Nest-site competition with blue tits and great tits as a possible cause of declines in willow tit numbers: observations in the Clyde area

4 Pages·2002·2.6 MB·

by  James Maxwell

GlasNgEoSwTNa-tSurIaTliEstC20O0M2.PVEoTluImTeI2O4.NPaWrtI1T.PHagBesL4U7E-50TITSANDGREATTITSASAPOSSIBLECAUSEOF
DECLINESINWILLOWTITNUMBERS:OBSERVATIONSINTHECLYDEAREA
JamesMaxwell
7LilacHill,Hamilton,MLS7HG
INTRODUCTION only on visual observation. Unlike blue tits P.
Willow tits Parus montanus are resident and caeruleusandgreattitsP.major,willowtitsonly
sedentary,defendingtheirterritorythroughoutthe nestincavitiesthattheyexcavateforthemselves,
year,andshowingahabitatpreferenceforareasof normallyintherottenstumpofatree.Particular
wet woodland (Perrins, 1979). Although the attention was given to the nest construction
numbers and range of this species across activitiesofwillowtitsinordertogleanindications
continental Europe are thought to be stable ofasuitabledesignforawillowtitnestbox,andto
(Hagemeijer & Blair, 1997), the ‘new atlas of monitortheirbreedingactivitytoseewhetherthe
breeding birds’ showed the willow tit to have populationdeclinemayberelatedtosomecauseof
contracted inbreedingrange inBritainbetween breedingfailure.
1970 and 1990 (Gibbons etal., 1993), with a The“nestbox“isbasicallyabark-coveredplastic
particularlylargereductioninScotland.By 1990, tubewithaninternalnestchamber,filledtothe
willow tits nested only in small pockets ofthe entrance hole with fine wood shavings (design
borders,Galloway,AyrshireandtheClyde,witha detailsaregiveninAppendix1);itwasfirstplaced
singlerecordnorthofthecentrallowlands.This inwillowtitterritoriesandusedbythebirdsin
contractioninScotlandfollowsdisappearancefrom 1995.Atpresent,thereare 136boxesdistributed
Inverness, Ross, Angus, Perth, Fife and the through22areasofLanarkshire(Figure1)where
Lothians in earlier decades, which has been willowtitshavebeenfoundholdingterritoryor
tentatively ascribed to factors such as severe wheretheyhavepreviouslybred.Ofthese,7areas
wintersduringthe 1940s-50sandlossofhabitat currently hold breeding birds; the species has
(Thom,1986).Since1990,declinesinnumbersand alwayseasilyjocatedthesepurpose-designedboxes
breedingrangeofthewillowtithavecontinued, andexcavatedthemreadily^
andperhaps accelerated,throughoutitsrangein Inadditiontomonitoringbreedingsuccessof
Britain. Willow tit numbers on Common Bird willowtitsinnaturalsitesandinnestboxes,since
CensusplotsoftheBritishTrustforOrnithology 1996thenestlingshavebeenmarkedwithnest-
fellby56%during1988-1998,andshoweda29% specificcolourringsinordertoprovideinformation
fallfrom 1998to 1999(Sandersonetal.,2000). ontheirpost-fledgingsurvivalandnataldispersal.
Lanarkshire is now the northern limit for the Anumberofadultshavealsobeencaughtontheir
species in Britain, and the neighbouring small territoryduringwinterbymistnetandmarkedwith
isolatedpopulationsinAyrshireandGallowayare individualcolourringcombinations,allowingtheir
inseriousdeclinetoveryfewpairs(Murray,2000). survivalandpairingstoberecorded.
Winterconditionsandhabitatlossseeminadequate RESULTS
as explanations for this drastic population Habitat,nestsites,nestconstruction,incubation
contraction.Willowtits are maintaininghealthy andfledging.
populations in much colder climates, such as Willowtitterritorieswere locatedinarangeof
northernNorway,FinlandandRussia(Hagemeijer habitats, from mature woodland with minimal
& Blair, 1997),whilemany areasofapparently groundcoverthroughregeneratingwoodlandwith
suitablebreedinghabitatinScotlandremain,but moderate understorey ofbrambles etc.,to thick
now lack willow tits. This study was therefore birchcarrwithheathergroundcover.Nestsites
undertakentotrytofindreasonsforthedeclineof werefoundonflatorslopingground,evenonthe
the willow tit,andinparticulartotestwhether sides of steep valleys. The preferred decaying
providing artificial nest sites within suitable timberisbirch,withalderanotherfavourite.The
breedingareascouldhelptomaintaintheremaining averagehole-heightabovegroundlevelinnatural
pairsinthenowtinyandisolatedpopulationin sitesis1.5m,butcavitiescanbeashighas10.5m
LMaEnaTrkHsOhiDreS. fsereonmttohmeagkreoutnrdia.lbDourriinnggsiMnarscevhe,rawlisltluomwpst,itsbuwterbye
WillowtitterritoriesinLanarkshirewerelocatedby Apriltheeffortisusuallyconcentratedononesite,
listeningforthe characteristic song andcontact with both birds actively engaged in excavation
calls of this species. Locating territories was work.Theentranceholedugoutisslightlyoval
enhancedbyamplifiedplaybackoftaperecordings (the long axis vertical) and about 3 cm across.
ofwillowtitvocalisations,whichwasextremely Debrisfallsunderneaththesiteatfirst,butasthe
effective inelicitingresponses from willow tits excavation proceeds to form a chamber in a
withinadistanceofasmuchas1km.Oncefound, downwarddirection,thebirdsturnandflyoutwith
pairsofwillowtitswerevisitedthroughouttheyear shavings and carry them progressively further
torecordtheirpresenceandbehaviour,especially away,eventuallytoupto20m.Atthisstage,birds
intheearlybreedingseason.Sincethereareno makeupto4visitsperminute,onebirdwaiting
marshtitsParuspalustrisintheLanarkshirearea, whiletheotherexcavates.Thisworkiscarriedout
speciesrecognitionwassimpleevenwhenbased inanopen,busyfashionandcancontinuefor
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Figure1.Locationsofwillowtitterritoriesinvestigatedon theR.Clydesystemduringthestudyfrom 1994-2001:
l=StrathclydeCPark,Motherwell;2=CalderGlen,EastKilbride;3=Baron’sHaugh,Motherwell;4=ChatelheraultCpark,
Hamilton;5=Candermoss,Stonehouse;6=GarrionGillfoot,Overtown;7=Mauldslie,Rosebank;8=RossTip,Hamilton;
9=Harestonehill,Newmains;10=EastmuirPlan.,Newmains;ll=UpperClyde,NewLanark;12=MillburnGlen,Larkhall;
13=Merryton, Larkhall; 14=Cleghorn Glen, Lanark; 15=Jock’s Gill, Carluke; 16=Greenhead Wood, Waterloo;
17=DrumpellierCpark,Coatbridge;18=ColtnessWoods,Coltness;19=AuchterWater,Newmains;20=GarrionGillhead.
Overtown;21=UpperMillbum,Ashgill;22=Canderwood,Stonehouse.
several days. When the cavity is complete,the produced14young.Fivepairswerelocatedin
femalethenbuildsaminimalnest-afelt-likepad 1998,producing28young.In1999,twopairswere
offinehairs,grassesandfibres.Sheincubates,and successfulinnaturalstumps,producing14young.
isfedonthenestbythemale,butoccasionally In2000thereweresixpairsproducing47young
leavestheeggsunattended,concealingthemwith (twopairsinnestboxes,fourinnaturalsites),andin
ruffled nest material. Both parents share chick- 2001,threepairsinnaturalstumpshad17young.A
feedingdutiesandwhentheyoungfledge,theyare fourthpairatColtnessusedaboxtothenesting
dependent for about a fortnight, then gradually stagebutthendeserted(seefurthernote).Sightings
disperse. ofunringedbirdshintedattheexistenceofother
Useofnestboxes,andbreedingdata breedingpairsintheareabutthereareprobablyno
The “nestbox “ (Appendix 1) has proved very morethan8-20pairsofwillowtitsnowremaining
successful,andisregularlyadoptedbywillowtits. inLanarkshire.
In 1996, 5 young fledged from a nest box at Sitefidelityanddispersal
StrathclydeCountryParkandapairheldterritoryat Acolourringedmalewillowtithasbredatthe
Baron’s Haugh. In 1997,two pairs bred in the samesiteatEastmuirPlantation,Newmains,each
WishawandLanarkareas,bothinnestboxes,and yearforfoursuccessiveseasons,buteachseason
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withadifferentfemale.Youngbirdsgivensite- DISCUSSION
specific colourrings were found establishing a In coldercountries such as RussiaandFinland,
territory,onaverage,onlyabout1-2kmfromtheir youngbirdsusuallyjoinadultsinadjoiningareas
natalsite.InLanarkshire,themainstrongholdof andcapitalize,inthewinter,onfoodthattheolder
willow tit breeding is in the areacentering on birds have stored (Cramp & Perrins, 1993). In
Newmains,WishawandColtness,withothersites Lanarkshire,storingfoodseemsnottobesovital,
nearLarkhall.Onefledglingtravelled6kmfrom andyoungstersareoftenfoundholdingterritories
Coltness to a site atBaron’s Haugh. From one ontheirowninthepost-natalyear.Willowtitsin
broodof9chicksatLarkhall(in2000),onemoved Lanarkshireseemrarelytojoinwintermixedflocks
toBaron’sHaugh(5km),onetoWishaw(4km), oftits,butremainintheirterritorythroughoutthe
onetoGarrionGill(3km)andonemoved2km,all year.Thedispersalofjuvenilesfromtheirnatal
indifferentdirections.TheGarrionGillfemalehas territorytoestablishingaterritoryofonlyafew
bred(in2001)withapreviouslydispersedmale hundredmeterstoafewkilometresawayistypical
birdfromLarkhall(1998)-i.e.thispairsharedthe ofwillowtitsinBritain;Cramp&Perrins(1993)
sameparentanddidthe samejourney,buttwo statethat78%ofwillowtitringrecoveriescame
yearsapart.Inspiteofthiskindofconsistencyin fromwithin5kmoftheringinglocation.Onlyone
dispersal,manyyoung,including3wholebroods recorded movement in Britainexceeded 50 km.
out of 16, have never been traced, so either ThiswouldsuggestthattheLanarkshirepopulation
dispersedtounknownlocationsordidnotsurvive. of willow tits is effectively a closed, isolated
ThetwoWillowTitsthatdispersedallthewayto population,sincethenearest(Ayrshire)population
Baron’sHaughweremalesandapparentlydidnot isalmostextinct,andthe(declining)Gallowayand
findfemalesin2001andhaveleftthatarea. Borderspopulationsareabout100kmaway,soare
Interactionswithblue0tits unlikelytoprovideimmigrantstotheLanarkshire
At nut feeders during winter, willow tits are area.
subordinatetogreattitsandbluetits.Similarly,at The specially designed nestboxes were readily
nestsites,willowtitscanbedisplacedbygreattits acceptedbywillowtitsandgoodnumbersofyoung
or blue tits. Observations ofwillow tits in the havebeenrearedintheseboxes.Wiredtoatreeat
Lanarkshire study area showed that these birds kneetoshoulderheighttheylooklikebark-covered
frequentlylosetheirnewlyexcavatednestsitetoa stumpswithatemptingbitofdecay,whichattracts
pairofblueorgreattits.Duringfiveyearsofstudy investigativepecking.Theysatisfyseveralcriteria;
till2000,ofonlysome30willowtitpair-years,I beinglighttocarry,cheaptomake,waterproof,
observed18nesttake-oversbybluetitsandtwoby fairlylong-lastingandunobtrusive,sothattheyare
greattits.Ofthese, 16weretake-oversofnewly notnoticedwheninvandal-proneareas.Theyhave
excavatednestboxes,andfourweretake-oversof alsoprovedinvaluableinmonitoringthepresence
newly excavated natural sites. This probably ofWillowTitsinnewareas,astheyarealways
underestimates the frequency of take-over of excavatedifthe species isthere.Although it is
natural sites since it was easier to make unlikelythatwillowtitsarelimitedbyalackof
observations atnestboxes. One example ofthis natural sites for nesting, the nestboxes are
interactionwasrecordedattheterritoryofapairof particularlyeasytoexcavate,andsotheenergetic
willowtitsatStrathclydeCountryParkin 1995. costofcavityconstructionwillbemuchreduced.
This pair excavated five successive nestboxes, Thismaybeimportantgiventheproblemswillow
losingeachinturntopairsofbluetits.Inmid-May, tits face from blue tits and great tits. My
theyatlastgottotheeggstageinanest-box,only observations strongly suggest that an important
tofail,duetoheavysnow.EventuallyinlateMay, factorinthedeclineofthewillowtithasbeenthe
theirlastboxwasexcavated,but,duepossiblyto tendency for blue tits and great tits, having
energydepletion,onlytoadepthjustunderthe witnessed all the afore-mentioned excavation
nyeosutn-hgoloep.enIlnythveullnaetrearbslteagteos,prtehdiastionresviatnadbltyhelebftrotohde naectsitvicthyam,bteorst,akfeorocviengrtnheewwliylleoxwcatvitastteodswtairltlaownetiwt
waslost(Nilsson1984).MeanwhiletheBlueTits excavationelsewhere.Aseriesofsuchthwarted
hadraisedfamiliessuccessfullyinalltheiracquired attemptstobreedmayimpairthebodyconditionof
sites.Inthe2001breedingseasonalone,therewere adultwillowtits,anditisageneralfeatureofbirds
7BlueTitand6GreatTittake-oversfromthenest- thatlatebreedingtendstobelesssuccessfuland
boxes.Intheafore-mentionedColtnessfailureat fledglingsrearedlateintheseasontendtohavelow
theneststage,bothBlueTitandGreatTitpairs survival prospects (Perrins & Birkhead, 1983),
were seen showing great interest in the nest, (BromssenandJansson,1980).Itislikelythatblue
althoughtheydidnotusethebox.Itmaywellbe titandgreattitpopulationshaveincreasedover
that even at the nest stage, aggression by the recentdecadesasaresultofincreasedprovisionof
dominant tits can be sufficient to make a pair winterfoodinsuburbangardens.Itisalsopossible
desert,aswaswitnessedatJock’sGillin 1999, thatthesespecies,facinggraduallyreducingnesting
whentheWillowTitswerewitnessedbeingchased facilitiesduetothegreatdevelopmentofimproved
aroundthenestareabeforedeserting. housingetc.sincethefifties,haveexpandedinto
typicalwillowtithabitattobreed;ifso,theirliking
fornew,ready-madesitesmaybethemaincauseof
49
fthuerthdeermirseseeaorfchw.ilAltowthetitss.ugTgheisstihoynpootfheCshirsisinMveitaeds Bromssen, A. VonREF&ERJEanNsCsoEnS, C. (1980) Ornis
het(tihevBtelisTpdOfei)ttrno,osctmepneilexta(siccitgainavntagi2ent0ewt0diht0ilhs)nleeoiswsntatudetgbijrgotaaxeccn,steeitsnobettnud;tbbobtpolxhexuaeret.smitittiPnhtrsitesphtaleaiiwkrwmaesiislnomlavaaoreynwyr CGsN7Wcir9eeab8sawnb8tmdo-epinA7r,nts9nal,9SvPa.7iaDs.cl&.aeTWoaf.P1r&e1,cr:BtrrRAii1eecnD7ies3Vdd,o-,Pil1ConJ.y7..gs8MBVe..IrBI.i&.(reOddCsxsh.f)aoipnr(m1d9BaU9rnn3i,i)tv.aReiT.rnhsAie.atnyB(di1P9rr9dIe3srs)es.ol.faTnthdhe:e
effective strategy, but although many nest-box Hagemeijer,W.J.M.&Blair,M.J.(1997).TheEBCC
placingswereconvertedtothissystemin2001, AtlasofEuropeanBreedingBirds.T&ADPoyser.
therewasstillnosignificantimprovement.Further Murray,R.(2000).1998.ScottishBirdReportNo.31.
experimentingalongtheselineswilltakeplace. ScottishOrnithologistsClub
ACKNOWLEDGEMENTS Nilsson,S.G.(1984)Ornisscandinavica15:167-175.
IRSaPmBmoasntdgNreatielfuDlatrorotchheHfaomrilhetlopnbinranwcihlloofwtthiet PPeerrrriinnss,,CC..MM..(&19B79i)r.khBeraidti,shT.TiRts..(C1o9l8li3n)s..AvianEcology.
wtsahounarrdnvkkes,yuNpiaponnorgdrtthIf,aiiLetnalhendLwaiBorvrkTiksnO.hg,isrMtSeaotnNCetHoufMnoaircntidcrlhiBenflg&olirnQgfthofterohirernefbisunittrned-drsbie.onsxgtI TBSi1nlah0an-obc1drmk3eei,.reeVs.do.inMn,g.Fb(.i1,r9dM8a6)r.cpohBpaiunrltda,stiJio.nn&Ssc,oGt1ll9ua9en8,d-.9D9T..&(AB2D0TP0O0o)y.NseeCwrhs.an2g2e8s,
thisstudy,andBobFurnessforgenerousadvicein
thepreparationofthispaper.
APPENDIX1.Detailsofthewillowtit“nestbox“designusedinthisproject.
TchhieckWeinllmoeswht.itTnwesottbinoxlidisscaornesltariudctoendsfcrroemwsatpolalsitmiicttthuebesiozfeo1f1tchmendeisatmecthearm,bceorvetore2d2wcimthhCigyhp,rewsisthbacrrkumhpelleddinnepwlsapcaepbeyr
usedtofillthespaceabovetheupperlid.Thetubebetweenthetwolidsisfilledwithwoodshavings.Anentranceholeof3
ctomadtiraemeettreurnkisactuatbionutthe1-t2ubme,of1f0tchemgfrrooumndt.hePltaocp.inTghneesttopbooxfetsheintupbaeirsis,saebaoluetd3wimthapaarptl,asstiecemcsovetor.beThtehenebsetstbwoxayistoatetnascuhreed
thatwillowtitsareabletonestinoneofthepairofboxesifbluetitsorgreattitsareactiveinthearea.
8cm
30cm
50