Tuesday, 31 March 2009

Logs yield a surprise

To anyone but a naturalist the following behaviour might seem a bit odd! However, I freely admit that I spent a couple of hours the other morning turning over logs in a bit of damp woodland, searching for invertebrates that might have been using the logs as somewhere to overwinter. Most of the logs I turned over, examined and then replaced, sheltered various woodlice, spiders, slugs and the occasional beetle. One, however, yielded the vivid orange and black belly of a Great Crested Newt, which had been sheltering within a small ‘newt-sized’ chamber in the soft soil beneath the log.

I still get a thrill when I encounter a Great Crested Newt even though I once lived in an old cottage to which they were regular springtime visitors! The cottage sat on top of an old cellar, connected to the outside world by a subterranean passageway and a door that emerged close to a pond in which the newts bred. As such, the newts used the cellar as somewhere to spend the winter, protected from the elements and with a dependable temperature range. Gaps within the brickwork allowed the occasional newt to find its way up into my bathroom, something that made bleary-eyed, early morning ablutions an interesting excursion.

Apart from the striking belly pattern, which is as unique as a fingerprint, a Great Crested Newt out of water is nothing to write home about. The dark brown, virtually black, skin is coarse and has a rough, warty appearance and the creature lacks the elegance and charm of a lizard. All this changes come the breeding season, when the male develops the crest along his back that he will use in his courtship display. Male Smooth Newts also develop a crest in the breeding season but this is smoothly indented and less pronounced in character.

It would not be long before this particular newt was on the move, a nocturnal journey of a few hundred metres that would be made at night once the overnight temperature approached five degrees. This terrestrial phase is easily overlooked and we tend to think of newts as living within ponds all year round, but many individuals will spend just a few short weeks living an aquatic existence before returning to the land. Even within ponds they can be secretive, being more nocturnal than our other native newts, and they are best revealed by carrying out a search for eggs or a survey by torchlight. The eggs are about 5mm in length and are laid individually on the leaves of submerged plants. The adult newt folds the leaf over the egg, leaving a characteristic crimped appearance. This was my first newt for this site, a useful record for the county database, so I left him be.

Monday, 30 March 2009

Has the cold weather hit our Wrens?

There is a chill to these bright mornings, the clear skies overnight allowing the mercury to dip below zero and delivering a brushstroke of silver frost to the short heathland turf. Even so, such bright mornings bring with them the hope of spring, lifting my spirits, and it feels good to be out at such an hour. The change of season appears to be having a similar effect on many of the woodland creatures, including the birds, and the ranks of conifers echo with bird song. The Robins have been singing right through the bleak days of winter but now their wistful song has a more strident tone. Blackbirds too, are delivering a purposeful chorus and many pairs will have already started to build nests or lay eggs.

There are other singers; the thrice-repeated call of the Song Thrush strongly sung, the ‘teacher-teacher’ of the Great Tit and, here and there, the less often heard songs of Siskin and Crossbill. What is missing, however, is one particular component of this early season orchestra – that delivered by one of our smallest songsters. In recent years, this part of the forest has been alive with the metallic ringing trills of the Wren. This species has fared well over recent years because of a run of mild winters and I fear that this year’s cold snap may have hit the Wren hard.

The Wren is one of our most numerous breeding birds but its numbers can fluctuate quite dramatically from one year to the next if the winter weather goes against it. The severe winter of 1962/63, for instance, resulted in an 80% decline in the breeding population nationally the following year. Another study, carried out in a Nottinghamshire woodland, saw virtually the entire adult breeding population lost after the very cold winter of 1985/86. In both cases, it took several years for the breeding population to recover to former levels.

While the most recent winter may not have been as severe or long-lasting as these, it might have been sufficient to reduce the number of Wren territories locally. One other characteristic impact of a cold winter on the Wren population is a noticeable change in habitat preferences. In the year that follows a cold winter, breeding Wrens are often absent from formerly favoured hedgerow and garden habitats. Those territories that remain occupied tend to be in woodland or alongside riparian habitats, suggesting that woodland is a high quality habitat, while hedgerows and gardens are less suitable and the last to be filled with breeding birds. We will have to see what long-term monitoring programmes, such as the BTO’s Breeding Bird Survey, reveal later in the year. Have our Wrens been hit by the cold?

Saturday, 7 March 2009

Watch out for Hedgehogs

Over the next few weeks we will start to see Hedgehogs emerge from their annual winter hibernation. Providing individuals managed to find a suitable site in which to hibernate, the cold weather of recent weeks might actually have proved beneficial, with individuals not tempted to emerge early because of unseasonable warmth. Hedgehogs which do emerge too early waste valuable energy reserves and may be unable to complete a successful hibernation should temperatures fall again.

The Hedgehog is one of our most familiar mammals and should be quite unmistakeable; after all, it is our only mammal with a spiny coat! As such, you would think that we should have a pretty good understanding of how it is doing within the county and, indeed, how it is faring elsewhere across Britain. However, our knowledge is far from complete and all that we can really say is that the population is, at best, stable or, more likely, in a gradual long term decline. One particular habitat within which there seems to be strong anecdotal evidence of a decline is gardens. The change here may be linked with the increased use of garden chemicals, some of which may harm Hedgehogs directly or reduce populations of their favoured prey.

Another reason why our knowledge of Hedgehog populations may be less than expected is because of their largely nocturnal habits. While most Hedgehog behaviour takes place at night, they may sometimes be seen at dawn or dusk, or even during daylight if food is in short supply. However, hedgehog droppings are fairly distinctive and this means that the presence of a Hedgehog within a garden can often be determined through a casual search for droppings, ideally on an area of lawn. Activity is most pronounced during May and early June when, on warm nights in particular, you may hear the loud rhythmic ‘snorting’ calls of courting Hedgehogs from your garden. Courtship is a rather ill-tempered affair, the female rebuffing the amorous approaches of a male. The noise may not only wake you from sleep but can also attract other male Hedgehogs who happen to be in the vicinity. This halts the courtship, the male having to see off his rival before returning to the object of his affections (who may have done a bunk).

A new survey is being carried out this spring in order to gain a better understanding of the distribution of the Hedgehog within Norfolk. The survey is being conducted by the Norfolk and Norwich Naturalists’ Society and a simple recording form can be requested from the County Mammal Recorder, Dr Dave Leech. Send a self-addressed envelope with a first class stamp to Dr Dave Leech, c/o BTO, The Nunnery, Thetford, Norfolk, IP24 2PU.

Friday, 6 March 2009

Antics in the tree-tops

It may seem a little early but the Great Spotted Woodpeckers at West Stow are just starting their breeding season. As well as the familiar drumming, there is plenty of chasing as rival males cavort through the tops of trees uttering short, sharp sounding calls. Breeding proper will not begin until April but the courtship taking place now may have been initiated back in December.

The birds usually only pair for a single season, choosing to maintain individual feeding ranges once the business of rearing chicks has finished, but pair bonds lasting up to three years have been recorded. An established male will tend to retain ownership of his breeding territory from one year into the next, drumming from favoured trees in an attempt to attract a mate. If successful, the pair will cement their bond and excavate a new nest hole into which the eggs will be laid.

Great Spotted Woodpeckers are not the only species to be drumming at the moment; although less common, Lesser Spotted Woodpeckers may also be heard, their drumming somewhat weaker and of more even tempo. The changing fortunes of these two species have been rather different, with great spots increasing and lesser spots in decline. The sparrow-sized lesser spot seems to have been constrained by being more selective in its requirements than its larger relative. Great Spotted Woodpeckers have shown their adaptability by exploiting garden feeding stations and also the rich protein available from wooden nestboxes used by nesting tits. Lesser Spotted Woodpeckers feed almost exclusively on invertebrates, taken from the surface of bark during summer and extracted from dead wood in the winter. Our increasing tendency to remove dead wood and to maintain over-tidy woodlands may have reduced the amount of invertebrate food available to the species, bringing about the pronounced decline witnessed since the early 1980s. Great Spotted Woodpeckers exploit a wider range of foods, including tree seeds, and this may have helped them to do well, buffering the effects of changing woodland management practices.

Early spring is a great time to catch up with these two woodpecker species. With their breeding seasons and associated courtship behaviour in full swing, there is plenty to see. Not only are they especially vocal at this time of the year but there is virtually no foliage on the trees to mask their courtship behaviour from prying eyes. Choose a bright, warm and still day and take a wander along a belt of mature trees or through one of Norfolk’s blocks of deciduous woodland. One of the best places to try is Holkham Park, particularly the woodland to the right of the entrance and around the lake. Here you are likely to encounter both species.

Thursday, 5 March 2009

A song before dawn

Lying in bed in the half-light before dawn I can hear a chorus of bird song. The upward shift in temperatures has delivered the first signs of spring and it seems that many of the local birds are responding to this. The chorus is dominated by Blackbirds but interspersed with their rich melodic warblings are others, the plaintive tones of a Robin and the thrice-repetitive notes of a Song Thrush. This is a pleasant way to start the day, especially since it is a Sunday; the post office vans and lorries are silent, leaving the birds unchallenged in this urban soundscape.

Early season song lacks the volume of later in the year but it does provide you with an opportunity to pick out individual songsters and to become more familiar with their particular songs. It is also a time when you really notice just how many birds are singing in the dark before dawn. Later into the year and dawn will have already come and gone while you are still deep in slumber. The question of why birds sing early in the morning, often before dawn, is one that has interested researchers for many decades and even now, despite the amount of work that has been carried out, we still do not have a complete answer. One of the current hypotheses is that birds sing at this time of the day because it represents a trade-off between the conflicting needs to defend a territory and the need to find food to replace overnight energy losses. Fitter birds should be able to sing for longer, so their delivery of song at this hour could be used by females as a sign of the male’s quality.

Studies have revealed that the dawn chorus peaks at a time when the level of territorial intrusions by other males is at its peak. As such, a territory-holding male should proclaim his ownership of the territory in order to counter this threat. Because of the low light levels just prior to dawn, visual means of display are limited in their effectiveness and song offers a more suitable alternative, the bird being able to deliver his message to would-be intruders. The low light levels may also limit feeding opportunities and, while there may be enough light to sing from a favoured perch, there may not be sufficient light to locate food safely and effectively.

One interesting aspect of song production is that a number of species will quite happily sing during the darkness of night itself, particularly in the presence of street lighting. Some observers mistake such nocturnal warblings for the song of a Nightingale, when they are far more likely to be Robins and Blackbirds.

Wednesday, 4 March 2009

The Watcher

The heron returned again this morning; perched on the roof of the pagoda two doors down, it stood immobile but alert. The pagoda had been constructed in response to the heron’s earlier visits, when it had lifted fish from the neighbour’s ornamental pond. The loss of prize fish triggered the construction of what was, in effect, a wooden cage, a space within which the heron would not feel comfortable, hemmed in and prevented from quick escape. The pagoda has served its purpose and the heron now merely uses it as a perch from which to eye up the wildlife pond situated just over the low flint wall. Although lacking in fish, it is used by amphibians and these are viewed by the heron as an equally acceptable snack.

There is an unhurried sense of patience about the heron, the way in which it can stand immobile, poised ready to strike at some creature within the water in which it stands. Unlike the busy foraging behaviour of the Little Egret, which stirs up the sediment with its stunning yellow feet, the heron adopts a passive approach; ‘good things will come to those who wait’.

I do, however, sense a degree of nervousness about the heron when it visits. After all, these are urban gardens and there are many unfamiliar sights and sounds; is the movement glimpsed at a window a threat? Is there a cat lurking nearby? Even so, the response of the heron is measured, the head slowly rotating to direct its piercing stare towards the perceived threat. The gaze can appear almost reptilian, cold and harsh; a shared ancestry brought to the surface. The reptilian nature is even more apparent when these birds are seen close up. A few years ago I helped to ring a number of heron chicks; delightful creatures that would vomit up the remains of their most recent meal in order to discourage you from handling them! Lacking the graceful plumage of an adult bird, these chicks were disgustingly reptilian and primitive in form, so far removed from the elegant lines they would attain once attired in their grey and white plumage.

These visits tend to come early in the morning, before much of the neighbourhood is up and about. I often wonder whether it is the same bird returning, or whether a number of individuals make use of the ponds as they pass over the town between other feeding sites. It is very easy to think of the town centre as being truly urbanised but from the air the long narrow gardens that characterise the old part of town must seem like a single green entity, an oasis replete with well-stocked feeding opportunities.

Tuesday, 3 March 2009

Pleasant addition to the garden

As a licensed bird ringer, I operate a net in my garden fairly regularly to catch and ring birds that happen to be visiting the feeding stations. For the most part these are familiar species, like Blue Tit, Blackbird and Greenfinch, and the information that I collect not only helps to determine where these birds go but it also helps researchers at the British Trust for Ornithology to follow changes in annual survival rates over time. Every now and then my routine ringing receives a welcome boost, either from a report that one of the birds ringed in my garden has turned up somewhere else (I have had a Greenfinch go to Guernsey and a Collared Dove go to the Wirral) or because something unusual has ended up in my net. Over the years I have been fortunate in my town-centre garden to have caught Blackcap, Redwing and even a juvenile Reed Warbler. Since it has been a fairly quiet winter bird-wise in the garden, the sight of a Marsh Tit in the net was something of a red-letter day, adding to the list of unexpected visitors.

The Marsh Tit is one of a pair of species that look very similar, so much so that the other partner in the pair, the Willow Tit, was the last British breeding bird to be identified and named. These two small tits share a buff, grey-brown plumage, off-white cheeks and a black cap and bib. There are some subtle differences in these features, notably in the glossiness and size of the cap, the shape of the bib and the colour of the feather edging on the main wing feathers. However, recent work has shown that such features may be unreliable in some cases, leaving the only clear means of separating the two species as their vocalisations and, usefully, the colour of the biting edge of the bill. In Marsh Tit the biting edge of the bill is pale along its length; something that is not seen in Willow Tit. Contrary to its name, the Marsh Tit is often associated with drier woodland habitats, where it nests in cavities excavated by other species (including those excavated by Willow Tit, which it can usurp).

Marsh Tit is the more commonly encountered of the two species within Norfolk (and indeed elsewhere these days) and it seems to be increasing its use of garden feeding stations. However, both species have undergone declines in their breeding populations, a pattern that has caused some concern among conservationists. Changes within woodland habitats are thought to be the underlying cause of the decline and efforts are being undertaken to help these birds recover something of their former status.

Monday, 2 March 2009

The deadly hermit

Living in an old house means that I live alongside spiders; from the delicate daddy-long-legged forms that hang in the upper corners of rooms to the scuttling species of Tegenaria that race across the floor at the end of summer. I also encounter spiders when I am out and about looking for beetles and it may be this that has increased my interest in these much-maligned creatures.

Although we lack any truly threatening species, there are a number of spiders found here that are seriously impressive, their bulky forms and large fangs sufficient to menace the casual observer. One of these is Atypus affinis – sometimes called the purse web spider – a primitive species that is closely related to the trap-door and bird-eating spiders that one often sees in television documentaries. Atypus is a scarce spider (there is just one Norfolk record) but it is widely distributed across the southern half of Britain. One reason for its scarcity may be its requirement for undisturbed grassland and heathland habitats; another may simply be that it is easily overlooked due to its largely subterranean habits.

Atypus lives a hermitic existence, cocooned for much of her life in a sealed silken tube within a burrow excavated in the soil. The silken tube can be up to 39 cm in length but is more usually 20 cm or so long, with about a third of the tube showing above ground. This ‘above ground’ portion of the tube is camouflaged with grains of sand and other debris and can easily be mistaken for a piece of old root. The spider waits within her silken tube until some insect wanders across its surface; then she strikes, her huge fangs puncturing the silk and stabbing into the victim. The fangs hold the victim in place, pinning it to the web and, once subdued, the spider disengages one of her fangs, using tiny teeth on the base of her chelicera (the basal part of the jaw to which the fang is attached) to saw through the silk, opening up a slit through which the victim can be drawn into the cocoon. Once inside, the spider takes her meal to the base of her burrow before returning to repair the slit, ready for the next unfortunate insect to wander by.

During the winter months the spider will effectively hibernate at the base of the burrow, the upper section of the web shrinking back to become even more root-like. Come spring and the top section has to be rebuilt, a process that may be carried out annually for the seven or so years of life that a fortunate Atypus may enjoy. As the great scholar of spiders, W. S. Bristow, noted ‘this is a spider of distinction’.