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. 

Sitting out the winter

The cold winter months, with their low temperatures and long nights, can prove challenging for many creatures. Food may be hard to come by and energetic costs high, so many insects, birds and mammals adopt different strategies to see out the winter days and wait for the arrival of spring.

Some birds, including many of our familiar summer songsters, will have migrated south to seek out more favourable conditions. It is those species that feed on insects and other invertebrates that would face the greatest difficulties were they to remain here during the winter and so many move into Africa, perhaps crossing the Equator to take advantage of the bounty that follows the seasonal rains. Some insect-eating species, however, choose to remain here. Wrens, for example, manage to scrape a meagre living by maintaining winter territories, often establishing these in river or lakeside habitats, where the damp conditions favour higher levels of insect activity. Others, such as the Pied Wagtail, seek the warmth of commercial glasshouses or the waste heat of city centres to reduce their energetic costs overnight.

Some of our insects over-winter as adults, perhaps entering torpor, reducing their ‘running costs’ and lowering their energetic demands. A few of our resident butterflies, for example, overwinter as adults, while nine species overwinter as eggs and eleven as pupae; the majority, however, spend the winter as caterpillars. It is also interesting to note that, with the exception of the speckled wood butterfly, the hibernating phase is always the same in a given butterfly species. Only in the speckled wood can hibernation occur as either a caterpillar or as a pupa. Other insects have a life cycle that sees eggs laid in summer or autumn used to secure passage through into spring. Eggs can be deposited in sheltered locations, they are often robust and require no external nutrition.

Mammals tend to cope with the conditions rather well and many species remain active throughout the winter, some even using these months for their mating season. A small number of mammal species enter hibernation, using fat reserves laid down during the bountiful conditions of autumn to get them through the winter. Others reduce the amount of time that they are active or retire to more favourable habitats.

What is particularly interesting about all this is the way in which so many different strategies are adopted. What suits one species does not necessarily suit another and even closely related species may do something completely different. This highlights that there are different evolutionary solutions to a common problem and this is one of the reasons why the study of natural history is so engaging. There is always something new to see and to discover.

This is mine!

The forest echoes with the calls of Tawny Owls in the dark before dawn. These are territorial birds, proclaiming their rights with a vocal display that carries through the otherwise still air. The ‘hoo-hu-huhuhuhooo’ of the male is answered by another more distant. More often than not his mate will also answer with the ‘keewik’ contact call, forming a duet that reinforces the message that this is an occupied territory. Female Tawny Owls may sometimes give a similar territorial hoot to that of the male, though it is higher in pitch, less well phrased and somewhat scratchy in tone.

The chances are that this pair will have bred on this territory earlier in the year, for the Tawny Owl is a sedentary species not prone to wandering. The sedentary habit and maintenance of a year-round territory provide the Tawny Owl with the familiarity needed to move around the territory safely – although good, even Tawny Owl vision cannot see in complete darkness and birds may occasionally collide with unfamiliar trees or branches – and to find sufficient food. Knowledge of the territory supports success and a successful pair will seek to maintain ownership with their vocalisations.

A fair amount of work has been done, looking into the structure of Tawny Owl calls and this has revealed some interesting things. It seems, for example, that the structure of each territorial call is particular to the individual allowing other owls to recognise each bird as an individual. Territory-holding owls use this information to identify neighbouring birds and to discriminate these from strangers who might be more likely to intrude into the territory. Calling is thought to carry a cost, perhaps because it takes up time that could be used for some other activity (such as feeding) or perhaps because it exposes the caller to an increased risk of predation. Because of this, you might predict that calling Tawny Owls would direct their efforts towards strangers and reduce the amount of calling that they direct at known neighbours, which is precisely what they do.

Tawny Owl calls also appear to carry some information about the bird making the call. The pitch and duration of the call appear to reflect the size of the bird calling and it has also been found that the calls of birds carrying high levels of blood parasites – common parasites in owls and other birds – produce less diverse calls than healthy birds. This suggests that the calls might provide an honest signal of the ‘quality’ of the bird making the call, something that could be used by a potential mate to determine the suitability of a potential partner. Whatever being imparted to other owls, to our ears the calls are simple, conjuring up the spirit of the forest at night.

Frost

The brightness of the moon, descending towards dawn, leaves the clear-fell bathed in light. Dead grass stems, thickened with frost, have the appearance of fragile bone, creating an expanse pale colour that contrasts with the dark depths of the silent conifers standing sentinel behind. Each of my two dogs leaves a visible cloud of exhaled air, like two furry steam trains puffing their way along the forest track. It is the end of a beautiful night and a bright clear morning lies ahead.

Overhead a procession of Rooks is heading out from the overnight roost to seek food in the surrounding fields. They are early risers, unlike the Woodpigeons who stumble from sleep and their treetop perches as I approach the shelterbelt that runs alongside this part of the track. A bird rises from the verge ahead of the dogs, a rounded body carried on broad wings – a Woodcock and my first of the winter in the forest. They are not uncommon here at this time of the year, resting by day in the cover of the forest and feeding by night on the soft arable that surrounds. Presumably, they must feed in the shadow of the forest on nights like this when the frost crisps the soil’s surface and makes probing for worms that much more difficult.

A larger shadow can be seen further ahead, slipping quietly across the track before pausing to take stock of me and the dogs. It is the fox whose scent I often smell along this particular stretch, stringent and clawing on the throat. Satisfied it slips into the undergrowth and away. A late Tawny Owl calls, the call itself somewhat shrill and incomplete. Perhaps this is a young bird setting up territory for the first time. The call is sufficient, however, for one of the resident birds to respond with a mature, resonant hoot. Soon other birds respond, a brief overture of noise before silence returns.

It is then that I pick up the flight calls of Redwing passing overhead. These birds may be on the move because of the colder conditions pushing in from further north. Frozen ground can spell disaster for them, restricting access to the soil-dwelling invertebrates on which they depend. These small thrushes seem to exist on a knife-edge at this time of the year, on the move continually to seek out the best feeding conditions and making journeys that may carry them south into continental Europe or west towards Ireland.

In many ways I find this the best time of the year to be out in the forest. There is none of the dry heat of summer or the damp of later autumn. It is crisp, clear and makes you feel alive.

Signs that our Otters are well-established

The loss of a young Otter, hit by a car as it left the relative safety of the river, was the sad news that greeted me as I arrived at work the other day. The Otter had died not far from where two had been seen playing and feeding the previous week and it underlined the threats that these amazing creatures face as they continue to re-establish themselves within our increasingly busy countryside.

The sad news was balanced somewhat by the sight of an Otter, alive and well, further downstream just a few hours later. Walking back to work along the river I had spotted the Otter break the surface near to the old bridge that echoes an ancient crossing point. This particular individual provided me with some of my best ever views of a wild Otter, as it worked the weed, flushing fish and then crunching on their silver forms. At one point the Otter was feeding within just a few feet of me and the small crowd of colleagues who had by now gathered for this impromptu display of aquatic dexterity. The Otter seemed completely unperturbed by the audience it had drawn, continuing to fish and crunch and, just occasionally, to look at us as if to say ‘move along now, nothing to see here.’

Move along we did, once our lunchtime viewing had extended somewhat into the afternoon’s work. Back at the office word soon got around and another party trooped down to the river to take in the spectacle. For them the viewing was even better, the enjoyment increased by the arrival of a second Otter – a wonderful sign of how well the Otters were now doing on this stretch of the river.

The sighting of the Otter had come a week after I had acquired a copy Miriam Darlington’s new book ‘Otter Country’ a beautifully poetic and personal account of her search for wild Otters. Miriam and I had chatted about ‘my’ Otters when she last came to the Brecks and she would have been mesmerised by the performance of these individuals and surprised by their indifference to us human observers. She might also have been surprised by the indifference shown by many of the people who walk, run or cycle alongside the river on a daily basis, unaware of the Otters. On some occasions, where I have pointed out one of the Otters or answered a query as to what it is that I am looking at, they stare blankly as if unable to comprehend the presence of such a creature here, so close to town. I dare not tell them that the Otters can sometimes be seen fishing just outside the local branch of Argos!

New virus hits Great Tits

The arrival of a new strain of avian pox has been in the news of late, thanks to the publication of a piece of research with which I was involved. The sight of any diseased bird can prove distressing but to see one with a huge growth covering part of its face is particularly upsetting. This, unfortunately, is what we have been seeing over the last few years in some of our Great Tits and it seems likely that we will see more individuals suffering from this virus as it spreads further across the country.

Avian pox is a familiar enough sight, with small lesions not uncommonly reported from Blackbirds, House Sparrows and Dunnocks, among others. This strain of pox virus is less severe and birds often recover. That recently found in British Great Tits is far more unpleasant and the large growths can restrict vision and movement, making the birds more prone to predation and to secondary infection.

My work at the BTO, carried out in association with vets at the Institute of Zoology, researchers at the RSPB and at the Edward Grey Institute in Oxford, has revealed that the virus being seen in our Great Tits is the same as that found in certain continental populations in the past. Not only that, but we have been able to trace its spread since the first case was diagnosed in 2006. Using information collected by BTO Garden BirdWatchers, who keep a weekly count of the birds and other wildlife using their gardens, we have been able to document the disease as it has crept northwards across the UK from an origin somewhere near the south coast. The pattern of arrival, coupled with our knowledge of Great Tit movements, underlines that the virus was almost certainly transported here by a biting insect, possibly a mosquito. British Great Tits are largely sedentary in their habits so it is very unlikely to have arrived via an already infected bird.

You may recall the arrival of blue tongue disease in East Anglia and the link to the continent via a plume of warm from the south bringing with it the biting midges that transport the disease. Something very similar may have happened in the case of the avian pox that we are seeing in these unfortunate Great Tits. Transmission between birds is primarily via biting insects but the virus may also be spread by bird-to-bird contact or via contaminated surfaces, so you should maintain suitable hygiene practices around your garden feeding stations. Hanging feeders and bird tables should be washed weekly, using disinfectant before being rinsed and then air-dried. If you see lots of diseased birds then consider ceasing feeding altogether for a few weeks.