Wildlife Trust: Na­ture is get­ting ready for the big sleep

We still have plenty to learn about the mys­ter­ies of hi­ber­na­tion, says Nor­folk Wildlife Trust am­bas­sador Dr Ben Gar­rod

EDP Norfolk - - INSIDE -

It is a feel­ing many, if not all, of us know a lit­tle too well; it’s been a long week­end, you’ve not had enough sleep and you just don’t feel ready for the week ahead. It is cold and wet out­side and to top it all off, there’s not even any food in the fridge.

You just want to head back to bed and wake up in a few months when it’s all nice and warm again. Sound fa­mil­iar?

For those of us not for­tu­nate enough to have a sec­ond home in the Ba­hamas, the prospect of such a su­per sleep might sound ap­peal­ing but un­less you have un­locked the se­crets be­hind slow­ing your heart rate by 99%, stopping your bones from wast­ing away and find­ing the means to avoid the ef­fects a very full bladder, then hi­ber­na­tion is prob­a­bly not for the likes of me or you. But as we me­an­der through au­tumn, with win­ter yet again around the cor­ner, many of our favourite Bri­tish species will be fac­ing the prospect of a long win­ter slum­ber.

His­tor­i­cally it was thought that many of our species hi­ber­nated through the frigid months. Even swifts were at one time be­lieved to hi­ber­nate. Now, although we know that hi­ber­na­tion and mi­gra­tion are es­sen­tially dif­fer­ent ways to over­come the same prob­lem, it is maybe sur­pris­ing how much we still have to learn about hi­ber­na­tion.

Firstly not all ex­tended win­ter sleep is hi­ber­na­tion. There is some­thing called tor­por.

Tor­por can broadly be de­fined as a short-term re­duc­tion of body tem­per­a­ture on cool days. Hi­ber­na­tion dif­fers mainly in that it is an ex­tended ver­sion of tor­por. Whereas hi­ber­na­tion is typ­i­cally as­so­ci­ated with changes in day length and al­tered hor­mone lev­els, tor­por is more closely linked to more im­me­di­ate en­vi­ron­men­tal tem­per­a­tures and food avail­abil­ity.

Other than th­ese dif­fer­ences, both share nu­mer­ous sim­i­lar­i­ties such as an of­ten-dras­tic de­crease in body tem­per­a­ture (of­ten to within 1-2C of the sur­round­ing tem­per­a­ture), a ma­jor drop in breath­ing rate and oxy­gen con­sump­tion and a fall in both heart rate and meta­bolic func­tion.

Ba­si­cally, the whole sys­tem goes on standby and the an­i­mal hov­ers be­tween life and death, for hours, weeks or even months. It’s a lit­tle like when your TV goes into standby mode... but with more jeop­ardy.

So, which of our favourite crit­ters opt for the big sleep? While there are a few you might

ex­pect to see, there are a few sur­prise names also. Whereas a range of species such as rab­bits, shrews, mice and voles all go in for a spot of tor­por, the only mam­mals to show true hi­ber­na­tion in the UK are hedge­hogs, dormice and bats.

Squir­rels are thought of as hi­ber­na­tors but in ac­tual fact they do not hi­ber­nate and are in­stead ac­tive through­out the win­ter. Badgers are also less con­spic­u­ous dur­ing the colder sea­sons and in­stead of hi­ber­nat­ing, opt for pe­ri­ods of sleep which can last for 29 hours at a time (a feat ex­ceeded only by hu­man teenagers).

Lead­ing the hi­ber­na­tors, rather sur­pris­ingly, are the but­ter­flies, with many of th­ese beau­ti­ful ephemeral in­sects shel­ter­ing in our homes through­out the cold dark months.

The brim­stone, pea­cock, comma, small tor­toise­shell and red ad­mi­ral all over­win­ter, so make sure you watch out for them and leave them well alone, as they’ll re-join the awake masses in April or May.

Maybe the best ex­am­ple of a true hi­ber­na­tor is the hum­ble hedge­hog. We all sort of know it prefers to sit out the worst of the win­ter but few of us truly ap­pre­ci­ate just how dif­fi­cult this is.

Firstly, the av­er­age heart rate for a happy hog is 190 beats per minute but this slows to a mere 20 bpm dur­ing hi­ber­na­tion. In or­der to stand any chance of sur­viv­ing hi­ber­na­tion (be­cause there is a fright­en­ingly high mor­tal­ity rate), a hedge­hog needs to for­age and bulk up be­fore the big sleep.

As much as dou­bling in weight, half of this may be lost be­fore spring. In se­vere years, a hedge­hog will sleep be­tween Oc­to­ber and April, only wak­ing pe­ri­od­i­cally to use the loo (many read­ers will ap­pre­ci­ate the need to get up at least once dur­ing the night, so imag­ine a six month sleep) or to look for the oc­ca­sional snack.

We still have no real idea as to why hi­ber­nat­ing an­i­mals spo­rad­i­cally wake up like this. The­o­ries abound, from the ben­e­fits of sud­den bursts of ac­tiv­ity and the in­crease in body tem­per­a­ture to pos­si­ble ad­van­ta­geous im­mune re­sponses. The truth is that we still have a long way to go be­fore we fully un­der­stand this life-sav­ing phe­nom­e­non.

One un­ex­pected area of hi­ber­na­tion re­search was

'The whole sys­tem goes on standby and the an­i­mal hov­ers be­tween life and death, for hours, weeks or even months'

re­vealed through the study of blood from hi­ber­nat­ing an­i­mals. When this ‘sleep­ing blood’ was ex­per­i­men­tally in­tro­duced to an­i­mal hearts (re­moved from their bod­ies) in lab­o­ra­tory con­di­tions, re­sults showed that the heart tis­sue sur­vived well past the ex­pected range, with sci­en­tists pre­dict­ing that hu­man hearts des­tined for trans­plants could sur­vive for much longer pe­ri­ods thanks to a bet­ter un­der­stand­ing of hi­ber­na­tion.

So although we may not fully un­der­stand how a hedge­hog hi­ber­nates, un­lock­ing this fairy-tale deep sleep might have real im­pli­ca­tions for trans­plant pa­tients around the world. With the ef­fort and en­ergy needed to un­dergo this mon­u­men­tal sleep, then we re­ally should do all that we can to help our hi­ber­nat­ing species through the com­ing win­ter.

Putting food out for hedge­hogs, al­low­ing but­ter­flies to rest undis­turbed and even in­vest­ing in bat boxes are all ways that you can help our nat­u­ral neigh­bours pre­pare for the sleep of their lives.

Nnor­folk­wildlifetrust.org.uk

FAR RIGHT:Ben Gar­rod, NWT am­bas­sador

BELOW:Brim­stone but­ter­fly on knap­weed

RIGHT:Rab­bit (Oryc­to­la­gus cu­nicu­lus)

LEFT: Hedge­hog

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