News: How heat hits wildlife

HOW WELL DID WILDLIFE WEATHER OUR SUM­MER? The heat­wave, while ex­treme, has not been the only scorcher in re­cent years. While we cooled off with a choc ice, our tem­per­ate mar­itime habi­tats suf­fered. If this is the fu­ture, how will our flora and fauna cope

BBC Wildlife Magazine - - Contents - Re­port by Richard Smyth

The UK’s long, dry sum­mer has been wel­comed by some – but it has had a se­ri­ous im­pact on na­ture

This is the year the UK swel­tered. The satel­lite heat-map was a rash of red. For six weeks many of us were sleep­ing badly and pray­ing for rain – and wild things were also feel­ing the heat.

Sus­tained warm, dry weather tests the re­silience of ecosys­tems like few other nat­u­ral phe­nom­ena. Cli­mate change will only make scorch­ing summers such as 2018, 2003, or most fa­mously 1976, more com­mon. How will plants, mam­mals, birds and in­ver­te­brates cope and what might the fu­ture hold as the global tem­per­a­ture mean creeps up­wards?

Some chal­lenges are ob­vi­ous. Hard-baked soil is im­pen­e­tra­ble to the bills of in­sec­tiv­o­rous birds – not just the black­birds on our lawns, but also breed­ing waders such as curlews (al­ready in steep de­cline).

As earth­worms and other soil an­i­mals bur­row fur­ther down in search of cool mois­ture, mam­mals are also li­able to suf­fer. Fox cubs and hedge­hogs are de­nied an in­valu­able pro­tein source; walk­ers might find starved moles, forced above ground in search of al­ter­na­tive food sources.

Con­ser­va­tion­ists are keep­ing a close eye on food-chains: if one link gives way due to dry con­di­tions, the reper­cus­sions for other species can be se­ri­ous. “Seed-eaters that rely on the au­tumn seed crop might be af­fected, as many seed-bear­ing plants are burned off in drought con­di­tions,” says Paul Stan­cliffe of the Bri­tish Trust for Or­nithol­ogy (BTO). “Fruit crops may ripen early and be smaller – that could mean a berry short­age for thrushes and mi­grant war­blers such as black­caps.”

Win­ners and losers

As with many in­sects, but­ter­flies were very vis­i­ble this sum­mer. “UK but­ter­flies tend to do very well in hot weather,” ex­plains Richard Fox of But­ter­fly Con­ser­va­tion. “It en­ables them to be ac­tive, find mates, dis­perse to new ar­eas and, most im­por­tantly, lay eggs for the next gen­er­a­tion.” But food plants wither in the heat. “Drought im­pacts se­verely on the sur­vival of cater­pil­lars of the cur­rent gen­er­a­tion,” con­tin­ues Fox. “This leads to de­pleted pop­u­la­tions in fu­ture. Af­ter the 1976 drought num­bers of but­ter­flies didn’t re­cover fully un­til 1984.” There are likely to be win­ners and losers – though it’s a del­i­cate bal­ance. “Some are more drought-sen­si­tive than oth­ers. Species such as the speck­led

wood and ringlet suf­fered large de­clines in 1996 af­ter the very dry sum­mer in 1995. But warm weather may speed the north­ward spread of but­ter­flies such as holly blue – as­sum­ing they aren’t hin­dered by drought im­pacts.”

Odd year for plants

Trevor Dines of Plantlife paints a grim pic­ture of the UK’s flora. “Grass­land that was full of wild­flow­ers this May and June was brown, parched and des­ic­cated by July,” he says. How­ever, it’s im­pos­si­ble to get a mean­ing­ful idea of the cur­rent con­di­tion of our plant life with­out con­sid­er­ing the longer-term con­text. As we swel­tered, it was easy to for­get that this year’s blis­ter­ing sum­mer fol­lowed a long and se­vere win­ter.

“It’s turn­ing out to be an ex­treme – and odd – year for plants,” Trevor says. “The long, hard win­ter was great as it helped a process called ‘ver­nal­i­sa­tion’, which stim­u­lates the pro­duc­tion of flow­ers. Though spring was long and cold, many plants flow­ered like mad through March, April and May. Even up un­til mid-June, mead­ows and grass­lands were look­ing fan­tas­tic.”

But with lit­tle sig­nif­i­cant rain be­tween May and mid-Au­gust, many plants were forced to adopt dras­tic sur­vival tac­tics. They jet­ti­soned flow­ers, leaves and even above-ground shoots in or­der to with­draw re­sources into the roots.

In some ways there’s noth­ing sur­pris­ing about a heat­wave. It’s sum­mer – isn’t it sup­posed to be hot? “I tend to think this year has been a rare re­turn to what was once nor­mal,” says Jon Dunn, a spe­cial­ist in or­chids. “That’s prob­a­bly been good for or­chids – and in­deed other wildlife.” But as the drought dragged on, he adds, lat­er­flow­er­ing or­chid species found life hard, wilt­ing or even fail­ing to flower.

The im­me­di­ate im­pacts of drought can be dra­matic, but what’s of­ten more im­por­tant is re­silience – the ca­pac­ity of a species or ecosys­tem to re­turn to good health once nor­mal ser­vice has been re­stored.

Jeremy Biggs of the Fresh­wa­ter Habi­tats Trust is keen to stress the nat­u­ral vari­abil­ity of wa­ter lev­els in ponds, lakes and rivers. “Droughts are nor­mal in fresh wa­ter,” he says. “About half of ev­ery­thing that lives in wa­ter is fine with drought. There’s a range of aquatic plants that are happy with, or even need, pe­ri­ods of drought. The plant star­fruit, for ex­am­ple, is fine in tem­po­rary ponds.”

Froglife pa­tron Jules Howard is sim­i­larly up­beat about the po­ten­tial of fresh­wa­ter habi­tats to han­dle the heat. “I’m not too con­cerned,” he says. “It has been a splen­did year for pond-watch­ing, be­cause so many an­i­mals are drawn to­wards them for wa­ter. Ponds have in­cred­i­ble value in years like this.” Jules goes into de­tail on life in the ‘draw­down zone’ – the area ex­posed as a pond’s wa­ter level is low­ered in the sum­mer.

“One of the myths

“Species of bird that feed on aerial in­sects had a bumper breed­ing sea­son, but species that de­pend on soil in­ver­te­brates suf­fered.” Paul Stan­cliffe, BTO

about ponds is that they should stay full all year. In fact, in the clas­sic ponds that na­ture cre­ates, each will reg­u­larly have sea­sons where the wa­ter pulls back, open­ing up this new en­vi­ron­ment. Most wet­land an­i­mals are adapted to deal with dry years or dry sea­sons. Some am­phib­ian tad­poles, for in­stance, speed up their growth in such years, meta­mor­phos­ing at a smaller size to get clear of the shrink­ing wa­ters.”

Prob­lems can arise, though – and the pic­ture can grow more com­plex – when we fac­tor in vari­ables other than drought alone. Us, for ex­am­ple. Con­sider peat bog: it’s a pretty tough habi­tat, when it’s al­lowed to be. Rob Stone­man, the chief ex­ec­u­tive of the York­shire Wildlife Trust, char­ac­terises sphag­num mosses, the key­stone species of healthy bogs, as the “ul­ti­mate ecosys­tem en­gi­neers”, adapted to wet con­di­tions yet re­silient to drought.

“A walk across a peat­land land­scape in the blis­ter­ing heat of sum­mer 2018 would have left foot­prints in white crispy sphag­num moss, dried and seem­ingly dead as the wa­ter-ta­ble fell away,” Stone­man says. “How­ever, sphag­num has evolved to cope with drought. It loses wa­ter from the top of the moss-mat, yet be­low, wa­ter within the peat is drawn up­wards to keep the moss alive. Through this ecosys­tem en­gi­neer­ing, sphag­num mosses

main­tain wa­ter-ta­bles close or near to the sur­face through­out the year.”

Things go wrong when we step in. “If we burn a bog to en­cour­age heather at the ex­pense of sphag­num, or cut drains to lower the wa­ter-ta­ble, the sit­u­a­tion changes,” Stone­man says. “The ecosys­te­mengi­neer prop­er­ties of sphag­num are lost. Ro­ta­tion­ally burnt peat­lands of the North York Moors in 1976 never re­cov­ered, as the peat was en­tirely burnt away in places. As this sum­mer’s wild­fires in Lan­cashire showed, the im­pact can be cat­a­strophic.”

The hu­man im­pact

Ponds and streams, too, be­come more vul­ner­a­ble if hu­man ac­tiv­i­ties skew the sys­tem. Jeremy Biggs stresses that a healthy re­sponse to ex­treme tem­per­a­tures is only pos­si­ble in a healthy fresh­wa­ter habi­tat. Where a wa­ter body is pol­luted, the re­silience of its ecosys­tem is com­pro­mised. A heat­wave low­ers the wa­ter level, but the level of pol­lu­tion re­mains the same, re­sult­ing in a more in­tensely pol­luted habi­tat. “From the per­spec­tive of clean stand­ing wa­ter, I don’t think droughts are prob­lem­atic,” Biggs con­cludes. “Droughts are oc­ca­sional, but pol­lu­tion is every­where.”

How oc­ca­sional droughts will be in fu­ture de­pends on the global cli­mate – which is get­ting hot­ter at a fright­en­ing rate. The long, hot sum­mer of 1976 was a Bri­tish phe­nom­e­non in a broadly nor­mal Europe, but this year we were locked into some­thing big­ger. Every­where in the North­ern Hemi­sphere was hot­ter.

“Cli­mate change has greatly in­creased the fre­quency of se­vere heat­waves over much of the globe,” says Corinne Le Quéré, di­rec­tor of the Tyn­dall Cen­tre for Cli­mate Change Re­search at the Univer­sity of East Anglia. “Stud­ies that have sep­a­rated the role of hu­man-caused cli­mate change from nat­u­ral cy­cles show that the risk of heat­waves has more than dou­bled due to cli­mate change so far in large parts of the world.”

How will our wildlife re­spond, if summers like this one be­come the norm? Change isn’t al­ways de­struc­tive for ev­ery­one. Droughts and hot weather cre­ate new habi­tats, and in­sec­tiv­o­rous birds such as swifts, swal­lows and spot­ted fly­catch­ers may pros­per in a hot­ter Britain. We might also see fur­ther coloni­sa­tion by Mediter­ranean birds such as hoopoes.

On the flip­side, Britain’s mon­tane habi­tats will warm, snow­lines will creep higher, and we could lose spe­cial­ist breed­ing birds such as snow bunting, as well as alpine flora such as sax­ifrages.

Wild things will of­ten find a way to cope, even as tem­per­a­ture records tum­ble. But the re­al­ity is that in the decades ahead, in Britain and be­yond, the flora and fauna of the land­scape as we know it will be tested to its lim­its.

No, it’s not In­dia or Aus­tralia. It’s a pond in an English vil­lage (in 2006, an­other chal­leng­ing year for wildlife). Such sights could be­come more com­mon in the UK. In­set, right: baked soil made it dif­fi­cult for in­sec­ti­vores such as black­birds to find food.

Right: the 2018 wild­fires, such as in Lan­cashire, may cause per­ma­nent peat­land dam­age. Far right, from the top: wa­ter­courses dried out, but many fresh­wa­ter habi­tats could cope; the heat ben­e­fit­ted some of our na­tive but­ter­flies, in­clud­ing the pur­ple em­peror.

Peat bogs can bal­ance drought and flood – but only if we leave them alone.

RICHARD SMYTH also wrote this month’s fea­ture on kit­ti­wakes (see p32).

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