Impacts of disease become evident

Many garden feeders have been busy with young goldfinches and greenfinches over recent weeks, suggesting that these small birds might have enjoyed a good breeding season. This news has, however, been tempered by reports of fluffed up and lethargic looking individuals, indicating the presence of disease within the population. The timing of these disease reports is suggestive of finch trichomonosis, the disease that first emerged in 2006 in the West Midlands before turning up in Norfolk the following year. Figures from the BTO Garden BirdWatch (www.bto.org/gbw) show that the impacts of those initial outbreaks are still being felt, at least within greenfinches.

We know about the disease thanks to the work of the Garden Bird Health initiative, a collaborative project involving a number of different organisations, supported by bird food companies, government agencies and private individuals. By pairing BTO Garden BirdWatch volunteers with wildlife veterinarians, it was possible to set up a systematic network to record the occurrence of disease at different sites across the country. Birds found dead could then be examined post-mortem to determine the cause of death and to identify the role, if any, of a disease agent. The project revealed the impact of the trichomonosis outbreak on finches, notably greenfinch and chaffinch, identified the likely origin as spill over from woodpigeons (which carry the Trichomonas parasite) and established the likely route by which it then spread to Scandinavia and continental Europe.

The full, longer-term impacts of the disease in finches have just been published in a paper for which I was an author. Working with colleagues at the Institute of Zoology, the RSPB and elsewhere, we have revealed the extent of losses sustained by the British greenfinch population. As a result of the disease we have lost in excess of 1.5 million greenfinches, a quarter of our breeding population and something that has seen the population decline to levels that were more typical of the 1980s. What is not clear is what will happen next. As I have already mentioned, Trichomonas is present within our woodpigeon population, something that has not stopped it from increasing, so a species can live with the parasite. Perhaps, since this is a new disease in the greenfinch, it will reduce the population through this initial stage but, longer term, it will rumble on at a much lower level.

Having systematic monitoring in place, both of greenfinch populations and disease occurrence, is obviously important. The presence of a network like the Garden Bird Health initiative (which has now ceased for lack of funding) would provide an early warning system for disease in wild birds. With new and emerging diseases a real possibility, let’s hope more funding is secured soon.

Autumn morning

The edge of the wood is bathed in sunshine and I can feel the warmth of the sun’s rays on my face as I emerge from the shadow. At the same time there is just enough of a chill in the breeze to underline that this is autumn, not summer, the strength of the sun’s warmth diminished as we tilt away from her reach. The breeze also carries with it the sweet smell of a bonfire, seemingly out of sight behind the shoulder of land that separates this little valley from the larger one beyond. It is a fine morning to be out and enjoying the clarity of light that autumn always seems to deliver.

It is too early in the day for the local buzzards to be abroad but other birds are much in evidence. A jay, I think it is just the one individual, is transporting acorns across the valley, preparing stores for the months ahead. Up to nine acorns may be carried by the bird during a single flight, the bird having a specially enlarged oesophagus and a liberal supply of saliva, both of which aid transportation. Autumn acorns are also taken by woodpigeons and rooks, so it pays the jay to hide those it can find away from the prying eyes of others. The jay’s store will be tapped throughout the winter, often beginning within a few days of the unhidden supplies being exhausted, and it is amazing to watch the way a jay can pinpoint one of its cached acorns with such ease.

Turning south, I skirt the edge of the wood before tacking left down the slope to the gate at the bottom of the field. My arrival at this gateway into another field sends a scatter of rabbits to their burrows and prompts the noisy flight of a pheasant that had been tucked in close by. With the smell of the bonfire still lingering in my nostrils I can just about pick up the scent of a fox, perhaps an individual that passed this point overnight or just as the dawn was breaking. I wonder if it had been stalking voles in the thick grass that dominates this piece of rough pasture. Deer slots show that the fox was not the only large mammal to have passed this way. One or more roe deer have worked this edge since yesterday’s heavy rain.

The hedgerow still has plenty of green colour, strewn with the dew-sodden webs of many hundreds of spiders and echoing to the wistful notes of a robin. A distant tractor hints that this is a working landscape and that I don’t have it all to myself. It is time to head home.

Some autumn insects

I found the remains of an old lady the other morning. Actually, to be more specific and somewhat less macabre, I found the wings from an old lady moth. The wings were on the floor of a passageway that runs under part of the house and out onto the street. This sheltered spot is well used by brown long-eared bats, which often bring the larger moths into the passage so they can devour them while clinging to the wall. The boldly marked wings of this large moth are easily recognised and they stood out from the remains of other species, taken more commonly by our local bats. The weather has been such recently that I have seen few moths against the kitchen windows of an evening and this makes me wonder if the bats are beginning to find things a little difficult. They have not had a good year by all accounts, with reports of underweight individuals and others seen on the wing during daylight, stressed by the lack of insect prey. It could be difficult for them going into the winter that lies ahead.

I have not experienced a late summer flush of other insects either, with few migrant moths and hoverflies evident in the garden. Not that there has been much late-summer nectar for them – the sedum and nettle-leaved bellflower only coming into bloom over the last few days. At least the sedum has been available for the small influx of red admiral butterflies that has been on the wing during those days when the sun shows against a bright blue sky. Late September and early October can be a reasonable time for insect immigrants; Camberwell beauty, a very impressive butterfly, tends to occur at this time of the year, although in very small numbers. The Camberwell beauty immigrants originate from Denmark, Poland and Sweden, which is why Norfolk delivers the greatest number of records in most years. It has been a while since the last major influx of this species and it is now very unlikely that we will see any influx this year.

There are invertebrates around if you know where to look though and can get out and about ahead of the first frosts. Bush-crickets can still be found in our hedgerows, along with various flies and smaller wasps, and there are plenty of spiders around at the moment, including some of the Tegenaria species that may be encountered dashing across the living-room carpet during the evening. There is a sense, however, that things are winding down, retreating ahead of the approaching winter and readying themselves for a sustained period of inactivity. Every now and then though you might still stumble across something of interest.

Grey Squirrels busy in the garden

I planted several hazels in the garden a number of years ago and they have now reached an age where they produce a crop of nuts each autumn. This has not gone unnoticed by the local squirrels and a scatter of shells, neatly split into two, can be see on the path by each tree. I say ‘squirrels’ but it might be just a single individual, one brave enough to make a living in this highly fragmented urban environment. Up until a couple of years ago the grey squirrel was such a rare visitor to the garden as to attract a surprised comment and, even now, the bird feeders are never touched by this agile forager.

The grey squirrel is a creature that generates a mixed response from us humans. For some it is vermin, a non-native ‘tree-rat’ that has displaced our native red squirrel and brought about the decline of many woodland birds; for others it is a much-loved resident of urban greenspace and one of the few mammals accessible and approachable to a generation of children, growing up divorced from the countryside and its wildlife. The accusations made against the grey squirrel do not always stand up to scrutiny but such is the vitriol delivered in some quarters that claims and counter-claims are rolled out as fact. Take the supposed predation of bird nests for instance. Research has failed to find a link between the decline of woodland bird species and squirrel numbers. In fact, the evidence suggests that grey squirrels are not great predators of nest contents but find only the more exposed, poorly hidden nests, such as those of blackbird and collared dove. If anything, it is the red squirrel that is more of a nest predator than the grey.

Having said this, the grey squirrel remains an introduced species and one that has played a key role in the loss of the red squirrel from most of its former range. Efforts should, quite rightly, be made to prevent the grey squirrel from displacing the red from its remaining haunts and, additionally, be directed to increasing our understanding of the squirrel pox virus and its transmission from grey to red. But what about elsewhere in the UK? Given that the grey squirrel is now so well established across lowland Britain, should we not embrace it as part of our mammal fauna? It is not alone in being an introduction (think of little owl, for example) and its adaptability does deliver an experience of nature into our towns and cities. To see the delight in a child’s face when it watches the antics of an urban squirrel is to sense the contribution this species continues to deliver.

Winds from the east

The last week of September delivered a feast of migrant birds for east coast birdwatchers. With winds from the east, coupled with cloudy and wet weather hanging over the coast, conditions were ideally suited to produce an autumn ‘fall’ of small birds to coastal hedgerows and shelterbelts. Good numbers of redstarts and pied flycatchers were widely reported, together with less common birds like yellow-browed warbler, red-breasted flycatcher and Richard’s pipit.

One of the real joys of birdwatching the Norfolk coast under such conditions is not knowing what you might find while out working a favoured patch of habitat. There is a chance of something unusual, something unexpected and, just occasionally, something rather special. It is just a chance mind you, but the more time that you spend out there the better are the odds of something really good turning up.

It is interesting to think about the birdwatcher’s perception of what is a good bird. While for some it is all about rarity, for others it is the challenge of securing the identification of a bird that is notoriously tricky. For me it is about the sense of place, the bird in the landscape and part of a wider experience. Looking back through my notebooks for this time of the year underlines this. Notes on a barred warbler I found at Kelling, for example, are mixed in with mention of late bush-crickets and the antics of some young common rats, clambering about in the bramble to get at the berries. It is not so much the bird that is the focus but the wider experience.

There are barred warblers about again this autumn and a chance that I might stumble across one, just as I might see young rats or something else, a chance encounter providing a lasting memory. Just being out provides the space to think and relax, to sense your place as the seasons shift and nature responds. Given how much time is spent in an office or in front of a computer, I believe that these moments spent outside have an important role, keeping us rooted in the natural world, reminding us that we are part of something more dynamic and responsive. Computers and televisions direct our gaze to a single point and narrow our horizons but being outside frees us from this, it allows us to gaze around, to be saturated by sounds and sights and to immerse ourselves in something real and tangible. Birdwatching provides an excuse to get out into the countryside and to engage with the natural world, just as walking, riding or volunteering can. It is about extending our horizons, being expansive and engaging with the natural world around us.

Roads take a toll

Over the course of this year, the motor vehicles using our roads will clock up some 300 billion miles of travel between them. With so much traffic on our road network, much of it moving at speed through rural areas, it is little wonder that wildlife casualties are a common sight; forlorn bundles that have been stripped of life and now lay in the gutter. The risk to our nocturnal wildlife is elevated as the autumn evenings begin to draw in and our evening commute home overlaps increasingly with the emergence of owls, deer and foxes.

The barn owl seems particularly susceptible to collision with motor vehicles and a great many, possibly 5,000 to 6,000 individuals, are killed on our roads each year. Much of this toll happens during the autumn, a period when young barn owls, newly independent and inexperienced, are moving away from their natal sites to set up home elsewhere. Over the course of three or four months they will cover a dozen or so kilometres. During this period they will, invariably, encounter a road. Whether or not they are then hit by a lorry or a car depends on a number of different factors. Vehicle speed and traffic volume are important but so are other things, such as whether or not the road is bordered by a hedgerow, whether it has a wide grassy verge and whether it is sunken or raised.

Various studies have revealed that a raised road, running across open country, poses a particular risk because an owl is likely to cross the road at bonnet level. Conversely, a sunken road is more likely to be crossed at a greater height, reducing the risk of collision. Hedgerows work in a similar manner, forcing the bird up and over the road. The presence of grassy verges can be a problem for a different reason. Such verges often support good numbers of field voles, a favoured prey species, and may actually attract owls to the road in those areas where other hunting opportunities are limited. Buffeted by the back draft from a passing lorry, the disoriented owl may then be pulled into the path of the next vehicle and hit.

While this knowledge may help us to plan the management of our roads and their boundary features better, reducing owl mortality, some of the solutions for owls may increase the risk of mortality to other wildlife groups. Replacing a grassy verge with densely-planted shrubs might stop an owl from hunting but it might increase thrush mortality, with birds attracted to the berries that such shrubs often carry. Mitigating the impacts of our busy road network needs careful thought and sensitive planning.