Provided byCONICETDigital Accepted Article CORE This by is protectedarticle reserved. Allrights copyright. doi: 10.1111/ibi.12587 lead to differences between this version and the throughbeen the copyediting, pagination typesetting, which process, may and proofreading hasThis article been accepted publicationfor andundergone peerfull but review not has SCARDAMAGLIA, ROMINA C. Running-head: Petra Editor: Sumasgutner, Paper :Original type Article DR. JUAN :0000-0001-5136-4574)CARLOS REBOREDA ID (Orcid DR. ROMINACLARA SCARDAMAGLIA (Orcid :0000-0002-5400-6083)ID exclusivelyhost. Femalesof both one layinrelative darkness,before dawn, relying extreme host isparasitizessocially generalist, latter and monogamous while the almost related brood parasites, sociallypromiscuousbut theformer is polygynousand an or Shiny *Corresponding author: [email protected].

2 Department Department of Zoology, South Parks Road, University of Oxford, OX1 3PS, KingdomUnited Roostingbehaviour is relatedreproductive to strategybrood in parasitic cowbirds 1 DepartamentoyEcología, deIEGEBA-CONICET, Genética Evolución& de Facultad Ciencias Exactas y Naturales, Universidad de BuenosUniversidadNaturales, de Ciencias y Pabellón Aires, Exactas Ciudad II Molothrus bonariensis Roosting behaviour in brood parasitic cowbirds parasitic brood in behaviour Roosting Universitaria, Universitaria, C1428EGA Buenos Aires, Argentina

1 * ALEX KACELNIK and Screaming Cowbirds Version of Record. Please Version as this cite of Record. article 2 & C.REBOREDA JUAN M. rufoaxillaris

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1

are closely are Accepted Article individuals do that not have information on the location of good feeding sites can obtain such proposed assemblagesthat birdassuch roostsinformation where couldactas centres, 1994, Paquet evidence eachfor of these in specificfactors systems (see Yom-Tov 1979, du Plessis informationpredation, and exchange,and some studieshave provided indirect or direct taxa. Functionsproposed includeroostsfor thermoregulation, reduction inprobability of communalroosting remains poorly and understood, explanations mayhave different across Laughlin2006, many thousandsto spend the overnight resting period together (Dhondt is commonItin gather many birdspecies groupsin individuals to for ranging a few from to This by is protectedarticle reserved. Allrights copyright. Keywords: ecologyofparasites’ brood ingeneraland behaviour inparticular. describe spatialthe and temporal patterns of a relatively poorly known aspectof avian levels association of during the day also showed high associationlevels of in the roost. We days.Screamingwere andthat males females trapped togethershowed and high known time window parasitism, with for earlier departures probably layingcorresponding to marked fidelityinroostinglocation,and roostdepartures occurred duringafter both and the tagged individuals. Female Shiny Cowbirds and both sexes of Screaming Cowbirds showed andindividual timing associations, of parasiticandroost spatialdepartures events, using between a recorded species. inter- fidelity roost,location a roost,to We fidelity within related to their breeding strategy(brood parasitism) and differencesreflects instrategies behaviour in these species to test the hypothesis roostingthat behaviour of cowbirds is informed roost associates. studiedWe the temporal and spatial patterns of roosting for host nest location on previous days’ prospecting activity, or possibly on following better- assemblage, space use, site fidelity, radio-tracking, et al. et et al. et 2016). An influential hypothesis elaborated by andWard Zahavi (1973) 2014).widespread Though a thebehaviour, functional of significance Molothrus et al. 2006, Winkler . et al . Accepted Article (Feare & Zaccagnini 1993). andone studyaddressed departure that roosttimes inShiny Cowbirds headed Cowbird anecdotal instudies analysingand activityhome-rangesmentions Brown- inthe patterns strategyparasites’ reproductive has not yet excepta beenstudied, for few secondary or byspecies (hosts) intheir eggs laying their nests. The roostsuse of in relation brood to diurnal (Morrison range Caccamise 1985).& roosting with sites, commuting upto from five different communal roosts toastable weretobe found their to faithful diurnalmore feeding rangesthantotheir communal centre’‘informationroost hypothesis for & function(Ward Zahavi1973), Common Starlings theyhave roosted before (Adams2011).In addition, andexpectations contradicting the from closer lasttheirto foraging locations rooststhan are that alsoknown whichin andthem to This by is protectedarticle reserved. Allrights copyright. arearoosts in the (Laughlin original roosting wouldthansite beexpected if theywerechoosing randomlythe among of 60%about the andtime, when roostthey roosts, significantlydo switch closer their to 1985).Caccamise Tree Swallows Conklin most have focused mainly on two aspects: roost site fidelity (Morrison & Caccamise 1985, apply communallyequallyacross species1987). (Weatherhead roosting individualsknowledgeempirical but thatdo, from isunlikelyand inconclusive the evidence to roost, whereasroost, others frequentlybetween switch differentroostsinthearea(Morrison & Common Starlings havestudies shownvariabilitygreat sitefidelityspecies. In and between within both inroost sites (Morrisonfeeding & 1985,1990, Caccamise Conklin Brood parasites, such as cuckoos and cowbirds, exploit the parental care otherof Only studies haveanalysed birdsactivityin roosts,of anda few the among those et al. 2007, Béchet 2007, Molothrus ater Molothrus Sturnus vulgaris et al. et et al. et 1994,Gates(Thompson &Evans 1998, Hahn 2010, Laughlin 2014). However, Dunlin Tachycineta bicolor Tachycineta , for example,, individualsremainfor a to highlysome faithful et al. al. et return to return the roost previously used 2014) and roost-use in relationto Calidris alpinaCalidris et al. 2007,Adams2011). These M. bonariensis use roosts that are that use roosts et al. 1999)

Accepted Article Cowbird This by is protectedarticle reserved. Allrights copyright. morning twilight, they of navigationalproblem the different reachinga face location nest daytime nestsandCowbirds search reach in for nests same the the following in must their orroost each night showedpreferenceparticularlocations). for Because Shiny female second, their location withinsecond, their (i.e.whether location fidelity roost settled individuals randomly within fidelity(i.e.whetherindividuals betweenor roosts joinedone roostmore communities),and between females. the studied roostingsiteWe different useattwo we scales: first, studied us expect to differencesin roostingof behaviour between twothe themales species, butnot Thedifferencesspecies. Shiny ofbetween systems the and Screamingmating Cowbirdsled their breeding strategyparasitism) andreflects (brood differences in strategiesbetween Gates &Evans 1998). large intheafternoonflocks feeding and roosting communally night(Thompson 1994, at spendmales andinsmallgroups the females inareasin host morning rich nests, joining observed inthe Brown-headed Cowbirds al. et inthe afternoon theygather tofeedinlarger (Scardamaglia flocks & Reboreda2014, Kattan throughout theday:duringthe individuals morning arein small aloneor found whilegroups, search nests(MasonScardamagliafor 1987, 2014). & Reboreda Socialbehaviour varies CowbirdsScreaming socially are and when males accompanymonogamous females they promiscuousor andfemalesnestssearch for without assistance ofthe while the male, CowbirdsScreaming Shiny differ intheir socially systems: Cowbirds are mating polygynous 2014). In addition differencesto in the degree of specialization in hostuse, Shiny and suggests that theirroostthey to target fly from directly nests (Scardamaglia &Reboreda cowbirds roost communally (Cruz 2017) in nests that they visitedon previous days (Scardamaglia 2016), grouping in communal roosts towards sunset. A similar behaviour has been Females of the host generalisthostofFemales Shiny the the and host specialist In this studyIn we thethis test hypothesisthat roosting behaviourincowbirds isrelated to M. rufoaxillarisM. lay eggstheir around dawn (Gloag et al. 1990, Feare & Zaccagnini 1993), and evidence Molothrus ater Molothrus , a closely related species, in which in , aclosely species, related et al. et et al. 2013, Scardamaglia 2017). isknown It that et al. et

Accepted Article Mockingbirds breedMockingbirds from untilmid-September mid-Januarynestsin and buildopen-cup Troglodytes aedon This by is protectedarticle reserved. Allrights copyright. Gloag Mockingbird residentsinAtarea.the intensely Shiny site thisCowbirds parasitizeChalk-browed field the ehrenbergiana interspersed woodland patchesdominated by two low, spiny trees, spiny hackberry February)2013/14.The 2010/11to ofhaarea comprises with floodinggrasslands ~500 Magdalena, inBuenos Aires Province,Argentina, breedingduring the seasons (October- Theatstudywas reserve the conducted 57.393ºW), ‘ElDestino’ (35.141ºS, the near town of Study siteand species METHODS occurthe on days fractionof areon which females lay. ready to lightintensity searchingunsuited nests or for departuresto is early foraging, roost may only proximity. Furthermore,laying because occurs dawn when mostlypoor during the twilight, the daynest-searching, andjoint weexpected Screaming Cowbird pairs roostto in close scoutingnest participatenot or dawn-laying in Given their spatialassociationduring trips. nests,Cowbirds,whichScreaminghost not but jointlyvisit Shinyto male do that Cowbirds, changingroostingsite between Theappliedcan same nights. be reasoning sexes both of to nests were not a problem, they could reduce the distance travelled eachfor laying bytrip sites, wheretwilight On navigation maybe easier. if hand, other the navigationtowards host layingto start nestsin well-knownHost typically arerelatively expeditions areas. in open predation reasons, Shiny Cowbirds order from maybenefit locationsroosting in atconsistent obvious.Sincehow isnot roosting dark, densesitesmay beconstrained to forest for everyexpectlaying One day dark. thistoaffect might inthe theirchoice of roosting site,but et al. et 2012) and to a lesser degree other species suchas Housethe Wren Mimus saturninus Mimus and coronillo (frequency ofparasitism: 50%, Tuero Scutia buxifolia Scutia (frequency parasitism 70-80%, of Fiorini& Reboreda2006; . Screamingand Shiny. year-round are Cowbirds et al. 2007). Chalk-browed Celtis Accepted Article have one which helpers, three to recruited after are egghatching1991, (Fraga Ursino February early late to December andare (FriedmannHoy1929, Ottow Fraga 1964, 1998,DeMársico & Instead, nestsin domedtheybreednest secondary or builtby boxes species, other cavities, This by is protectedarticle reserved. Allrights copyright. Advanced TelemetrySystems, Minnesota, gluedIsanti, USA). theradio-transmittersWe to transmitters (model PicoPip Ag392 Biotrack,from UK orWareham, model A2455 from 2010/11 and 2011/12 theanimals were g fitted with 1.2 glue-on beeper-VHFradio- (Scardamaglia & Reboreda 2014, Scardamaglia radio-tags because this studyoutsimultaneouslywas carried with two projects other three seasons, breeding in2010/11,2011/12and 2013/14. used twodifferent types of We Two Shiny Cowbird females were tagged twice, in 2010/11 and 2013/14, and one female in plastica numberedleg bands colour was bandaluminium and and a fitted radio-tag. with numbergreater tagged of Each birdwas females. with markeduniquecombination a of (Scardamaglia inthe number birds of trapped and taggedwasdueto the inaconcurrent that fact project usingwalk-inbaited with traps or between The funnel difference sexesmist-nets. millet, the femalesand 5 duringthemales) breeding seasons (October-February)2010/11 2013/14to trappedWe 36Shiny and (27andCowbirds females 32Screaming 9 males) Cowbirds (27 Radio-telemetry 2011). De Mársico Mason 1980, 1998, frequencyparasitism is80-90% andof nests areparasitized most times (Fraga multiple CowbirdsScreaming parasitizeGreyish exclusively the Baywing andif anest pair same can attempt the fails, timesre-nesting several (Fraga 1985). shrubs or withtrees dense foliage, ataheightof They 1.5–2.5 perm. clutch, lay 3–5eggs et al. et 2017)were we in interestedbehaviour, more resulting female ina et al. et 2010). Greyish Baywings rarely build their own nest. cooperative breeders. Assisted pairs generally et al. et 2017). During the breeding seasons et al. et Agelaioides badius Agelaioides 2010). They breed from . The et al.

Accepted Article This by is protectedarticle reserved. Allrights copyright. hadthe birdprevious inthe During the roost maintained day, the tracked night. cowbirds we when thetag signal was recorded moving away eventually(and lost) from the fixed location breeding seasons 2010/11, 2011/12 and 2013/14 respectively. A departure was detected ahand-heldeach receiver 47, hto 04:30 from morning hin 34 06:30 and 29days the in birds, wepresent fewer thisspecies. data for recorded departure We rooststimes from using forest area where access was in difficult the dark and impeded reliable identification of the forproper20 m codereading. of Becausesome theScreaming deep Cowbirds in a roosted rangewaslimited:it distance betweenrequired for the and receiver tag to be no more than SRX-400A,model Lotek Canada).Ontario,Wireless,The coded tags hand-held receiver radio-tracking receivers(beeper model Sika,tags: Biotrack, UK;Wareham, codedtags: technique (White& GarrottCowbirds1990). werearound monitored dusk using hand-held deployment(see SM1 inScardamaglia cowbirds’ behaviour, since visitedfemales and parasitized nests as soon as 18 h after tag OnlineMaterial Supportingdetails). The more for radio-tagshadnoobvious on effects variables we (seebelow) not measured differ did significantlybetween tagging methods (see wholelife duration of were tag (tags designed 79runto days). for that the found We Scardamaglia &Reboreda while 2014), withbackpackfitted those tags carried them for the radio-tags carried for 35.8them ±21.0 days ± (mean rangesd,days, =6 - 68 yieldeddifferences in the time the birdscarried the transmitters. Birds fittedwithglue-on fitting theradio-transmitter lastedless thantwo 15 These minutes. different techniques harness (Rappoletechnique &Tipton 1991).The procedureofthe cowbirdmarking and using TeflonCanada) Philadelphia, Ribbon (BallyUSA) RibbonMills, andtheRappole gfitted with1.0 backpack codedradio-tags (model NTQB-4-2, Ontario, Lotek Wireless, theHenkel, respectively). and 2012/13 During breeding2013/14 were seasonsthe the bird’sback usingcyanoacrylateand adhesive an activator (Loctite401 andLoctite 770, To roost welocations, determine tracked cowbirdsusingon foot, homing the et al. et 2017). n = 34, see Accepted Article the cowbirds trackedduringthe first two breeding seasons (Scardamaglia Reboreda 2014)& these breaksdiscrete delimit to roosts. usedhome-rangedata We previously publishedfor This by is protectedarticle reserved. Allrights copyright. night. Because there were definedWe aroostoperationally an areawhere as birdsof agroup gather spend the to Data analysis nest-daysmonitored 156 of 150 andmockingbirds nest-days of baywings. nest failure (i.e. abandonmentdepredation), orwhichever occurred Overall, first. we moment logger data that wasthe deployed until3 hostandcompletedlays the egg). its first nest activityWe monitored the continuously, from were construction orpre-laying inthe stages (definedas lapsedsincetime the nestliningis data loggerson theground directly and16 below 29mockingbird baywing (Fig. nests that 1) al. tagged cowbirdwithincame detection ~30 range, theantennafrom m (seeScardamaglia 'listened'nearby for tags andrecorded thetag identitycode, dateandtimewhenever a antenna (Biotrack, UK)andtoaWareham, 12V battery. car The continually data-loggers loggers (DataSika, Biotrack, Wareham, UK) that were connected to an omnidirectional Shiny hostCowbird Screaming nests using visits digitallyto and encodedproximitydata- comm.).pers. Additionally, seasons 2012/13and duringthe we 2013/14, recorded tagged theyare pronetodesertif during disturbed pre-laying the or laying De MársicoC. period(M. PVR500ECO)theof base placedat video the baywingtree. record did not We nests since suspended above the nest and connected to a digital video recorder (Lawmate PVR1000 or colour 420CCD usingacamera micro-camera) nests activity (Handykam in mockingbird (and that any absence from the roost was not due to a faulty or lost radio-tag). check on to foot the that radio-tags werestillbirds activeandthatthe area remained inthe 2017 for detailsmore onrecordingtaggedvisits ofof birds tohost nests). placed the We To detect parasitic taggedTo events detect in wevideo-recordedfrom allseasons females,

clear breaks in the distribution of birds (see Results), we used – 4 days after the onset of incubation or et Accepted Article This by is protectedarticle reserved. Allrights copyright. distancesignificantly tobe expected thanshorter it by fellbelowchance if 95 the OnlineMaterial Supportingdetails simulation). of more for observed considered this We the determined bydistancebetweenopposite the the endsroost,of with a1resolution m (see ranging 0 from located(the birdinthem same placein twodifferent nights) a to maximum procedure ( roost at random each night. The simulation consisted of a Monte Carlo randomization mean distance between locationsof a simulated distribution of birds that settled within the observedwe the compared between distance mean each nightlocations of individual the to To whetherdetermine were birds to faithful thelocations theywithindiscrete used a roost, withinFidelity aroost atmonitorednightsleast on four (maximum available 23nights). agiven roostit For wasdetected. that estimatewedatathis birds used from werethat We defined fidelity a to roost as the percentage of nights on which a bird was searched atfor withinSite fidelity a roost individual. eachdistance between points for these to calculate both the diurnal ranges centroids and roost centroids, and estimated the gCentroid function in rgeos package (Bivand & Rundel 2016) in R 3.3.1 (R Core Team 2017) wherelocations (i.e. searchthey and nests). host locate for this, we Toused the do to determine distance the and betweenindividuals’the restinglocations their diurnal distribution of generatedthe by simulation. the n = 1000 runs) where bird locations along a linear roost could take integer values

th percentile Accepted Article This by is protectedarticle reserved. Allrights copyright. aatarriving hostnest theparasitize sameto on day. presentedthe data here arenotdirectobservations departing of females roostthe and from timesalltagged for each females andrecordmorning, activity allpotential nests,target at (http://www.usno.navy.mil/). Becauselogistically itwasnot record departure possible to recording for proper comparison, accountto for variation insunrise times through seasonthe timesdeparturesof and eventsparasitic weretosunrise standardized ontheday relative of andcomparedintervals, between Mann-Whitneythese thetwospecies using The U-tests. agenerating ofdistribution frequency of timing the sets both events of at five-minute analysedWe timingboth the of departure of females theroost and from parasitism events by Timing of roost departures and parasitism events during the day. separately (i.e.in the same trap but at different and times) that did not show association frequencyassociation inof ofthe roost two two and males thatwere females caught association duringthe day, &Scardamaglia 2014). Reboreda Ascontrol, a werecorded the in pairs (i.e. individuals caught intogether the same trap and showing levels ofhigh theduringdata night,weused three femalesand from captured had that three been males whetherTopairsinvestigate Screaming of diurnal Cowbirds association their maintain Association between Screaming Cowbird pairs

Accepted Article Screaming Cowbird males. 1646 m, This by is protectedarticle reserved. Allrights copyright. 494.9 m (range = 219-889 m, was 1311m. distributedina band (Fig. of 1b).Theforest between distance oppositeends this of roost individuals) 4029 wererecordedup Screamingapart. to Cowbird m roost locations were the diurnalhome-ranges birdsof taggedthe Other(Fig. 1a). smaller roosts(ofonly afew wasroostwas and it 755m alongaband located trees of nexta low-use to adjacentroad, to birdslocations tagged of The recorded. were oppositethe betweenof distance this ends Shinyroost’ for where a few hundredbirds Cowbirds, night each and roosted 93% where of wereShinyrarely in males study inthe Cowbird roosts found a area. ‘main detected We used one roost, which was maintained throughout the breeding season (see below). Tagged tagged Screaming Cowbird males. corresponding andlocations), difficulty deep-forest 33locations inaccessing the to five females(we didnotrecord anylocationroosting other for the ninetagged femalesdue to outside our study area), 97 locations corresponding to 18 Screamingtagged Cowbird detected in areathe during the butmorning never around dusk, so they must have roosted corresponding Shinytagged to (theotherfive Cowbird males weretaggedfour males other two tagged females were not detected in the area after tagging), 10 locations recordedWe atotal240 ofcorresponding locations to 25taggedShiny(the Cowbird females Characteristics of roostinglocations RESULTS The distance median between the centroidroost and the diurnal range centroid was ShinyRadio-tracked and sexesCowbird females both Screaming of Cowbird mainly n = 8) Screaming = for Cowbird and=554-1710 females (range 974.5 m m, n = 13) for Shiny= 13) = for 628-(rangeCowbird 966.7 females, m n = 5) for Accepted Article This by is protectedarticle reserved. Allrights copyright. fidelity their roosting to site( For Screaming Cowbirds, precise data were available only for birdsthe tagged with beeper radio-tags in seasons 2010/11 and 2011/12. Both and males females showed 100% season 1;80% fidelityinseason 2;84%3). fidelity in season in fidelity (29% seasons breeding three across tracked female the for roost the of use 2: 100% fidelity in season1 and 89% fidelity in season2), while there was variability in the usedthe2013/14 sameacross roost years (Female 100% fidelity 1: both in seasons; female 17 – 100%, average, returned females tothe same82 % roost± 25%of thenights (mean± sd,range = ShinyFemaleone were toroost faithful throughout Cowbirds breeding the season. On roost a to Fidelity = 16-122 m, between15) a Screamingnights withinroost, Cowbird57.8 females ±moved 35.5 (range m onShiny62.3 average moved females Cowbird ± 28.8 ±(mean m 20-102 sd,range = m, Fidelity within aroost Cowbirds. 2) (Fig. Shiny both for night) each roost the in random at located birds the that betweenmovements nights were significantly than shorter expected by chance(i.e. if Shiny for1311 m CowbirdsScreaming and simulations respectively.showed MonteCarlo distribution birds, of defined which the simulations,values weremaximum inour 755 and m n

= 3) (see Supporting Online Material Fig. S1). The distance between opposite ends in the n n =22 females). The two trackedduringfemales theseasons and 2010/11 = 11)and Cowbird Screaming ± 44.6 males moved 18.9 (range=m 23-58 m, n = 5 = females, n = 3 males). and Screaming n = Accepted Article near their diurnal home-ranges throughout the breeding season. Males of Screaming, but roost use. Females of both Shiny and Screaming Cowbirds mainly used a communal roost Radio-tagging birds allowed us toanalyse individualthe temporal and spatial patterns of presentedWe datadynamics onthe roostof brood useby cowbirds. of two species parasitic DISCUSSION departures occurred during the time window of parasitism (Fig. 3B). Cowbirds 100% parasitism of eventsoccurred well andsunrise, before 22% roost of roost departures coinciding with the parasitism time window (Fig. 3A). In Screaming Table S1). 0.001, Shiny Cowbirds both species, earlier in Screaming than Shiny Cowbirds (Mann-Whitney U-test, Online Supporting Material Table S1). Parasitic events occurred in a short time window in This by is protectedarticle reserved. Allrights copyright. Whitney CowbirdScreaming roost the left earlierfemales thanShiny(Mann- Cowbird females Timing ofroostdepartures parasitism andevents 0/1 respectively). and (0/4 records the of of respectively,records the control two‘pairs’show didnotany while inany the association ‘pairs’. The pairstracked three were recorded associated intheroostin12/12, 11/12and3/4 of association during the day showed higher levels of association in the roost than control CowbirdScreaming were and malesfemales that trappedshowed and together highlevels Association between Screaming Cowbird pairs In Shiny Cowbirds, 86% of parasitic events occurred before sunrise, with 59% of U -test, -test, U = 41.5, n = 21, Screaming Cowbirds P < 0.001, Shiny< 0.001, Cowbirds n n = 11, Online Supporting Material = 19, Screaming Cowbirds z = 4.6, = n = 11, = 11, P < Accepted Article This by is protectedarticle reserved. Allrights copyright. Thesewithinroosts. maytobe related parasitesfindings thatthese the brood fact must (Scardamaglia& Reboreda2014), andshowedof fidelity highlevels both between and close range of their diurnal home-ranges, namely areas the where they search for host nests roosting behaviour, remains achallenge research.for further potential host nests occurs, and how the balance costsof and benefits combine to determine followed be a must significant liability. Identifying whether information transfer about those thatIn typicallylaying,before sincecowbird follow. fact, being females eggs destroy hypothesis, this identifydoes not scenario informed animals, only but the for benefits for prospected target (Gloag probably uninformeddue to ‘tailing’that those previously a fly determinedly females towards recorded Shiny inthe where Cowbird, hostarrive at frequentlyfemales in nests tandems, additionalroosting communally.to benefit activeIndirect evidence forhas been following information not on feeding sites but on the location of suitable nests,target seems a likely do. cowbirds, thepossibilityindividuals In that mayeavesdrop,females acquiring that information havenot good on of the location suchcan obtain feeding sites knowledge from suchasroostsassemblages couldworkas information centres,where do that individuals mate (Bijleveld increased anti-predator predator vigilanceor andhigherprobability confusion) finding a of cowbirdscommunally for includea lower mayprobability predation risk, dilutionof (through communally roostingspecies (reviewed by 1999), Beauchamp the benefits of roosting thanearlier Shiny females. Cowbird parasitism. ScreamingCowbird departed females from the roostparasitized and nests before and after sunrise, a with offraction departures coinciding with the time window of association maintained their in theroostnight. at species both of Females lefttheroost Shinynot and communal shared the pairs roost, Screaming Cowbirdsoffemales’ Cowbirds Shiny Cowbird females andShinyboth Screaming females Cowbirds sexes used roostsof Cowbird within radio-taggedMost cowbirds were groups. foundroostinginlarge Similar toother et al. et 2010). Furthermore, (1973) andZahaviWard proposed thatbird et al. 2013). As with the foraging version of the Ward-Zahavi Accepted Article This by is protectedarticle reserved. Allrights copyright. consequently do not need to navigate in the dark with idea is consistent because they this hostrelocatesearch donot orfor nests and wethat find didnot roostingShinymale near inthe area Cowbirds diurnalhome-rangestheir more important than reducingdistance the betweenroosting-site and nest.target The fact a veryin intensity.Navigating conditions of well-known from light low areamaytherefore be roostingleavetheir and navigate place towards nests host windowa limited within time and information, O’Keefe & Nadelinformation,& O’Keefe 1978) inbothas sexes inthis species, theto opposed sex relative enlargement of hippocampusthe(an of area in braininvolved the encoding spatial alongside presence hostofnearfemalesguarding. nestsissimply the result Themate the day, remains unclearwhether it activelyiftasksthesetheir ormales in participate relocate neststogether (Friedmann 1929,Mason since they1987),inpairs travel throughout has itproposedbeenWhile and that Cowbirds female male Screaming search and for diurnal social monogamy (Scardamaglia and2014) Reboreda extends totheroost aswell. 2017). shownareas in previous studies(Scardamaglia&2014, Reboreda Scardamaglia nocturnal additiontoroosting sites in theconstant diurnalhome-ranges and prospecting before parasitism. Moreover, inthis studycowbirdshow we that are their to faithful females ShinyCowbirdScreaming conducted and to prospectingfemales visitsdays hostneststhe by followinga Infemales. Scardamaglia informed study,related little having with locating of nestson layingfemales chance suitable target other days, than evidencesome that cowbird females fly the directlynestshost totargetroost from atdawn, way,inthis synchronizebe ableto laying host. ofthat their with This the study also provides ranges ondays,would consecutive which progresshost nests’ allow to females and monitor (2014) showedShinythat Cowbird diurnaland Screaming relativelymaintain stablefemales females search hostfor nests to Inmate. a previous study, Scardamaglia and Reboreda roost near areas of higher food availability and during move the morning to areas where Theassociationstrong roostingof pairs Cowbirds found Screaming for shows that . It It is possible that ShinyCowbird males et al. et (2017)showed that et al . Accepted Article percentage roost of departures oftiming thatoverlap distributionparasitism in with the cowbirds breeding duringthe Thebetweendifferenceobserved season. inthe species layinga day andconsequentlyor not, estimate numberhelp to the eggs of laid by female forage. The timing of departure from the roost may be a predictor of whether a female is on occurring afterwards have must been non-parasitic visitsor females leaving the roost to windowlayingtime have notbeenassociated with egg-laying, departures may most weThus, although cannot rule outthat departuressome roost occurred that during the 22%Screaming Cowbirddepartures of roost overlapped withthe parasitism time window. the later. dataOur roost supportthisexpectation. We found that59% Shiny of Cowbird and to lay,the only and willmorning searchingbe spent on nests, they leave and feeding for can egg of completion formation anddaylight. However,on days whennotan they have do egg roostingleavetheir and place nestsreach target within alimited time window,between our mating to that beennotknowledgeany explored has in to date. detail difference in systems mating responds to differences in parasitic specialization, an aspect of and copulatory behaviour of both species, it is reasonable to expect that the marked corroboration,systems stillneed and is information necessary more daily about the routines also2014),Reboreda confirmed byobservations our on roosting. genetic the While mating Shinysocial promiscuityillustrated by (Mason of Scardamaglia 1987,& the Cowbirds innumbersincrease both of andmates for & (Hauber females Dearborn asmales 2003), avianregarding systems predictcare theabsence that parental ofmating leadanto should strategy unusualamongbrood is parasites Dearborn&(Hauber Several 2003). hypotheses inthemfemalesor assist nestsearching and Thisrelocation. socially mating monogamous Sharing theroost would adaptive Screamingfor be guard Cowbirdpairs if just males male and female Screaming Cowbirds share the nest-searching and relocating tasks. where females search and host relocate with isconsistent alone, later for that ideathenests This by is protectedarticle reserved. Allrights copyright. betweendifferences found males andfemalesin (ReboredaShiny Cowbirds Parasitic cowbird asopposedParasitic nest-building to are constrained females, to species, et al. 1996), Accepted Article This by is protectedarticle reserved. Allrights copyright. Ethics statement: approvalrequirebe of published. to finalthe manuscript influence content on or submitted of the published the ourof None manuscript. funders yCientífica UniversityandTecnológica BuenosofAires. of our None funders had any ThiswasCONICET.work supported by Agencia grants Nacional de Promociónfrom ayTécnicasJ.C.R Research is (CONICET).Investigaciones Científicas Fellow of statement: Funding and DanielCampionipreparationEl Destino helpin Figure of for 1. thankFundaciónWe Elsa Shaw dePearson allowingfor to conductstudythe us in Reserve relatively poorly known aspects of the behaviour of brood parasites. Ourstudy howtheuse of illustrates radio-tracking technologies understandmayhelp to nestshost and timing the that roost of departures potentiallyparasiticbehaviour.can predict and Screaming Cowbirds roosted near the area whichat they searched for and parasitized parasitism time window inScreaming Cowbirds. potential underestimate ofthepercentage ofdepartures from theroost withthat coincide the times and access to locations,roost especially Screamingfor Cowbirds. This leads to a hand-held tracking receiver in the roost area. Hence, there was a limit on the recording of worked 24h a day,while departures from the roost were recorded byresearcherwith a a type event: of parasitism wereevents recorded by automatic data-loggers in the nests that earlier).or This different may tothe beattributed thatmethods wereused to recordeach recorded inthe -55 to-50 timebin butnomin roost departures recorded for thesame period departuresfor from earlier 50 than min before events may anunderestimatebe dueto early of bydepartures ScreamingData Cowbirds. To we summarize, showed that throughout breedingthe season females of Shiny All compliedwith work Argentinean Law. R.C.S wasNacionalde theR.C.S byscholarship Consejo supported from a sunrise are missing (there are parasitic events Accepted Article This by is protectedarticle reserved. Allrights copyright. T.Cruz, AndrewsA., and Manolis, R. Reproductiveinteractionsof (1990). Shiny the Cowbird B.Colwell, J.M. Lank (2007). andD. Conklin, a J., R. 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Auk 111:979–990. test the effect of droppings on plumage quality. Ibis 121:331–333. Radio-TrackingAcademic California.Diego, of Press,San Data. Wildlife Studywithareaduring area used day the (polygon), roostinglocationscentroids (2007).ofshiny Effectsparasitism on cowbird Accepted Article This by is protectedarticle reserved. Allrights copyright. distance betweenbelow95 nightsfalls the distances of settled if females at withinthe roost mean each random The night. observed a sample of 15 female Shiny Cowbirds and distribution offrequency expected observations 2. Figure correspond to 7 different females in 7 different nests. 11) wereevents (n= recorded byautomated the Baywingtelemetry at system nests and times(n28) correspond = 11Screaming to Cowbirddifferent in1-6 females days.Parasitism identified invideo-recordings) in20different nests. Screaming Cowbirdroostdeparture correspond a to different 18of maximum becould not femalesfemales (some reliably recordingsautomatedthe or telemetry at system Chalked-browedand Mockingbird nests different days. Shinyevents Cowbird parasitism= 21) (n wererecordedeither by video- Cowbird roost departure times (n = 97) correspond to 19 Shiny Cowbirdin females 1-14 differentat Shiny time intervals for Cowbird ( 3. Figure chance. femaleslocated they locationscloser the to significantly used previously byexpected than Distributionofproportion the of androost departures parasitic eventsoccurred that Observed betweenwithin distance each mean location of the female roost the for th percentile of the distribution, indicating percentile theof distribution, that A ) andScreaming Cowbird) ( B ) females. Shiny Accepted Article Figure 1

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