Let’s start by imagining a fine Persian carpet and a hunting knife. We set about cutting the carpet into thirty-six equal pieces, each one a rectangle, two feet by three ... But what does it amount to? Have we got thirty-six nice Persian throw rugs? No. All we’re left with is three dozen ragged fragments, each one worthless and commencing to come apart.
—David Quammen, The Song of the Dodo1
It’s early May. Your annual pair of house martins has returned – the miracle of summer. Weighing barely more than 15 grams, they have flown over 8,000 kilometres from southern Africa – even now, we don’t know from exactly where – to spend summer below your eaves. In navy and white overalls, they’ve returned to last year’s nest: a gravity-defying mud castle cemented upside down, one beakful at a time, below your roof. It’s a glorious summer, and you idly watch your martins bringing flies to hungry nestlings. By late June, the clumsy first brood are twittering away on wires beside your house. Then, it’s time for round two. The first lot of kids are sent packing, and soon your industrious martins get to work on their second family. But in a wet spell, the second set of chicks do not survive. Still, you’re pleased to see the first family have done well – and quietly wish them all the best on their journey to Africa.
As summer fades, they’re gone. But the next year – the castle is abandoned. Your martins haven’t come back. You’re outraged. They’re house martins. Your house is most certainly still there. But then, a few years before, your spotted flycatchers didn’t come back. They might have had to fly from Africa, but your local starlings didn’t have to. And they didn’t come back either last spring.
You can’t understand it. You’re not spraying your garden. You’re doing nothing wrong. Birds are fledging the nest. You know enough to know that nothing has changed. Each summer, these little dramas of loss and puzzlement play out for many nature lovers in Britain, whether in our gardens, our nature reserves, or the countryside at large. And the reason is chilling. Your single house martin pair were, in ecological terms, already dead. Your spotted flycatchers were islanders. Your starlings were the last survivors of their tribe.
By this stage in their decline, it didn’t matter what you did. These birds were living history. Birds, like other animals, have evolved to exist in boundless populations, connected across large tracts of preferred habitat. There is no precedent for any species, anywhere, to evolve as a single pair, standing the test of time in isolation from the rest of their kind.
Populations of birds, by contrast, provide security. Landscape populations of birds allow for starvation, predation, disease, mate selection, and mitigate a whole spectrum of problems that naturally befall a species, such as poor summers or problems on migration.
Meta-populations, or meta-communities, can provide even better mechanisms for survival. In a meta-community, distinct populations are strengthened by dispersal between them, increasing survival, promoting gene flow and allowing for local extinctions and recolonisations across the geographical range.2 Amazingly, a robust population of birds, in a natural environment, is adapted to withstand losses of up to 80% in one season – yet still survive.3
Isolation, by contrast, breeds extinction. It is fundamentally unnatural for that single pair of house martins in your village to be defying the community-based rules by which their species evolved. Only birds in robust populations stand the test of time. In this chapter, we’ll find out how big landscapes alone can help prevent a mass extinction of our nation’s wildlife, and why scale is the only language that nature understands.
The headlines tell us birds are falling into decline – both our resident birds and our enterprising migrants, arriving from Africa each summer. But in some areas of our country they’re not declining at all:
The whinchat is an example of a species that was once common across England but has suffered major declines in recent years: 55% since 1995. A large, stable population of whinchats persists on Salisbury Plain.4
The lesser spotted woodpecker was once widespread in woodlands across the UK, but its drumming is an increasingly rare sound. In Hampshire it has also become a scarce resident. However, the New Forest remains an important stronghold.5
The strongest capercaillie populations are in the Cairngorms National Park. The last national survey in 2009–2010 showed 80% of the UK capercaillie population was estimated to be in the Park, with the vast majority in Strathspey. Numbers there currently appear stable.6
Despite national concern, willow tits seem to be doing very well in County Durham. Excellent populations were noted in the coalfields area including 13 at Rainton Meadows, 10 at Hetton Bogs, eight at Elemore GC.7
Contrary to the national trend, numbers of nightingales in the Cotswold Water Park have been maintained over the previous 10 years. A superb total of 20 singing males were recorded in 2012.8
These quotes refer to migratory and resident birds, Scottish and English, specialists and generalists. These birds have only two things in common. Firstly, they have suffered, or are suffering, massive declines and now, in most cases, face the real prospect of extinction in Britain.9 Secondly, each has found a refuge that is not only hanging on to these birds – but defying the national trend.
When declining birds do well, you’re onto a winner. That conservation gold dust, time, is on your side. You can begin to see what is missing in other areas, and work out why these birds are declining everywhere else. All of our good-news stories have one thing in common. And it’s expressed rather well by site manager Gareth Harris, at the Cotswold Water Park in Gloucestershire:
Although the nightingale population fluctuates widely, it appears self-sustaining and stable in the long term … As nesting sites become too old or unsuitable, new nesting sites become available and are colonised … the size and extent of the landscape is key.10
Size and extent, alone, determine whether your conservation efforts will be successful or in vain. Scale is what makes populations possible and gives them the chance to weather bad times. Narratives of scale are stories of success. But how big does a population of birds need to be to survive?
The size of an island has a huge impact on the life of the creatures cast away there … Of all the species that have become extinct in recent years, around 80% of them have been islanders.
—Sir David Attenborough, Planet Earth 211
In 1939, the RSPB bought North Warren, Suffolk, for its breeding bird communities, which, at that time, included red-backed shrikes. Even before the war, the shrike was on the cusp of a really severe plummet in fortunes, after already a century of decline. Buying a carefully selected piece of land was a smart move by the RSPB, and one that’s proven the salvation of many birds, such as roseate terns, with the entire future of the species in Britain now safeguarded on Coquet Island in Northumberland.12 Yet, by 1960, there were just 27 pairs of shrikes left along the coast around North Warren.13 By 1989, shrikes no longer bred regularly in England.
Shrikes, it seems, were vanishing even in good areas of habitat, with good protection by conservationists. Their decline was operating on a scale that no nature reserve could contend with. But why were heathland reserves like North Warren unable to hold onto their 5, 10 or 20 pairs of shrike? The answer, as for all our vanishing birds, lies in something known as critical mass.
Viktoria Takács is an ornithologist who has done a lot of work on red-backed shrikes in eastern Poland, in the realisation that the species is vanishing elsewhere in Europe. In her study, Viktoria looks at a stable population of red-backed shrikes in east Polish farmland.14 She asks a simple question: how many pairs are needed to keep things as they are? What if the food and habitat remain prime? What if you factor in a bad summer, which, in Poland, happens every four years? What if you have 30 pairs? What if you have 200? How likely is it, in 50 years’ time, that such a population will still exist?
Viktoria puts these questions to VORTEX. I pictured a small black hole, but in fact it’s a piece of software for population viability analysis (PVA), a modelling tool for estimating extinction probability in a population. The more data you put in, the better and more accurate the results you get.
In Poland, the team knew things like the percentage of shrikes laying one, two, three, four and five eggs. They knew the breeding age of females, who are ready at a tender one year old but past it by nine. They knew the mortality of young and adult birds. As with many smaller migrants, just a third of red-backed shrikes make it back from Africa the following spring, to sing pretty badly on European soil. Armed with a lot of facts about her shrikes, Viktoria and her team calculated roughly how many shrikes you need in a single population to stand the test of time.
The study revealed that for a shrike population to have a 95% chance of surviving for 50 years, in favourable conditions, you’d need 80–90 pairs in that population. Not one, not twenty. Not even fifty. Such a population, alone, provides viability – where insurance is provided against predation, bad summers, inbreeding and other mechanisms that drive decline. Even if things are going well, then, for a bird like a red-backed shrike to survive, any one landscape must be rich enough to support at least 170 adult birds. In a British context, such a figure is alarming. It reveals how food-rich landscapes alone, not tiny pockets of amenable land, are often the only solution for preventing extinction. Tiny pockets of birds can persist for quite a long time, even decades. Yet, as history shows, they have no viable future at all.
Until the late 1800s, the corncrake bred commonly in almost every county across Britain. A century later, a national survey in 1993 recorded just 480 birds, with almost all of these on the Hebrides.15 The corncrake would bounce back thanks to conservation work by the RSPB. But how was this work possible after a collapse comparable to that of its meadow compatriot, the red-backed shrike?
On islands in the Hebrides lay the last places where tall, late-cut, insect-rich grasslands existed on a scale large enough for corncrakes to survive. But even though corncrakes were on the brink, they were staying in touch. In 1993, there were 106 calling male corncrakes on Lewis, 116 on the Uists and 111 on the island of Tiree.16 These populations were close to one another, forming meta-populations. Numbers from the key strongholds in 1993 were, in most cases, close to Viktoria’s 50-year threshold for shrikes. Like shrikes, corncrakes are long-range summer migrants, of whom only one-third make it back the following summer, to sing pretty terribly on European soil.78 Corncrakes, however, had the decency to persist in one large population. This bought the RSPB time to consolidate their range.
A similar ‘refugee’ story has involved nightjars, which in the early twentieth century bred in every English county and on many village commons. By 1981, the low point for nightjars in Britain,18 over a tenth of the remaining population was concentrated in the New Forest.19 The nightjar was on the brink – but, as with the corncrake, its refuge was large and rich. Since this time, the nightjar has consolidated its populations, yet, like the corncrake, it has rarely moved out of landscapes where birds can network and connect. And whilst many insectivorous summer migrants are on the way down, nightjars, in these areas, are increasing.20 With a strong enough refuge in one place, conservation efforts to improve nightjar habitat then pay off, because this work is acting in tandem with population dynamics. With nightjars, new ‘islands’ of heathland are now being grafted onto existing landscapes. The RSPB call this a ‘stepping stones’ approach. But to create stepping stones at all, your island of birds has to be large enough in the first place.21
If those ‘stones’ are placed just a short way away from your main island, RSPB research has shown that nightjar recruitment is far lower. Preserving continuous landscapes, therefore, is not an optional nicety in conservation, but a basic necessity for preventing extinction.
Figure 12 is a ‘live sightings’ map compiled by the website Devon Birds.22 Each dot on the map represents someone’s sighting of a cuckoo. The vast majority of Devon’s cuckoos are now found on Dartmoor – most of them in its lightly wooded margins.
The first thing this map shows is hope. Dartmoor is buying conservationists the time to act. Notice the overlap between those dots on the map. As well as having caterpillars, wooded grassland, and 20,000 meadow pipit hosts, Dartmoor’s cuckoos are keeping in touch with one another. There are enough birds to make up for bad summers, predation, and a turbulent migration to the Congo and back.
Whilst Devon’s cuckoos have declined by 75% since the 1980s, the BTO calculates that Dartmoor’s have declined by only 24%. Such is the power of landscape. With around 100 male cuckoos and an unknown number of females, Dartmoor’s cuckoos still have critical mass. The other thing the map shows is that cuckoos have long stopped being the summer sound of our wider countryside. Once calling across Devon’s farms and gardens, cuckoos have been forced into a moorland retreat. Only here, in the moth-rich landscape of Dartmoor’s wooded grasslands, can the cuckoos of Devon now survive.
One reason for this large-scale retreat is that cuckoos place far more demands on a landscape than many other birds. Females must prospect many host nests to lay their eggs in, roaming widely across large areas of land, whilst eating huge quantities of hairy caterpillars. In Devon, Dartmoor alone maintains the facilities that this landscape nomad requires.
Indeed, the importance of Dartmoor stretches far beyond Devon. In the whole of southern England, the cuckoo may only truly be saveable in the foodscapes of Dartmoor or the New Forest. Who would have thought that a bird a mere 35 centimetres long might require 950 square kilometres of amenable habitat to survive? Birds are far more demanding on space than we might possibly imagine.
Lesser spotted woodpeckers, having crashed catastrophically in Britain, remain common in countries where the amount of deciduous woodland cover reaches above the 40% mark. Nobody in Poland or Germany is worrying about the possible extinction of this dappled delight. There are estimated to be around 1,000 pairs of lesser-spots left in Britain,23 but with many pairs isolated in tiny, starving woods, few places show any signs of viability. Yet in one place they have found a haven: the New Forest, still, remarkably, home to over 100 breeding pairs.24
In April 2016, on a beautiful morning, local expert Rob Clements kindly walked me around the pasture-woodlands south of Lyndhurst. Rob had cautioned, beforehand, that we might encounter an unreasonable number of lesser spotted woodpeckers. When he used the word ‘common’, I had a sinking feeling. I’d never met Rob and wasn’t sure this could be right.
Dedicated birders invest several visits in March to see one lesser-spot in a year. Most counties now have no more than a handful of pairs. Yet in two hours, an extraordinary session passed. We heard one woodpecker, on average, every 10 minutes. At one stage, four birds answered one another in the same clearing. Having studied the species for some time, I saw more lesser-spots in two hours than during the previous two years, and the density here is comparable to that in Poland’s Białowieża Forest. As for poor Rob, I shouldn’t have doubted him. He just suffers from having the finest local patch in Britain. So what is going on in the New Forest?
Whilst any one of the New Forest’s ancient pasture woods would die, like a severed branch, if cut out and placed in the modern landscape, the combined effect of having all these caterpillar-rich ancient woods in one place achieves the opposite result. In other words, the New Forest is a single, living organism the size of a small county: far greater than the sum of its parts. Whilst most of Britain’s woodlands are what David Quammen would call ‘ragged fragments’ – isolated and starved of caterpillar food – the New Forest remains an ecosystem.
You cannot, viably, conserve a tiny woodland island for wide-ranging birds like lesser spotted woodpeckers. But you can, as the New Forest shows, preserve a refuge in the hundred-pair range. That requires habitat richness of a really large scale. A scale far larger than a sparrow-sized, caterpillar-eating bird might reasonably be expected to require.
Until the 1950s, the classical view of the way populations worked was based around the idea of competition. Individuals in healthy ecosystems were better off if fewer others were competing with them for resources. Populations with a lot of competition were thought to experience a slower growth rate, and eventually level off.25
In the 1950s, however, American ecologist Warder Allee, studying goldfish, noticed something very different. He found his goldfish grew faster, not slower, when there were more individuals in the tank. He worked out that in colonial species, survival increased with numbers. Cooperation aided the survival of some species.26 A ‘strong Allee effect’ is now the term given to populations that require a critical population size. Below this size, population growth actually begins to fall. And goldfish, it turns out, are vital for understanding British bird decline.
Hawfinches, for example, are birds of a hive-mind. They operate more as a ‘collective’ than as individuals. In areas like the New Forest, there are woods of plenty, and woods of poverty, so hawfinch roosts and colonies are usually clustered around favoured areas. This means that if there is a change in the New Forest, whether a troublesome jay, or a change in habitat, your hawfinch ‘hive’ can up and fly for 15 kilometres into the next area of prime woodland. Such a strategy, however, places serious demands on the size of your landscape.
Studies in the New Forest have shown that in winter, most roosts of hawfinches are placed close to active goshawk nests.27 This smart strategy puts hawfinches a long way away from their crow predators, either fearful of the goshawk’s ferocity or already transformed into supper. Even where they are very common, as in Poland’s Białowieża, hawfinch populations still have nest survival rates as low as 27% after predation.28 But by operating as a collective, hawfinches have evolved to absorb such losses. In the breeding season, hawfinches exercise communal distraction against jays. Tagging of birds in the Forest of Dean shows they also make local migrations, moving several kilometres in response to changing food supplies, or predator pressure, across a season.
Such communally minded birds cannot function in the way they have evolved, however, in most of Britain’s postage-stamp woodlands. In other words, you either have a large, sympathetic landscape, like the New Forest or the Wye Valley, with a lot of hawfinches – or you don’t have any hawfinches at all.
A host of other birds that we might see as individuals actually operate best in loose colonies. One we might not think of in this light is the osprey. The conservationist Roy Dennis regards ospreys as semi-colonial: you either have a cluster of birds prospering, or that cluster dies out.29 This is because ospreys do better by fishing at communal feeding sites. White-tailed eagles, hardly a bird we’d consider colonial now, most certainly were at one time. In Russia, these communal hunter–scavengers can nest just hundreds of metres apart.30
As you start to look around, you’ll notice all kinds of birds benefiting from close connection. The blue tits in your garden may be territorial in summer, but they’ll join up in winter to form flocks. We may see blackbirds and woodpigeons as individuals, but they in fact form meta-populations across our suburban worlds.
As a rule, we always underestimate the scale and connection that birds need, perhaps because these connections have been lacking from our landscapes for so long. We also forget that aggregation is important to a whole range of species. Not just martins, swallows and swifts but wagtails, waders and many other families benefit from aggregation. Wading birds exercise better defence against predators in large populations, alerting one another to danger.31 This is one reason a Polish river valley can be filled with foxes, badgers, lynx, martens and birds of prey, yet still teem with lapwings. House sparrows, too, are highly colonial: you cannot have a single pair for long. Connecting landscapes, rural or urban, allows for aggregation. The collective is what wins.
Eight kilometres of wind-waving reeds now run in an east–west line across the Somerset Levels; many of these dug from old peat workings. As the bittern flies, this forms one continuous refuge, and there are now more bitterns here than anywhere else in Britain. But the benefits of aggregation are now being seen all across the returning wetlands of the Avalon marshes.
Almost all of Avalon’s birds are forming populations able to exploit this significant area – and requiring such an area to flourish. You can watch groups of garganey, brimming with duckish frustration, flying from one marsh to the next. You can find hundreds of pairs of reed warbler chattering away in the reeds. Sand martin colonies thrive in the peat. Whilst a contracting landscape enforces isolation, Avalon reveals the living opposite. The growing scale of the reedbeds now means that ‘overshoot’ birds from the continent have settled here to breed. Little bitterns, for example, have sung here in their first year then come back with mates to nest. Each overshoot bird arriving in good habitat has the best possible chance to establish a population.
In Norfolk, too, any young birdwatcher grows up learning the hallowed names of Cley and Titchwell, Holkham and Holme. But these are just the names we give reserves in order to identify who owns them. As the wetland bird flies, this coast is a connected wonderland. Between the eastern edge of the Wash and Sheringham, the web of coastal marshes extends for 65 kilometres in one unbroken length.32
Marsh harriers, once down to a single pair at Minsmere in Suffolk, have saturated the reedbeds of the East Anglian coast, being able to expand for miles from a precarious single pair. When Norfolk’s first spoonbills nested at Holkham, they were seen commuting miles along the coast to feed. Our East Anglian coast isn’t just the result of outstanding habitat, but the combined effect of aggregation in its birds. By ‘lining’ our coasts with nature reserves that join up, we combine the benefits – and multiply the birds.
Conservation support of farmland has happened as part of the fight to make the Common Agricultural Policy less terrible for wildlife. It’s happened most of all on our cereal farms. Other countries have not adopted this approach, focusing instead on a clear demarcation – between areas of intense production and wild reserves for nature.
One reason for the approach here at home, however, is that a quarter of Britain is covered in arable land. Over half of this is given over to growing cereals. Arable has been around for a very long time, and most of us have only ever seen grey partridges and yellowhammers in such places, so this is where we seek to put them back. And as arable supplies our food and isn’t going anywhere, damage limitation seems a reasonable option.
A farmer with a pair of yellow wagtails on his land, and the conservationists who’ve helped him regain them, can rightly feel pleased. The wagtails, however, have evolved in grazed wetlands, connected to hundreds of other pairs of their kind. They are adapted to nest in the company of fellow grazed-grassland species, like lapwings33 – because this improves their vigilance against predators. So that pair or two only becomes significant if you have yellow wagtails on the next farm, and the next, and the next. So if we are intent on investing conservation money in farmland, which to some degree we must, it only pays any dividend if farmland landscapes act as one.
The Marlborough Downs, in Wiltshire, is one landscape working for seed-eating birds. Hundreds of tree sparrows and corn buntings are doing well. Farms join up and guarantee a population of these birds. There are enough farms with strips for seeds and insects that a few ‘bad’ ones fail to spoil the picture. In north Norfolk, drive inland and you’ll still swerve to avoid wobbly crèches of grey partridges on the roads around the villages near Ringstead or Snettisham. A lot of wealthy arable farmers in Norfolk have also, collectively, invested in barn owls. Miles of fallow strips have joined up – and barn owls are, again, a common sight.
The Lancashire Mosslands are a large area, stretching for 25 kilometres from Crosby to the Ribble. Unlike most of our farmlands, the Mosslands are still alive with birdsong each spring. You can see yellowhammers, corn buntings, grey partridges, tree sparrows, hear quail, find hundreds of lapwings, and the air is still filled with skylarks. The Mosslands hold one of the highest densities of barn owls in Britain.34 The Mosslands are all about joinery. Across the crops in this area run lines of wide marginal land, scruffy willow stands and plenty of insects and cover. The original ‘mosses’ that remain (wide areas of long grassland and damp woods) support other birds, like whinchats and woodcocks. The net result is a landscape of mixed quality, but an overall abundance of food and places to raise a family.
Until extensive rewilding becomes the new default of conservation, such large farmland refuges are still worth funding and protecting. ‘Cooperative’ landscapes, like the mosses, can speak at least a few key phrases in the language that nature understands. But support of agricultural islands most often fights the fundamental laws of nature.
What has often been pursued is a series of tiny triumphs, in the hope they will add up to a big one. But birds do not acknowledge human targets. You cannot have one farmland cuckoo stand the test of time. You can only have closer to one hundred. Investing in the one is dead money – and money that could be used elsewhere.
Able to travel widely over our country as they arrive from Africa each summer, you might think our summer migrants might be able to survive in far smaller landscapes than our resident birds. Surely they can just drop into a patch of habitat and get on with it? In fact, the reverse is most often true. Summer visitors need larger landscapes than residents. That is because of the 33% rule. On average, around two-thirds of nightingales, corncrakes, turtle doves and many other long-range migrants do not make it back to their breeding grounds the following year.35 And what’s more – this is how things should be.
Migration has always been a dirty business. With the age-old threats of predators, extreme heat and exhaustion, migratory survival rates have always been low for fragile migrant birds. Human depredation in Egypt, Malta and Cyprus, to name but three, has, for centuries, had terrible impacts on species like the turtle dove.36
If you’re a small migrant, with the odds rigged against you, pumping out a lot of healthy chicks, ready for their journey to Africa, is imperative – if an equal number of birds are to return the following year. That strategy requires robust numbers of birds arriving, each year, in the same place. If you are a migrant coming all the way from Africa, it is vital that you arrive to find yourself surrounded by abundant peers, in the likely event that last year’s wife or husband has snuffed it somewhere between the Congo and England. Abundance means opportunity, whether online dating, interviewing multiple candidates for a tough job (see online dating) or assessing which house to buy. In contrast, the isolation effect, silently killing thousands of our birds in Britain each summer, is sometimes best appreciated from the perspective of just a few families of birds.
In 2012, I studied three nesting pairs of nightingales in Avon, as part of the BTO’s Nest Records Scheme. One pair hatched young but abandoned them, as driving wind and rain chilled the nestlings to the bone. A second pair’s eggs were robbed, twice, by a predator, most likely a weasel. Only the third pair fledged four young.
Had each of these nightingale pairs hatched and fledged five chicks, from five eggs, then 21 birds would have started the journey back to Africa. Even if all 21 nightingales had left my local wood, BTO data suggest that only around seven birds would have returned. This would have restored the population of three pairs from the year before. In reality, a maximum of 10 birds began the return journey that summer. With such tiny numbers involved, only three nightingales returned to my wood in 2013. In 2014, nightingales failed to nest in Lower Woods for the first time in living memory. But my local jazz maestros weren’t wiped out by weasels or weather. They perished, like most of Britain’s isolated wildlife, by living on an island of habitat too small to meet their needs.
Nightingales are birds of a successional, dynamic landscape. The spiky scrub blanket they require is ripe only between about five and eight years old.37 Before that, it’s not dense enough to form a shade-shell, under which nightingales forage like ninja robins. After that, the scrub grows towards tree height, admitting light and predators at the bottom.
That twenty pairs of nightingale still nest in Gloucestershire’s Cotswold Water Park might seem insignificant. But that such a number has remained unchanged for over two decades is very important. This outpost is way outside the national range, holding on to these birds when almost all of western England’s nightingales have vanished completely. The Cotswold Water Park, a brownfield mosaic of flooded gravel pits, is no wilderness reserve. Its secret is dynamism.
Arriving from Africa each spring, the nightingale population here is able to disperse locally, across an area of scrubland six kilometres across, and four kilometres from north to south. Nightingales can, as a collective, move around over the course of the passing years, as the landscape continues to evolve.
Dynamism is the most crucial ingredient that a larger landscape can provide – but that an isolated nature reserve cannot. In many cases, straitjacketing our nature reserves’ pure habitats proves extremely damaging for our nation’s birdlife, evolved in mosaic habitats that shift naturally across a landscape over time. The BTO, for example, observes that ‘scrub is a dynamic habitat, constantly changing as it evolves into woodland. Nightingales seem to be particularly sensitive to this gradual change and will only use scrub for the few years when it is most vigorous and dense.’38
Scrubland birds thrive in a world designed for constant change. As a result, scrublands have more declining birds associated with them than any other habitat. Willow and garden warblers, nightingales and bullfinches, willow and marsh tits, scrub residents and scrub migrants alike, are all vanishing from Britain.
If, in managing a landscape, you forget that habitats are supposed to shift and evolve, then successional habitats like scrub are the ones you’re most likely to ignore or fail to understand. When did you last read a press release that read: ‘the processes of glorious decay, shifting habitats and the spread of scrublands is the core policy of this reserve’? Dynamism lies at odds with management. The smaller the reserve, the more dynamism is seen as a threat. By contrast, larger landscapes can absorb change, and cater for the freestyling habitats on which birds such as nightingales depend. Dynamic landscapes are not linear, but cyclical. Scale allows the space for this to happen.
The loss of dynamic landscapes lies at the heart of many crushing bird declines. Every time you read about foxes preying on Britain’s curlews, that entire conversation is only happening because dynamism has been lost. In large wetlands, waders simply move – avoiding the extremes of predator pressure, whereas many predators remain tied to their dens. Like the hawfinches that roost in close proximity to a goshawk, curlews naturally reduce predation, too, by moving closer to the territories of kestrels, which act as a powerful deterrent against members of the crow family.39 Again, this requires large landscapes that allow curlews the chance to jump ship.
Many of Britain’s curlew populations are getting foxed to extinction or their nests raided by crows, one sorry isolated pair at a time.40 It is only the possibilities of shifting habitats, adapting populations and dynamic landscapes that will buy curlews, nightingales and many other birds a future in the British Isles.
Stories such as those of Avon’s last nightingales or perishing populations of curlews, subject to intense levels of predation, illustrate a universal phenomenon, known to scientists as ‘stochastic extinction’. This is what happens once a landscape and its birds have fragmented. At this stage, even the normal fluctuations acting on a population conspire to wipe them out. The smaller the number of species on an island, the greater the chance that a fluctuation, or ‘bad luck’ event, will reduce that population to zero.
There are tales of the last birds of populations on New Zealand islets being wiped out by just a handful of cats.41 The smaller your island and the lower your numbers, the more luck you need to survive. Big populations can absorb a lot more bad luck. Birds like nightingales are designed to take huge losses, but only large populations survive those losses. Once you are left with a tiny population, everything has to work perfectly in order for the species to survive – yet by default, nature does not cater to the perfect survival of any one species.
Ideal populations of British birds in one place, therefore, should not constitute ten or twenty but at least the low hundreds of pairs. Not only do we underestimate the size of landscapes needed to prevent extinction. We often lose sight of how many birds make a future, and waste critical time, and money, in propping up populations already sentenced to extinction.
With its last sympathetic landscapes now reduced to the size of postage stamps, Britain has become an island of islands. Only the largest of these are proving big enough to sustain populations of birds. If food is why individual pairs of birds are failing to survive, and bad stewardship is preventing the return of our wildlife, isolation is why birds are vanishing from the map – as populations in habitat-islands collapse all at once.
Isolation is why that spotted flycatcher hawking your bee-rich buddleia in an otherwise sterile village is a pretty bit of history. Isolation is why the situation for British birds is far worse than most of us might expect, and cannot be ‘read’ from habitat or distribution alone. It is the piecemeal loss of ecosystem scraps that will ensure the continuing extinction of British birds for decades to come, if conservation does not change. Birds will continue to vanish until we slowly join the scraps back up – into the rich tapestry that nature understands.