Battling Blackcaps

One surprising visitor to favoured winter bird tables is the blackcap, a species of warbler more commonly regarded as a summer visitor to these shores. The presence of blackcaps in Britain during the winter is not a new phenomenon but the numbers of individuals wintering here is.

It appears that those blackcaps choosing to overwinter here are not simply birds that bred here during the summer and which have chosen to remain. Instead, they are birds from the central European breeding population, arriving in late autumn and then remaining through until early spring. Some birds from the breeding population have probably always overwintered here but the rapid increase in the numbers that now do this, instead of migrating south to the Mediterranean, is thought to be linked to our warming climate and the number of households providing food, in the form of suet-based products and other bird food.

Research has demonstrated that those blackcaps from the central European breeding population that choose to winter in the UK get back to their breeding grounds ahead of those that winter further south. They then tend to pair with similar individuals and get good territories and show good levels of breeding success. The tendency to travel to the UK for the winter is, therefore, being passed from one generation to the next and we are seeing evolution in action, as a new pattern of autumn migration develops.

One of the most interesting aspects of the winter distribution of these birds within the UK is the way in which they favour the southwest of the country and seem to prefer urbanised landscapes over rural ones. This suggests that winter temperature may be important, as indicated by the birds choosing to winter in the mildest regions and habitats. Temperatures in urban centres may be several degrees warmer than the temperature in the surrounding countryside, a consequence of all of the waste heat lost from our homes, shops and offices.

Another interesting aspect is the behaviour of the blackcaps. It appears that they are somewhat quarrelsome birds and that they will attempt to defend a food resource – such as your bird table – against all-comers. Those birdwatchers whose gardens attract these wintering blackcaps often comment on the way in which they see off robins, finches and other birds. Some gardens may attract several blackcaps over the winter, although many hold just single birds.

It is not clear what, if anything, will happen to those blackcaps that breed here. Will they follow the example of their continental cousins and alter their migratory habits? Might we see them stay here and become residents rather than summer visitors? Who knows, but it will be fascinating to see how things change.

Nocturnal movements

There have been some nights recently when, taking the dogs out just before bed, I have heard the calls of golden plover and lapwing from high above me in the dark winter sky. These are birds on the move, perhaps local flocks moving between feeding sites within Breckland or recent arrivals from the Continent, pushed west by changing weather conditions. Such movements are common at this time of the year but they largely go unnoticed as birds pass overhead in the darkness while we are, for the most part, tucked up in the warmth of our homes.

Evidence of the range of species on the move comes not only from the occasional calls heard and noted down by birdwatchers, but also from the corpses that are sometimes found beneath office block windows in our urban centres. It is thought that some of these nocturnal migrants collide with lit buildings, perhaps even drawn to the light of illuminated office windows. Other individuals may be taken by urban peregrines, hunting at night with the aid of urban light pollution. Such behaviour has been little studied here in the UK but a growing interest in cities like Bristol is beginning to reveal the extent of the behaviour and the range of species taken. As BBC Winterwatch revealed, the Bristol peregrines have taken woodcock, snipe and even little grebe.

Many other birds are on the move at the moment, though not always at night. Changing weather conditions across large parts of continental Europe, with temperatures falling and waterbodies freezing over, may see an influx of waterbirds, including geese and swans, into the UK. The warming influence of the Gulf Stream means that Britain and Ireland present more favourable wintering conditions than those of the near Continent and east towards Russia. A flight of swans over Thetford just the other may have been such an arrival.

Of course, some birds are leaving our shores at the same time. Wintering blackbirds and other thrushes may move further south or southwest with the arrival of snow. Redwings, in particular, find cold conditions challenging and so tend to be very mobile. Some of those to have wintered here may move some way south into Iberia, perhaps even reaching the Mediterranean. The waxwings that have been such a feature of this winter are also very mobile, although in this case the movements are made in response to the availability of (or lack of) the suitable berry crops on which they depend.

If you can spare time to wrap up warm and stand in your garden on a still, clear night then you too might be treated to the soft calls of birds, passing overhead in the dark of night.

Puck

It is one of those cold but bright winter mornings, where the light has a certain clarity that lends itself to photography. Picking up my camera and long lens I wander down to the river that skirts the town centre before heading out towards the forest and the fens beyond. Soon I am working my way upstream. Above the slow moving water hangs a barely perceptible mist, most evident where the weak winter sunshine cuts between the trees to strike the river’s surface; it would appear that the river is warmer than the surrounding air.

I am on the lookout for the local otters and kingfishers, both of which could form a striking photograph in this light. A kingfisher breaks from a concealed perch and whirrs away on its metallic wings ahead of me. Skimming low above the water I lose sight of it as the bird disappears around the bend. A bit further on, as I reach the ancient bridge that marks an even more ancient crossing point, I spot an otter in the water. It pushes through some emergent vegetation to slip as a dark, torpedo-like shape, beneath the bridge. Retracing my steps I find that the otter is searching for food, diving down to work the waterweed and then surfacing, its broad head sleek and shiny with water.

Quietly, I lower myself into a seated position, back against a waterside tree and camera braced by my knees. The otter is now just feet away and I have to zoon the camera out slightly to get a frame-filling shot of its head. It is hard to take the otter in and to soak up its character and charm through a camera lens and once I have taken a few shots I stop filming to enjoy its presence. The broad face, dark eyes and white chin are framed by thick whiskers and, as the otter crunches on some morsel that it has collected from below the water’s surface, I am reminded of a cheeky schoolboy, crunching nonchalantly on a humbug. It is a humorous scene and one that brings a smile to my face.

I have not been alone in my otter sightings this week and several colleagues and friends have watched in delight as more than one otter has put in an appearance. One individual was seen to ‘porpoise’ across the water, seemingly chasing fish, while another made a lunge at a woodpigeon that was sitting at the water’s edge. At times, crowds of locals have gathered to watch ‘their’ otter and it is wonderful to know that not only are these magnificent creatures being enjoyed but also that they seem completely unperturbed by the interest they have stimulated.

How was your weekend?

How was your garden over the weekend? Was it full of birds, attracted in by the food provided in hanging feeders, scattered on the ground or placed on your bird table? In many thousands of gardens across the country, householders will have spent some time watching the birds and recording their observations for the RSPB’s Big Garden BirdWatch (see www.rspb.org.uk). This once-a-year, mass participation project is a fantastic example of how to get people engaged with their garden birds and the concept of ‘citizen science’.

So, how was your garden over the weekend? Did you notice more coal tits and siskins than you would normally see; did you have more birds visiting because of the weather or because you’d topped your bird feeders up in preparation for the weekend? There’s a lot of subtlety to the patterns seen in garden use by birds. The numbers visiting are not simply related to population size but are strongly influenced by weather, food availability and where your garden is located. This year, for example, we know that coal tits have increased their use of gardens, starting last autumn, because the 2012 conifer seed crop was so poor. The same is true for siskin (another conifer specialist) but, since this species only turns to gardens in big numbers from late January, we can make the prediction now that you will see increasing numbers of these birds over the weeks ahead.

The failure of other tree seed crops and the poor showing of autumn berries might see other birds increase their use of gardens this winter, although some – notably the thrushes – may have pushed further south into France and Spain to seek more favourable conditions there. Freezing temperatures elsewhere on the Continent, will have been behind the movements into Britain of other thrushes over the last two weeks, so it is a very dynamic picture. What is clear, however, is that what you will have been seeing in your garden reflects what has been happening at a much wider spatial scale.

You might wonder how we know that coal tits increased their use of gardens last autumn, that late January is when the siskins arrive or that there have been fewer thrushes in gardens over the early part of the winter? Well, it’s all down to another group of citizen scientists, those who take part in the BTO’s weekly Garden BirdWatch survey (see www.bto.org/gbw). By charting what they have seen on a weekly basis, these citizen scientists have delivered a wealth of information on how the use of gardens by birds (and other wildlife) varies throughout the year and in relation to other factors, like seed crops, weather and local habitat; all very useful stuff.

It takes two

On much of the county’s older stonework you will find round, crust-like patterns of rich ochre and sulphurous yellow. These are lichens, formed slowly over many years on this most inhospitable of substrates. Elsewhere, on rocks or ancient trees you will find other, more delicate, lichens that hang in limp shaggy forms. As a schoolboy these forms fascinated me, all the more so for knowing that lichens were not a single species but the result of a partnership between a fungus and an alga.

Time has moved on, and so has our understanding. While it is no longer strictly correct to think of a lichen by the definition with which I was schooled, it remains a convenient one to use, even if the alga is sometimes replaced by a cyanobacterium. I sometimes think of lichen as a form of fungal lifestyle, rather than a distinct taxonomic entity, even though each lichen is named after the fungal partner it contains. Roughly one in five fungi are lichenised but a much smaller number of algal or cyanobacterial partners are involved. A consequence of this is that some algae occur in a wide range of very different lichens.

Lichens have a long history and you will even find reference to them in some of the Anglo Saxon charters used to define village boundaries. These definitions used local features as a means by which the boundary could be interpreted; an ancient hazel hanging thick with lichen, for example. A tree that was shaggy with lichen would be described as ‘har’ (hoar) and it is from this root that we get hoarfrost. Lichens feature throughout the following centuries as food, dye for fabrics and medicine. The use of lichen as a medicine stems, in part, from the Doctrine of Signatures: the belief that the Creator had marked some plants as suitable for treating illness and disease through resemblance in form to that which they treated. The various forms taken by lichen meant that some were readily taken for use in herbal preparations, the lichen often steeped in milk or wine for several days. While the use of lichens faded as medical knowledge increased, it is interesting to note that the simple ‘acids’ produced by many lichens have basic antiseptic properties and some of the compounds present in lichens have been found to act on cancer tumours.

For those who study lichens there is much still to learn but for those, like me, who simply admire them with a very basic understanding there is much to appreciate, be it their colour, structure or ability to cope with difficult conditions. To see lichens on our buildings lends a sense of great age and a certain degree of character.

Flying in the cold

As you might expect, the majority of our moths sit out the winter as eggs, larvae or pupae, stages that are more resistant than the adult form. Among the macro-moths, just two-dozen species are active as adults during the wider winter period, underlining the difficult conditions that these fragile creatures face at this time of the year. The biggest challenge is the temperature, with subzero temperatures likely to kill any moth exposed to them. A few species remain active, however, and some have evolved behavioural or physiological adaptations that prevent them from freezing solid. While behavioural adaptations may see individuals seek out sheltered overwintering sites, physiological adaptations may involve the creation and addition of glycerol or other antifreeze chemicals into the vulnerable body cells.

Perhaps surprisingly, a number of British moths emerge from their pupal stage to take adult form during the winter, before seeking out a mate and depositing eggs. One of these is the winter moth, Operophtera brumata, which emerges during the final months of the year. While the males of this species are fully winged, the females are wingless and unable to fly. Newly emerged females face an arduous climb from the ground up onto the trunks of deciduous trees. Here they rest and release a pheromone to attract a mate. Once mated, the female resumes her climb towards the highest parts of the canopy, where she will lay her eggs before her brief life cycle comes to an end. When the eggs hatch in early April the emerging caterpillars should find that the leaf buds have just burst, providing an abundance of food.

The success of this strategy can be seen from the vast numbers of winter moth caterpillars that may be encountered during spring, sometimes to the extent that large areas of canopy are defoliated by their activities. It is for this reason that the winter moth may be familiar to gardeners and other horticulturalists growing apples and other fruits. The winter moth caterpillars also form an extremely important food source for nesting tits.

The names of some of our other moths also indicate adult activity during the winter months. Some readers will, for example, be familiar with the november moth, pale november moth and december moth. All three species may be encountered in Norfolk during the first half of the winter. Another important winter-active species is the mottled umber; like the winter moth it is one of the ‘looper moths’ that may cause widespread defoliation in years of peak abundance. Also like the winter moth, the female is wingless and uses pheromones to lure in prospective partners. Occasionally one of these moths may be attracted to the light of a kitchen window so do keep an eye out for them.

Reflections on a poor nesting season

Looking back at summer 2012, it is easy to see why the preliminary results emerging from the British Trust for Ornithology’s Nest Record Scheme (www.bto.org/nrs) highlight a poor nesting season for many bird species. Interestingly, 2012 got off to a good start, with February and March both warmer and drier than average. This prompted early-nesting species like tawny owl, song thrush and long-tailed tit to initiate nesting attempts far earlier than the five-year average. Song thrush was, on average, starting a week earlier than usual and tawny owl a fortnight earlier.

In contrast, newly-arriving migrants returning from their African wintering areas just a few weeks later were faced with some awful weather, not just here in Britain but also further south in Europe. The consequence of this was a delay in arrival dates for many species, with courtship, nest construction and egg-laying also delayed. Whitethroats were 15 days later than usual in starting, reed warblers 11 days and Swallows 7 days.

As the cold and wet weather continued there were problems for resident breeders as well. Blue tits and Great Tits, which depend on caterpillars for their growing young, faced particularly challenging times. In both of these species clutch and brood sizes were down and the number of young fledged was significantly reduced. Again the BTO figures suggest that the number of blue tit fledglings produced was down by 13% on the five-year average, the comparable figure in great tit being nearly 18% down. Looking longer-term, the preliminary results suggest that, for great tit, 2012 saw the lowest number of chicks fledged per breeding attempt since the scheme began in 1966. For many of the volunteers involved in monitoring nests this was the worst year they had encountered. Some, notably those working on waterbirds, waders and reed warblers, faced large losses as widespread flooding washed out vulnerable nests. It was a season to forget, but nonetheless important for charting the impact of what might become a more common weather pattern in the face of a changing climate.

What happens longer term will depend on what happens over the winter. With fewer young recruited into the population there should be less competition for winter food and we might see a prompt recovery if we have a good breeding season in 2013. Many of these species are facing other pressures, however, and so things might not be as simple as they first appear. What is clear though, is that the efforts of volunteers who give up their spare time to count and monitor birds are central to our understanding. Without their passion and enthusiasm, we simply would not know about the effects of a changing climate on our birds and other wildlife. 

A waxwing winter

It has been something of a waxwing winter, with good numbers of these stunning birds arriving from the boreal forests of Scandinavia and western Russia. That they arrive here at all is very much down to their irruptive habits, with birds moving en-masse under particular conditions. In some years, very few waxwings are to be found in Britain during the winter but in others many thousands of birds may arrive. The size, timing and location of these arrivals are determined by the success or otherwise of the breeding season and the availability of rowan berries during the autumn months that follow. Rowan is the favoured food, so in years when the crop has been poor the birds are forced to move on elsewhere and it is these movements that bring them to our shores.

The autumn saw a good arrival in Scotland and northern England, with birds filtering south as the berry crops there were depleted. However, even here in Britain many berry crops have been poor this autumn so the waxwings have tended to be rather mobile. While this means that they have been turning up in lots of different places, it also means that they have not tended to stay in one place for long, much to the frustration of those birdwatchers and photographers hoping to catch up with them – there is little that makes a more festive photograph than a waxwing on a berry bush! One of the quirks of the winter distribution of waxwings is the association with industrial estates, new housing developments and supermarket car parks, all of which are places where berry-producing shrubs are used as amenity planting.

Another interesting aspect of waxwing behaviour is its alcohol tolerance. Berries are rich in sugars and fats and are a valuable food source during the autumn and winter months. Over time, however, the sugars in the berries begin to ferment and alcohol levels increase. For any bird that eats a lot of berries there is the potential for drunkenness and the resulting impairment of normal activities, like flight or vigilance for predators. Those species that specialise on feeding on berries, like the waxwing, are better able to metabolise alcohol. In fact the alcohol tolerance of the waxwing is reputed to be equivalent to an average-sized man drinking more than two and a half pints of 5% beer every hour from dawn until dusk! By comparison, the equivalent figure for the greenfinch, which feeds on berry seeds rather than the pulp, would be just half a pint each hour. If you have a berry-producing bush or shrub in your garden with berries still present then you might just get a visit from these Nordic nomads.

Trees that shape the landscape

For me, it is the trees that give the landscape of lowland England its character, not just providing a backdrop to her vistas but also delivering a real sense of place. The character of some of these trees, such as that of the oak, have been enshrined in our literary tradition and used to say something about our own English character. Others, however, have been overlooked and undervalued, a reflection of their timber having little commercial value. Perhaps the most overlooked of these has been the native black-poplar, a tree of lowland flood plains that has lost out to years of agricultural drainage.

That the black-poplar should have slipped from our collective awareness is perhaps surprising. It is a large and highly distinctive tree, with its gracefully arching boughs, massive size when mature and an often-leaning trunk. During the 1970s, however, a burst of interest in the tree was revived thanks to the efforts of Edgar Milne-Redhead. Having recently retired from his job at the Kew herbarium, Milne-Redhead began to track down and document the locations of mature black-poplars across southern Britain, with much of his efforts concentrated here in East Anglia. The results of this work, coupled with that of more recent studies, suggest a national population somewhere in the region of 6,000 individuals.

References to native black-poplars in Norfolk can be found in the older literature, the earliest seemingly that included in a letter from Sir Thomas Browne to John Evelyn. James Grigor, writing in 1841, included a number in his records of notable trees from the region, some of which can be traced to individual trees still standing at sites within the county. The natural distribution is confused, however, by the presence of hybrid black-poplars planted because of their more upright form and faster growth. ‘Natural’ establishment requires the presence of male and female trees in close proximity, at sites where suitable conditions for seedling establishment are to be found. Many mature trees stand isolated, or are present in single-sex groups, leaving them, as Richard Mabey writes ‘marooned’, the ‘ghosts of a wilder and wetter landscape’.

In places, particularly where associated with a village, individual trees have been ‘adopted’ by the community and their importance is recognised and respected. As our knowledge of these trees increases, so we our discovering and documenting more relict populations. This knowledge should help to safeguard the future of this great tree, whose associations with the East Anglian landscape are captured in the works of Constable and other English landscape painters. The late Ted Ellis once wrote in his EDP column of a visit that he made to a particular black-poplar and later this year I hope to pay my respects to this ancient tree.

As the year ends

There is a sense of new beginnings as one year rolls over into another. It is as if the canvas has been primed afresh and, gleaming white, awaits the confident brush strokes that will surely follow. The New Year is optimistic and exciting, full of possibilities and new opportunities. Many of those with an interest in birdwatching will be out in the countryside today, with new notebooks at the ready to note down the first song thrush of the year or the first kingfisher or pink-footed goose. Perhaps a hundred or more species will be notched up on the 2013 year-list and tonight birders will boast to their friends and relatives of the day’s achievements.

Of course, nature doesn’t recognise this sudden and wholly artificial transition. Seasons slide slowly from one into another; a run of warmer days suggestive of the distant spring may be tempered by a return to colder conditions. Some creatures respond to these subtleties more readily than others. Perhaps, as in the case of the song thrush delivering his almost jarring notes outside my window as I write this, a run of warmer conditions may trigger activity more correctly associated with spring.

The changing of the year is also an opportunity to look back over the previous 12-months and to reflect on encounters with the natural world. Missed opportunities suggest ideas for the coming year, perhaps places you had meant to visit but not quite made it to. I often use the dark winter evenings as an opportunity to look at maps and read natural history books, making plans for visits to be made the following year. There are species to see and photograph, new places to explore and trips away to be planned. The form that these will take is shaped by the previous year’s encounters, by developing interests in new groups of species or by ideas for pieces of research needed to support new writing projects.

For me then, the year has a distinct pattern, moulded by the seasons and shaped by my interests. The New Year delivers an additional bolt of optimism that helps to set up future plans - the old year no longer slipping towards its end but a new year offering new opportunities and the prospect of an approaching spring. The first trips out to pin down the likely locations of nesting long-tailed tits will begin before February’s end, and then it will be the early blackbirds and thrushes that will have my attention. Until then, however, there is time to enjoy what remains of the winter, to take in the visiting waterfowl and to make plans for those summer trips. New Year may be an artificial construct but it provides a welcome boost.