No relationship between chronotype and timing of breeding when variation in daily activity patterns across the breeding season is taken into account

Abstract

There is increasing evidence that individuals are consistent in the timing of their daily activities, and that individual variation in temporal behavior is related to the timing of reproduction. However, it remains unclear whether observed patterns relate to the timing of the onset of activity or whether an early onset of activity extends the time that is available for foraging. This may then again facilitate reproduction. Furthermore, the timing of activity onset and offset may vary across the breeding season, which may complicate studying the above-mentioned relationships. Here, we examined in a wild population of great tits (Parus major) whether an early clutch initiation date may be related to an early onset of activity and/or to longer active daylengths. We also investigated how these parameters are affected by the date of measurement. To test these hypotheses, we measured emergence and entry time from/into the nest box as proxies for activity onset and offset in females during the egg laying phase. We then determined active daylength. Both emergence time and active daylength were related to clutch initiation date. However, a more detailed analysis showed that the timing of activities with respect to sunrise and sunset varied throughout the breeding season both within and among individuals. The observed positive relationships are hence potentially statistical artifacts. After methodologically correcting for this date effect, by using data from the pre-egg laying phase, where all individuals were measured on the same days, neither of the relationships remained significant. Taking methodological pitfalls and temporal variation into account may hence be crucial for understanding the significance of chronotypes.

Full text

Ecology and Evolution. 2022;12:e9353.  
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1 of 11
https://doi.org/10.1002/ece3.9353
www.ecolevol.org
Received:28February2022
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Revised:30August2022
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Accepted:5September2022
DOI: 10.1002/ece 3.935 3
RESEARCH ARTICLE
No relationship between chronotype and timing of breeding
when variation in daily activity patterns across the breeding
season is taken into account
Marjolein Meijdam | Wendt Müller | Bert Thys | Marcel Eens
ThisisanopenaccessarticleunderthetermsoftheCreativeCommonsAttributionLicense,whichpermitsuse,distributionandreproductioninanymedium,
provide d the original wor k is properly cited.
©2022TheAuthors.Ecolog y and EvolutionpublishedbyJohnWiley&SonsLtd.
DepartmentofBiology,Behavioural
Ecology and Ecophysiology Group,
UniversityofAntwerp,Wilrijk,Belgium
Correspondence
MarjoleinMeijdam,Departmentof
Biology,BehaviouralEcologyand
EcophysiologyGroup,Universityof
Antwerp,Universiteitsplein1,2610
Antwerp,Wilrijk,Belgium.
Email:marjolein.meijdam@uantwerpen.be
Funding information
FondsWetenschappelijkOnderzoek,
Grant/AwardNumber:G052117Nand
G0A3615N;UniversiteitAntwerpen
Abstract
Thereisincreasingevidencethatindividualsareconsistentinthetimingoftheirdaily
activities,andthatindividualvariationintemporalbehaviorisrelatedtothetimingof
reproduction. However,itremainsunclear whether observedpatternsrelatetothe
timingoftheonsetofactivityorwhetheranearlyonsetofactivityextendsthetime
thatisavailableforforaging.Thismaythenagainfacilitatereproduction.Furthermore,
thetiming of activityonset andoffsetmayvaryacrossthe breeding season, which
maycomplicatestudyingtheabove-mentionedrelationships.Here,weexaminedina
wildpopulationofgreattits(Parus major)whetheranearlyclutchinitiationdatemay
berelated to an earlyonsetofactivityand/ortolonger activedaylengths. Wealso
investigatedhowtheseparametersareaffectedbythedateofmeasurement.Totest
these hypotheses,wemeasuredemergenceand entry timefrom/intothe nestbox
asproxies foractivity onsetand offset infemalesduring theegg layingphase.We
thendeterminedactivedaylength.Bothemergencetimeandactivedaylengthwere
relatedtoclutch initiationdate. However,amoredetailedanalysisshowedthatthe
timingofactivitieswithrespecttosunriseandsunsetvariedthroughoutthebreeding
season both within andamong individuals. The observed positive relationships are
hence potentially statistical artifacts. After methodologically correcting for this
dateeffect,byusingdatafromthepre-egglayingphase,whereallindividualswere
measuredonthesamedays,neitheroftherelationshipsremainedsignificant.Taking
methodologicalpitfallsandtemporalvariationintoaccountmayhencebecrucialfor
understandingthesignificanceofchronotypes.
KEYWORDS
activedaylength,chronotype,circadianrhythm,clutchinitiationdate,emergencetime,Parus
major
TAXONOMY CLASSIFICATION
Behaviouralecology

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MEIJDAM et al.
1 | INTRODUCTION
Circadianrhythmsoccur onadiel (24 h)time scale andareubiqui-
tousinalllivingorganisms.Theyareendogenouslyorchestratedby
the biological clock, but entrained by the light– dark cycle, so that
they match the 24 h daylength (Pittendrigh, 1993). However, the
free-runningperiodlength(τ),whichrepresentstheamountoftime
ittakestheendogenousclocktorepeatitselfintheabsenceofen-
vironmentalcues, oftendiffersslightlyfrom24 handitintriguingly
varies amongindividuals too (Helm& Visser,2010). This individual
variationinthefunctioningofthebiologicalclockbecomesvisibleat
thephenotypiclevelasconsistentamong-individualvariationinthe
timingofactivities. The earlyorlatetimingofeventsisreferredto
as“chronotype.”Ittypicallycapturesthetimingwhenanindividual
startswithitsactivityinthemorningandwhenitbecomesinactive
inthe evening. In humans, variation in the preferred timing of ac-
tivitiesis referred to as“morningness”and “eveningness” (Arrona-
Palaciosetal.,2020).Variationinthetimingofactivitypatternshave
beenfoundinavarietyofothertaxa,includingmammalsandbirds,
bothinlaboratorysettingsandfree-livingpopulations(e.g.,Labyak
et al., 1997;Lehmannetal.,2012;Refinettietal.,2016;Steinmeyer
et al., 2010).Thus, it iscommonlyaccepted that individualsconsis-
tentlydifferfromeachotherinthetimingoftheiractivitypatterns.
Understanding how this individual variation in chronotypes is
maintained in natural populations is of outermost relevance, but
knowledgeabout theevolutionand adaptive significance of chro-
notypesinnaturalecosystemsisstillscarce(Dominonietal.,2017;
Helm et al. , 2017). However, recently there is an increased inter-
est in this topic. Furthermore, while existing studies are often
laboratory-based,where testing functional consequences or even
fitnessconsequences isdifficult (Van der Veenet al.,2017), stud-
ies on chronotypes are now taken into the wild. Here, it can be
expec ted that chron otypes are u nder both sexu al and natura l se-
lection,aschronotypes mayinfluencethetimingof the expression
ofcertain traits(Hauetal.,2017).Forexample,dawnsonginmale
birds shou ld be timed pre cisely to the pre sence of (receptive) f e-
males (Hau etal.,2017), whiletiming mightalsoplay an important
roleforminimizingpredationriskandmaximizingforagingefficiency
(DeCourseyetal.,2000;Helmetal.,2017).
Still,empiricalevidenceonthefitnessconsequencesofchrono-
typesis mixed. Both male and female birds thatengaged in extra
pair copulations, which particularly occur at dawn, had earlier chro-
notypesthanotherbirds(Halfwerketal.,2011 ;Poeseletal.,2006),
butthiscouldnotbeconfirmedinalaterstudy(Schlichtetal.,2014).
Mauryetal. (2020) andSteinmeyeretal. (2013)foundthat clutch
size and number of fledglings were independent from temporal
phenot ype in female s, but Graha m et al. (2017) repor ted that fe-
maleswhichhadanearlieronsetofactivityinthemorninghadear-
lierclutch initiation dates.Thelatteriscommonly assumedtobea
fitnessmeasure,as earlier hatchedchickshave higherrecruitment
rates(e.g., Verboven&Visser,1998).This suggeststhatthetiming
ofreproductionratherthanthereproductiveinvestmentmightvary
with chronotype.
However, if early rising females have a similar timing for the
offset of a ctivity as l ate rising female s, this would leng then their
active day(i.e., thetime theyspend outsidethe nestbox) andthe
timetheycan,forexample,spendonforaging.Earlyrising,andthus
increasing active daylength, would then allow individuals to make
moreefficientlyuseofthelimitedresourcesatthebeginningofthe
breedingseason, as they wouldhave moretime available. The ac-
tive daylength can be further increased by delaying the cessation
time, ashas recently been reported for female Europeanstarlings
(Sturnus vulgaris),where individuals with an early onset of activity
had later ce ssation times t han females whic h had a late onset of
activity (Maury et al., 2020). Alsoin bluetits(Cyanistes caeruleus),
substantial variationamong individuals has beenshown for active
dayleng th, so that a dis tinction be tween long- and shor t-sleepin g
individualscouldbemade(Steinmeyeretal.,2010). This altogether
impliesthatarelationshipbetweenactivityonsetinthemorningand
clutchinitiationdatemaynotonlydependonthetimingofdailyac-
tivitybutcouldalsobetheresultofanincreaseinactivedaylength
in early rising individuals.
Furthermore,aconcernthathaspotentiallynotsufficientlybeen
takenintoaccountinpreviousstudiesonthefitnessconsequences
ofthedailytimingofactivityisthecontributionoftemporalvariation
acrossthebreedingseasonasunderlyingdriverofsuchrelationships
betweenfitnessandtimingofactivity.Emergencetime,entrytime,
and therewith active daylength, which are key parameters when
studyingindividualvariation intemporalbehavior,vary throughout
the year (Schlicht & Kemp enaers, 2020; Steinmeyer et al., 2010;
Stuberetal.,2015),evenaftercorrectingfortheseasonalchangesin
thetimingofsunriseandsunset.Thissuggeststhatthesignificance
ofsunrise andsunsetfor determining activity patternsmay differ
acrosstheyearorwithdateofmeasurementbothwithinandamong
individuals. The date of measurement may thus be a confounding
factorwhenanalyzingrelationshipsbetweentheactivity parame-
ters andfitnessestimates suchas clutchinitiation date,which are
temporalparametersinitself.
Here, we study the relationships between activity patterns
at the onset of reproduction and clutch initiation date (Graham
et al., 2017),asmeasuredbyregularnestchecksinanestboxbreed-
ingpopulationofgreattits.First,weinvestigatewhetherindividual
variatio n in activity p atterns is consiste nt (i.e., repeata ble) within
andacrossperiods(pre-egglaying and egglaying)inthebreeding
cycle.Then,weinvestigatewhetherthedailytimingofonsetofac-
tivit y in the mornin g is related to the se asonal timin g of onset of
reproduction,thatis,startofegglaying.Byconsideringbothonset
(here:emergencetimefromthenestbox)andoffset(here:nestbox
entry timein the evening) of dailyactivity,wealso investigatethe
hypothesisthatearlierrisingfemaleshavelongeractivedaylengths
(i.e., advancedonset but not advanced offset), which allowsthem
toaccumulatetherelevantresourcesearlierinthebreedingseason,
so that they can start reproduction earlier in the season. Finally, we
investig ate whether th e above describe d relationship s may be af-
fectedbyvariationinthedailytimingofactivityacrossthebreeding
season.

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2 | MATERIALS AND METHODS
2.1 | Population
Thisstudywascarriedoutinasuburbannestboxpopulationofgreat
tits,locatedinWilrijk(Antwerp),Belgium(51°09′46.1”N,4°24′13.3″ E)
duringthebreedingseason(March–June)of2020(Raapetal.,2016;
Rivera- Gutie rrez et al., 2012; Van D uyse et al., 2005). About 170
nestboxes, suitableforgreat tits,areplaced intreesat aheight of
about 2 m. A ll individua ls that had bee n captured du ring previou s
breedingseasonsorduringroostinginwinterwereequippedwitha
ringcontainingaPIT-tag(passiveintegratedtransponder;EM4102,
125KHz,EccelTechnologyLtd)andauniquecombinationofcolor
rings,enablingindividualrecognition.Thenestboxeswerechecked
every fewdaysfornestbuilding,egglaying,and incubation. In our
population, great tits can have up to two broods per year, but this
studyonlycontainsdataoffirstbreedingattempts.
2.2 | Emergence and entry times
Todetermine the timeat whichfemales leave the nest box inthe
morning(emergencetime)andenterintheevening(entrytime),we
usedSongMeters(SongMeter™SM2+;WildlifeAcoustics, Inc) and
radio-frequency identification (RFID) loggers (EM4102datalogger,
EccelTechnologyLtd).RFIDloggersconsistoftwoantennas,which
wereplacedaroundtheopeningofthenestbox,oneontheinside,the
otherontheoutside.WhenaPIT-taggedindividualpassesthrough
theantennas,theRFIDlogger registersthe uniquePIT-tagnumber
andthe timeofpassing(for more details,see Iserbyt etal., 2018).
The readersampleinterval wasset to 250 msand the sleep mode
between 10:00 p.m. and 03:00 a.m. As not all individuals in the
populationwereequippedwithPIT-tags,wealsousedSongMeters
todeterminetheemergenceandentrytimes.SongMetershavetwo
microphonestorecordsoundsbothinsideandoutsidethenestbox.
Bothmicrophonesproducesonograms.Beforetheclockchangedto
summer time,soundwasrecorded in themorningfrom 04:00 a.m.
to08:00 a.m.CETandin theeveningfrom05:30 p.m.to08:30 p.m.
CET.Afterthe clock changed to summertime, we recordedsound
from03:00 a.m.to08:00 a.m.CETinthemorningandintheevening
from 05:30 p. m. to 09:00 p.m. CE T. Morning e mergence time an d
eveningentrytimecouldbedeterminedbythesoundofthefemale's
claws on the n est box (microphon e inside) and the sound of h er
wings whe n taking off (micr ophone inside and o utside; Halfwe rk
et al., 2011).Furthermore,aspecificsoundcausedbyachangeinair
pressurecanbe heardwhen the female passesthe openingofthe
nestbox.DatarecordedbySongMeterswereanalyzedusingAvisoft
SASLabPro5.2.14(Specht,2002).
Emergenceandentrytimeswere measuredduringtheegglay-
ing phase ( i.e., after the fir st egg was laid and b efore incubation
started)andforasubsetofindividualsalsoduringthepre-egglaying
phase (i.e.,when nest building was completed andbeforethe first
egg was laid;see below).As individualsshiftthe timingofactivity
substantiallybetween thedifferentstages of breeding (Schlicht&
Kempenaers, 2020), the physiological state should not dif fer be-
tweenindividualswhenmeasuringactivitypatterns.Duringthepre-
egglayingphase,allindividualsshouldthusbemeasuredoncenest
buildingiscompleted.However,notallfemalessleepinthenestbox
duringthisphase,andmanyfemalesfinishnestbuildingonlytheday
beforeegglayingstarts.Thisdoesnotallowobtaininglargesample
sizesduringthepre-egg layingphase.During theegg layingphase
however,all femalessleep in the nest box and measuring all indi-
viduals inthe samephysiological state is relativelyeasy.As timing
ofactivityisthoughttobeconsistentweexpectedthatindividuals
withrelativelyearlytimingduringtheegglayingphasewouldalsobe
early duringthepre-egg layingphase. Weshowed thatemergence
timeisrepeatableonthelongterm(i.e.,acrossyears)infemalegreat
titsinourpopulation(Meijdametal.,2022).Therefore,wedecided
tomeasureemergenceandentrytimesmainlyduringtheegglaying
phase.
Weusedacombinationofboth SongMetersandRFID loggers.
Emergencetimesweremeasured88timeswithbothSongMeterand
RFIDlogger.Twenty-sevenpercent ofthemeasurementsbyRFID
loggersdidnotcorrespondwiththeSongMeter.Visualvalidationof
ourRFIDloggerswasperformed inpreviousyearsbothinbluetits
andgreattits.Inbluetits,inadatasetof242parentalvisits(N = 10
nests),86.8% of all entries and 43.8% of all departures were reg-
istered (Iserbytet al.,2018). In great tit s, the correlation between
feeding ratesoffemalesmeasuredwithRFID loggersand cameras
was0.78(Thysetal.,2021;note:whenfeedingchicksfemalesboth
enter and depart from the nest box so there are 2 chances to be
registered). Thus, even though the speed when passing the RFID log-
gerismuchhigherduringchickrearingwhencomparedwithleaving
theboxafter awakening,andisalsofasterinbluetits,thereisstill
achangethat the entryoremergencetime into/fromthenest box
willbemissedbyourRFIDloggers.Inalmostallinstancesinwhich
theSongMeterdatadidnotcorrespondtotheRFIDloggerdata,the
RFIDlogger showedlateremergencetimesandearlierentry times
thantheSongMeter.Therefore,SongMeterdataarelikelymoreac-
curate andit is highly likelythat theRFID loggers missed thefirst
emergen ce and last entr y from/into the nest b ox. Unfortunate ly,
we do not have data to visually validate the data collected by
SongMeters. However, determining emergence and entry times
using SongMeters is straight forward (see Figure S1) and has suc-
cessfullybeenusedinpreviouspapers(e.g.,Halfwerketal.,2011).
Forthesereasons,wedecidedtouseonlydatafromSongMeters
if both SongMeter and RFID logger data were available. If only
RFID logg er data were availa ble (nobservations = 58 on 30 fe males),
onlymeasurementsthatfellwithin the rangeof emergence times
measuredbytheSongMeterswereincludedinthedataset(127 min
beforesunriseupto63 minaftersunrise;thisresultedintheremoval
of16datapoints). For entrytimes,the error was 12%on 82 mea-
surements,sohere,weusedthesameprocedureasforemergence
times(anoverviewofthesamplesizesafterthedataremovalcrite-
rion was applied is presented in Table 1.Acomprehensiveoverview
ofthe number ofbirds sampled per day is presented in Table S1).

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Completely excluding the RFID data from the analyses did not
changetheoutcomeorinterpretation(theseresultswillnotbefur-
ther discussed).
For both Son gMeter and RFID dat a, we determined em ergence
timesrelativetosunrise(negative=befo resunrise,p osi tiv e=afte rsun-
rise)andentrytimesrelativetosunset(negative=beforesunset,pos-
itive =aftersunset).Wealsodeterminedtherelativeactivedaylength
(negative = shorter active period than the period between sunrise
and sunset, positive = longer active period than the period between
sunriseandsunset).Hereafter,emergencetime,entrytime,andactive
daylengthalways concernrelative times,unlessit is specificallymade
clearthattheyconcernabsolutetimes.Temperaturedat awasret rieved
via: h t t p s : / / w w w . w u n d e r g r o u n d . c o m / h i s t o r y / d a i l y / b e / a n t w e r p .
Inmodelscontainingemergencetime,weusedthetemperature
(T°)atsunrise,andinmodelscontainingentrytime, we usedT°at
sunset,andinmodelscont ainingactivedaylength,weusedthemax-
imumdailyT°onthedayofmeasurement.
2.3 | Statistical analysis
AllstatisticalanalysiswereperformedinR4.0.2(RCoreTeam,2013).
We used the “rptR” package (Stoffel et al., 2017) to calculate
repeatabilities, which uses parametric bootstrapping to quantify
confidence intervals, and likelihood ratio testing to determine
statistical significance. Statistic al significance of fixed effects for
each linear mixed model was obtained with stepwise backwards
eliminationusinglmerTest(Kuznetsovaetal.,2017). For all statistical
tests,thesignificancelevelwassetatα = 0.05.
Totestifanindividual'saverageentrytimedependedonitsav-
erageemergencetime,bothmeasuredduringtheegglayingphase,a
linearmodelwasused.Second,weusedtwoseparatelinearmodels
totestwhetherclutchinitiationdatedependedon theindividual's
averageemergencetimeoritsaverageactivedaylength.Clutchini-
tiationdatesrangedfromMarch22uptoApril20(=30 days).Inboth
models,femaleage(years)wasincludedasfixedeffect.
Althoughweusedrelativevaluesfor emergenceand entry time
to account fo r changes in the onset of d awn and dusk across t he
breedingseason,avisual inspectionof the datarevealedthat there
could still be temporal variation in both parameters. To explore
thesepatterns, wemodeledvariationinactivityparametersinrela-
tion to thedateof measurement,using random regressionanalyses
(Dingemanseetal.,2010 ;Nusseyetal.,2007).Threeidenticalmodels
wererunforemergencetime,entrytime,andactivedaylength.The
models includedthe average date (starting asacount from April 1)
onwhichanindividualwasmeasured(=among-individualeffect),the
deviationfromtheaveragedate(=within-individualeffect;VandePol
& Wright, 2009),theirinteraction and age ofthe femaleasfixedef-
fects.Theamong-individualeffectallowstotestwhetherfemales,on
average(population-level),differinactivitypatternswhenobserved
ondifferentdates.Thewithin-individualeffectallowstotestwhether
females , on the populatio n level, plastic ally adjust thei r activity as 
the date progresses. The interaction allows to test whether plasticity
depend s on mean date of testi ng. As temper ature is known to af-
fect theactivity patterns ingreat tits(Lehmann et al.,2012;Stuber
et al., 2015), we also included the temperatureas describedabove.
Randomintercepts(=chronotype;i.e.,doindividualsdifferfromeach
otherinaverage activitypatterns?)wereincluded forfemaleIDand
random slopes on the level of the deviation from the average date
(=individual plasticity in activity patterns in response to date; i.e., do
individualsdifferfromeachotherinplasticity?)wereincludedforfe-
male ID as wel l. Stepwise back wards eliminat ion of non-s ignificant
termswasperformedtoobtaintheminimumadequatemodel(MAM).
Likelihoodratiotestswereusedtodeterminesignificanceofrandom
effects (i.e., individualinterceptand slope). Adjusted repeatabilities
foremergencetime,entrytime,andactivedaylengthduringtheegg
laying phase were calculated from these MAMs as the variance ex-
plainedbyfemaleIDrelativetothetotalvariance.
As we suspected that the var iation in emergence t ime, entry
time, and a ctive dayleng th across the bree ding season may have
confounded the relationships between clutch initiation date and
emergence time/active daylength, we decided to use additional
datathatwehadcollected duringthepre-egglayingphase.During
thisphase,weplacedSongMeterson25nestboxeswithneststhat
were compl eted, but with no e ggs yet. For the se 25 females, we
measuredemergenceandentrytimesbetweenMarch26andMarch
30.Temporalvariationwasthusverylimited.Weusedlinearmixed
models to test whether emergence time, entry time, and active
daylengthwere affected by thedateofmeasurement,thenumber
ofdayspriortoclutchinitiation,thetemperature,andthefemale's
TAB LE 1 Samplesizesofemergencetime,entrytimeandactivedaylengthduringthepre-egglayingphaseandtheegglayingphase.
Phase Variable
Number of
females
Number of measurements
Mean per female
Repeats per female
1 2 34 5 6 7
Pre-egglaying Emergencetime 23 2.96 122 0
Entrytime 24 3.04 317 4
Activedaylength 22 2.95 121 0
Egg laying Emergencetime 121 3.84 1 5 49 27 36 2 1
Entrytime 116 3.54 323 30 35 19 5 1
Activedaylength 114 2.98 245 26 36 41 0

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age(inyearssincebirth,withage=0isyearofbirth;fortheresults,
see Figure S2 and Table S2).Inallmo del s,r and ominterc ept swe rein-
cludedforfemaleidentity(ID).Afterexcludingnon-significantfixed
effects,wecalculatedtheadjustedrepeatability.
Weperformed similar analyses as before to determine the re-
lationships between emergence time/active daylength measured
during the pre-egg laying phase and clutch initiation date. Here,
clutchi n i t ia t io nd a t e s r a n g e d f r o mM a r c h 2 9 u p t oA p r i l 1 5(=18 days).
Additionally, using a separate model on the subset of females
measuredduringboth the pre-egg laying and the egglayingphase,
weestimated the between-periodrepeatabilityofemergence time,
entry time,and activedaylength (nemergencetime = 23, nentry time =24,
nactive daylength =21).We inclu d edthe repro d uctivephas easa t wo-le vel
factor(i.e.,pre-egglayingvs.egglaying)andthemeasurementinter-
val(i.e.,thenumberofdaysbetweentheaveragemeasurementdate
duringthepre-egglayingphaseandtheegglayingphase;mean= 8.3,
min.=3,max=18.5)asacontinuouscovariate.Non-significantfixed
effects were removed from the models. Both female ID and the
uniquecombinationofperiodandfemaleIDwereincludedasr andom
effects,therebyspecificallyallowingtoestimatethebetween-period
repeatability,followingAraya-Ajoyetal.(2015).Thatis,theadjusted
between-period repeatability wascalculatedfrom thismodel as the
varianceexplainedbytheindividualrelativetothetotalvariance.
2.4 | Ethical note
ThisstudywasapprovedbytheethicalcommitteeoftheUniversity
of Antwerp (ID numbers: 2016–87 and 2018–50) and was
performed inaccordance withBelgian and Flemish laws regarding
animal wel fare, adhered to th e ASAB/ABS guidelines f or the use
ofanimalsin behavioralresearch and teaching, and complies with
ARRIVE guidelines.TheRoyalBelgian Institute ofNaturalSciences
(KBIN) provided ringing licenses for all authors and technicians.
Handlingtimewasminimizedasmuchaspossible.Allothermethods
describedabovearenon-invasive.
3 | RESULTS
Duringthepre-egglayingphase,emergencetimesrangedbetween
76 minbeforesunriseand21 minaftersunrise(Table 2).Entrytimes
rangedfrom63 minutesbeforesunsetupto10minutesaftersunset
andactivedaylengthsfrom56 minshorterthanthedaylightperiod
upto 46 minlonger.Duringtheegg layingphase,emergencetimes
ranged from 127 min before sunrise up to 63 min after sunrise.
Entrytimesrangedbetween136 minbeforesunsetand13 minafter
sunset. T he shortest ac tive daylength we measure d was 153 min
shorter than the daylight period and the longest active day was
35 minlongerthanthedaylightperiod.
3.1 | Repeatability of daily activity patterns
Bothduringthepre-egglayingphaseandtheegglayingphase,the
adjusted repeatability was significant for emergence time, entry
time, and a ctive dayleng th (Table 3). In contrast,between-period
repeatabilitiesforemergencetime(R[95%CI]=0.09[0 ,0. 3 0]),entr y
time(R =0.20 [0,0.42]),andactive daylengthwerenotsignificant
(R =0[0,0]).
3.2 | Clutch initiation date and daily activity
patterns during the egg laying phase
Femaleswithanearlieremergencetimeduringtheegglayingphase
endedtheiractivitiesoutsidethenestboxlaterduringthedaythan
females thatshowedalater onsetofactivity (t =−2.62, df= 112,
p < .01). Emergen ce time was posit ively related t o clutch initiat ion
date(t =3.85,df= 118, p < .001;Figure 1a). Individuals that started
their activityearlyduring theday laid their first eggearlierduring
thebreedingseasonthanindividuals withlateemergence times.In
addition, active dayleng th was negatively related to clutch initiation
date(t =−6.96,df= 111, p < .001;Figure 1b). Individuals that were
longer ac tive during th e day laid their fir st egg earlie r during the
breedingseasonthanindividualsthatwereactiveforashortertime
period.
3.3 | The influence of date on daily
activity patterns
Datehadanimportantinfluenceonemergencetime,entrytime,and
active daylength(Figure 2; Table 4). Early in the season individuals
emergedclosetosunrise(=0),whilelaterintheseasonemergence
times becamelater (=positive values; Figure 2a). Thus, date had a
Phase Variable Min. Max. Mean SD
Pre-egglaying Emergencetime −76 21 −17. 51 13.64
Entrytime −63 10 −23. 07 17. 2 5
Activedaylength −56 46 −6.25 21.92
Egg laying Emergencetime −127 63 5. 81 17. 5 9
Entrytime −136 13 −39.18 24.67
Activedaylength −153 35 −45.35 32 .51
TAB LE 2 Summaryofthemeasured
valuesforemergencetime,entrytimeand
activedaylength(inminutesrelativeto
sunrise, sunset and the period between
sunrise and sunset respectively) during
thepre-egglayingandegglayingphase.

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positiveeffectonemergencetimes(Averagedateeffectisgivenin
Table 4). This ef fect was par tly driven by an a mong-indi vidual ef-
fect, but at the same time, emergence time became later oncon-
secutive days within individuals (Date deviation effect in MAM:
t =3.23,df=296.72,p < .01;Figure 2a).Furthermore,olderfemales
hadearlieremergence times (Table 4).Temperature at sunrise did
not affec t emergence t imes. On average , entry time b ecame ear-
lierasthedateprogressed(Figure 2b) and active daylength shor ter
(Figure 2c; Table 4).Withinindividuals, theseeffectsonentrytime
andactivedaylengthbecameinbothcasesstrongertowardtheend
ofthe breeding season, as indicated by thesignificant interaction
betweenaveragedateanddatedeviation(Table 4).Agedidnothave
aneffectoneitherentrytimeoractivedaylength.Activedaylength
waslongeronwarmerdays(Table 4),buttemperatureatsunsetdid
notaffectentrytime.
3.4 | Clutch initiation date and activity patterns
during the pre- egg laying phase
During t he pre-egg l aying phase entr y times were not relate d to
emergencetimes(asubsetoffemales, n = 23, t = −0.44,df= 22,
p = .66). Furthermore, during the pre-egg laying phase, neither
emergencetime(t =−0.25,df= 3,18, p = .81), nor active daylength
(t =1.58,df= 2 ,19, p = .13) were related to clutch initiation date.
4 | DISCUSSION
Ourinitialanalysissupportedthepreviouslyreportedfindingthatfe-
malegreattitswithanearlyonsetofactivitystarttoreproduceearlier
inthe season (Graham et al.,2017 ). Thedata equallysupported our
hypothesis that the relationship between clutch initiation date and
emergencetimeisdrivenbyac tivedayleng th,thatis,thetimeafemale
hasavailableforforaging.However,whentakingthedateeffectonthe
activitymeasuresinto account,byusingdatafromthepre-egglaying
phase(whereallindividualsweremeasuredonthesamedays),neither
oftheserelationshipsremainedsignificant.Theconsequencesthereof
forthisandpreviousstudieswillbediscussedbelow.
4.1 | Repeatability
During the egg laying phase, repeatability of all activity measures
was high, w hich suggest s the existence of c hronotype s in female
great tits (Lehmann et al., 2012; Maury et al., 2020; Schlicht &
TABLE 3 Adjustedrepeatabilityforemergencetime,entrytime,
andactivedaylength(inminutesrelativetosunrise,sunset,andthe
periodbetweensunriseandsunsetrespectively)duringthepre-egg
laying and egg laying phase.
Phase Variable
Adjusted
repeatability
Pre-egglaying Emergencetime 0.39 [0.10, 0.62]
Entrytime 0.27 [0.018, 0. 52]
Activedaylength 0.45 [0.17, 0.67]
Egg laying Emergencetime 0.54 [0.43, 0.63]
Entrytime 0.77 [0.71, 0.83]
Activedaylength 0.71 [0.63, 0.80]
Note:AllrepeatabilitieswerecalculatedbasedontheMAMforthe
respectiveperiodandvariable(forinformationonsignificantfixed
effectsseeTableS2 and Tabl e 4).95%confidenceinter valsareshown
betweenbrackets.Estimatesinboldarestatisticallysignificant(p < .05).
FIGURE 1 Averageemergencetimesinminutesrelativeto
sunrise(negativevalue=beforesunrise)(a)andaverageactive
daylengthinminutesrelativetotheperiodbetweensunriseand
sunset(negativevalue= shorter active than the period between
sunriseandsunset)(b)asmeasuredduringtheegglayingphase
bothaffectedtheclutchinitiationdate(startsasacountfromApril
1(= 1)).

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Kempenaers,2020). Also during thepre-egg laying phase, activity
measure s were moderately a nd significant ly repeatable . Contrary
to our expectation, the between-period repeatability (i.e., across
thepre-egg layingand egglaying phase)ofemergencetime, entry
time,andactivedaylengthwas non-significant.Whenstudyingthe
relationship between daily timing of activity and clutch initiation
date,the timingofactivity should thuspreferentially bemeasured
beforeegglayingstart s.However,inourinitialanalyse sa ndinprevi-
ousstudiesonthisrelationship,thetimingofactivitywasmeasured
during lat er periods (He re: egg laying ph ase, Graham e t al., 2017:
incubation, Maury et al., 2020:incubation,Helm&Visser,2010: au-
tumn).Thelackofrepeatability betweenthedifferentperiodsmay
be due to the smallsample sizesduring the pre-egg laying phase.
Especiallyforlongertermrepeatabilitysmallsamplesizescancause
greatimprecisionintheestimateforamong-individualvariationand
lowpowertodetectsignificance,whichaffectstherepeatabilityes-
timate (Araya-Ajoy et al.,2015).Therefore, it willbe of interest to
investigatelong-term(i.e.,cross-seasonandcross-year)repeatability
ofactivitypatternsinmoredetailandwithlargersamplesizesinthe
future.
4.2 | Emergence times versus active daylength
Initially,usingthedatafromtheegglayingphase,wefoundaposi-
tiverelationshipbetweenemergencetimeandclutchinitiationdate,
whichisinaccordancewithresultsofarecentstudyongreattitsand
dark eyed ju nco's (Junco hyemalis,Gr aham et al., 2017). However,
this relationship had not been found in captive great tits (Helm &
Visser,2010), infree-living European starlings(Mauryetal., 2020)
andinfree-livingbluetits(awakeningtimewasused,whichishighly
correlatedwithemergencetime,Steinmeyeretal.,2013). One pos-
sibleexplanation forthediscrepancy between these studies might
bethatenvironmentalfactorsthatcouldaffecttherelationshipmay
varyfromyeartoyear.Forexample,springtemperaturemaymodu-
latetheeffectoflightastriggerfortheonsetofbreeding(Dominoni
et al., 2020). Studying the relationship between chronotype and
clutchinitiationdateinmultipleyearsmayrevealtheimpactofsuch
environm ental variat ion. As we hypot hesized above, a nother pos-
sibilitycouldbethatactivedaylengthratherthanemergencetime
playsaroleindeterminingonsetofegglaying.Ourinitialanalyses
indeed show that individuals with longer active dayleng ths initiated
egg laying earlier in the season and that individuals that emerged
earlier fromthenest box entereditlatercomparedwithlate rising
individuals(Mauryetal., 2020,Steinmeyeretal.,2010,but Stuber
et al., 2015onlyshowedthiseffectwithinindividuals).
However,emergencetime,entrytime,andactivedaylengthwere
measuredduringegglaying,andasa consequence,theyweremea-
sured soon after clutch initiation (i.e., most often, measurements
FIGURE 2 Activitypatternsinfemalegreattitsaredependent
onthedate:(a)emergencetimesrelativetosunrise,(b)entrytimes
relativetosunset,and(c)activedaylengthinminutesrelativetothe
periodbetweensunriseandsunset.Allindividualshaveseparate
regressionlines(individualscanbedistinguishedbycolor).Date
startsasacountfromApril1(= 1).

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started1or 2 days afterclutchinitiation).Thedateof measurement
was thus very tightly linked to the laying date of the first egg and
differencesinactivitypatternsbetweenearlyandlatelayingfemales
couldpossiblybeexplainedbyenvironmentalchangesovertime(e.g.,
temper ature, food avail ability, predatio n risk, and light in tensity at
thenestboxduetoan increaseinleafcoverage)insteadofintrinsic
differencesinchronotypes.Therefore,weexpectedthatthedateof
measurementmaybeaconfoundingfactorwhenanalyzingtherela-
tionshipsbetweentheactivityparametersandclutchinitiationdate.
Totacklethisproblem,andbec ausewedidnotf indrepeatabil-
ity in the daily timing of activity between the differentperiods,
we perfo rmed additi onal analyses t hat suppor ted our presump -
tionthatthedateofmeasurementisa confoundingfactorinthe
relationship between activity patterns and clutch initiation date.
First,wetriedtostatisticallycorrectfordateofmeasurementby
using individual intercepts and slopes. However, it is not possible
todisentanglethedateofmeasurementfromclutchinitiationdate
with thismethod. Instead, weused emergencetimesand active
TAB LE 4 Resultsfromlinearmixedeffectsmodelswithrandominterceptsandslopesfortestingtheinfluenceofdateonemergence
time,entrytimeandactivedaylength(inminutesrelativetosunrise,sunsetandtheperiodbetweensunriseandsunsetrespectively)during
the egg laying phase.
Dependent variable Fixed effects βSE tdf p
Emergencetime Averagedate 0. 61 0.21 2 .94 106 .72 <.01
Date deviation 1.25 1.31 0.95 80.28 .34
Age −2 .98 1.29 −2 .31 92. 37 .02
Tsunrise −0.31 0.25 −1. 2 5 350.26 .21
Averagedate × date
deviation
0.11 0.1 2 0.95 76.49 .56
Randomeffects σ2χ2df p
IDintercept 118.07 119.34 1<.001
IDslope 14.33 3.79 2.15
Corrintercepts-slop es −0.03
Residual 93.14
Entrytime Fixedeffects βSE tdf p
Averagedate −1 . 96 0. 27 −7.19 9 9.32 <.0 01
Date deviation 0.66 2.45 0.27 111.0 4 .79
Age −1.7 9 1.62 −1. 11 8 7.96 .27
Tsunset 0.14 0.17 0. 81 293.66 .42
Averagedate × date
deviation
−0.94 0.21 −4.48 9 9. 28 <.001
Randomeffects σ2χ2df p
IDintercept 212. 57 114. 89 1<.0 01
IDslope 83.25 50.76 2<.001
Corrintercepts-slop es 0.32
Residual 87. 2 3
Activedaylength Fixedeffects βSE tdf p
Averagedate −2 . 71 0.34 −7. 9 4 105.84 <.001
Date deviation −0.54 3.07 −0.18 75.59 .86
Age 0.34 2.11 0.16 87.68 .87
Tmax 0.76 0. 26 2.91 262 .75 <.01
Averagedate × date
deviation
−1. 0 5 0.27 −3 .87 7 3. 51 <.001
Randomeffects σ2χ2df p
IDintercept 30 4 .74 92.30 1<.0 01
IDslope 83.97 6.83 2.03
Corrintercepts-slop es 0.01
Residual 184.06
Note:Estimatesinboldarestatisticallysignificant(p < .05).

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daylengthsfrom asubsetof females, thatweremeasuredduring
the pre-egg laying phase. All females were measured multiple
timeswithinarangeof5 days(i.e.,thedateof measurement was
independent fromthe clutchinitiation date). We foundthat nei-
theremergencetimenor active daylengthmeasuredduringthe
pre-egglayingphasewererelatedtothe initiationofegglaying.
Thus, as emergence times and active daylengths were not re-
lated to clut ch initiation date wh en methodologi cally correct ed
forthedate of measurement,weconsideritmost likelythatthe
relationships we initially found are confounded by the date of
measurement.
4.3 | Variation in emergence time and active
daylength across the breeding season
Thedateonwhichanindividualwasmeasuredaffecteditsemergence
time,entrytime,andactivedaylengthrelativetosunriseandsunset,
thatis,evenaftercorrectingforchangesinsunriseandsunsetover
time.Emergencetimedelayedwithdate,whileentrytimeadvanced.
Asimilareffectwasrecentlyreportedinindividualblue titsduring
theegglayingphase,butdateeffectsonthe populationlevelwere
notinvestigated(Schlicht&Kempenaers,2020).
As circ adian clocks ar e entrained by t he light–dark cycl e (e.g.,
Berson etal., 2002; Wright Jr et al., 2013; Zeng et al., 1996), light
intensityislikelyaveryimportantdeterminantforactivitypatterns
inthewild(seealsoSockman&Hurlbert,2020foradiscussionon
the role of ac tive daylengt h on migratory beh avior). In great tits
andbluetits,lightintensityatthenestbox significantlyinfluenced
emergencetimeand awakeningtime in the morning,respectively
(Steinmeyeretal.,2010;Stuberetal.,2015). However, the variation
that we observed in emergenceand entry time relative to sunrise
andsunsetovertime bothwithinand amongindividuals, indicates
thatthelightintensitiesthattriggeremergencefromandentryinto
thenestboxchangeovertime.
At present , we can only specu late about the unde rlying driv-
ers. During winter, whenthe days are short, individuals may have
to make use of the f ull daylight pe riod, while in s pring, when t he
daysaremuchlonger,theymaynotneedthefulldaylightperiodto
performallnecessary tasks.Conversely,greattits may alsoneeda
minimalamountofsleep.Therefore,emergencetimesmaydelayrel-
ativetosunrisewhenthedayslengthenwhileentrytimesadvance.
However,duringthebreedingseason,wewouldthenexpecttheab-
solute activedaylength toremainconstantfromacertainmoment
onwards,butinfact,itstartedtodecreasewhilethedaylightperiod
was still lengthening.
Inadditiontolightintensityalternativezeitgebers(i.e.,environ-
mental factors that canentrain the biological clock)and masking
factors(i.e.factorsthatdo notchange the internalclocktime, but
instead modifythe expressionofbehavioral rhythms) maybe im-
port ant (Helm et al., 2017). Fo r example, earl ier studies showe d
thatwildgreattitsdelayedentrytimesonwarmerevenings(Stuber
et al., 2015), while captive great tits had later activity onset and
earlier activityoffsetinwarmerconditions(Lehmann etal.,2012).
Wefound that an increase in maximum temperature was related
tolongeractive daylengths, although temperature at sunrise and
sunset didnot significantlyinfluence emergence andentrytimes.
Temperature may thus modulate the activity patterns, but it
could not fully explain the changes over time as observed in our
population.
Another environmental factor that could affect emergence
and entry timeisthe food availability(Hau & Gwinner,1997, Rani
et al., 2009,Vivanco et al.,2010). When food is not continuously
available,butonlyduringspecific timeframes,thiscanentrainthe
biologicalclock and individualsmayshift theircircadian phase, to
meettherequirementsofoptimalforaging.Alternatively,foodavail-
abilit y may have acted as a mas king factor. For exa mple, on days
withhighfoodavailabilitygreattitsmayneedlesstimeforforaging
inorder to meet their energyrequirements,whichenables earlier
cessatio n of activity in t he evening (Bach et al. , 2017, Northeas t
et al., 2020, but see Inoue et al., 2016). However, as we do not have
data on food availability, the influence of environmental factors
like foodavailability on emergence and entry times needs further
investigation.
Furthermore,theamountoftimespentonnighttimeincubation
mayhave affected activity patterns during egg laying. During this
phase,femalesalreadystartincubatingtheeggsatnight.Witheach
subsequentegg,theamountoftimespentonnighttimeincubation
increas es (Lord et al., 2011; Pod las & Richner, 2013) an d females
withlateegglayingdatesincubatelongeratnightthanfemaleswith
early laying dates (Haftorn, 1981). Night time incubation normally
starts immediatelyafterenteringthe nest box, but whether entry
timesadvancewhennighttimeincubationincreasesisyetunknown.
Yet,noneoftheabove-mentionedfactorsseemstofullyexplainthe
observedtemporalpatternsinemergenceandentrytimes.
Aspointedoutabove,thesignifi canceofsunriseandsunsetfor
determiningactivity patterns changes overtimebothwithinand
amongindividuals. This isrelevantfor interpreting this andpre-
vious studies, even though most of the previous studies did not
finddateeffectsonemergencetimesduringthebreedingseason
(Graham e t al., 2017; Maury et al., 2020; Woma ck, 2020). This
discrepa ncy may be caus ed by our much larg er sample size and
alarger rangeofdates on which we measured emergence times.
Therefore,itispossiblethatalthoughGrahametal.(2017) did not
find date ef fects on em ergence times , their results m ay still be
confoundedbydate.Theymeasuredemergencetimesduringthe
incubation period, which isslightly differentfrom our approach.
However,ifemergencetimeismeasuredatafixedtimeafterclutch
completion,itcouldstillbepossiblethatdateinflatestherelation-
ship between clutch initiation date and emergencetime. In fact,
Steinmeyeretal.(2013),whorecordedsleepbehaviorduringmul-
tiplemonthsinwinterinmultipleyears,foundthatsleepparame-
ters(including awakeningtime)variedgreatlybetweenrecording
datesandthereforethey corrected awakeningtimes for thedate
ofmeasurement. Thecorrected awakeningtimes then again did
notaffectclutchinitiationdates.

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5 | CONCLUSIONS
We showed that both emergence time and active daylength
(measured during the egg laying phase) were related to clutch
initiation date, but both relationships were confounded by date
of measurement, as the timing of measuring activity patterns
was tightly coupled to the initiation of egg laying. When using
methodologically corrected data from the pre-egg laying phase,
wedidnotfindasignificantrelationshipbetweentimingofactivity
and clutch initiation date. Furthermore, our results showed that
the relevance of sunrise and sunset for the timing of activities
varies throughout the breeding season, possibly in response to
environmentalfactors,suchastemperatureorfoodavailability.This
makesitmethodologicallyextremelychallengingtocorrectfordate
ofmeasurementeffects.Futurestudiesonfunctionalconsequences
ofactivitypatternsshouldhenceaimtovarythetimespanbetween
thedependent(here:layingdate)andindependent(here:timingof
activity)variable,forexample,bymeasuring activitypatternsof all
individ uals on the same day (s),w hile being in the sa me breeding
phase. Such confounding factors are possibly very common
in statistical analyses including date. In addition, if individuals
respondplasticallytotemporalchangesintheenvironment,spatial
differencesintheenvironmentmayalsoaffectactivitypatternsand
could be partially responsible for differences in emergence times,
entry times,andactivedaylengthsamong individuals,whichasyet
needs to be investigated.
AUTHOR CONTRIBUTIONS
Marjolein Meijdam: Conceptualization (equal); formal analysis
(equal);investigation(equal);methodology(equal);writing–original
draft(equal).Wendt Müller:Conceptualization(equal);methodology
(equal); writing – review and editing (equal). Bert Thys: Formal
analysis (equal); writing– review andediting (equal). Marcel Eens:
Conceptualization (equal); methodology (equal); writing – review
andediting(equal).
ACKNOWLEDGMENTS
We thank Peter S cheys and Geer t Eens for their f ield assist ance.
This workwas supported by theUniversity ofAntwerp andFWO
Flanders(FWOprojects ID: G0A3615NandG052117NtoMEand
RiannePinxten).Wethankbothfortheirsupport.
CONFLICT OF INTEREST
Theauthorsdeclarenoconflictofinterest.
DATA AVAIL AB I LI T Y STATE MEN T
All data that support the findings of this study are available via
Dryad(https://doi.org/10.5061/dryad.2rbnzs7rk).
ORCID
Marjolein Meijdam https://orcid.org/0000-0002-4034-2035
Wendt Müller https://orcid.org/0000-0001-7273-4095
Marcel Eens https://orcid.org/0000-0001-7538-3542
REFERENCES
Araya-Ajoy,Y.G.,Mathot,K.J.,&Dingemanse,N.J.(2015).Anapproach
toestimateshort-term,long-termandreactionnormrepeatability.
Methods in Ecology and Evolution, 6,1462–1473.
Arrona-Palacios,A.,Díaz-Morales,J.F.,Adan,A.,&Randler,C.(2020).
Sleep habits, circadian preferences and substance use in a
Mexicanpopulation:The use oftheMorningness-Eveningness-
Stability-Scaleimproved(MESSi).Chronobiology International, 37,
111– 122.
Bach,T.H., Chen,J.,Hoang,M.D.,Beng,K.C.,&Nguyen, V.T.(2017).
Feeding behavior and activity budget of the southern yellow-
cheekedcrestedgibbons(Nomascus gabriellae) in a lowland tropical
forest.American Journal of Primatology, 79,e22667.
Berson, D. M., Dunn, F. A., & Takao, M. (20 02). Phototransduction by
retinal ganglion cells that set the circadian clock. Science, 295,
1070–1073.
DeCoursey,P.J.,Walker,J. K.,&Smith,S.A .(2000). A circadian pace-
maker in fre e-livi ng chipmunks : Essential for s urvival? Journal of
Comparative Physiology, 186,169–180.
Dingemanse,N.J.,Kazem,A.J.,Réale,D.,&Wright,J.(2010).Behavioural
reaction norms: Animal personality meets individual plasticity.
Trends in Ecology and Evolution, 25, 81– 89.
Domino ni, D. M., Åkesso n, S., Klaasse n, R., Spoe lstra, K. , & Bulla, M.
(2017). Methods in field chronobiology.Philosophical Transactions
of the Royal Society B, 372,20160247.
Dominoni, D. M., Kjellberg Jensen, J., de Jong, M., Visser, M. E., &
Spoelstra, K . (2020). Artificial light at night, in interaction with
springtemperature,modulatestimingof reproductioninapasser-
ine bird. Ecological Applications, 30,e02062.
Graham,J.L.,Cook,N.J.,Needham,K.B.,Hau,M.,&Greives,T.J.(2017).
Earlytorise,earlytobreed:Arolefordailyrhythmsinseasonalre-
production. Behavioural Ecology, 28,1266–1271.
Haftorn,S.(1981).Incubationduringtheegg-layingperiodinrelationto
clutch-sizeandotheraspectsofreproductionintheGreatTitParus
major. Ornis Scandinavica, 12,169–185.
Halfwerk,W.,Bot,S.,Buikx,J.,vanderVelde,M.,Komdeur,J.,tenCate,
C., & Slabbekoorn,H. (2011).Low-frequency songs lose their po-
tency in n oisy urban cond itions. Proceed ings of the Nationa l Academy
of Sciences of the USA, 108,14549–14554.
Hau, M., & Gwinner, E. (1997). Adjustmentofhouse sparrow circadian
rhythms to a simultaneously applied light and food zeitgeber.
Physiology and Behavior, 62,973–981.
Hau,M.,Dominoni,D.,Casagrande,S.,Buck,C.L.,Wagner,G.,Hazlerigg,
D.,Greives, T.,& Hut,R. A . (2017). Timing asasexually selected
trait:Therightmateattherightmoment.Philosophical Transactions
of the Royal Society B, 372,20160249.
Helm,B.,&Visser,M.E.(2010).Heritablecircadianperiodlengthinawild
bird population. Proceedings of the Royal Society B, 277,3335–3342.
Helm, B., Visser,M.E.,Schwartz, W.,Kronfeld-Schor,N.,Gerkema,M.,
Piersma,T.,&Bloch,G.(2017).Twosidesofacoin:Ecologicaland
chrono biological p erspect ives of timing in t he wild. Philosophical
Transactions of the Royal Society B, 372,20160246.
Inoue, Y.,Sinun, W., & Okanoya,K. (2016). Activity budget, travel dis-
tance, sleeping time, height of activity and travel order of wild
EastBorneanGreygibbons(Hylobatesfunereus)inDanumValley
ConservationArea.Raffles Bulletin of Zoolog y, 64,127–138.
Iserbyt,A., Griffioen, M., Borremans,B.,Eens,M., &Müller,W.(2018).
Howto quantify animal activityfromradio-frequency identifica-
tion(RFID)recordings.Ecology and Evolution, 8,10166–10174.
Kuznetsova,A.,Brockhoff,P.B.,&Christensen,R.H.B.(2017).LmerTest
package:Testsinlinearmixedeffects models.Journal of Statistical
Software, 82,1–26.
Labyak , S. E., Lee , T.M., & G oel, N. (1997). Rhy thm chron otypes in a
diurnal rodent, Octodon degus. American Journal of Physiology –
Regulatory, Integrative and Comparative Physiology, 273,1058–1066.

|
11 of 11
MEIJDAM et al.
Le hma nn,M.,Spo els tra, K.,Vis ser,M .E .,& Hel m,B .(201 2).Ef fec t softe m-
peratureoncircadianclockandchronotype:Anexperimentalstudy
on a passerine bird. Chronobiology International, 29,1062–1071.
Lord, A . M., McCl eery, R., & Cr esswell, W. (2011). Inc ubation pri or to
clutch completion accelerates embryonic development and so
hatchdateforeggslaidearlierinaclutchinthegreattitParus major.
Journal of Avian Biology, 42,187–191.
Maury,C.,Serota, M. W., & Williams,T.D. (2020). Plasticity in diurnal
activityandtemporalphenotypeduringparentalcareinEuropean
starlings, Sturnus vulgaris. Animal Behaviour, 159,37–45.
Meijdam,M.,Müller,W.,&Eens,M. (2022).Intrinsic individual variation
in daily ac tivity onset and plastic responses on temporal but not spa-
tial scale s in female great tits[manuscriptsubmittedforpublication].
DepartmentofBiology,Universit yofAntwerp.
Northeast,R.C.,Vyazovskiy,V.V.,&Bechtold,D.A.(2020).Eat,sleep,
repeat:The roleof the circadian system in balancingsleep–wake
control with metabolic need. Current Opinion in Physiology, 15,
18 3 – 1 91.
Nussey,D.H.,Wilson,A. J., & Brommer,J.E.(2007).Theevolutionary
ecology of individual phenotypic plasticity in wild populations.
Journal of Evolutionary Biology, 20,831–844.
Pittendrigh, C. S. (1993). Temporal organization: Reflections of a
Darwinianclock-watcher.Annual Review of Physiology, 55,17–54.
Podlas, K ., & Richne r,H . (2013). Partia l incubatio n and its fun ction in
great tits(Parus major)—an experimental test.Behavioural Ecology,
24,643–649.
Poesel, A., Kunc, H. P., Foerster, K., Johnsen, A., & Kempenaers, B.
(2006). E arly birds ar e sexy: Male a ge, dawn song and e xtrapair
paternityinbluetits, Cyanistes(formerlyParus)caeruleus.Animal
Behaviour, 72, 531– 538.
Raap,T.,Pinxten,R.,&Eens,M.(2016).Artificiallightatnightdisruptssleep
infemalegreattits(Parus major)duringthenestlingperiod,andisfol-
lowed by a sleep rebound. Environmental Pollution, 215,125–134.
Rani,S.,Singh,S.,Malik,S.,Singh,J.,&Kumar,V.(2009).Synchronization
ofIndianweaver bird circadian rhythmsto foodand light zeitge-
bers:Roleofpineal.Chronobiology International, 26,653–665.
RCoreTeam.(2013).R: A language and environment for statistical comput-
ing.RFoundation forStatisticalComputing. https://www.R-proje
ct.org/
Refinetti, R., Wassmer, T., Basu, P., Cherukalady, R., Pandey, V. K.,
Singaravel, M.,Giannetto, C ., & Piccione,G. (2016). Variability of
behavioralchronotypesof16mammalianspeciesundercontrolled
conditions. Physiology and Behavior, 161, 53– 5 9.
Rivera-Gutierrez,H.F.,Pinxten,R.,&Eens,M.(2012).Tuningandfading
voicesinsongbirds:Age-dependentchangesintwoacoustictraits
acrossthelifespan.Animal Behaviour, 83,1279–1283.
Schlicht,L.,Valcu,M.,Loës,P.,Girg,A.,&Kempenaers,B.(2014).Nore-
lationshipbetweenfemaleemergencetimefromtheroostingplace
andextrapairpaternity.Behavioural Ecology, 25,650–659.
Schlich t, L., & Kemp enaers, B . (2020). The e ffect s of season, s ex, age
and weath er on popula tion-level var iation in the t iming of act iv-
ity in Eurasian blue tits Cyanistes caeruleus. Ibis (London 1859), 162,
1146–1162.
Sockman,K.W.,&Hurlbert,A.H.(2020).Howtheeffectsoflatitudeon
daylightavailabilitymayhaveinfluencedtheevolutionofmigration
andphotoperiodism.Functional Ecology, 34,1752–1766.
Specht,R.(2002).Avisoft-saslabpro:Soundanalysisandsynthesislabora-
tory.AvisoftBioacoustics.http://avisoft.com/SASLab_deutsch.pdf
Steinmeyer,C.,Schielzeth, H., Mueller,J.C., & Kempenaers, B.(2010).
Variationinsleepbehaviourinfree-livingbluetits,Cyanistes caeru-
leus: Effec ts of sex, age and en vironment. Animal Behaviour, 80,
8 5 3 – 8 6 4 .
Steinmeyer,C.,Mueller,J.C.,&Kempenaers,B.(2013).Individualvaria-
tion in sleep behaviour in blue tits Cyanistes caeruleus:Assortative
matingandassociationswithfitness-relatedtraits.Journal of Avian
Biology, 44,159–168.
Stoffel,M.A.,Nakagawa,S.,&Schielzeth,H.(2017).RptR:Repeatability
estimationandvariancedecompositionbygeneralizedlinearmixed-
effectsmodels.Methods in Ecology and Evolution, 8,1639–1644.
Stuber,E.F.,Dingemanse,N.J.,Kempenaers,B.,&Mueller,J.C.(2015).
Sources of intraspecificvariationinsleepbehaviourofwild great
tits. Animal Behaviour, 106, 20 1– 221 .
Thys, B. , Eens, M., Pinx ten, R., & Is erbyt, A . (2021). Pathways lin king
female p ersonalit y with reproduc tive success ar e trait-and yea r-
specific.Behavioral Ecology, 32,114–123.
Vande Pol,M.,& Wright,J.(2009).Asimplemethodfordistinguishing
within-versusbetween-subjecteffectsusingmixedmodels.Animal
Behaviour, 77,753.
VanderVeen,D.R.,Riede,S.J.,Heideman,P.D.,Hau,M.,vanderVinne,
V.,&Hut,R. A.(2017).Flexible clocksystems:Adjustingthetem-
poralprogramme. Philosophical Transactions of the Royal Society B,
372,20160254.
VanDuyse,E.,Pinxten,R., Snoeijs, T.,& Eens,M. (2005).Simultaneous
treatment withan aromatase inhibitor and an anti-androgende-
creasesthe likelihood ofdawn songin free-living male greattits,
Parus major. Hormones and Behavior, 48,243–251.
Verboven, N., & Visser, M. E. (1998). Seasonal variation in local re-
cruitment of great tits: The importance of being early.Oikos, 81,
5 1 1 – 5 2 4 .
Vivanco,P.,López-Espinoza,A.,Madariaga,A.M.,Rol,M.Á.,&Madrid,
J.A.(2010).Nocturnalisminducedbyscheduledfeedingindiurnal
Octodon degus. Chronobiology International, 27, 233– 250.
Womack,R.J.(2020).Clocksinthewild:Biologicalrhythmsofgreattits
andtheenvironment.http://theses.gla.ac.uk/81345/
Wright,K.P.,Jr.,McHill,A.W.,Birks,B.R.,Griffin,B.R.,Rusterholz,T.,
&Chinoy,E.D.(2013).Entrainmentofthehumancircadianclockto
thenaturallight-darkcycle.Current Biology, 23,1554–1558.
Zeng,H.,Qian,Z.,Myers,M.P.,&Rosbash,M.(1996).Alight-entrainment
mechanism for the Drosophila circadian clock. Nature, 380,
12 9 – 1 35.
SUPPORTING INFORMATION
Additional supporting information can be found online in the
SupportingInformationsectionattheendofthisarticle.
How to cite this article: Meijdam,M.,Müller,W.,Thys,B.,&
Eens,M.(2022).Norelationshipbetweenchronotypeand
timingofbreedingwhenvariationindailyactivitypatterns
across the breeding season is taken into account. Ecology and
Evolution, 12, e9353. https://doi.org/10.1002/ece3.9353