Long-termmonitoringofaninsularpopulationofBarbary Falcon
Falcoperegrinuspelegrinoides
ManuelSiverio1*,FelipeSiverio2,Beneharo Rodríguez3andAiram Rodríguez4
1Constitución 17-3, E-38410 Los Realejos, Tenerife, Canary Islands, Spain
2Los Barros 21, E-38420 Los Realejos, Tenerife, Canary Islands, Spain
3La Malecita s/n,E-38480 Buenavista del Norte, Tenerife, Canary Islands, Spain
4Department ofEvolutionary Ecology, Estación Biológica de Doñana, CSIC,Avda. Américo Vespucio s/n,E-41092 Seville, Spain
* Corresponding author, e-mail:
Territoryspacingandbreedingratesofaninsularpopulation(north-westernTenerife,CanaryIslands)ofBarbaryFalcon Falcoperegrinuspelegrinoideswasstudiedfrom1993to2008.Thepopulationincreasedconstantlysincetheoutset,from twopairsin1993to12in2008.Meandensitywas5.48pairsper100km²andmeannearestneighbourdistance was
3119m.Theregularityofthespatialdistributionpatternofthenests,observedinmostyears,maybemaintainedinthefuture despitetheexpectationthatnewpairsmayoccupystill-vacantterritories.Consideringthe79breedingattemptsanalysed,the meannumber of fledged youngperterritorial pairwas1.92,perlaying pairwas2.0 (n=76),andpersuccessfulpairwas2.24 (n=68).Nosignificantvariationswereobservedbetweentheannualmeannumberoffledgedyoungperlayingpair,nor betweenthenumberof fledgedyoungof pairsaccordingto densityina5kmradius.Allfledglings(broodsizeoneto four)left thenestinthemonthofMay. Inordertoavoidaffectingbreedingsuccess,sportingactivitiespractisedinthebreedingareas mustbe correctly managed by the appropriate authorities.
Introduction
The taxonomic status of the Barbary Falcon is still notentirelyclear,sinceithasbeenregardedbothas asubspeciesof PeregrineFalcon(Falcoperegrinus pelegrinoides;DelHoyoet al.1994)andasadistinct species(F. pelegrinoides;CrampandSimmons1980, Ferguson-Lees and Christie 2001). With few exceptions, resident falcons in the Canary Islands show Barbary phenotypes(Delgadoetal.1999,Rodríguezetal.2011). Apreliminarygeneticstudy,inwhichthreefalconsfrom the Canary Islands with Barbary phenotypes were used, showedhybridisationwithPeregrineFalconF. p. brookei, astwoof thesebirdsampleshadidenticalhaplotypesto thelatter(Amengualetal.1996).Other preliminarystudies show a very close genetic relationship between Barbary FalconandPeregrineFalcon,whichindicatesthat the former ‘represents a subspecies rather than a true species’ (WinkandSeibold1996,Winketal.2000).
Mainlyasaconsequenceof theuseof dichlorodiphenyl- trichloroethane (DDT) and derivatives, populations of Peregrine Falconfromdifferentgeographical areas decreaseddramaticallyduringthe1950sand1960s(Cade etal.1988,Ratcliffe1993).After theprohibitionoforgano- chlorated pesticides and with increased legal protection, the greater part of those populations has gradually recovered naturallyorbymeansof reintroductionprogrammes (Castellanosetal.1997,HorneandFielding2002,Powell et al.2002,Dzialaket al.2005,SielickiandMizera2009). Although the precise causes are unknown, the falcons in the Canary Islandswererarely seen atleast from the
1950s to mid-1990s (Rodríguez et al. 2009). Indeed, ina census carried out in 1987 and 1988 only seven pairs were observed,andtheirdistributionwaslimitedtotheeastern islandsandisletsof thisarchipelago:Fuerteventura, Lanzarote,AlegranzaandMontañaClara(Hernándezet al. 1991). Falcons are currently present on all the islands andthenumberofpairshasbeenestimatedtobeabout
144(Siverioetal.2009).Theirpresenceontheisland of Tenerifehasbeenknownsincethebeginningof the twentieth century (Thanner 1909), but the uncertainty surrounding subsequent sightings led to their being consid- eredextinctfor manyyears(Hernándezetal.1991).Once nestingwasconfirmedin1991(Hernándezet al.1992), their numbers have increased until the present day, and 35 pairsisthelatestpopulationestimatefor theentireareaof the island (Rodríguez etal. 2009).
In general, the density and breeding parameters of manysubspeciesofPeregrineFalconhavebeenstudied in depth (Mearns and Newton 1988, Mendelsohn 1988, Ratcliffe1993,Zuberogoitiaet al.2002,Rizzolliet al.2005, VerdejoandLópez-López2008).Withtheexceptionof the Canaries, where their biology and ecology have received someattention(Delgadoetal.1999,RodríguezandSiverio
2006,Rodríguezet al.2007),theacquiredknowledgeof the Barbary Falcon throughout itsdistribution range is still scant (Ferguson-Lees and Christie 2001). In this regard, many of the data available regarding Morocco, its area of occupa- tionclosestto theCanaries,areconfusingsincetheycould alsopertaintoothersympatricracesofPeregrineFalcon
(Thévenotetal.2003).Inthepresentstudyweassessthe
100 km
ATLANTICOCEAN
evolutionof demographicandreproductiveparametersin an increasing Barbary Falcon population during 16 years. Our maingoalsaretodescribeannualvariationindensity, nestspacingandbreedingrates, andevaluatetheeffect of density on breeding performance.
Canary Islands
AFRICA
La Palma
Enlarged area
Tenerife
La Gomera
Lanzarote
Fuerteventura
28° N
Studyarea
Our studyareaissituatedinthenorth-westsectorof Tenerife, the highest (3 718 m) and largest (2 034 km2) islandof theCanarianarchipelago,locatedsome100km off thenorth-westcoastof Africa(Figure1). Thiszoneisa verysteepmassifknownasTeno,of whicharound105km² have been studied (taking into account its coastal platforms) withinanaltituderangeof 0–1350m. Thesouth-west flankischaracterisedbythepresenceofagreatseacliff (c. 12kmlongandwithseveralsectorsalmost500mhigh) cut byasuccessionof perpendiculardeepravines.Oneof thebest-preservedlaurelforestsinTenerifeistobefoundin themiddlealtitudezonesof thenorthernflanks.Thehuman populationof theareaisestimatedat 10770inhabitants ( distributed in villages (inland valleys) andtowns(particularlyonthecoastalplatforms).A good partof thissurfaceareaisincludedintheCanarianNetwork
El HierroGran Canaria
CANARYISLANDS
15° W
Tenerife study area
AFRICA
of ProtectedNaturalAreas(Governmentof theCanary Islands): Parque Rural de Teno (80.63 km²) and Sitio de Interés Científico de Interián (1.01 km2).
Methods
ATLANTICOCEAN
TENERIFE
N
WE
Duringthebreedingseason(February–May)from1993to
2008thepreviouslyoccupiedterritoriesof BarbaryFalcon werevisited,inadditionto potentialbreedingsites(allthe cliffsoftheTenomassif, bothcoastalandinland,were inspected).Itwasassumedthat aterritorywasbeing occupied when the birds frequently used perching sites, courtingbehaviourwasobserved,or, inthemajorityof cases,whenthenestwaslocated.In orderto assess breedingrates, nestsurveillancewasperformedwith telescopes (20–60×) and binoculars atdistances ranging from250to 600m. In orderto estimatethedistancesto the nearestneighboursaglobalpositioningsystemreceptor andageographicinformationsystem (ArcView3.2)were used.On thoseoccasionswhentheirpositioncouldnotbe established,becauseof thedifficultorographicconditions, thepointonthebreedingcliffwherethebehaviourof the birdspointed clearlyto theexistenceof anest(nestlings calling, adults bringing prey and newly fledged young) was takenintoaccount.Theageofbreedingbirds(adultsor youngof2cy)andthesexofthefledglingsweredetermined bymeansof thecolorationpatternsandsize,respectively (Ferguson-Lees and Christie 2001).
Inordertoavoidbiasinthereproductiveparameters, breedingpairswerecloselymonitoredfromanearlydate (February),todeterminewhichpairslaideggs(takingturns duringincubation)orwhichfailed.Todefinethereproduc- tive parameters we consulted Steenhof and Newton (2007). The populationgrowth rate was calculated by means ofthe formular=Ln(Nt−No)/t,whereNtisthefinalnumberofpairs,
No theinitialnumberofpairs,andtisthenumberofyears
elapsed.Theannualrateof multiplicationwasestimatedwith
S
Figure 1:MapoftheCanarianarchipelagoshowingthestudyarea forBarbary Falcon on the island ofTenerife
theformulaλ=er,affordingtheannualgrowthrate(%)as (λ−1)×100.Theregularityofthespatialdistributionofthe nestingsiteswasanalysedbymeanoftheG-statistic(based on thegeometric mean/arithmetic mean ratio of thesquared distancesbetweennearestnests),whoserangeofvalues variesbetween0and1, andwouldindicatearegularnest spacingifitisgreaterthan0.65(Brown1975).Toassess the possible repercussion of pair density on reproduc- tion,wehaveexaminedannuallythesizeofthebroodsas afunctionofthenumberofneighbourpairs(0,1,2,3and
4–5)inaradiusof5km. Thesaidsurfaceareawaschosen after weighingupthemeandistancesandrangesbetween neighbouringnests,bothof PeregrineFalcon(Ratcliffe1993, Gainzarainet al.2000,Zuberogoitiaet al.2002)andBarbary Falconinourstudyarea.Thedatawereanalysed bymeans ofthe Kruskal-Wallisnon-parametrictestandthe chi-squared test(SokalandRohlf1981).Themeanvaluesarefollowed bythestandarderror(±SE).
Results
Density
Thepopulationincreasedfromtwopairsin1993to12 in2008(r=0.119,λ=12.7%;Figure2a).Fouroutof10
new territories were occupied by young females. Their subsequent mating, once adulthood was reached, involved oneadultandthreeyoungmales.Inanotherterritory, also occupiedforthefirsttime, thepairconsistedofanadult femaleandayoungmale.Birdsof theremainingterrito- ries (63.6%) were adults. Moreover, a paired adult male was replaced by a young male approximately one year after disappearing from the territory.
Mean density for the entire study period was
5.48 ±0.64 pairs per 100 km2(range 1.90–11.43). Mean distance between nearest-neighbour nests varied signifi- cantlybetweenyears(H15 =50.81,p0.001;Figure2b)and
12(a)
10
8
6
4
2
theoverallmeanwas3119±332m(n=16).Inmost years (n=12)thespatialdistributionpatternwasregular(Figure2c). Thenumberofnestsrecordedperterritoryfluctuatedbetween oneandfive(mean2.27±0.38).Inthoseterritorieswithmore thanonenest, thesewerealwaysverycloselyplacedonthe samerockface(200m),withtheexceptionsofsixover
1000mdistantfromthelastnestused.
Reproductive parameters
Reproductive parameterswereanalysed using79breeding attempts.Takentogether,152chicksfledgedthenest, themeannumberoffledgedyoungperterritorialpairwas
1.92±0.12,thatperlayingpairwas2.0±0.12(n=76), andthat persuccessfulpairwas2.24±0.10(n=68).The nestingsuccess(proportionof layingpairsthatraiseat least one young) was 89.5%. Mean annual productivity (number of fledgedyoung/layingpairs)didnotvarysignificantly betweenyears(H15 =20.55,p0.05;Figure2d),andno
differenceswereobservedbetweenproductivityofpairs
with0,1,2,3and4–5neighbouringterritoriesinaradius of5km(H4 =5.792,p0.05).Twobreedingattemptsby themixedpairs(adult–young)provedsuccessful,whilethe
7000
6000
5000
4000
3000
2000
1.0
0.9
0.8
0.7
0.6
0.5
(b)
(c)
remainderofthesepairs(n=3)didnotlayeggsjudging by their behaviour. The breeding success observed in 74 breedingattemptsofadultpairswas89.2%(n=66).All thefledglingsthat leftthenestdidsoduringthemonthof May, andthebroodsizevariedbetweenoneandfour: 14 (20.6%)hadonefledging,27(39.7%)hadtwo, 24(35.3%) hadthree,andthree(4.4%)hadfour. Fledgingsexcould bedeterminedin49individualsbelongingto22broods,of
0.4
(d)
2
4
3
3346 6
487
2 247
7
which 61.2% were male (χ2
=12, p 0.01).
1
Discussion
0
Density
In themid-1980s,noneof thepresentterritoriesof the studyareawasoccupied(FS andMSpers.obs.), andthe scantsightingsoffalconsbothintheremainderofTenerife
YEAR
andinotherwesternislandsof theCanarianarchipelago weresketchy(Hernándezetal.1991).After thelackof informationsincethebeginningof thelastcentury(see Introduction),thefirst reliableobservationsofBarbary FalconsinTenerifetookplacerelativelyfrequentlyduring
1989/90at Teno(Rodríguezet al.2009),wheretwopairs were confirmed to have bred one year later (Hernández et al.1992).Alltheabovepointsto arecolonisationof Teno (and,byextension,of Tenerifealso),beginningintheyears immediately preceding the study period, probably from the easternCanaries(SiverioandConcepción2004)orfrom
Figure2:Annualvariation(1993–2008)in(a)numberofpairs, (b)meandistancebetweenneighbouringnests,(c)spatialdistribution pattern, and (d) mean productivity ofthe Barbary Falcon population at TenoMassif(Tenerife),CanaryIslands.Productivitywascalculatedas thenumberof fledgedyoungperlayingpair(theannualsamplesize doesnotrefertothetotalofpairs,butpairsthatcouldbemonitored)
north-westAfrica. Thisapparentexpansion,whichbegan likewisetobeobservedintheremainingcentralandwestern islands(Delgadoetal.1999),mighthavealsotakenplace
from North Africa towards the Sahel, where observations of thebirdshavecontinuedtoincrease(BrouwerandMullié
2000).Thehugepopulationincreaseinourstudyarea,asin theCanaryIslandsingeneral(Siverioet al.2009),couldbe becauseofcoincidenceofseveralfactors including,among others,legalprotectionofthespeciesandhighavailabilityof foodresources(nowadays,feralpigeonsconstituteaplague in many natural sites ofthe islands; MS pers. obs.).
If population dynamics during the Teno study are taken intoaccount,thecasesof youngterritorialfemalesand mixedpairs(adult–young) detectedcannotbetakento indicateanegativetendency(e.g. replacementofbirds inducedbyhumanpersecution),asreportedfor stable populationsoffalconsandotherbirdsofprey(Ferreretal.
2003,Pandolfietal.2004).On thecontrary,ourexamples (sightedthroughoutthemonitoring period)appearto be morerelatedto populationgrowthinanenclavewithahigh load capacity, where the young produced occupy optimal vacantsites, attimesonanindividualbasis(females).On theotherhand,theuseof newnestswithinaterritorycould notbeattributedtosubstitutionsofbreedingfemales(see Zuberogoitiaetal.2002for thePeregrineFalcon)owingto the factthatthe birds were unmarked.
Fortheentireislandof Tenerife,Rodríguezet al.(2007) foundadensityof 1.27pairs100km2 andameandistance betweenneighbouringnestsof5868m.Inthisstudy, the importance of Teno is already noteworthy (given the high availabilityofsuitablecliffsandotherfactors)asbeingone of theareasof theislandwithagreaterdensityof Barbary Falcon.Thus, theavailabilityof thesecliffsfavoursthe abundanceof falconsandotherrupicolousspecies,both here(Rodríguezetal.2007,Siverioetal.2007,Rodríguez et al.2010,presentstudy)andincontinentalenvironments (Newton1988,Gainzarainetal.2000,JenkinsandvanZyl
2005,Rizzollietal.2005).On theotherhand,annualdiffer- encesindistancesbetweenneighbouringnestsdetected in Teno are because theywere greater when there were fewerpairsatthebeginningofthestudy. Whentheir numbersubsequentlyincreased,theabundanceoftrophic resources may have minimised intraspecific conflicts and, consequently,favouredtheregularityof thespatialdistribu- tionpatternrecordedinmostyears(seee.g.Solonen1993). On theotherhand,theirregularityofthespatialdistribution pattern observed between 2005 and 2007 (Figure 2c) was causedbyanewpairestablishedatamuchgreaterthan averagedistance(5 000m). Consideringthat Tenostill offers potentialnestingterritories,itisforeseeablethatthe populationwillcontinuetoincreaseandwhenitstabilises (c.15pairs)spatialregularitywillbemaintained.Indeed, intheItalianAlps,thespacingof astablepopulationof PeregrineFalconwasalwaysregularineachof thesix yearsstudied (Rizzolli et al.2005), although intheCape Peninsula (South Africa) observed spacing was irregular, probablybecauseof theequallyirregulardistributionof cliff sites (Jenkins and van Zyl 2005).
Breedingparameters
Thevaluesofthebreedingparametersofourstudyarewithin therangeof thoserecordedinpopulationsof Peregrine Falcon (see reviews in Zuberogoitia et al. 2002, Rizzolli et al.2005).ForF.p.babylonicus,averysimilarracetothat
dealt with here, the scant data published give the most usual brood size astwo(Dementiev 1957). According to theavailableinformationonthefewpopulationsof Barbary Falcon monitored, particularly in the Canaries, no disparity is observed between the mean values found in the islands and thoseofthestudyarea(Table1). Thesoleexceptionisthe considerablyhighervalueof theTenofledgingrate(fledged young/successfulpairs)versusthat oftheislandofTenerife (Teno included), which may well be caused by a greater sampleintheformercase(Table1).
It is highly probable that the very scant rainfall in our study area (mean values for March–April, 2000–2008:
37.68±6.5mm,range11.2–74.8; com) does not limit productivity, as occurs in other regions where rainfall is abundant (Mearns and Newton 1988, Olsen andOlsen1989,Zuberogoitiaet al.2002).Moreover,ifwe considerthatagreatnumberofnestsitesinTenoareon cliff ledges under an overhang and in cavities (MS pers. obs.), theabsenceof differencesbetweenyearsisnot surprising.Afurtherfactorlimitingproductivityinbirdsof preyistheavailabilityofpreyspecies(Newton1979).In our study area, both wild and feral pigeons Columba livia are abundant and may represent a substantial contribu- tiontothedietduringchickrearing(93.3%,n=45nest preydeliveryobservations).It isnoteworthythat insome populationsofPeregrineFalconthecontinuousavailability of largeprey,suchaspigeons,implieshighproductivity (López-López etal. 2009).
In birdsof prey,populationincreasecanalsoinvolve decreased productivity, as the new pairs occupy lower- qualityterritories(presenceandabsenceof floatingpopula- tion,trophicresources,etc.), andnarrowingof territories (FerrerandDonázar1996,Carreteetal2006).However, inTeno,eventakingintoaccountthegradualdecrease in distance between neighbour territories (Figure 2c), thegoodqualityof territoriescouldminimisethedensity- dependenteffectonproductivity.Thecausesofbreeding failure(10.5%)mayhavebeenrelatedto thedisappear- anceof amaleduringincubation,theapparentnestrobbing ordepredationofabroodatearly-stageandtheprobable infertilityof theeggsof sixclutches(incubationwasverified, but no chicks were subsequently observed).
Conservation
Both the information contained in the present study and thatprovidedbyRodríguezetal.(2007)andDelgadoet al.(1999)for allofTenerifeandthearchipelago,respec- tively,provideevidencethat Tenoisoneofthebestareas forBarbaryFalconintheCanaries.Despitethefactthat its population has, in general, increased in the Canarian archipelago (Rodríguezet al.2009),itsconservation status (IUCN criteria) remains Endangered (Siverio and Concepción2004).Thegreaterpartof theterritoriesare locatedinProtectedNaturalAreasof theCanaryIslands, anditisthusimprobablethat itsnestinghabitatwillbe significantlymodified,at leastintheshortandmedium term. Despìtealltheabove,manypeoplepractiseoutdoor sportssuchasrockclimbing,abseiling,andhang-gliding inTenoandothersites,implyingapotentialriskforthe falcons, as well as other birds of prey, during the breeding season.Indeed,itisknownthattheproductivityofthe
Table1:Productivityestimatesforpopulationsof theBarbaryFalconacrossitsdistributionrange.Samplesizeisshowninbracketsfollowed by the number ofyears monitored
Region
Mean number offledging young per pair
Territorial pairLaying pairSuccessful pair
Source
Morocco––2.30 (10; ?)Thévenot etal. (2003) Lanzarote – 2.53 (54; 7) 2.48 (37; 5) Delgado etal. (1999) Tenerife 1.55 (37; 2) – 1.76 (30; 2) Rodríguez etal. (2007) Teno 1.92 (79; 16) 2.00 (76; 16) 2.24 (68; 16) This study
Peregrine Falcon is lower in nests situated on rock faces whereclimbingispractised,unlikesitesthat remain undisturbedbysuchactivity(Brambillaet al.2004).On the other hand, since the Barbary Falcon population began to increase in Teno and in the Canaries in general, problems have arisen between certain pigeon fanciers (because of pigeon capture) and hunters (for alleged disloyal competi- tion) on the one hand, and the appropriateauthorities on the other. Although such conflicts should be resolved, the most pressing issue atpresent is the efficient management by the relevant authorities of the above-mentioned sporting activi- ties where necessary. Likewise, before implementation of conservation measures such as modifying the legal conser- vationstatus of thespecies,werecommendacensusbe undertaken of the entire Canarian archipelago in order to assess the current statuscorrectly.
Acknowledgements — All expenses incurred during this study were defrayed by the authors. We thank Pauline Agnew and Luis Cadahía for assisting with the English translation, FranciscoM Gonzálezforlogisticsupport,andPilarBelloforpreparingFigure
1.ThanksarealsoduetoIñigoZuberogoitiaforhiscriticalreview ofthe initial manuscript, and two anonymous referees for their valuable comments and corrections.
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Received July 2010, acceptedAugust 2011
Editor: M Virani