Thursday, 28 February 2013

Introduced deer

It is at this time of the year that the local muntjac turn their attentions to the flowerbeds and shrubby borders of the garden at work. Over the years we have discovered which of the plants in our wildlife garden are on the menu for these introduced deer and which are not. In part, selection appears to be driven by the weather and feeding conditions elsewhere. When times are tough, less favoured plants and shrubs may find themselves back on the menu and over recent days the deer have been much in evidence.

The presence of muntjac can be seen in our woodlands as well. Crouch down and look across the woodland floor and you’ll soon spot a clear browse line, below which the deer have stripped back much of the vegetation. The impact that such browsing has goes beyond the damage it does to the plants themselves. The herb and shrub layers in woodland provide important habitat for insects, cover for small mammals and nesting opportunities for birds like blackcap, willow warbler and nightingale. Increasing deer numbers have been shown to reduce the local populations of some of these species (e.g. the nightingales in Bradfield Woods) but the effects are not always negative. Browsing can, for example, sometimes open up more of the woodland floor, providing habitat for butterflies whose foodplants, unpopular with the deer, get a chance to increase in numbers now freed from competition.

Originally from south-east China and Taiwan, the muntjac was introduced to Woburn Park in 1894, from where the species was then released into neighbouring woods. Further releases, escapes and translocations have followed and the species (more correctly called Reeves’ muntjac) is now well-established across much of England, with a population thought to be in excess of 50,000 individuals.

Unlike the roe, red and fallow deer that are also to be found in the Brecks, the muntjac can be surprisingly tolerant of our presence. Those individuals using the garden at work or the scrubby habitats that border the river will tolerate a reasonable approach, particularly if you keep quiet and still. Sometimes there may be three or four of these compact deer browsing on the edge of the lawn and seemingly uninterested in the staff that traipse to their cars parked nearby.

Keeping these compact deer out of a garden can prove difficult. Their small size and great strength allows them to force through or under fencing and they are even capable of jumping a four foot wall (as we discovered in our town centre garden several years ago). They do remain a conservation issue, albeit one that is unlikely to ever be resolved, so perhaps we should learn to live with them.

Wednesday, 27 February 2013

Spider webs, lichen and moss

A pair of long-tailed tits has been visiting the garden most mornings over the last fortnight. While the visits of long-tailed tits are not that unusual, the presence of just two birds at this time of year suggests that they are about to breed nearby. Long-tailed tits are one of the earliest species to set up home and late February is the time when you need to keep an eye on them if you want to find out where they are going to be nesting.

The nest itself is a beautiful construction, a dome of moss and hair, bound together with the silk from spider webs and then camouflaged with lichen. Placed within a thorny shrub or up against the trunk of a tree, the nest can be particularly difficult to spot once finished and it is far easier to locate its position while the birds are still building. During the period when the birds are prospecting they move about noisily, checking possible locations and you should soon be able to pin down the area they are likely to settle in.

Once building begins the birds may be seen carrying nesting material and they can then be watched back to the nest location. The build may take up to three weeks and during the latter stages, when the birds are collecting hundreds of feathers to make up the nest’s lining, the repeated visits quickly give away its location. The completed nest appears to be left for some time before it is then used and I sometimes wonder if the birds are testing to see if the activity of building has attracted the unwanted attention of potential nest predators. Long-tailed tit nests are often raided by members of the crow family, the ‘roof’ ripped off and the efforts of the parent birds torn apart to leave a ragged mess scattered across the vegetation. A curious feature of these nests is their elasticity, something clearly evident when you see a predated nest and the sheer volume of material that had been compacted into the space used.

With a bit of effort, the coming weeks should reveal a dozen or more long-tailed tit nests under construction on our local nature reserve. These also serve to signal the start of the nesting season when we, as nest recorders for the BTO, will be out and about charting the breeding attempts of these and many other species of bird. It often surprises people to discover that the breeding season proper begins so early but at least it begins gradually, giving you time to get your eye in and to work up to the busiest period in May and June, when resident breeders are joined by returning migrants.

Tuesday, 26 February 2013

On the edge of the Fens

It is a dull afternoon in late February and the weak winter light leaves the landscape starved of colour. Grey skies hang sullen over featureless fields bordered by bleached stands of scruffy vegetation, long since dead. There is no hint of life, no suggestion of the vigorous growth that will surge forth in just a few short weeks with the arrival of spring. It is a landscape that can leave you feeling drained; such is its scale and the sense of emptiness. It is almost as if the vastness of the heavy grey sky has pushed down on the land to squeeze the colour from it.

A flight of swans swings over from the west, their passing announced by the pulse of wing beats and, looking up, I see how their whiteness is intensified by the backdrop of brooding snow-filled clouds that are now pushing in. These swans are long-distance travellers, wintering here but breeding many thousands of miles away to the north and over the ocean. There is no hint of their exotic origins and they remain the essence of the winter fens.

As the afternoon light begins to fade I can pick out other white objects within the landscape, this time a flurry of black-headed gulls gathered on the deeper brown of a recently ploughed field. I suspect that they have been feeding on earthworms disturbed by the plough, a favoured food and one for which they will ‘paddle’ on occasion. This ‘paddling’ takes place on damp ground and not, as the name might suggest, in water. Stepping up and down in a comical fashion, the gull is effectively tapping on the soil’s surface, something that is thought to draw earthworms to the surface by mimicking the sound of falling rain.

Less obvious in the failing light is the mixed flock of crows, jackdaws and rooks that has gathered prior to going into roost. Such gatherings are another feature of the winter landscape, the communal roosts providing birds with the opportunity to discover who has had a successful day feeding in the fields and who might be worth following in the morning to discover an easy meal.

It is time to turn for home, to seek comfort and warmth in the cottage and to leave the emptiness of the winter landscape at the door.  A couple of warmer days earlier in the month have hinted at the approaching spring and my focus has shifted away towards what lies ahead. Winter is done; warmth, growth and colour are to come and this evening I will browse through books and maps, planning trips and visits for the coming months and the season of plenty that they will deliver.

Saturday, 2 February 2013

Early sounds of spring

The fickle nature of the weather at this time of year can produce some interesting effects. Just the other week for instance, before the snow came, a run of warm bright days prompted some birds to start singing. A song thrush at the bottom of our garden was in full song every morning for nearly a week, joined by blackbird, dunnock and even great tit. All of these birds were under the impression that spring was on its way and so we received an impromptu dawn chorus. Even our young cockerel tried to get in on the act. On the river, mallards were mating and a pair of mute swans was seen to deliver some half-hearted courtship display.

Of course, most of these early signs will not lead to an early nesting attempt, though some will. I suspect that within the next week or so I will find a female mallard incubating a complete clutch of eggs at the base of one of the riverside alders or limes. There will also be early-nesting robins and blackbirds, mostly likely reported from an urban area, perhaps because of the supplementary food on offer or because more of us live in towns and cities and are therefore more likely to spot a bird that happens to be nesting early.

In most years, we’ll have received reports of early nesting for around a dozen bird species by mid-February. Invariably it is the same species that are being reported, with tawny owl and collared dove joining some of those already mentioned. In fact, there has already been one report of an orphaned tawny owl youngster taken into care. Nesting so early in the year is a risky strategy; any deterioration in the weather and the attempt will fail. It seems likely, therefore, that most early nests are made in error, the birds caught out by a period of unseasonal warmth. Some birds do, however, nest very early in the year, with crossbill and tawny owl two such species. Common crossbills, some of which breed in Thetford Forest, are often sitting on eggs by the end of February, with some individuals already on eggs now.

Winter can seem to go on for a long-time but by February some of our resident species are already gearing up for the breeding season ahead. Increasingly, as the winter slips by, we will see more days that are warm and bright. Gradually, more birds will be prompted to sing and the dawn chorus will gradually build. It will, however, continue to be a stop-start affair, the promise of an approaching spring raised and dashed on more than one occasion. It does, at least, feel as if spring is approaching.

Friday, 1 February 2013

If you know where to look

Winter might appear to be something of a bleak time for the entomologist, the low temperatures putting a stop to the activities of our invertebrate fauna. However, there are insects and other small creatures to be found if you know where to look.

Perhaps one of the most profitable places to look for overwintering invertebrates is under the bark of fallen trees. Here you are likely to encounter woodlice, slugs and beetles of various kinds. Woodlice in particular make an interesting group, with 40 or so species recorded outdoors; other ‘indoor’ species are typically those that have been accidentally introduced to the UK in plants and which have established populations living within commercial and botanical glasshouses. Woodlice are an important part of the process of decomposition and nutrient recycling so finding them overwintering within dead wood or under bark is unsurprising. It is the larger species that are most commonly encountered, the smaller soil-dwelling species hidden below ground. Thanks to an excellent new atlas showing their distribution and a key to their identification produced by the Field Studies Council, this is a group that the amateur entomologist can readily tackle and to which you can make an important contribution. You’ll need a hand lens and, ideally, a microscope – some of the cheap ‘USB’ microscopes that plug into a computer and project the image on screen are ideal.

Slugs, on the other hand, are more difficult. The identification of many species requires examination of the genitalia and, since these are held internally, the slug needs to be killed and dissected, not something most of us would choose to do. There are even species that can only be reliably separated through examination of their DNA! Consequently, our understanding of which species occur in the UK, where and in what numbers, is rather limited. Of course, there are other slug species that can be readily identified in the field.

Many of our beetle species can also be identified in the field, or back at home with a hand lens and a key or guide. One species commonly found overwintering under bark is the carrion beetle Silpha atrata. While many of the carrion beetles feed on carrion, others, including Silpha atrata feed on molluscs; the elongated head that sticks out from the front of their otherwise shield-like body is probably an adaptation to this habit. Silpha atrata is usually black in colour, with pronounced ridges (or keels) on its hard wing cases (the elytra), and is often to be found in woodland. Other black beetles may be found sheltering under bark, many of them belonging to the genus Pterostichus (pronounced ter-ros-tic-us). All are equally interesting and well worth the effort at this time of year.