BBC Wildlife - UK (2019-12)

HIBERNATION

68 BBC Wildlife December 2019

Someinsects,suchasbutterflies,

ladybirdsandsomebees,overwinter

intheadultstage.Ofourbutterflies, 9

overwinterasanegg, 32 asa caterpillar, 11

asa pupaand6 asanadult,includingthe

brimstone,redadmiral,smalltortoiseshell,

commaandpeacock(plusthevery

rareCamberwellbeauty.)Inthecaseof

butterflies,overwinteringteetersbetween

simpletorporanddiapause;thoughthe

insectis outwardlyanadult,it maynotyet

bereproductivelymature.

Yetagain,asexotherms,alltheseadult

insectsareliabletoberoused

byunseasonablysunny

days.Everyyear,

peacockbutterflies,

forexample,are

spottedaround

ChristmasandNew

Yearflyingingardens,

withnewspaperssubsequently

predictingtheendoftheworld.I have

seena brimstoneflyinginmyDorset

gardeninJanuary.Youmightalsofind

butterfliesonthemoveinsidea house,

whereunseasonablywarmcentralheating

hasrousedthemfroma hidingplace.

Onceagain,thisis neitherunusual

nornecessarilyfatal.Thenextdropin

temperaturemaysendthembackinto

coveragaintoresumetheirdormancy.

However,therecanbea shadowtosunny

winter-dayforays.A shortarousalfrom

torporwon’tnecessarilyharma butterfly

directly,butthecostsinenergyexpended

inflyingaboutandlookingfora new

hibernationsitemightcauseit stresslater

on.It mightrunoutofitsfatreservesand

diebeforethespring.

Thingsareheatingup

Warmwinterweathercanhaveanother,

perhapssurprising,effect– notjuston

butterfliesbutonallanimalsthatenter

intoa stateoftorpidity.Warmexternal

weatherheatsuptheanimalandincreases

itsmetabolicrate,usingupmoreenergy

thanwouldhappeninverycoldconditions.

Whileextremeconditionsofwintercold

aredangerous,sois unusualwarming.

Andthat,ofcourse,is a problemthat

is certaintoincreaseinthefuture,asthe

worlditselfwarmsup.Climatechangehas

hadtheeffectoftakingtheedgeoff winter

inmanyareas,includingBritain.Could this

bea problemforhibernatinganimals? The

answer,unfortunately,seemstobe yes.

Asfarastriggersareconcerned, the onset

ofhibernationis generallygoverned by

threethings:day-length,temperature and

foodsupplies.Therearealsosome gender

andagedifferences.Day-lengthis usually

thetriggerforthedeep-seatedendogenous

changesandpreparations,andif it was

downtophotoperiodalone,theeffects of

warmingwouldbedampened.The problem

is temperature,andparticularly,warming

inthespring.Thiscauseshibernators to

emergetooearly,toexithibernation while

theirfatreservesareseriouslydepleted and

beforethereis enoughfoodtosustain them

intheenvironment.

A studyon 14 speciesofNorthAmerican

hibernatorsshowedthat,forevery 1°C rise

inannualtemperature,hibernation was

Sleep long

and prosper

While hibernation is well

known as an avoidance

mechanism for adverse

winter weather conditions,

it also has another

benefit. It reduces

predation and thus boosts

lifetime reproductive

potential. Dormice have

a significantly increased

chance of overwinter

survival compared to

non-hibernators of the

same size, and overall

the figure is around

50 per cent. On the

whole, hibernators also

have longer lifespans

compared to similar-sized

equivalents. Bats may live

20 years or more in the

wild, and a dormouse can

live five or six years in the

wild, as opposed to just

one or two.

Top: the pipistrelle

may be the UK’s

most common

bat, but you're

unlikely to see

one in winter. Left:

slow-worms enter a

deep sleep known

as brumation.

The onset of hibernation

is generally governed by

day-length, temperature

and food supplies.

Clockwise from Slow worm: Tony Phelps/NPL; T. Douma/AGAMI/Alamy; Eric Medard/NPL; Roger Tidman/FLPA; Jelger Herder/Alamy; Jim Hallett/NPL