BBC Wildlife - UK (2020-08)

3 questionson

ORNITHOLOGY

Whyarecardinalssored?

N

ortherncardinalsarewell

knownfortheirvibrant

andalluringplumage,and

aretheofficialstatebirdin

moreUSstates(seven)than

anyotherspecies.Buthowdo

thesebeauties,a commonsight

acrosstheeasternUSA,gettheir

fabulouscolours?Malecardinals

arebrightred,whilefemales

arepalerbrown,withredfound

onlyaroundtheirwings,tailand

crest.Carotenoidpigmentsare

responsiblefortheredcoloration.

Thesepigmentsarenotproduced

automatically,butinstead

obtainedthroughdietarysources,

muchasflamingosfamously

do.Inthecaseofcardinals,they

comefromcarotenoid-richfruits,

berriesandseeds,andcertain

otherplantparts.

It hasbeensuggested

thatthereddestmales

attracthigher

qualityfemalesand

managetopair

upearlierinthe

season,whilealso

obtaininghigher-

qualityterritories.

LaurenPharr

1

WHATMAKESACORNSGO

KNOBBLY?

Knoppergalls,asthey’reknown,are

causedbythelarvaeofa tinywasp,

firstrecordedinBritaininthe1960s.

It belongstoa famousfamilyofmaster

architects,thegallwasps,whichare

parasiteswhoselarvaedevelopinside

plants.Therearethoughttobearound

90 speciesinBritainand

nearlyallofthemuseoaks,

givingrisetoa weirdand

wonderfulrangeofgalls.

From‘artichokes’to

‘apples’,they’refound

throughouttheyear.

2

BUTHOWDOGALLSFORM?

Weusedtothinktreesformedthem

asdamagelimitation,butnowknowthe

wasplarvaeareeectivelyhijackers.

Theyseemtosecretechemicalsthat

somehowmanipulatetheirhostoak

treeintoproducingabnormalgrowth.

Thisincludessnugchambersforthe

larvae,concentrationsofnutrientsin

surroundingtissuesforthemtoeat,

anda toughlayeroflignintoprotect

thegall.Manytypesofgallhave

extradefensivefeatures,such

asthickenedouterlayers,false

internalchambers

orspines.

3

DOGALLSHELP

THETREE?

Probablynot.Butsome

gallssecretenectar,which

attractsants.Theantsmightprovide

defenceagainstleaf-eatinginsects,so

inthatsensecouldbenefitthetreeto

anextent.Andthewasplarvaearen’t

aloneintheirsafehouses.Gallscanbe

hometorichcommunities,including

thelarvaeofbeetles,moths,other

gallwasps,andotherparasiticwasps

andflies,nottomentionfungi.Quitea

crowd!Sothosespeciesbenefit,even

if thetreedoesn’t.

LaurieJackson

Themysteryofoakgalls

Seeing red: the northern

cardinal’s eye-catching

coloration may help

it attract a mate.

August 2020 BBC Wildlife 83

Q&A