Satellite telemetry revealsindividual variation injuvenile Bonelli’seagledispersal areas
LuisCadahía & PascualLópez-López& VicenteUrios
Juan JoséNegro
AbstractNataldispersal isthetimeelapsedbetween departing fromthenatalsiteandsettlingtoattempt breedingforthefirsttime.Inlong-lived specieswith deferredsexualmaturity thisperiodmaylastseveralyears, makingthisprocesscrucialfortheirsurvivalandconser- vation.Herewepresentalarge-scaleoutlineofjuvenile Bonelli’s eagle’s dispersalareasintheIberianPeninsula. Wedescribetherangingandmovement patternsof14 juvenileBonelli’seaglesduringtheirdispersal period, studiedbysatellitetelemetry. Threedistinctphasesduring thejuveniles’firstyearoflifeweredetected,namely,the dependenceperiod,thedeparture fromtheparental territo- ry,andthesettlement indispersalareas.Ingeneral, between-sexdifferencesin relation to ranging behavior
CommunicatedbyC.Gortázar
L.Cadahía
CentreforEcological andEvolutionarySynthesis(CEES), DepartmentofBiology,UniversityofOslo,
P.O.Box1066Blindern,
0316Oslo,Norway
P.López-López(*)
Cavanilles InstituteofBiodiversityandEvolutionaryBiology, TerrestrialVertebratesGroup,University ofValencia,
PolígonodelaComas/n,
46980Paterna,Valencia,Spain e-mail:
V.Urios
GrupodeZoologíadeVertebrados,University ofAlicante, Apdo.correos99,
03080Alicante,Spain
J.J.Negro
EvolutionaryEcologyDepartment, EstaciónBiológicadeDoñana,CSIC,C/AmericoVespucios/n.IsladelaCartuja,
41092Sevilla,Spain
werenotsignificant.Interestingly,thereseemsnottobea few,clearlydelimited,overlappingBonelli’s eagle’s juve- niledispersalareaswithintheIberian Peninsula.Atotalof
17dispersal areasweredetected,withsomeanimals using morethanone.Theseareaswerelocated ineight autonomouscommunities(Spanishadministrative units), beingthemostimportantCastilla-LaManchaandAndalu- cía.Juveniles weremorefrequentlylocatedincultivated man-managedareas,withnon-irrigatedherbaceouscrops. Thisisprobablyduetohigherpreyavailabilityandhigher efficiencyinpreycapture intheseopenareas,aswellasto theabsenceofbreedingpairs.Thishasimportant manage- mentimplications, suggestingthatconservationefforts shouldfocusonthewholelandscape matrixofman- managedecosystemsratherthaninafewclearlydelimited geographicareas.
Keywords Aquilafasciata.Conservation.Dispersal. Hieraaetusfasciatus.Management.PTT.Raptors. Remotesensing
Introduction
Dispersalisanecologicalprocesswithimportant implica- tionsinspatialpopulationstructure,survival,and geneflow among populations(Clobertet al. 2001; Bullocket al.
2002),henceaffectingpersistence,evolution,andconser-
vationofspecies (Clobertetal.2001;Bullocketal.2002). Theecologicalandevolutionary aspectsofdispersalare directly linkedwiththeprocesses of‘nataldispersal’ (movementbetweenthebirthplaceandthefirstbreeding site)and‘breeding dispersal’(movementbetweensucces- sivebreedingsites;GreenwoodandHarvey1982),which aretheonesthatinvolveflowofindividualsandgenes
amongdifferentareasandpopulations.Thetimeelapsed betweendeparturefromthenatalsiteand settlingtoattempt breeding forthefirsttimemaylastseveralyearsinlong- livedspecieswithdeferredsexualmaturity.Thismakesthe fate ofdispersingindividualsduring thistimecrucial,since whetherornotanimalscompletesuccessfully thenatal dispersalperiodandtransmit theirgenestothenext generationwillimportantlyaffectthemaintenanceofthe speciesinthelong-term.
Bonelli’seagleAquila fasciata(Accipitridae, Falconi- formes)reachessexualmaturityat3–4years(Crampand Simmons1980).Thisbirdofpreyiscatalogued as“Least Concern” inEurope(BirdLifeInternational2009)andas “Endangered”inSpain(Real2004),where themain fraction ofthepopulationfromtheWesternPalaearctic dwells.Studyingdispersal inthisspecieshasbeen traditionallydifficult,basicallyowingtothelongmove- mentsthat juvenilesperform.Studieshavereliedonthe use ofringsandwing-tags (Cheylan etal.1996;Realand Mañosa2001;Hernández-Matíasetal2010)orconven- tionalradio-tracking(BalbontínandFerrer2009).However, thereisnoclearpictureofwherejuvenilesfromdifferent areasofthedistribution rangestayduringtheirjuvenile dispersalperioduntiltheyarerecruitedintothebreeding population.
Bonelli’seagle nestlingsfledgeatanapproximateageof
60days(Realetal.1998;Mínguez etal.2001)andspend severalweeksinthenestsurroundingsuntiltheyleavethe parentalterritory(Realetal.1998;Mínguezetal.2001; Balbontín 2003;Cadahíaetal.2005,2007).Previous studies based on direct observationsand radio-tracking datahaveshownthatjuvenile Bonelli’seaglesperform long-distance movementsandsettleintheso-called dispersalareas.Theseareasarecharacterizedbyhighprey abundance,mainlyrabbits andpigeons,wherejuveniles settleduringlong-timeperiodsbeforerecruitment intothe breedingpopulation,sometimes sharedwithjuveniles of otherraptorspeciessuchas GoldeneagleAquilachrysaetos andSpanishImperialeagle Aquilaadalberti(Cheylanetal.
1996;RealandMañosa2001;Balbontín 2003;Cadahíaet al.2005,2007;BalbontínandFerrer2009;Moleónetal.
2009a).However,dispersalareasholdseveralthreatsthat directly affectbirds’survival,mainlydirectpersecution, birdelectrocutionindangerouspolesofpowerlines,and poisoninginextensive gamereserves(Realetal.2001; Real2004;Cadahía etal.2005).Thishasbecome especially importantaftertherabbitviralhemorrhagic diseaseandmyxomatosisoutbreaks,whichhaveleadto theconfinementofBonelli’seagletoareaswith arelatively highlevelofhumaninfluence,henceincreasing juvenile’s mortalityrisk(Moleónetal2009a).Forthisreason,the accurate delineationoftheseareasisofparamount importance in order to establish adequate management
actionsaimedatensuringthelong-term persistenceofthe speciesinSpain.
Hereinwedescribethemovement andrangingpatterns of14Bonelli’s eaglesduringjuveniledispersalinSpain, usingcontinuous,long-term satellite trackingdata.The maingoalsofthisworkaretoexplorethedistancingpattern fromthenatalareas,andtooutlineanddescribe the dispersalareas,discussingtheimplications fortheconser- vationofthisendangeredspecies.
Methods
Between 2002and2004,wetagged14Bonelli’seagle juveniles,12nestlingsandtworecentfledglings, with satellitetransmitters(hereafterPTTs—platform transmitter terminals)ineasternSpain(autonomouscommunitiesof Catalonia, ValencianCommunity,andMurcia,encompass- ingalatitudinalrangebetween41°18′05′′Nto37°36′26′′ N;Fig.1).Allnests were locatedinrocky cliffs,exceptfor oneonapinetree,surroundedbyMediterraneanscrubland. Allbirdswereweighed,measured, andfittedwithPTTs usingaTeflonharness(Kenward2001).Birds’genderwas establishedbymolecular techniquesusingabloodsample (FridolfssonandEllegren1999).
Three typesofPTTswereused: five 30-gbattery poweredArgos/PTT-100s, seven35-gsolarpowered Argos/PTT-100s, andtwo45-gArgos/GPSPTT-100s, manufacturedbyMicrowaveTelemetry,Inc.( wavetelemetry.com). CombinedArgos/GPStransmitters permitbirdstobetracked bytheArgosandtheGPS systemssimultaneously, whereasfortheothertransmitters information wasprovidedbytheArgossystem.Trans- mitters weresettoan8-hon/120-hoffdutycycle,except forthetwoArgos/GPSPTTs,whichweresetto16-hon/
72-hoff.Transmitter weightneverexceeded3%ofthe birds’bodymass(2.1±0.5%SD;n=14;range,1.3–3.0%), asrecommendedbyKenward(2001).Todeterminebest timefortagging (ca.50daysold),nestlings’agewas estimated basedonfeatherandplumagepatternusinga spottingtelescope(Gil-Sánchez 2000).Whenactually handlingthe birds,we estimatedage morepreciselyas age=0.200×taillength(mm)+16.262 (Mañosaetal.1995).
Locations’initialmanagement wasmadebyArgos,a satellite-basedlocationreceptionanddatacollectionsys- tem.Asatellites networkcollectsPTTs’dataandrelays themtogroundprocessingstations(Argos2008).Argos/ PTTspositions arecomputed basedonmeasuring the Doppler shift (for a detailed description see Kenward
2001and Argos2008).Thissystemprovidessevenlocation classes(LCs)thatreflectthenominalaccuracyofeachdata. TheseLCsarenecessary becauseseveralfactors, either intrinsic or external to the PTT, may affect locations
Fig.1 LocationofBonelli’seaglejuveniles’dispersalareasinSpain.Natalnestsare representedbyastar.Notethatsomebirdsuseduptothree distinctdispersalareasduringnataldispersal
accuracy(thoroughlydiscussedinKenward2001;Soutullo etal.2007;Argos 2008).Inthisstudy,weusedLCs3,2, and1,withnominalaccuracy<250,250–500,and500–
1,500m,respectively (Argos2008).Wealsoincluded locationsoflowerquality(LC0,A,andB),butfiltered themusingavailableinformation oneagles’movements, basedoncomparisonswithhigh-qualityGPSdataandon Argosaccuracytests(Cadahíaetal.2007;Soutulloetal.
2007).Toavoidbiasconnectedwithspatialandtemporal autocorrelation,wecomputedtheharmonicmeansofallthe locationscollectedoneachgivenday(DixonandChapman
1980; Kenward 2001) and used them for subsequent
calculations.
Theonsetofdispersalwasconsideredtooccurwhenbirds flewbeyondtheaverageinter-nestdistance (11.4km)anddid notreturnwithinthatdistanceinthefollowingtwolocations, asdescribedinCadahíaetal.(2008).Tostudythedistancing patternattheonsetofdispersal,thefirstyearoflifewas dividedinto30-daylongmonthsandmonthlydistanceto natalnestwascomputedasthemeanofalldistanceswithina given month (Soutullo et al. 2006). For each bird, we
recordeddateandageattheonsetofdispersalandestimated homerangesusingkernelcontours (Worton1989;Kenward
2001)optimizedbyaleastsquarecrossvalidationprocedure
(Kenward2001;Kenwardetal.2001).Weconsideredas totalareathesurfaceenclosedwithina95%kernelofthe whole-transmitting-period collectedlocations.Dispersal areas’sizewasestimatedwiththe‘Animal MovementSA v2.04’extensionforArcView3.2(HoogeandEichenlaub
1997). Fordispersalareas estimation,weuseda25%kernel computed afterdeparturefromnatalareas.Weusedthis figureinparticular becausehourlyanddailydistances coveredwithinandoutsidethesoestimated areaswere observedtobesignificantlydifferent(Cadahíaetal.2007), enablingdistinction betweenexploratory movementsand settlements indispersalareas(Ferrer 2001).Inthose individualswithmorethanonedispersalarea,weconsidered thepooledsizeofallofthemforcalculations.Wecomputed thegravitycenterof dispersalareasas theharmonicmeanof allthelocations containedwithineacharea(Dixonand Chapman1980;Kenwardetal.2001)andmeasured the distancebetweenthispointandthenatalnestineachcase.In
birdswithmorethanonedispersalarea,weestimated this distance usingtheareawheretheystayedlonger.The numberof autonomouscommunities(Spanishadministrative units)withpartoftheirterritorywithinadispersalareawas alsoregistered.
WeusedaKruskal–Wallistesttosearchfordifferences amongmonthlydistancestonatalnestsduringthefirstyearof lifeandaGames–Howelltest(Zar1999)toperformmonthly pairwisecomparisons.TheMann–Whitneytestwasusedto testbetween-sexdifferencesindateandageatdispersal, differences inmaximumdistancereachedduringthewhole transmittingperiod,sizeoftotalrangesandnumber,andsize anddistancetonatalnestsofdispersalareas.
Toexplorewhetherjuveniles spentmoretimeincertain typesofhabitatthanexpected bychance,theGlobalLand- coverMap2000(Pekeletal.2003)wasusedtoroughly characterizedispersalareaintermsofsoilcoverage.This GIScoverageincludes18different habitattypes,varying fromforests,scrublands,cultivatedareas,wetlands,grass- lands,water bodies,andurban areas (foradetailed description seePekeletal.2003).Weusedthe‘Animal MovementSA v2.04’extensiontoselect50points randomlydistributedwithinthedispersal areasandthenthe
‘Getgridvalue’extension toassignaland-useclassbothto theserandompoints andtothetelemetrylocations.Weonly used thehighestqualitylocationclasses(LC3,2,and1)for thisanalysis.Tosearchforbetween-individualsdifferences inthehabitatoftheirdispersal areas,wecompared the frequency ofrandompointsineachtypeofcoverageusing contingency tables(Soutulloetal.2008b).Tofindout whetherbirdspreferablyselectedparticular habitattypes (within-individualsdifferences),wecomparedthefrequency ofeachtypeofcoverage ineachgroupofpoints,i.e., locations andrandompoints,usingaχ2 testforeach individual.AllstatisticalanalyseswereperformedwithSPSS
ver.13.0.Significancelevelwasestablishedatp0.05.
Results
Birdsweretrackedduringtheperiod2002–2006(Table 1). Theendoftransmissionoccurredduringthedispersalstage inallbirdsbutone,whichwasrecruited intothebreeding populationwhen itwas4yearsold(Cadahíaetal.2009).In relationtosex,females tendedtodisperseyounger(ageat dispersal:Mann–Whitney,U=4.000,Z=−2.160,p=0.034) butnotearlier thanmales(dispersal date:Mann–Whitney, U=12.000,Z=−0.926,p=0.414;Fig.2,Table2).Monthly distancevariedthroughoutthefirstyearoflife(Kruskal– Wallis,H=58.308,df=9,p0.001).Threedistinctphases were observed (Games–Howell,p0.069 in groups of similarmonths):aninitialstageofrestrictedmovements aroundthenestduringthethirdandfourthmonthsoflife
(the“dependenceperiod”),followedbyarapidincrease in distancetothe nest(includingthe “onsetofdispersal”),and asettlingfromtheseventhmonthonwards.Theonsetof dispersal, thathappenedsuddenlyandinshorttime, occurredbetweenthefifthandsixthmonthinfemales and inthesixthmonthinmales(Fig.2).
Consideringthewholetransmitting period,maximum distanceto natalnestsrangedbetween90 and 663km (after excluding birdsno.6,8,and12forwhichonlyafew locationsafterthe onsetofdispersalwererecorded)anddid notdifferbetweensexes(Mann–Whitney,U=17.500,Z=
−0.077,p=0.940),similartothetotalrangesizecoveredby juveniles(Mann–Whitney,U=8.000,Z=−1.543,p=0.148; Table2).Dispersalareas’sizeandtheirdistancetonatalnests didnotdifferbetweensexeseither(size:Mann–Whitney,U=
7.000,Z=−1.697,p=0.106;distance:Mann–Whitney,U=
17.000, Z=−0.154, p=0.940; Table 2). Dispersal areas encompassed landfromeightautonomouscommunities, mainlyCastilla-LaManchaandAndalucía(Fig.1,Table1). Interestingly,onlybirds7and11overlappedtheirdispersal areas,atleastpartially,whiletheothersremainedgeograph- icallyseparated(Fig.1).
Overall, ten land-use classes were present in the
dispersalareas,andsignificantdifferences werefound amongjuvenilesregardingthehabitatcompositionofthese areas(χ902=65.336,p=0.002).Inmostofthem,thehabitat class“cultivatedandmanaged areaswithnon-irrigated herbaceous crops”wasmostabundant,whereasothers showedamoreheterogeneous mixtureofhabitats.By individual,inallbirdsbuttwo(bird4:χ42=11.649,p=
0.02; bird 9: χ82=180.506, p0.001), there were no
differencesbetweenthefrequencyofsatellitelocationsin theassortment ofland-useclassesandtheproportionof thesehabitatsobserved withinthedispersalareas(remain- ingindividualsp0.115).Thus,juvenileswerefoundmore frequently inthemostabundanttypeofhabitat,i.e., “cultivated andmanagedareas,withnon-irrigatedherba- ceouscrops”,and,secondarily,in“cultivatedandmanaged areaswithirrigated herbaceouscrops”andin“closed scrubland”.Thetwobirdswithsignificantdifferenceswere alsofoundmorefrequently inthesetwotypesofland-use classes,althoughtheirdispersal areasshowedamore heterogeneoushabitat.Infact,nodifferences amongindividualswerefoundregardingthefrequencyoflocations inthedifferentland-useclasseswithintheirdispersalareas
(χ902=39.949,p=0.158).
Discussion
Thejuveniledispersalperiodhasremainedoneofthemost unknownstagesoftheBonelli’s eagle’s lifecyclesofar, mainlybecauseofthelong-distancemovementsthesebirds
Table1 Summarydataof14juvenileBonelli’seaglesstudiedbysatellitetelemetryinSpain
Bird / TypeofPTT / Origin / No. locations / No.
filteredlocations / Tagging date / Signal end / Transmitting time(days) / No.
dispersalareas / Autonomouscommunities includingdispersalareas
1 / Solar / Murcia / 115 / 63 / 22/04/2002 / 01/12/2002 / 223 / 1 / Murcia,Comunidad
Valenciana
2 / Solar / Valencia / 701 / 394 / 26/04/2002 / 12/06/2006 / 1,508 / 2 / ComunidadValenciana, Castilla-LaMancha, Murcia,Andalucía
3 / Solar / Alicante / 300 / 148 / 08/05/2002 / 14/01/2005 / 982 / 1 / Castilla-LaMancha
4 / Battery / Alicante / 144 / 64 / 08/05/2002 / 13/07/2003 / 431 / 1 / Castilla-LaMancha
5 / Solar / Castellón / 665 / 459 / 09/05/2002 / 04/03/2006 / 1,395 / 1 / Castilla-LaMancha
6 / Battery / Castellón / 17 / 10 / 09/05/2002 / 31/12/2002 / 236 / – / –
7 / Battery / Barcelona / 139 / 85 / 20/05/2002 / 23/11/2003 / 552 / 1 / Castilla-LaMancha
8 / Solar / Alicante / 25 / 15 / 30/04/2003 / 26/08/2003 / 118 / – / –
9 / GPS / Castellón / 885 / 876 / 14/05/2004 / 21/02/2005 / 283 / 2 / LaRioja,Navarra,Cataluña
10 / GPS / Castellón / 576 / 576 / 17/05/2004 / 13/11/2004 / 180 / 2 / Andalucía
11 / Solar / Tarragona / 248 / 160 / 11/06/2004 / 09/04/2006 / 667 / 3 / Madrid,Castilla-LaMancha
12 / Solar / Tarragona / 45 / 29 / 11/06/2004 / 20/09/2004 / 101 / – / –
13 / Battery / Alicante / 125 / 85 / 11/08/2004 / 18/02/2005 / 191 / 2 / Castilla-LaMancha,Andalucía
14 / Battery / Alicante / 120 / 67 / 11/08/2004 / 17/04/2005 / 249 / 1 / Andalucía
No.number
performduringthisperiod.Atpresent,theonlyavailable datacamefromtraditionalringing,wing-tags,andradio- tracking methods(e.g.,Cheylanetal.1996;Realand Mañosa2001;BalbontínandFerrer 2009;Hernández- Matíasetal.2010).However,althoughnecessarywhen nootherinformation isavailable,thesemethodsusually providefewdata(withsomeexceptions,e.g.,Hernández- Matíasetal. 2010),arehighlytimeconsumingandmaynot beeffective atgatheringgood-qualityinformationabout eagles’movements,giventhepotentialbiasduetobirds’ movementsoutsidesurveyedareasandthelimitedaccuracy ofdatathatcanbeobtained.Asanalternative, satellite telemetry allowscontinuoustrackingoftheindividuals, regardless oftheirrangingpatternsandthegeographic extensionoftheir movements (Cadahíaetal.2005; Soutullo etal.2006).Althoughthistechniqueisexpensive ineconomicterms,hencelimitingthenumberofbirdsthat canbetracked,itsmainadvantageisthatitisespecially usefultoobtainaccuratelocationssystematically and permitslong-termtrackingofbirds’ movements,insome casesaslongasbirdsarerecruited inthebreeding population (Uriosetal.2007;Cadahíaetal.2009).This information isthereforeespecially usefulinidentifyingthe mainthreatfactorsinrisk-assessment studiesaimedat establishingoptimalmanagementactions.
Thispaperpresentsalarge-scale outlineofjuvenile Bonelli’seagledispersalareasintheIberian Peninsula. Interestingly,thereseemsnottobeafew, clearlydelimited, overlapping,dispersalareaswithintheIberianPeninsula.
Bycontrast,althoughbirdstrackedinthisstudycomefrom awidegeographicrange,thereisnoclearoverlapbetween juveniledispersal areas,andeachbirdseemstousea different oneduringtheirfirstyearsoflife.Infact,17 dispersal areasweredetectedfor11birds,withsome animalsusingmorethanone.Thisindividualvariationhas importantmanagementimplicationsandthereforesuggests thatconservation effortsshouldfocusonthewhole landscapematrixofman-managedecosystemsratherthan inafewclearly delimitedgeographicareas.
Ourresultsshowthatthefirstmonthsofdispersalare madeupbyseveralphasesthatprobablyreflect successive stagesof the species’ ontogeny(Fig. 2; Soutulloet al.
2006).Initialmovementstake placewithinthe parental
territoryandrepresent theso-calleddependenceperiod,in whichjuveniles stilldependupontheirparentsintermsof food supply (Real et al. 1998; Ferrer 2001). Fledging occursinSpainwhennestlingsare44to69daysold(Real etal.1998; Mínguezetal.2001),andtheonsetofdispersal weregisteredheretookplacebetween114–177daysold (Table2).Hence,thepost-fledgingdependenceperiodin Bonelli’s eaglelasts70–108days,whichisinagreement withdatapreviouslyreportedwhenstudyingthespeciesby othermethods (Realetal.1998;Mínguezetal.2001; Balbontín2003).Averageageattheonsetofdispersalis coincident withformerstudieswiththespecies,with reported data of 142 days old (Cadahía et al. 2005),
147daysold(Balbontín2003),149daysold(Mínguezet al.2001),andslightlylowerthanthe163daysreported by
Fig.2 Evolutionofmonthlydistancetonatalnestin11Bonelli’s eaglejuvenilesduringtheirfirstyearoflife.Blackdotsmales;white dotsfemales; dottedlineallindividuals’mean(standarderror–SE linesaredepictedinthiscase)
Realetal.(1998).Inotherraptorspecies,likeSpanish
Imperialeagle orGoldeneagle(Ferrer2001;Soutulloetal.
2006),atransitional phasebetweenjuveniles’indepen- dencefromtheirparentsandthe definitedeparturefromthe parentalterritoryhasbeendescribed,named‘localdispers- al’byFerrer(2001).Unlikethesespecies,Bonelli’s eagle showscleardisperserbehavior(sensuWallsandKenward
1995),andoncejuvenilesleavetheparentalterritory, they coverlongdistances,withoutremaininginthesurroundings oftheirnatalarea.Thisbecomes evidentintheabrupt increaseintheaveragedistancetonatalnestduringthefifth andsixthmonth after birthinallbirds(Fig.2;forafurther discussiononthe estimationofthe onsetofdispersalinthis species,seeCadahíaetal.2008).
Aroundtheendofthefirstyear,weobserved aslightly (non-significant)decreasein the distance to natal nests (Fig.2),which iscaused byfourjuveniles’behavior. Interestingly,twomalesandtwofemalesperformedshort movementsoutoftheirusualdispersalareasandmoved towardstheirparentalterritories. Inthesemovements, approaches tothenatalnestsasshortas33kmwere recorded.Similar resultswerefoundbyBalbontínand Ferrer(2009)whoalsoreported natalreturnsduringthe secondyearof16radio-trackedjuvenileBonelli’s eagles comingfromtheCádizpopulation (southern Spain). Returnstonatalareashavebeenobserved inotherspecies, suchastheSpanishImperial eagle(Ferrer 2001),the Golden eagle(Uriosetal.2007),ortheCommonBuzzard Buteo buteo(WallsandKenward1995),andwerealready suggestedtooccurinBonelli’s eagle(RealandMañosa
2001).Thisbehaviorcouldbeexplainedbyfoodsearching strategiesbasedon theirpreviousknowledgeofthelocation
Table2 Range-relatedvariablesandbetween-sexdifferencesof14juvenileBonelli’seaglestrackedbysatellitetelemetryinSpain
BirdSexDispersaldateAgeatdispersal
(days)
Totalrange size(km2)
Max.distance nest(km)
Dispersalarea size(km2)
Distancedispersal area–natalnest(km)
1F01/08/20021505,2929090381
2M04/09/200217715,2053672,132245
3F09/08/2002150980185264148
4M16/08/200215839,1305896,929421
5F05/07/20021146,692541844442
6F31/07/2002135
_a367__
7F09/09/200216324,9386636,409534
8F_b
__19__
9M20/08/200415049,48834610,125321
10F22/08/200414717,4885923,815519
11M02/10/200415413,1264713,180433
12F15/09/2004141
_a377__
13F21/08/20041354,9562781,296256
14F03/09/200414863,7755487,906513
Males(n=4)2September±21160±1229,237±17,930443±1115,592±3,657355±89
Females(n=7)14August±22144±1517,732±21,956414±2253,062±3,049356±191
Max.–min.2October–5July177–11463,775–980663–9010,125–264534–81
Total21August±23148±1521,915±20,479425±1853,982±3,349356±156
Valuesrepresentmean±standarddeviation.Notethatforrange-relatedcalculationsonlyn=7femaleswereusedintheanalysis
aOnlyoneortwolocationswerereceivedafterdispersingfromtheparentalterritory,sonorangesizecouldbecomputedforthesebirds
bThisbirddidnotstartdispersalfromthenatalterritory
ofpreypatchesandbycheckingthebreedingpopulationin thesearchforavacancyinanactiveterritoryorapotential mate.
Inrelationtosex,significantinteractionsbetweensex andareaofbirth havebeenreported, withfemales dispersing fartherthanmalesanddiffering between populations(Hernández-Matías etal.2010).Different resultswerefoundbyBalbontínandFerrer(2009),who didnotfindbetween-sexdifferencesinrangingbehavior andmovement patternsofjuvenileBonelli’seagles.The maindifference betweenourstudyandotherswerethe distancesbetweenthenatalpopulation andthedispersal areas,shorterinthecaseofBalbontínandFerrer(2009), with two juvenile females recruited as far as 4.4 and
120.8kmfromtheirnatalnest,andlargerinHernández- Matíasetal(2010)thatreported ameannataldispersal distanceforrecruitedbirdsof107.1±103.5km,ranging from19.4to430km.Inourstudy,onlyafemale was recruitedinthebreedingpopulation441kmawayfromits natalnest(Cadahía etal.2009).Theseresultsruleoutthe existence of compulsory philopatryin the species, and couldbeaconsequenceofthedifferentoriginofthebirds tracked,fromtheCádizpopulation(BalbontínandFerrer
2009),Catalonia,andFrance(Hernández-Matíasetal2010) and from the eastern Iberian populations of the birds trackedinthisstudy.Differences inrangingbehaviorand recruitmentdistancesamongbirdsofdifferentgeographic originshouldbeexploredindetailinthefutureasmore birdsaretracked.Itwouldbelikelythatdispersal areasin southernSpaincouldbeactingaspopulation sinksfor juvenilescomingfromotherIberianpopulations(Moleónet al.2009a).Geographicvariation inpreyavailability could beanunderlyingmechanism explainingthetendencyof birdsofeasternpopulationstodispersefurtherthanthoseof southernpopulations(Moleónetal.2009b).
Thedevelopment oflightweightsatellitetrackinghas enabledresearcherstogainnewinsightsintojuvenilebird movements andareascoveredduringthisimportantlife stageofthisendangered species.Wehaveshownthat juvenileBonelli’seaglesuseduringdispersal anumberof areasdistantfromtheirparentalterritories. Ourstudy corroborates theautonomouscommunities ofCastilla-La ManchaandAndalucía(totalsurface=166.731km2,32.9% of theSpanishterritory)tobethosewiththemostimportant youngBonelli’sassemblages(specially theprovincesof Toledo,Albacete, andCádiz),butalsohighlightsthe relevance ofotherareasinnorthernandeasternSpain (between NavarraandLaRioja,innerCatalonia,and southernAlicante;Fig.1).Habitatcharacterizationpoints
outthatjuvenilesconcentrateinopenhabitats,particularly human-managedareaswithextensivenon-irrigatedcrops andherbaceousplants.Higherpreyavailability, suchas rabbitsorpartridgesintheseopenareas,alongwiththe
absenceofbreedingpairs,wouldaccountforthisprefer- enceandfor thespatialdistributionofdispersalareasinthe IberianPeninsula (Mañosa etal.1998;Real2004;Moleón etal.2009a).However,theseareasposeimportant threats, likedangerouspowerlines,ordirectpersecution, since,in someinstances,dispersalareasareplacedwithinthelimits ofprivatehuntingreserves inwhichpoisontocontrol predatorsisillegallyused(Realetal.2001;Real2004).
Thepossiblesource-sink dynamicsandtheexistenceof severalnon-overlapping dispersalareashavemajorimpli- cationsfortheconservation ofthespecies.Sincedispersal areasarelocatedoverterritories managedbydifferent autonomouscommunities withparticularjurisdictions,this bringsintofocustheneedfororganizationamongregional governmentstoundertakeinter-regionalconservationmeas- urestargetingthenon-breedingfractionofBonelli’s eagle population.Anadequate actionplanforthespecieswill needacombinationofinternational andinter-regional coordinatedactionsaimedatimprovingjuvenilesurvival. This,asdemographicstudiesofpopulationviabilityhave demonstrated (Soutulloetal.2008a),willultimatelybe reflectedinanenhancementofthepopulationtrendofthis endangeredspecies.
Acknowledgments Thisprojectwasprincipally fundedbyTerra NaturaFoundation.TheauthorsareindebtedtotheConselleriade TerritoriiHabitatgeoftheGeneralitat Valenciana(J.Jiménez,P. Mateache,A.Izquierdo,andA.García),ConsejeríadeIndustriay MedioAmbiente ofRegióndeMurcia(E.AledoandE.Cerezo), DepartamentdeMediAmbientoftheGeneralitatdeCataluña(X. Parellada),theUniversityofBarcelona(N.Pocino,J.Real,andA. Tintó),theICRA(M.R.JanéandT.Borau),theUniversityMiguel Hernández(M.CarreteandJ.A.Sánchez-Zapata),andtheSpanish Ministerio deMedioAmbiente(V.García andP.García)for inestimablefieldassistance,permissiontoaccessthenests,andpartial funding.M.Moléon,M.Ferrer,andanonymousreferee made interestingcommentsinanearlydraftofthismanuscript.L.C.and P.L.-L.weresupportedbyFPUgrantsoftheSpanishMinisteriode EducaciónyCiencia(references AP2001-1444andAP2005-0874, respectively). ThispaperwaspartofL.C.’sPhDthesisatthe UniversityofAlicante.Thefirsttwoauthorscontributedequallyto thispaper.
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