BBC Wildlife Magazine
To understand and save our declining farmland birds we must look to when mammals shaped the landscape
To understand – and save – our farmland birds, we must look to when mammals shaped the British landscape landscape millennia millennia ago.
What did turtle doves feed on before farmers helped scatter weeds? How did skylarks cope before conservationists created skylark plots? Where did barn swallows nest before there were barns? And where did corn buntings live before there were corn fields? In short, what did farmland birds do before the farm?
When trying to conserve corn buntings nowadays, we try to conserve the corn. Corn buntings, however, like all grassland birds, evolved not beside the tractor or the plough. They evolved in shifting polar steppes and wooded plains that we have all but forgotten today. So to really understand the problems facing these species in our current landscape, we should take a much longer, wilder view. We need to travel back in time to when humans colonised what is now Britain.
Early human species, Homo antecessor, set foot in Britain about 900,000 years ago
during the Pleistocene period. For hundreds of thousands of years, the Pleistocene was an age of extremes – of shifting warm and cold. Glacial and interglacial periods would transform the character of the British landscape several times before it arrived at our modern temperate climate.
The human pioneers had walked across land to an island yet to be: an island still connected to Europe. Norfolk’s climate, at that time, had warmer summers but harsher winters. Our ancestors were dwarfs in a land of giants. Woolly rhinos, giant elk and southern-mammoths cast their shadows over saiga antelope, wild cattle and wild horses, in a landscape perhaps most similar to the steppes of northern Mongolia today.
Fossils from Britain’s caves allow us to piece together some of the birds that lived beside our hairy ancestors. In the Creswell Caves of Derbyshire lie the bones of demoiselle cranes, a species we now associate with Central Asia and India. Just imagine: these birds may once have chased mammoths away from their nests on the border of what is now Derbyshire and Nottinghamshire.
Even at such an early moment in time, all of the birds we recognise today had already evolved. And they did so in the presence of large ecological site managers.
During Britain’s cool glacial periods, the dominant herbivores were mighty mammoths and woolly rhinos. Recent African studies show that rhinos are apex ecosystem engineers that keep grasslands short and open. Likewise, elephants trample trees and shrubs, maintaining space. It is amazing to think that the jangly song of corn buntings and the soaring melodies of skylarks most probably evolved in the presence of grassland giants similar to these.
The fossil record provides the proof. A cave near Port Eynon in Wales is filled with the bones of cave hyenas, as well as those of socalled ‘farmland’ birds – skylarks, swallows, starlings and red kites. These are birds of spacious grassland and scattered trees – habitats consistent with the action of large herbivores. Skylarks, kites and their fellow grassland birds took to the farm later.
We often assume the British Isles used to be densely wooded, with a closed canopy. But for most of its ecological history, it was not. Instead, enormous mammals shaped the landscape, and fossils from many eras reveal that grassland birds were dominant.
Between the glacial periods, with their wellknown parade of woolly giants, came warmer spells that maybe shaped the evolution of our birds even more. From red-backed shrikes that nest in hawthorns but catch insects in grassy areas, to cuckoos that watch grass-nesting meadow pipits from nearby trees, almost all British land birds are best adapted to a mosaic of trees and open land. Red-backed shrikes last bred regularly in Britain in the 1980s and 90s, after a long decline, yet once were abundant and widespread here. Many shrikes can still be seen in elephant-crafted country in sub-Saharan Africa. Our landscape once looked much the same.
During these warmer interglacial periods, the cool steppes gave way to wooded grasslands, probably similar to the Serengeti. Now it was the turn of a different suite of giants – including straight-tusked elephants
and European hippos – to shape places such as the fertile plains of the Thames Valley. Beds of these elephant bones, from human hunts uncovered in Essex, take us back to a time when we were harvesting the giants around us. Yet the fossils also show that alongside wallowing elephants dabbled gadwall ducks, the same species familiar at wetland reserves.
These links between our past and the birds we see today are everywhere. The next time you watch a bird foraging in disturbed earth call to mind what would have created that disturbance in the first place. From the wallowing of elephants and rhinos to the digging of wild boar, disturbance has shaped the ecology of Britain’s birds.
The hawthorn’s vicious spikes grow far higher on the tree than any living British mammal can reach. Our so-called ‘hedgerow’ birds, from bullfinches to lesser white-throats, have all evolved to nest in these dense castles of thorns. They are fortresses against attack – hawthorn is probably designed to resist the probing of elephants.
Between 13,000 and 10,800 years ago, Britain’s cold climate became warmer. The trees surged back. The fossil record corroborates the suggestion of climatologists that the landscape moved towards a type of taiga, rich in willow and birch. Soldier’s Hole cave at Cheddar in Somerset has revealed the fossils of red grouse and ptarmigan, which favour open moor and steppe, as well as hazel and black grouse, which need areas of woodland. This species mix may indicate a change from cold conditions to a more wooded environment.
At the same time, as the last glacial period came to a close, there was a shocking loss of giants that played out across temperate ecosystems. The Quaternary Extinctions were the most extreme loss of the planet’s wildlife since the extinction of the dinosaurs.
Woolly mammoths held on in the British Isles until 14,000 years ago. The bones of woolly rhinoceros were still being used for painting 15,000 years ago by our ancestors at Cresswell, but by 10,000 years ago these grazers had disappeared. Giant elk died out in Britain around 9,000 years ago.
How did ecosystems as impressive as those of the modern-day Serengeti vanish, in ecological terms, overnight? Two competing theories have long been put forwards: climate change, and the ‘overkill hypothesis’ – that is, excessive hunting by humans.
Megafauna shape the conditions in which trees grow as surely as human foresters today. Large herbivores do not live within grasslands: they create them. If the herds of megafauna had been healthy, they may well have been able to survive the changing climate. But our ancestors had harvested these slow-breeding animals for thousands of years, and we forget the enormous impact that would have had on Britain’s birds.
Across the world, birds are not the architects of landscapes. They receive stewardship from the dominant mammals and forces of nature around them. And the more stewards you remove, the poorer and less diverse the picture gets.
Most ecologists use the early Holocene, dating from around 12,000 years ago, as the benchmark for what vegetation in the British Isles as we know it would naturally look like. The last glaciers were retreating and climatic conditions were temperate, broadly similar to those prevailing today. So we must look to the landscape and assemblage of animals at that time to discover the original context in which today’s birds used to live.
In recent decades, the long-standing theory that Britain was then carpeted in dense forest has given way to the idea that it was actually a wooded mosaic, dominated by a contest between trees and animals.
In 1960, the respected biologist Thomas Southwood documented the numbers of insects dependent on different species of native tree. The more insects a tree supports, so his theory holds, the more abundant it was. Topping the chart is oak – Britain’s cathedral of life – followed by willow, birch and hawthorn. Then comes poplar, apple, pine, alder, elm and hazel. All of these species are well adapted to light – to pastures, wetlands, marginal habitats or grasslands. Not one is adapted to dense forest.
The reason why these light-loving trees
“Britain was dominated by a contest between trees and animals.”
were so plentiful comes down to the animals present at the time. Britain’s temperate woodland once had a rich assembly of herbivores that worked in tandem within the landscape. Wild horses and cattle were busy creating spacious glades and diverse mosaics in our wooded grasslands. Have you ever watched a group of yellow wagtails closely following a herd of cows? That behaviour is nothing new. Do you ever wonder why starlings are adapted to nest in roofs and feed on your lawn? These are birds of wooded herbivory, adapted to nest in tree-holes and to feed in grazing pasture.
Have you ever wondered what turtle doves did before farming? The spectacularly successful rewilding experiment at the Knepp Estate in Sussex has shown these birds are best adapted to forage for weeds in disturbed ground. At Knepp that ground is disturbed by free-roaming Tamworth pigs, an ancient breed standing in for the wild boar that once did the same job. We also know that ‘moorland’ was once managed by giant elk – animals best suited to nibbling upland birch and willow. These mammals were the original stewards of species such as red grouse and curlews.
Places such as the wonderful Biebrza Marshes in Poland remind us that elk once stewarded our wetlands too, preventing their succession into species-poor scrublands. There is a reason why willow tits like to excavate their nest-holes in elder. Elder is poisonous, so it’s the only floodplain tree that beavers leave alone to rot in peace. Robins have made quite a journey too – from following predictable boar, with snouts, to rather less predictable humans, with hoes.
It is so long since mammals like boar, beavers, elk, aurochs and tarpan were making their presence felt throughout Britain that we have come to accept the myth that the country was a dense canopy forest, which we slowly cut down over time. But when it comes to restoring birds to rewilded lands – it is the role of these mammalian stewards, most of all, that we must remember. Three thousand years ago, when aurochs vanished, is the ecological blink of an eye.
If we want a truly exciting future for British wildlife, it is the glorious chaos of natural stewardship we must restore. For the corn bunting, the corn was no more than a flash in the pan. Its character, its habitat, its song, evolved in the wild – under the oldest stewardship of all.
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