Saturday, 7 February 2009

Challenging times for the entomologist

The winter months can be difficult for those of us with an interest in invertebrates. The short days, low temperatures and relative lack of activity on the part of the objects of our chosen study, make a trip out seem hardly worth the effort. Roll on the warm days of summer, the air filled with the soft drone of a myriad of insects and the grass alive with chirping grasshoppers and bush crickets! Of course, the insects that we seek have not necessarily vanished with the arrival of winter; many are holed up, hidden within the stems of plants, under bark or in subterranean chambers awaiting the arrival of the warming days of spring. It is just a case of getting out there and finding them. In fact, winter can be a particularly rewarding time for finding certain creatures.

Finding invertebrates is very much about knowing where and when to look. This means that there are some habitats and microhabitats that are not worth examining during the winter because they will yield very little of interest. Others, however, are very much worth a look. One of these is flood debris, the vegetation and detritus that has been deposited by rivers that have topped their banks. The best of this debris is the finer material, formed from small pieces of grass and other vegetation. Within such material it is possible to find many hundreds of small beetles, from various families. The material needs to be examined carefully and, ideally, sieved so as to remove the larger debris. A hand lens can be particularly useful, especially as some of the beetles will remain motionless for some time after first being disturbed.

Another worthwhile microhabitat exists behind pieces of loose bark. In addition to finding some of our larger beetles, you may also find woodlice and other invertebrates protected, behind the bark, from the worst of the winter weather. Make sure that you do not remove too much bark and remember to replace what you can to ensure some shelter remains.

Other methods can also deliver some interesting species. Many entomologists give a piece of summer vegetation a good hard tap over a white tray to dislodge whatever happens to be feeding upon it. The same approach can work in the winter, revealing the smaller number of species still active on the tree, for example some of the weevils that feed on fungi. The first of the season’s catkins are also worth investigation, also producing a number of beetles of interest. You can even use pitfall traps (a small plastic tub sunk into the ground), baited with fish and placed in a Rabbit burrow. This should draw out some of the more interesting subterranean beetles!

Friday, 6 February 2009

Waxwings arrive in town

The first of the winter’s Waxwings have reached Thetford, with two reported from the very edge of town just the other day. Given that a good number of these birds have been in the country for much of the winter, they seem to have been a little tardy in getting to me. Perhaps I have been expecting too much, particularly as a closer examination of the reports shows that there are, in reality, fewer here this winter than when we last had a decent invasion (and when I had a flock of 30 birds at the end of the street). While I have not managed to catch up with this particular pair of winter visitors, I did manage to catch up with the flock that was hanging around Thorpe St. Andrew at the turn of the year; so perhaps I should be content with that.

Waxwings are fantastic little birds. About the size (and shape) of a Starling, with peachy brown plumage, a little crest and a black bandit mask and chin. The name Waxwing comes from one other useful identification feature, namely the waxy-red appendages to some of the wing feathers. These occasional winter visitors originate from the belt of boreal forest, which stretches across Scandinavia and Russia. Following a bumper breeding season, the bird’s population swelled by a good berry crop the previous winter, Waxwings are often faced by a much smaller crop of their favoured berries come autumn and so are forced to move further afield in search of food. The large-scale movements which can result from such conditions, bring the Waxwings to western Europe in much greater numbers than is usual.

Flocks and individual birds start to arrive in eastern Scotland and the Northern Isles during the autumn. Should they arrive particularly early, then this usually means that we will receive a bigger influx later into the winter. As the winter progresses, so the birds begin to move further south and west, moving on to find new sources of berries as supplies are exhausted locally. Interestingly, the sorts of berries taken (including Rowan and Cotoneaster) often come from plants that are favoured by architects and town planners for urban sites. Among these are the amenity plantings used on new housing estates, industrial parks and around supermarket car parks. As such, it is not unusual to see groups of birdwatchers wandering around such sites looking for these birds. So, if you have a Cotoneaster in your garden or a Rowan still heavy with berries, then there is a chance this winter that you might be visited by one or more Waxwings. It seems that it is not just our nature reserves that can attract rare visitors.

Thursday, 5 February 2009

Where are the Stoats in Ermine

By all accounts it has been a cold winter, with temperatures across the county dipping to their lowest level for many years. Under such freezing conditions you might expect there to be a few records of Stoats in ermine, the white winter fur that has long been valued as regalia for nobility and the judiciary. However, here in Norfolk the record of a Stoat in ermine continues to be a very rare occurrence. As we shall see, there is a good reason for this.

The white winter coat of a Stoat is a feature of northerly populations, the brown fur replaced with white during the autumn moult and only the black tip to the tail retaining its colour. In temperate latitudes, such as our own with its variable climate, the moult into ermine is most frequently seen in Scotland, Wales and Northern England. For example, in the extreme northeast of Scotland, some 90% of adult Stoats turn white in winter. Further south, there are occasional reports of individuals in ermine, together with others which may appear mottled.

Temperature at the time of moult has an influence on whether or not an individual Stoat will go into ermine. Research has demonstrated that there is some form of chemical switch in the Stoat’s brain, triggered by temperature, which determines whether or not the new coat is white or brown. The switch determines whether or not melanin is produced in the growing fur and, in its absence, the fur is devoid of colour (i.e. it is white). Since fur on different parts of the body is replaced at different stages of the autumn moult, and because the switch changes position (on or off) with changes in temperature, it is possible for some tracts of the coat to emerge brown and others white. It is this that gives rise to the mottled individuals that are sometimes seen. Here, in Norfolk, the temperatures at the time of moult are normally sufficiently warm enough to just produce brown coloured winter coats, and so Stoats in ermine remain rare.

However, it is not quite as simple as this, because there is also a genetic component to the transition into ermine. Clever experiments, one translocating a Stoat from the Alps to England, and another keeping a Stoat from a northerly latitude in a warm room, illustrated that temperature does not act alone. More recent studies have confirmed this and have demonstrated that there is a hereditary basis to coat colour that is also sex-linked. This results in females being more frequently found in ermine than males. Having a white coat is advantageous in cold, snow-covered latitudes, providing both protection from predators and better insulation. Further south, a brown coat is advantageous.

Wednesday, 4 February 2009

Wet weather hard for Treecreeper

The almost mouse-like Treecreeper, with its delicate down-curved bill and mottled brown plumage, is most often seen working its way up the trunk of a tree, before flying to the base of a neighbouring trunk to begin the process over again. Although a relatively common breeding bird – there are estimated to be some two hundred thousand breeding pairs in Britain – it is easily overlooked. Unobtrusive in nature, and with a weak and high-pitched song, it is easy to see why it remains an unfamiliar bird to many observers.

Within Britain, the Treecreeper is primarily a bird of broad-leaved woodland but elsewhere in Europe it is replaced in this habitat by a close relative, the Short-toed Treecreeper. On the Continent our version, so to speak, is to be found in upland conifer forests and this may well explain why it managed to reach us at the end of the last ice age, while the Short-toed Treecreeper didn’t. The first trees to become established following the end of the ice age would have been coniferous and by the time that broadleaf trees became established, Britain had become separated from the rest of Europe. Now you might think that the English Channel is not sufficiently wide enough to prevent an avian colonist from reaching us. In most cases this is true, but Treecreepers are extremely sedentary birds and rarely move any real distance. A long-term study in a Nottinghamshire wood revealed that most birds move less than 500m once they find a territory in which to breed. Young birds may move several kilometres.

Being such a small bird and feeding on invertebrates, makes the Treecreeper susceptible to poor winter weather. At such times many different individuals may gather together within a suitable cavity or behind a flap of bark in order to share body warmth. This is a feature also shown by other small birds, such as Wrens. It is not just very low temperatures that can cause a problem but, in particular, the combination of low temperature and rain. This can result in a glazing frost which forms over the trunks of trees, preventing the Treecreeper from reaching its prey.

Treecreepers can be attracted to garden feeding stations, especially those gardens positioned close to woodland, by fat or suet that has been rubbed into the bark of a suitable tree. Make sure that you use a hard fat though, because soft fat can contaminate the feathers and reduce the insulative properties of the plumage. Specially designed Treecreeper nestboxes are marketed as another way of attracting the species into your garden. However, they are almost invariably ignored by Treecreepers (even in suitable woodland habitat) suggesting that the design is not quite right.

Tuesday, 3 February 2009

An exceptionally early nest

The run of cold days, with a bitter wind and freezing temperatures, have brought with them growing numbers of wildfowl. Along with the Tufted Duck and the first of the winter’s Goosander are dozens of Coot, all making the most of the small amount of water that remains free from ice in the corner of this old gravel pit. Out on the ice itself is a small gathering of Black-headed Gulls, accompanied by a few Common Gulls that have, perhaps, been pushed inland by the poor weather. It is a complicated picture, with individuals of many different species forced together on the tiny expanse of open water, and I take my time to count them, adding my totals to the regular notes that I keep of the birds seen on this particular site. The counting is made easier by the small electronic tally counter that I carry with me these days when I go out birdwatching. I no longer need to keep a running total in my head; all that I need to do is click the button each time I see an individual of the species I happen to be counting. Once I have worked carefully across the lake, I look at the digital screen which informs me that I have just counted 94 Coot – a fair total given the weather.

It is as I am working through my count of Canada Geese that I am distracted by a rustling in the vegetation near my feet. Pulling my head back from the telescope I look down to see a female Mallard leaving a nest of 13 eggs. I almost do a double-take – those are eggs and that is a Mallard’s nest, and that is a semi-frozen lake in the middle of January! Even by Mallard standards, this is an exceptionally early nesting attempt and one that is, given the weather conditions, almost certainly doomed to failure. Before the Mallard can reach the water I retreat in the hope that she will quickly return to her task of incubating the eggs and protecting them from the freezing temperatures. Once back by the fence I turn around; she is not on the water so must be back on the eggs, though out of sight within the dead vegetation that affords a modicum of shelter.

Returning a week later, I make a careful approach to the nest. The female is nowhere to be seen but the eggs are still there, covered in vegetation and somewhat dirty. They are cool (but not cold) to the touch and it seems likely that the female has deserted, no doubt beaten by the continuing poor weather. I will make a final visit in a few days, just to be sure.

Monday, 2 February 2009

An unusual bird

The Woodcock must have dropped in close to the woodland feeding station where we had erected our nets, set on a regular basis throughout the winter to catch birds. Normally each visit yields a few dozen individuals, mostly tits and thrushes, some of which already carry individually numbered metal rings, fitted by licensed ringers operating at other sites. Our studies help researchers to both understand the movements made by birds and to establish variation in the survival rates over time. It is enjoyable and worthwhile work even if, as at this time of the year, it involves an early start on a particularly cold morning. While the work might seem routine, it is never dull and there is always something new to learn or see. Then there are those occasions where you catch something completely new, a bird that is exciting and unexpected.

So it was the other morning; rounding a corner by the main nets, there was a sudden, audible burst of wing beats as a Woodcock erupted from the ground, taking flight only to deposit itself in one of our nets. Each net is made of very fine material, virtually invisible to the bird, which is strung in such a way that the bird is held within a shelf-like pocket, untangled but sufficiently restrained so as not to effect an escape. There was our Woodcock, the first that I had seen in the hand; a beautifully marked reddish-brown bird, medium-sized and with an exceptionally long thin bill. Highly secretive in nature and largely nocturnal throughout the winter months, the Woodcock is a rather unusual bird. Although it belongs to a group of birds known as waders, the Woodcock isn’t exactly the sort of bird that you would see feeding on coastal mudflats or alongside saline lagoons. Instead, it is a bird of woodland, probing the soft ground for earthworms and living a predominantly solitary existence.

During the winter months, Woodcock can be found at night feeding in damp or marshy fields, close to the woodland to which they retreat at dawn. In summer, they switch to daytime feeding but remain, largely overlooked, within woodland. They seem to prefer open woodland, not too draughty, but with open rides and good stands of bracken. Looking at this particular bird, I could see how the beautifully marked plumage would provide fantastic camouflage when settled on the woodland floor. The bands of darker colour, set on a russet base, served to break up the outline of the bird and matched the range of colours that you would expect to see on a woodland floor. As it whirred away upon release, I felt incredibly privileged to have seen such a bird in the hand.