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.

BBC Wildlife Magazine - - Contents - By Ben Mac­don­ald

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.

WANT TO COM­MENT? What have we learnt from the past and how can we look af­ter wildlife for the fu­ture? Email us at wildlifelet­ters@im­me­di­ate.co.uk

Straight-tusked ele­phants and Euro­pean hip­pos lived along­side many fa­mil­iar birds we see in Britain today.

Right: demoi­selle cranes and woolly rhi­nos once thrived in Britain. Be­low: Tur­tle doves and robins for­aged in the foot­steps of wild boar.

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