergate and Chedgrave.

These owls are often portrayed as opportunistic wanderers, nomads that track the volatile breeding populations of their favoured small mammal prey. In a good vole season the owls do well and I suspect that this has been one such season. Come the end of summer, however, the small mammal population may sometimes crash, prompting the owls to look further afield for a meal. This combination of a good breeding season followed by a decline in prey abundance may drive the mass arrivals here but there is still a great deal that we do not know about these birds and their movements.

With its piercing eyes, tendency to hunt in daylight and buoyant flight, the Short-eared Owl holds a special place in my affections. Seeing one lifts the spirits on those flat winter days out on the marsh. Seeing several in the air together leaves me grinning from ear to ear! The buoyant flight, a characteristic shared with the Barn Owls that also hunt these wild places, comes about because of the shape of the wings. The broad wings are energetically efficient, allowing the owl to slowly quarter the fields and marshes over which it hunts, while scanning the ground for prey.

Examination of Short-eared Owl pellets – like other owls, Short-eareds cough up the undigestible parts of their prey – reveals that their winter diet in Norfolk is dominated by Field Voles, with other small mammals and small birds making up the balance. These pellets can be collected from the rough vegetation in which these birds roost. Some of the roosts can hold a dozen or more owls, the birds returning to the same site over many days. Knowledge of favoured hunting areas and their accompanying roosts make the Short-eared Owl one of more reliable winter visitors, providing viewing opportunities for the birdwatcher. In cold weather they can be surprisingly approachable (with care), affording stunning views.

Thursday, 10 November 2011

Adventurers Fen

If you follow the formidable Devil’s Dyke – a Dark Age earthwork that cuts across the chalk escarpment north-west of Newmarket, you will come to Reach and the edge of the Fens. It is border country, a line of Fenland villages that sit on a narrow strip of land between the slowly rising chalk behind and the vastness of the Fens beyond. Running north from Reach is a fenland lode (a drainage ditch) that joins the River Cam at Upware, just to the west of Wicken Fen. To the north-east of Reach is the village of Burwell, with its own lode, also tracking north-west and skirting Wicken Fen before joining the Reach Lode. Sandwiched between these two ditches, in a block of land that narrows to a triangular point, is Adventurers Fen, made famous by the artist and nature writer Eric Ennion.

In the early 1990s and new to the area, I had arrived already carrying knowledge of Wicken and its Fen, the last remnant of rich fenland vegetation, but I knew nothing of Adventurers Fen and its champion. Eric Ennion was born in June 1900 and grew up in Burwell; he went on to become doctor there in 1926. It must have been an exceptional time to be in Burwell in the 1920’s and 30’s. Secure in a reliable profession, Ennion was spared the hardships of the agricultural depression but able to watch nature’s return to a landscape that was ‘falling into disrepair. His interest in natural history, which had germinated in his childhood years, was channelled into sketches and paintings of the fenland wildlife. His sketches, often made from beneath a tarpaulin flung across his punt, are vibrant and alive; Ennion’s fellow inhabitants captured in pencil and watercolour. The combination of artist and naturalist, documenting a landscape soon to be lost.

With the outbreak of the Second World War everything changed. The fens around Burwell were drained and returned to agriculture, something that prompted Ennion to write a lament to the landscape he had felt so rooted in. Adventurers Fen, the book that was published in 1942, displays the intimacy that Ennion had with his local patch, not just the wildlife but also the villages, ditches and waterways. While it marks the sad passing of a watery world it also champions the local naturalist, highlighting the value of working a local patch over many years. Redshank, Coot and wild duck would have been Ennion’s everyday birds but, even so, he writes about them and paints them with enthusiasm and passion. His work has relevance today, with efforts underway to recreate something of this lost landscape, and through this work you can see something of the man and his world.

Lead beetles not always welcome

The Chrysomelids or leaf beetles are one of our more accessible groups of beetles. Most are rather colourful, many are relatively large in size and quite a few have an English name by which to refer to them. Although one of the largest beetle families worldwide, we have just 260 or so species here in Britain, some of which will already be familiar to farmers and gardeners as pests of agriculture, horticulture and forestry.

As the name suggests, leaf beetles feed on plant material, taken from a vast range of plant species, including ‘primitive’ plants like mosses and horsetails. Most show some degree of specialism, again highlighted in the name, for example: Rosemary Beetle (Lavender and Rosemary), Belladonna Flea Beetle (nightshades, Henbane and Thorn-apple) and Lily Beetle (lilies and fritillaries). The association with particular host plants may explain the seemingly steady arrival of species new to Britain, transported here on plants shipped around the globe to satisfy gardeners’ demands for the new and exotic. The Rosemary Beetle, a specimen of which was presented to me just the other day by a work colleague, is a recent arrival from the Mediterranean. First recorded from Surrey in 1963, it is now found in many counties across Britain.

Some of the larger Chrysolmelids, like Rosemary Beetle, are fairly long-lived (lasting two or more years). Others are interesting because of the ways in which they seek to avoid being eaten. The flea beetles, for example, have enlarged hind femora. These work in association with muscles to store energy that can be released with a spring-like action, catapulting the beetle away from danger. Some species feign death when disturbed, e.g. Lily Beetle, while others make a noise by rubbing two rough surfaces together in a stridulating action. Perhaps the most impressive forms of anti-predator device are deployed by the Bloody-nose beetles, who are able to deploy reflex bleeding from their joints. The ‘blood’ that emerges contains noxious and often toxic compounds which are quite enough to deter most would-be predators.

Many of the leaf beetles are capable of flight, taking to the wing on warm days. Mind you, perhaps with the exception of ladybirds and maybugs, we don’t tend to think of beetles as flying insects. This may be because their wings are so well concealed under the hard wing cases or elytra. Some of the leaf beetles are particularly good swimmers, with some species associated with waterside habitats. Again, this is a somewhat unexpected behavioural trait that is easily overlooked.

While the leaf beetles may be unwelcome by those of a horticultural bent, they are a fascinating group for the entomologist. Varied, colourful and sometimes unexpected in their habits.

Wednesday, 9 November 2011

Goldfinches attain clown-like masks

The garden has been teaming with Goldfinches over the last few months, with the good numbers of young suggesting it has been a successful breeding season for these delightful little birds. Initially, the young Goldfinches could be told from their parents by their lack of the characteristic red and black facial markings. By now, however, they have moulted through into their adult plumage and can no longer be distinguished by eye, as I watch them on the feeders through the kitchen window.

In the hand, when caught during a ringing session, it is possible to identify juvenile Goldfinches by looking at subtle differences in the shape of the tail feathers and the colour of certain wing feathers. Such differences come about because of the way in which these birds renew their feathers during moult. In most small birds that breed and winter here, the adults undergo a complete renewal of their feathers once the breeding season is over. Some species undergo a second, ‘partial’, moult just before the start of the next breeding season. Many of our summer-visiting migrants, however, will not undergo their annual moult until they have reached their wintering grounds, although some start the moult here before interrupting it just ahead of their long journey south. 

Most young birds follow a different strategy, replacing some feathers after the breeding season and growing others for the first time, but not acquiring full adult plumage until after the next breeding season is over. You can see this for yourself by looking carefully at male Blackbirds in the early summer. If you spot a male Blackbird who is all black apart from a few dark brown feathers in his wing, then he will be a bird born the previous year.

Getting young birds out of the nest quickly is an important strategy because it reduces the period when they may be particularly susceptible to predation. Young birds grow rapidly in the nest and need to be able to fly when they fledge. Because of this, the young tend to invest relatively little in the growth of body feathers, concentrating their efforts instead on the all-important flight feathers. As a result, newly-fledged young often look rather fluffy and ‘loose feathered’, but they will soon grow the remaining feathers, often acquiring adult body plumage over a period of several weeks. These different moult strategies are useful for me, as a ringer, since they enable me to age most birds with relative ease. There are, however, some species where the young moult through into full adult plumage soon after leaving the nest – House Sparrow and Long-tailed Tit are two examples – and these birds cannot be aged once they have gone through the autumn moult.

Tuesday, 8 November 2011

Pallid Swift makes for tricky identification

The final week of October saw many Norfolk birdwatchers turn their attention to the skies above some of our coastal towns. Reports of one or more Pallid Swifts set pulses racing, as people grappled with the tricky task of clinching an identification of this rare visitor.

Up until fairly recently, the commonly held view was that any pale swift, seen off the back of a warm southerly airflow in late October or early November, was likely to be a Pallid Swift. Although this species breeds throughout the Mediterranean, from Greece west to Iberia, it is absent from many parts and rare in others. It has only recently been found breeding on the Atlantic coast of France and also in Switzerland, highlighting that our knowledge of the species is still far from complete.

The difficultly of securing an identification comes about because of potential confusion with late Common Swifts, either juveniles or birds of the Asian race pekinensis, both of which look similar to Pallid Swift. Many of the key identification features are difficult to pick out on a bird that is not only moving but also often viewed in silhouette against a paler sky, making the assessment of colour difficult. There is one structural feature that can prove helpful, however, as the two outer wing feathers in Pallid Swift are of similar length, giving the appearance of a blunt wing-tip. In Common Swift, the outer of these two feathers is longer, giving the wing a more pointed appearance.

The presence of any swift in these late autumn skies gives pleasure enough, a last glimpse of summer’s sprite and a sense that part of summer lingers still. Our Common Swifts will be in Africa by now – in fact many will have been there for some weeks – their brief sojourn to Britain a faded memory. Unlike our Common Swifts, the Pallid Swift is double-brooded, squeezing in a second nesting attempt from late July which delivers newly-fledged young from early October. It may well be these individuals that reach southern and eastern Britain on the back of strong southerly airflows, such as the one we experienced in the first few days of November.

That there should be discussion over the identity of those Swifts seen here over the last couple of weeks, highlights the complexity of movements made by these cracking birds. It also underlines the identification skills needed by birdwatchers seeking to add a new species to their list. It will be interesting to see how the recent flurry of records is treated by the Norfolk Rarities Committee, a group of knowledgeable individuals who assess records of rare birds by looking at the evidence provided in support of the claim that has been made. 

Monday, 7 November 2011

The stench of success

It is not so much the stench that gets you but the waste, the sheer volume of household detritus that is scattered layers deep over such a vast area. This is my first time on a waste tip and it is truly shocking to see the fragments of furniture, unwanted toys, endless plastic trays and countless shoes that have ended up here for landfill. This is not a place I want to be but it is where we stand the best chance of catching gulls for a colour-ringing project with which we are involved.

Setting the net is a well-drilled exercise; we roll out the hessian, onto which the net is neatly folded, then set up the ‘cannons’ whose projectiles, when fired, will carry the net over the feeding birds. Everything is checked and double-checked before we retreat some distance to wait. One of the bulldozer drivers adds some fresh refuse to the catching area and then the gulls appear. 

Hundreds of gulls that had been loafing around the site take to the air and I am reminded of sleet against a dark November sky, such is their number. The first birds down to feed are the Black-headed Gulls, but the larger gulls quickly follow them: mostly Herring and Lesser Black-backed Gulls, with the odd Great Black-backed lurking menacingly. The net can only be fired when the safety-zone is clear of gulls so we miss taking several catches because of gulls stood too close to the folded net. The flock feeds quickly and then is gone. More fresh refuse is added and the process repeated until, finally, we can fire. There is a loud bang and the net is up and over the birds in an instant. We rush from our hiding place to secure the net and carefully extract the gulls, which are then placed in hessian sacks to keep them still and calm.

It is only when you get these birds in the hand that you appreciate the delicate nature of the Black-headed Gulls and the brute strength of the Herring Gulls. All of the larger gulls are immatures, either born this year or last, and we work our way through the sacks, ringing and recording before the colour rings are fitted. These also carry a number and are visible enough for birdwatchers to read the number and report it. It should tell us a lot about gull movements, something already evident from this morning’s catch as we have caught a bird ringed in Denmark and one from the Czech Republic. One of the gulls, its foot covered in the expandable foam used by builders, highlights the hidden dangers of feeding at landfill sites and underlines our impact on the natural world.