Better times for House Sparrows

The end of summer always sees a peak in the number of house sparrows visiting my garden, as the young from this year’s breeding attempts join the local flock at my feeding station. Judging by the numbers of young birds present over recent weeks, I suspect that it has been a good breeding season despite the slow start to the year.

More widely, there is also evidence that house sparrows may be doing rather better than they have for a while. The weekly observations made by the BTO’s Garden BirdWatch volunteers (www.bto.org/gbw), for example, suggest that the long-running declines in the house sparrow’s fortunes have levelled off. Of course, any improvement needs to be viewed in the context of several decades of decline – house sparrow populations have fallen from 12 million breeding pairs in the 1970s to just under 6 million breeding pairs now.

The reasons for the longer-term decline are unclear, at least within the urbanised landscapes where the bulk of the breeding population is to be found. Loss of nest sites and feeding opportunities are likely to be the main drivers behind the decline but other factors, such as increased levels of competition, predation and pollution, may have also played their part. Although adult house sparrows feed on seeds, they require invertebrate food for their chicks and this resource is likely to have suffered as gardens have become more tidy, with greater use of pesticides and the preference for exotic plants and shrubs over native ones. Interestingly, a study carried out in urban Bristol showed that house sparrows fared better in areas of lower quality housing than they did in more middle class housing – a reflection, perhaps, of the different levels of house and garden maintenance that come from inequalities in household income.

Just as the reasons behind the decline have yet to be unravelled, it is unclear why things might have improved over recent years. Is the message about wildlife-friendly gardening now hitting home, or could it be that house sparrows now face less competition from a greenfinch population hit by the 2006 outbreak of disease? More work will be needed to find out but, for my part, I am delighted to have my sparrows back.

Help to find out about birds and berries

It is at this time of the year that I start to see migrant thrushes, newly arrived and busy feeding on the abundance of berries and other fruits that adorn the county’s hedgerows. Berries provide a ready meal for blackbirds, song thrushes and redwings – the latter not arriving in numbers until later into the year – and in return the birds disperse the plant’s seeds into new areas.

Follow the progress of the berries through the winter and you’ll discover that some seem to last longer than others, perhaps because they ripen later or because they are less favoured and are only used when other fruits have been stripped. In some cases, a berry-bearing shrub may be defended by a mistle thrush or fieldfare seeking to secure a food reserve for future use. Whatever the reason, the seasonality of berry availability is likely to be important, influencing where birds feed and when. Taken to an extreme in a species like waxwing, individual birds may range of vast distances to find an area where berries are plentiful.

The interaction between birds and berries is something that has attracted the interest of the BTO, who are running a study this winter to look at how thrushes make use of the berries to be found within our gardens. Some of these garden berries may be native in origin, others introduced and some will be domesticated varieties of wild species. Since berry colour can provide an honest signal to birds of the nutritional value of a particular berry, it is possible that some of the varieties we have selectively bred to produce a particular berry colour (e.g. pink or white) may now be unattractive to the birds. Birds may also preferentially select native fruits over non-native ones, or vice versa – the selection influenced by availability and/or the timing of fruit production.

In order to examine these questions the BTO has asked for our help. By making simple observations of berry availability and of berry use, we can provide the information needed to better understand the relationships that exists between plants and the birds that disperse their seeds. If, for example, non-native plants are favoured over native ones, then this might give them an increased opportunity to become established more widely across the countryside. Could we expect to see Cotoneaster and Pyracantha becoming established in our woodlands and hedgerows? The work should also provide better guidance as to which shrubs to plant for the benefit of our wintering thrushes and other berry-eating birds.

To find out more and to receive a free guide to berries, write to Birds and Garden Berries, BTO, The Nunnery, Thetford, IP24 2PU or email gbw@bto.org.

Goldfinch with abnormal plumage

This Goldfinch has been visiting the garden over several weeks. In place of the black heading markings is an area of white, meaning that this bird is suffering from some form of plumage abnormality. The BTO is running an Abnormal Plumage Survey and wants to hear from you if you have seen a bird with unusual plumage, perhaps a Blackbird with some white feathering. You can access the BTO pages on abnormal plumage here.

Finch disease spreads

That Britain has an important role in the wider pattern of bird movements is particularly evident at this time of the year, as many species – both rare and common – are noted arriving and departing by birdwatchers. As the first of our wintering geese arrive, so the last of our summer-visiting warblers depart. The scale of these movements is sometimes more difficult to gauge, however, particularly when it comes to common and familiar species like Greenfinch, Goldfinch and Chaffinch.

It is easy to assume that these finches, together with our other ‘resident’ species, are here all year; after all, they fill our hedgerows and woods with song in the summer and make use of our garden feeders come winter. Thanks to the efforts of licensed bird ringers we know that many of our wintering Chaffinches and Greenfinches arrive here from elsewhere, and that some of our breeding Goldfinches leave Britain for a winter spent in France and Spain.

The degree to which our finch populations are connected with those elsewhere in Europe was brought home to me recently through a piece of work with which I was involved. For several years now, I have been studying the impacts of an emerging infectious disease in finches. This disease, caused by a protozoan parasite, is known as trichomonosis and was first seen in wild finches in 2005. During 2006 we had our first outbreak, centred on the West Midlands and the Southwest of England, but in 2007 we saw it hit East Anglia. Our work has shown the disease to have reduced the Greenfinch population in affected regions by a third and the Chaffinch population by a fifth. This is the first time that anyone has been able to document a population level impact in a widespread European bird resulting from an infectious disease.

Worryingly, in 2008 a case was diagnosed in Sweden, followed by others the same autumn in Finland and Norway. Working with vets at the Institute of Zoology in London and molecular biologists at UEA, we have found that the trichomonad parasites taken from these birds are identical. This implies that the parasites arrived in Sweden, Finland and Norway via birds that had migrated from Britain. By examining bird movements we have been able to demonstrate that the most likely candidate is the Chaffinch, individuals of which migrate from eastern England to these countries come spring. Wintering Greenfinches, on the other hand, tend to migrate between eastern England and western Norway, away from where recent cases have been seen. With a foothold in these northern European populations we may see the disease emerge elsewhere in Europe, as migratory individuals mix over time. More on the disease can be found at www.bto.org/gbw

Rare visitor amid the throng

Each morning, the Siskin flock announces its arrival at the garden feeding station with a cacophony of twittering calls. Perched at the top of the neighbouring sycamore, the Siskins will soon drop down through the branches to the feeders below. Despite the busy appearance of the flock itself, the birds are initially reluctant to move from the security of their lofty position. Perhaps the uncertainty stems from this tiny urban garden being so different to the acres of conifers and riverside alders that these birds will have been using over previous weeks.

Siskins are winter visitors for most of us, moving into gardens from February or March once the crops of wild seed are depleted. Many will have come from breeding grounds further north but some, notably in the west of the county, may be local breeders from Thetford Forest. The arrival of the Siskins is predictable, even if their numbers are not, but this year they have been joined by unusually large numbers of redpolls, which intermingle with their more common cousins. Redpolls are small finches, generally off-white and grey in appearance, with a prominent red forehead and soft brown nape and back. When seen alongside other visiting birds, they are fairly obvious.

Our redpoll was thought to be a subspecies of the Common Redpoll until fairly recently, subtly different in plumage, voice and behaviour. However, during the 1990s it was discovered that our redpoll is actually a different species and, having been elevated to full species status, it was given the name of Lesser Redpoll. Understandably, with many of the bird books on our shelves pre-dating the ‘discovery’ of this new species, there is still a fair bit of confusion among more casual birdwatchers, not least because the Common Redpoll is no longer the common species here! Having said this, Common Redpolls do turn up in Britain but always in much smaller numbers; their breeding grounds are positioned well to the north and east of us, stretching across the birch forests of northern Europe.

This winter has seen both increased numbers of Lesser Redpolls at garden feeders and an unusually large number of Common Redpolls in the country. With the former fairly regular in the Siskins flocks doing the rounds of Thetford’s feeding stations it is perhaps not surprising that there has been the odd Common Redpoll tagging along as well. Several have been caught and ringed by BTO staff at the various feeding stations operated throughout the Brecks and I was amazed to see one here in the centre of town. A neighbour, and fellow bird ringer, had caught it in his garden, a wonderful thing to see and something that made my week!

Gardens shelter snakes and lizards

I know that my garden supports a small number of frogs and toads. While the frogs were quick to lay claim to my new wildlife pond, spawning in the first spring after the pond had been dug, the toads show a more terrestrial existence, most often appearing on the patio on damp nights to frighten the dogs. The fact that our garden is walled on three sides and located in the middle of town, is probably sufficient reason for the lack of any other amphibians or reptiles. It is known that only the common frog readily penetrates the urban landscape, possibly because of its greater dispersive powers or, more likely, because it is assisted by householders moving spawn from one pond to another.

It seems that the range of reptiles and amphibians you can attract into your garden is, to a greater extent, determined by where your garden is located and the nature of the habitats that surround it. There are some gardens, recently built on former heathland sites in Dorset, that have visiting Adders and Smooth Snakes, the latter a rare species these days. Other rural gardens might support a thriving population of Great Crested Newts or Grass Snakes, and I know of gardens in Norfolk that have both. Less common in most Norfolk gardens is the Slow-worm, not a worm but a legless lizard, with a beautifully patterned body (in the case of the adult males).

Recent research has underlined that the features you have within your garden can also have an influence on which amphibian and reptile species you can support. Open compost heaps are used by Grass Snakes, the elevated temperatures within the mound of decomposing vegetable material help the Grass Snake’s eggs to develop, while stacks of logs and piles of rubble provide shelter for this and other species. There is a garden just down the road from here where the owner has placed sheets of corrugated tin at various points around his large, wooded garden, He now has an impressively large population of Grass Snakes and Slow-worms.

If you are an active gardener like me, then you are more likely to stumble across one of these garden-dwelling reptiles or amphibians but in many gardens they will go unnoticed. Having said this, cat owners sometimes find that their pet has delivered some unfortunate frog, Slow-worm or Grass Snake, which would otherwise have gone unnoticed. The impact of cat predation on some of our reptile and amphibian species might be quite significant, at least in terms of the numbers killed each year. There are likely to be other risks (lawn mowers and garden chemicals to name but two) so the garden can be a difficult place for some species.

Birds of a feather roost together

The bird table and hanging feeders are busy first thing in the morning, underlining the urgency with which many of the smaller birds need to replenish energy reserves lost overnight. Winter is a difficult time for small birds, the long nights and low temperatures placing strain on the small fat reserves these birds carry. If temperatures hover around freezing, or dip below, then these reserves are quickly depleted, something that can be a particular problem for our smallest birds, like Wren, Long-tailed Tit and Goldcrest. Research has shown that both Blue Tits and Great Tits lose some 5-10% of their body weight over the course of a typical winter night, possibly a lot more if the conditions are particularly poor.

Heat loss is, in part, dependent on where you choose to roost. Pick somewhere warm and you’ll be able to maintain your body temperature at a safe level more easily than if you pick somewhere cold. It is for this reason that some of our birds will roost communally, seeking the warmth from street lighting (Pied Wagtails) or from huddling together in a nest box or roosting pouch (Wren, Blue Tit or Coal Tit). Others roost within vegetation, a behaviour which sees Long-tailed Tits form up in a line along a branch or stem, huddled together within thick cover and out of the wind.

The use of nest boxes for roosting is something that is easily overlooked, especially if the birds pile into the box just as it is getting dark. There are some records of observers witnessing these arrivals; in one case at least 60 Wrens squeezed into a single box, but the behaviour is likely to be more common than these occasional reports would suggest. It is for this reason that the British Trust for Ornithology (BTO) has asked us to look at our nest boxes over the course of the next few weeks. If you take a look at your nest box one afternoon and then another the following morning, you should be able to tell if it has been used as a roost. This is because you are likely to find fresh droppings come morning if a bird has used the box overnight.

You might be fortunate enough to have a nest box camera attached to your box. If so, turn it on each evening to see if a bird is using the box for roosting. More details will shortly appear on the BTO website: www.bto.org/gbw. Other birds form roosts that are more obvious. Starlings, for instance, gather together in very large flocks, which pulse and whirl about the sky prior to the birds dropping down and into the chosen site – often a large conifer.

The Great Arrival

More than one author has conjured up the image of a Great Arrival, the 16 million or so migrant birds all heading north to summer on these northern breeding grounds. Most recently, in his excellent book Say Goodbye to the Cuckoo, Michael McCarthy speculated on how we would react were all these birds to arrive in a single flock. Such a flock would fill the sky; people would stop what they were doing in order to take in the spectacle and it would become an important signal that spring had reached our shores, celebrated with street parties and a public holiday.

Of course, our summer migrants do not arrive all at once in some grand flock; instead they turn up in small numbers or individually, with many arriving at night when the energetics of migration are better balanced. These overnight arrivals do provide one thing however; they deliver a sense of the unexpected to us birdwatchers, the thrill that the night just gone might have delivered some exciting find to an early morning trip to a patch of coastal scrub or waterside reedbed. Even those who would not describe themselves as a birdwatcher derive a thrill from seeing the summer’s first Swallow or hearing May’s first Cuckoo.

While these individual encounters act in some small way as a talisman for a wider arrival, the movement of this mass of birds, streaming out of Africa and up across Europe, goes largely unnoticed. Taken for granted, we find ourselves unaware of the problems faced by these many and varied travellers, problems which have resulted in dramatic population decline for some species. We only know of the changing fortunes of our summer visitors because of the work of organisations like the British Trust for Ornithology (BTO), whose partnership between researchers and birdwatchers provides regular monitoring of the birds breeding across Britain and Ireland. Yet even with this information we only know that something is wrong, we don’t fully know why. Are the numbers of Wheatears, Cuckoos, Turtle Doves and flycatchers falling because of difficulties here or is it because of problems on their wintering grounds or along their migration routes?

Recently, the BTO and RSPB have launched projects in Africa to look at our migrants on their wintering grounds, seeking to understand what is happening to the habitats they use during our winter. This work is only the start of a wider process which, ultimately, will need to feed into conservation action targeted at the different species across their whole range. The scale of this work also serves to bring home the message that while we view these birds as being ‘ours’, they are only ours for part of the year.

Urban birds are lazy

The divide between town and country is one that you often see mentioned in the news. Be it a story about economics, social attitudes, crime or even quality of life, the differences between town and country are much trumpeted. One difference that you might not expect, however, is the difference that has been found between how particular bird species behave in towns and how they behave in the wider countryside. Research that I have been involved with has just revealed that urban birds are lazy, at least when it comes to getting up in the morning to visit garden feeding stations! Urban-living populations of Robins, Greenfinches, Blackbirds and many other species arrive at garden feeding stations, on average, a few minutes later after first light than their country cousins.

Of course, this is not really a case of lazy birds but the result of different factors operating in each of the two habitats, influencing the birds’ behaviour. On cold winter nights (the time of year when we carried out our study) many small birds struggle to survive the low temperatures and long nights without access to food. In order to keep warm, many of these small birds will burn off much of their body’s fat reserves, reserves that need to be replenished as soon as possible after dawn. It is these energy losses that prompt the early arrival at garden bird tables and hanging feeders, the birds arriving as soon as it is light enough for them to see what they are doing.

Now you might think that with all the street lighting that exists within our cities, urban living birds would be able to start feeding earlier because of the extra light available to them. That this is not the case suggests that another factor is operating on our urban birds, working in the opposite direction. This factor is temperature. Because of all the heat that escapes from offices, shops, factories and houses, our urban areas are typically several degrees warmer than the surrounding countryside. In fact, some of the largest urban areas (think of London, Birmingham and Manchester) may be as much as eight degrees warmer than the surrounding land. This is known as the urban heat island effect and in winter it can counter the effects of lower ambient temperatures. If it is less cold overnight for urban-living birds then they will not have to use up so much of their energy reserves keeping warm, meaning that they are not so pressed to replenish fat reserves come first light. This allows them to make a more leisurely start to the day than hard-pressed relatives who happen to be living in rural areas. Sometimes an urban existence pays dividends.

Take up the armchair challenge

The last weekend of January saw many thousands of people up and down the country take part in the RSPB’s Big Garden BirdWatch. This annual event provides a very brief snapshot of garden bird populations and, more importantly, engages them with the concept of citizen science. Citizen Science is all about large-scale scientific studies made possible by the contributions of volunteers. For example, most of the biological recording carried out within the United Kingdom is citizen science, the records collected by unpaid volunteers used to underpin conservation policy. These volunteers are often referred to as amateurs (as opposed to professional fieldworkers or researchers). However, this title does them great disservice because many are experts in their chosen field. A more appropriate distinction would be to call them unpaid volunteers (as opposed to paid professionals).

The tremendous importance of this army of volunteers can readily be seen once you realise just how much time they give to support nationwide surveys and national projects. One organisation that clearly benefits from volunteers is the British Trust for Ornithology (BTO), whose 30,000 or so supporters collect the information needed by Government to monitor the changing status of our breeding and wintering birds.

One particular BTO project, the BTO/CJ Garden BirdWatch, deploys some 16,000 ‘armchair’ birdwatchers, who keep simple records of the birds using their gardens each week throughout the year. These records enable the BTO to examine the way in which different birds use gardens and how this use varies with season and over the longer term. Participants in the BTO/CJ Garden BirdWatch not only give generously of their time, typically spending 1-2 hours each per week watching and noting down what they see, they also support the project financially, through an annual subscription of £12. This covers all of the running costs of the project, including time for analysts to study and report on the figures, the production of recording sheets and the quarterly colour magazine that feeds information back to participants. An impressive number of scientific papers have been published based on the records collected by the volunteers, a fitting testament to their efforts in supporting this project and providing the all-important records.

The BTO/CJ Garden BirdWatch survey builds on the enthusiasm generated by the RSPB’s high profile once-a-year event. Many of those bitten by the bug that is armchair birdwatching go on to get involved in the weekly recording offered by the BTO study. By doing so they learn more about their garden birds, discovering how the patterns that they see in their own gardens fit into the wider picture of what is happening on a seasonal basis across the country. Why not get comfortable in your armchair and get involved.

Where have all my birds gone?

Over recent weeks, increasing numbers of garden birdwatchers have contacted me to ask where all their birds have gone.  Familiar species like robin and blackbird have deserted gardens, leaving birdwatchers concerned that something untoward may be happening. Fortunately, this exodus is an annual event and one that forms part of the regular seasonal pattern of garden use. Autumn is a time of plenty, when Nature’s larder is packed full with wild fruits, seeds and nuts. As such, many birds will shun the food provided at garden feeding stations, in favour of beech mast, rose hips, berries and haws. The extent of this sudden switch in where to feed can be seen very clearly from the weekly records collected by the 16,000 BTO/CJ Garden BirdWatchers. Examination of the results for a species like blackbird (www.bto.org/gbw) shows an abrupt decline in the use of gardens, something which extends over several weeks. Once the supply of wild fruits is exhausted, the blackbirds return to gardens and the Garden BirdWatch reporting rate increases again.

You only have to wander out into the Norfolk countryside to see that many fruit or seed-producing plants have produced a bumper crop this year. Crops of acorns and beech mast are particularly large; that for beech being the largest since 2002. With such an abundance of food, seed-eating birds (such as coal tit, chaffinch, brambling, jay, nuthatch and woodpigeon) are likely to make very little use of garden feeding stations over the course of the winter months.  Work carried out by David Glue of the British Trust for Ornithology has demonstrated this link between seed availability and the use of gardens by coal tits.  During winter, when insect food is in short supply, coal tits switch to feeding on beech mast. When there is little beech mast available, more coal tits move into gardens to feed on peanuts and sunflower seeds. When there is a bumper crop of beech mast, they can remain within their favoured woodland habitats.

Many trees vary their production of seeds from one year to the next, using environmental cues to synchronise the size of the crop across large areas. This results in a run of years when seed crops are quite small, followed by the occasional year when they are very large. This large crop is known as a “masting” event and the strategy itself is designed to reduce the amount of seed taken by seed predators. If trees produced a similar crop each year then seed-predator populations would increase and the amount of seed eaten would be high. By having a series of small crops, followed by one big one, the trees effectively swamp the predators during the masting year, insuring that more seed survives to germinate.