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. 

In search of the wild

It is all too easy to think of wild as something remote and unobtainable, to imagine that it exists only on some distant mountain slope, offshore island or in some hidden sunken lane. We sense that our increasing reach and untidy habits leave even the most remote of places touched by our activities, the wild tamed or tainted. While all this is true, it is easy enough to discover wildness much closer to home. Wild is the late November wind that batters the shutters, the rain that runs down the window, the dark shadow of that slips into an urban river and the plants that push up between the cracks in the town centre pavement. Wild is everywhere and however much we try to conquer it, it will always find a way.

It is not so much that the wild has been tamed but more that we have become too comfortable with our modern existence and can no longer see it. Part of the reason for this is that we rarely, if ever, have to face the dangerous wild, the wild that challenges us, scares us and has the potential to harm. No large predators stalk our countryside; we have just the one venomous snake and there are few creatures with enough bite or sting to threaten. No longer do we have to take risks. We are comfortable and secure but sense there is something missing. It is this sense of something being missing that drives some of us to seek out the more remote parts of our archipelago, to promote ‘rewilding’ and daydream of the return of big cats and other missing carnivores.

Of course, we do not have to go as far as reintroducing Lynx or Wolf to rediscover our missing wild. All we need to do is step outside from time to time and engage with the natural world around us. It might appear a bit ‘new age’ to suggest immersing yourself in a late summer hay meadow or to insinuate yourself into the middle of a blackthorn thicket, but to do so will envelop your senses with the buzzings and scratchings and sniffings of wild. Peer at the weedy looking plant emerging from the narrowest of cracks in the pavement and discover the vitality that drives it to conquer our attempt to blanket it out. Seek out the creatures that have gained access to your home, the spiders, silverfish, moths and woodlice, and delight in their persistence.

The wild should never be completely understood, and perhaps it should probably carry a hint of danger, but it needs to become a more central part of our daily lives. It is part of us and we are part of it.

The wandering water-ouzel

On the south-east edge of Thetford stands an aged bridge; it is stone-built, strongly arched and full of character. No longer used by traffic, other than of the pedestrian kind, the bridge is partnered by a more modern construction a few metres to the south over which the main road now runs. It is here that the Otters are sometimes sighted and it was here, just a fortnight ago, that a wandering ‘water ouzel’ put in an appearance. ‘Water ouzel’ is an old name for the Dipper, a bird of the bubbling, fast-moving rivers and streams of the north and west of Britain.

Other than a few local or altitudinal movements to escape the worst of the winter weather, British Dippers are sedentary in their habits and unlikely to stray into the flatlands of Eastern England. This suggests that the individuals which turn up in Norfolk are likely to have arrived from overseas, most likely from Scandinavia. Usefully, most of these longer-distance visitors are ‘Black-bellied Dippers’, distinctive in appearance and belonging to a different race to the one which breeds in the west of Britain.

Reminiscent of a thrush or a rather solid and chunky looking Robin in structure, the Dipper is a dark-coloured bird, deep brown across the upperparts, with a white chest. In size it is similar to a Starling. The belly has tones of warm chestnut in the British race, while in the black-bellied race it is black or dark brown. This is a bird of character, not least for its ability to feed underwater, probing between submerged boulders and pebbles in search of aquatic invertebrates. The compact body shape, coupled with strengthened bones, no doubt aids the bird as it battles against the current and its own buoyancy.

The Dipper has a tendency to make small bobbing movements when perched, like tiny curtseys, something that is reflected in the name. These add to the character and I always feel a flush of excitement when I watch a Dipper. It is a bird that lives on the margins of two different worlds, a bird which swims and dives but which can also take to the air.

Much of the river along this section appears unsuitable for a visiting Dipper, being deeper and slow-flowing, but there are a few places along its length where the water flows over stony shallows providing feeding opportunities. Whether or not the bird will spend the winter here is unclear and it may be that it moves on to seek out more favourable conditions elsewhere. While it has been present it has attracted a good deal of interest from local birdwatchers and even the local dog-walkers have been talking about the bird and the crowd it has drawn.