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J. Field Ornithol., 70(2):230-235

HABITAT COMPOSITION OF MAURITIUS KESTRELHOME RANGES

Jo ELLENCARTERANDMICHAELHUNT JONES,3Departmentof BiologyBoiseState UniversityBoise, Idaho 83725 USA

Abstract.--Lossof its original native forest habitat has been identified as one causeof thepopulation decline of the Mauritius Kestrel (Falcopunctatus).During the 1988-1989 breed-ing seasonwe examined the size and habitat compositionof the home rangesof two pairsof nesting Mauritius Kestrels,one located in a traditional location and the other in a newnest cavityat the edge of agricultural ields and other non-nativevegetation.Kestrelhomeranges were determined by radio tracking. Habitat typeswere identified using overstorycanopies nly.Nativevegetation omposed 2-41% of kestrelhome range area,with exoticwoodland,agricultural and, and scrubcomposing 5-40%. Kestrelswere observed akingprey from non-nativehabitats,and both pairs ledgedyoung.These MauritiusKestrels ppearto have adjustedsuccessfullyo non-nativehabitats.COMPOSICION ELHABITATQUE OCUPA ALCO UNCTATUSSinopsis.--Una de las causasde la reducci6n poblacional del Falc6n de Mauricio (Falcopunctatus)ha sido a pfirdida de habitat pot la destrucci6nde susbosques ativos.Durantela fipoca eproductiva e 1988-89 examinamos l tamafioy composici6n el habitatde fireasutilizadas home ranges) de dos paresde falcones.Una de estas ocalidades e encontrabaen un /trea tradicionaly la segundaen el borde de un campo agrfcolacon vegetaci6nno-nativa. Las fireasutilizadaspor las aves ueron determinadasutilizando radio localizaci6n.Seidentificaron os habitatsutilizando tan solo a vegetaci6ndel docel del bosque.De un 12-41% del /trea de utilizaci6nde las avesestuvocompuesta e vegetaci6n ativay de un 15-40% de firbolesex6ticos, ierra agricolay vegetaci6n rbustiva.Ambasparejascriaron en losdos tipos de habitatsy se observarona los falconescazandoen el /trea con vegataci6nno-nativa. E1 Falc6n de Mauricio parece haberseajustadoadecuadamente habitatsno-nativosen su lugar de origen.

The Mauritius Kestrel (Falco punctatus), one of the rarest falcons inthe word, is endemic to the island nation of Mauritius in the southwesternIndian Ocean (Temple 1977, Cade 1982,Jonesand Owadally1988). Be-causeof its preference for arboreal geckosand method of still-hunting,which requires an open canopy, he Mauritius Kestrelwasthought to bedependentupon native orest (Temple 1974, 1977, 1987;Jonesand Owa-daily 1988). Most of the kestrel'soriginal native forest habitat has beenlost to cultivation or commercialdevelopment (Cade and Jones 1993).The remaining native orest s severely ltered by invasionof exoticplantspecies,which changethe composition,structure,and densityof the for-est canopyand the understoryvegetation, n turn affectingthe availabilityof potential prey species.By 1974, MauritiusKestrelshad declinedto a1 Currentaddress: epartment f MedicalMicrobiology,he Ohio StateUniversity, olumbus,Ohio 43210 USA.9 Current address: epartmentof Evolution,Ecology, nd OrganismalBiology,The Ohio StateUniversity,Columbus,Ohio 43210 USA.Author to whom eprint equestshouldbesent.

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Vol. 0,No. MauritiusKestrel abitats [231low of four individualsn the wild (Temple1977). ntensive onservationefforts, ncluding releaseof captivelybred birds and those reared fromharvestedeggs nto areasof native vegetationand other habitats (Joneset al. 1991), have ed to recoveryof this species.Here we describe he size and habitat compositionof home rangesoftwo pairs of nestingMauritiusKestrels ccupying eterogeneous abitatsduring the late 1980s.One pair occupied a traditional nest cavity n theregion of the greatest emaining native forest,and the other occupiedanew nest cavityat the edge of degraded forest and agricultural fields.

METHODSStudyarea.--Mauritius s an oceanic,subtropical sland (1860 km2) inthe southwestern ndian Ocean, 800 km east of Madagascar.Since colo-nizationbegan n the 17th century,mostof the islandhasbeen clearedfor cultivation and development. nhabited by more than one millionpeople, most of the islandremains ural. Forests re limited primarilytosteepridgesand gorgesand someriparian areas.At the onsetof thisstudy,kestrelswere found only in the vicinity of the Black River Gorges (55km2) on the southwestcorner of the island, and only 10 nesting pairswere known.This area was he only region of the islandnot systematicallytreatedwith pesticidesCheke1987).Native reesstill occupymostof the

gorges,but manyareasare dominatedby one or more exoticspecies, ndother areasare a mosaicof native and non-nativespecies. he gorgesaresurroundedon all sidesby cultivated ands,providingavenuesor invasionof non-nativeplants.Breeding airs.--During the 1988-1989 breeding season, wo nestingpairs of Mauritius Kestrelswere studiedduring three nestingstages Table1). One pair used a traditional nest site on Mr. Zaco in the Black RiverGorges.Both birds were wild (i.e., not captively eared) but had beenbanded severalyears previouslyand had successfullyledged young thetwo seasons rior to the start of the presentstudy.The secondpair nestedon the Trois Mamellesmassifat the fringe of the gorges.The male wascaptively red and hackedapproximately km away,whereas he femalewasa wild bird. The male wasobserved ourting he female n September1988. The pair searched or cliff cavities acing forestedand unforestedaspects, nd eventuallychose a cavity acing agricultural and. This sitewas unique because t was the first nest cavity ocated outside forestedareas.

Both pairswere providedwith approximately30 g of white mice directlybelow heir respective estsitesdaily.Supplementaleedingwasbelievednecessary y the local kestrel conservationorganization, the MauritiusWildlife Appeal Fund, to facilitate reproductivesuccess nd conservationgoals.The behaviorof both male kestrelswasapparentlymodifiedby thissupplement because hey remained near the feeding site for approxi-mately 1-2 h prior to the feeding, and remained in the vicinity as longas the workersdelivering he food remained at the site.Habitat classification.--Nativeorest and many exotic tree and shrub

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232] J. E. Carter ndM. H. Jones j. Field rnithol.Spring 1999TABLE1. Mauritius Kestrel home range size and habitat composition or the Mt. Zaco andTrois Mamelles nest sites n 1988-1989. The bottom portion of the table shows hepercentageof habitat type within each home range, followedby the percentageof sta-

tistically ndependent radio tracking observationsmade in each habitat.Site

Mt. Mt. Trois Trois TroisZaco Zaco Mamelles Mamelles Mamelles

Sex male male maleNestingStage incubation post-fledging nestlingHome Range (kin2) 0.80 0.80 1.54Habitat Type (%)/Observations %)

male femalepost-fiedging post-fiedging1.61 0.79

Native forest 12/12 13/6 29/12 34/32 41/11Mixed exotic wood-land 40/54 40/37 1/0 0/0 0/0Agricultural 0/0 0/0 39/61 37/47 29/38Monotypicexotic 9/0 9/2 2/0 2/0 2/2Open ground 7/4 9/25 3/0 1/1 1/9Rock 3/4 2/0 10/15 6/5 10/9Scrub 25/15 24/27 15/7 18/6 16/16River Reserves 0/0 0/0 3/5 4/9 3/16Acacia 4/12 4/2 0/0 0/0 0/0

-For Mt. Zaco, this categorycombines he tecoma (Tabetruia allida) and terrainalia (Ter-minaha sp.) habitat types; or Trois Marnelies, his type wasprimarily Liane de Cerf (Hipragebenghalensis)

species n Mauritius have distinctive anopies hat are readilydistinguish-able from one another when viewed from vantagepoints available n theBlack River Gorgesarea. Native forest s heterogeneous n terms of speciescomposition and canopy structure, and native trees are taller than mostexotic vegetation. n contrast,many exotics orm monotypicstands, itherthrough deliberate planting or invasion of native vegetation. Further-more, many exotic species ave canopystructures hat are too dense orkestrel light, do not supportkestrelprey,or both (Jones1987). Kestrelshunt primarily in the inner portion of a tree's canopy by still-hunting(i.e., perching to watch prey and then pursuing by hopping or flyingamong he branches; ones1987). The structureof the overstory anopyis therefore important to kestrel ecology. By identifying habitat typesbasedsolelyon overstorycanopies,we produced habitat categoriesmean-ingful for kestrel research and conservation,and avoided the need toidentify vegetation communities using more rigorous floristic methodsrequiring extensivesamplingand ground truthing.

We used previousdescriptionsof native forest by Vaughan and Wiehe(1937, 1941) to identifynativehabitat ypes vailableo the breedingpairsincluded in this study (Table 1). Becausenative forest is now extensivelyinvadedby exotic plants (Lorrence and Sussman 988), we establishedthresholdof 25% canopycoverby native tree speciesor a habitat to beconsiderednative forest. Forestedareaswith less han 25% canopycoverwere defined as mixed exotic woodland. We also used Vaughan and Wie-

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Vol. 0,No. MauritiusKestrel abitats [233he's (1937, 1941) descriptionof riparian vegetation, alledriver reserves.Outside of the Black River Gorges,river reservesare narrow bands ofexotic trees and other vegetation,with native trees present in some lo-cations.Agricultural lands usuallyabut these corridors and are typicallyplanted in sugar cane. We identified an additional habitat type calledmonotypic exotic that included a single exotic specieswithin any onemapped habitat type. Habitat patcheswere mapped if they were a mini-mum of 25 m in one dimension.Radio tracking.--Kestrelswere captured using bal-chatri traps. Radiotransmitters Terry Roundy, Salt Lake City, Utah, U.S.A.) weighing ap-proximately g (3.1-3.5% of kestrelbodymass)were clipped o the twocentral retrices,as describedby Kenward(1978, 1980). Batterieswerefield-replaceable, acilitating continuous tracking and minimizing han-dling. Three-channel eceivers RB4 "Falconer,"CustomElectronics, r-bana, Illinois, U.S.A.) with three-element hand-held Yagi antennas andearphoneswere used to locate the birds. Signaldirection wasdeterminedusing the null-averagemethod.Kestrelswere observedduring three nesting stages, ncluding incuba-tion, nestling,and post-fledging ver a 3-mo period from October 1988-January 1989. Locationswere triangulatedevery 15 min during each ob-servationperiod using at least two receivers.Samplingwas conducted0600-1800 h, at 3-10 h intervals.Each hour of the day from 0600-1800h was sampled an equivalent number of times. We tested for indepen-dence of data points following Schoener (1981) and Swihart and Slade(1985). Upper and lower critical t2/r 9 valueswere calculated or eachbird. If data were autocorrelated for the 15-min observation intervals, weused longer time intervals (i.e., multiples of 15) until data achieved n-dependence.Homerangesizeand habitatusedetermination.--Homeange sizesweredetermined using he minimum convexpolygonmethod (Macdonaldetal. 1980, Schoener 1981). Total size of home range and habitat type areaswithin home-rangepolygonswere calculatedusinga digitizer.From thesewe calculated he percentagesof habitat typesavailable o each individualkestrel during each nesting stage.

RESULTS AND DISCUSSIONMauritius Kestrelsmaintained home ranges hat encompassedmosaicsof native and non-nativehabitat types Table 1). For the Trois Mamellespair, native forestand agricultural and each accounted or roughly33%of the birds' home ranges,with scrub and rock making up most of therest. Some 47-61% of the observations of the male and 38% of the femaleat Trois Mamelles were made in sugar cane fields. Both birds were fre-quentlyobserved aking Calontes ersicolor,50-gexotic errestrialagamidlizard that was common only in sugar cane fields. This was the first re-corded instance of agricultural land being used for hunting within aMauritius Kestrel home range. Kestrels rom Trois Mamelles were ob-served hunting on the wing, hovering, and hopping or sitting on the

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234] J. E. Carter ndM. H. Jones J.Fieldrnithol.Spring 1999ground, unusual behavior for this species.The home range of the TroisMamellesmale was 1.5 km2, roughly wice he sizeof the Mt. Zaco male.However, his male was a yearling, and this washis first nestingattempt.The Trois Mamelles pair successfullyledged young the year this studywas conducted.

Most of the Mt. Zaco male home range was made up of mixed exoticwoodland 40%) and scrub 25%), while only 12% wasnative orest Ta-ble 1). The relativeproportionsof thesehabitat types aried ittle betweennesting stages,but the proportion of times the Mt. Zaco male was ob-served n each habitat type changedsubstantiallyor most habitat typesfrom the incubation o post-fledging tage Table 1). One of the predom-inant non-native rees n severalhabitats n the Mt. Zaco home range wasTerminaliasp. This tree typicallyhas arge diameterbranches, relativelyopen canopystructure,and peelingbark, characteristicshat are believedfavorable or Phelsuma eckos, he kestrels'primarypreyspeciesGardner1984, Jones 1985). Carter (1991) found that severalnon-native tree spe-cies n Mauritius Kestrel home ranges, ncluding Terminalia,supportedPhelsuma opulationsgreater than those n native forest, but that otherexotic speciessupported few geckos.The Mt. Zaco pair also successfullyfledged young the year of this study.Prior to this study, t was believed that even though home ranges n-cluded non-nativehabitat types,kestrelswould nevertheless ely heavilyon native forest for prey. Although the number of kestrelsexamined inthis studywas nsufficient o draw conclusionsegardinghabitat use, ourdata show that Mauritius Kestrels selected home ranges that includedrelativelysmall proportionsof native forest, and that kestrelsdid not ap-pear to spend a disproportionateamount of time in native forest relativeto other habitats.Supplemental eeding undoubtedly had an effect onkestrel behavior and the way in which the data can be interpreted, butthe importanceof supplemental eeding to MauritiusKestrelconservationat the time of this study clearly outweighed short-term researchgoals.Since this studywas completed, kestrelshave been observed o nest innon-native habitats on many parts of the island not known to be previ-ouslyoccupied.By 1991 there were asmany as 145 non-captivendividualson the island (Cade andJones1993,Joneset al. 1991), and by 1996 some100 breeding pairs in the wild.

ACKNOWLEDGMENTS

This work was conducted n collaborationwith and supported by the Mauritius WildlifeAppeal Fund, ForestryQuarters,Black River,Mauritius.Principal financial supportcamefrom the Raptor ResearchCenter at BoiseState Universityand the World Center for Birdsof Prey n Boise, daho, with additional ogistical upportprovidedby Air Mauritius.We thankC. Jones, R. Lewis, L. Duverge, L. Jenkins, R.-M. Cretien, K. Swinnerton,and K. Evans orkestrel researchassistancen Mauritius. Botanicalassistance as providedby D. Lorrence,W. Strahm, and the staff at the Mauritius Sugar Research nstitute herbarium. Thanks to J.Munger, M. Bechard,and T. Cade for their many forms of guidance,and to E. Atkinson,K.Bildstein,and C. R. Chandler for additionalhelpful comments.

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Vol. 0,No. MauritiusKestrel abitats [235LITERATURE CITED

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