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Home , Crested serpent eagle, Microhierax, Philippine eagle

TheAuk 115(3):713-726,1998

PHILIPPINE OF PREY: INTERRELATIONS AMONG HABITAT, MORPHOLOGY, AND BEHAVIOR

ANITA GAMAUF, • MONIKA I•RELEUTHNER,AND HANS WINKLER2 KonradLorenz-Institute for ComparativeEthology, Austrian Academy of Sciences,A-1160 Vienna,Austria

ABSTRACT.--Wesought to clarify relationshipsamong morphometrics, behavior, and eco- logicalvariables for 21 speciesof raptorsin the .Morphological space was de- fined by 42 externalcharacters analyzed as shapevariables with respectto body length (without tail). Seventeenvariables were usedto characterizehabitat and five to characterize foragingbehavior. Three PCA componentsaccounted for 68%of the total variancein the habitatdata and separated living in denseforests from those using degraded habitats or coastalareas. Two PCA components explained 81% of thevariance in huntingmode, with transitionsfrom sit-and-waitto flap-gliding,and with contrastsbetween soaring and flap- gliding.Three PCA components accounted for 70.5%of thevariance in morphologicalshape. Thefirst component separated species with narrowwings and less-pronounced notches from specieswith broad,deeply notched wings. The secondand third componentswere associ- ated with the contrastbetween pointed and roundedwings and prey-captureapparatus (feet,bill). Five morphologicalcharacters were highly correlated(R = 0.934)with the first principalcomponent of thehabitat data, indicating that species inhabiting forested habitats havesquare tails, roundedwings, and strongclaws. Hunting modeand habitatalso were closelyrelated (R = 0.900).Soaring correlated well with the numberof notchedprimaries, tail shape,and measuresof the trophicapparatus, but poorlywith wing loadingand aspect ratio.Behavior, ecology, and morphologyof this subsetof raptorswere closely interrelated. Amongthe Philippine raptors, species that inhabit rain forests are the most endangered, and we suggestthat morphologicalconstraints limit their useof secondaryhabitats. Received 21 January1997, accepted2 February1998.

DIFFERENCES IN EXTERNAL MORPHOLOGY the designof birdsand their environment (Led- amongspecies can reliably predict differences erer 1984, Winkler 198% Wainwright 1991). in habitatuse and foragingbehavior That this Commondifficulties in ecomorphologicalanal- is true is the premiseof ecomorphologicalanal- ysesof this kind are charactersets that contain ysesof communities(Karr and James1975, only few or irrelevantcharacters, or both (Leis- Leisler 1980, Miles and Ricklefs 1984, Niemi ler and Winkler 1997).Analyses of closelyre- 1985,Miles et al. 1987,Wiens 1989). Yet, this as- lated speciesare usually most successfulin sumptionis rarelytested with dataon behavior showingecomorphological relationships (Led- and habitat acquired simultaneouslyin the erer 1984, Leisler and Winkler 1985), whereas field, and comparativelyfew studieshave at- hypothesesof wider phylogeneticscope face tempted to clarify relationshipsamong mor- increasingdifficulties because of oversimplifi- phometryand the behavioror environmentof cation(Lederer 1984) and becausephylogeny the speciesin question(but see Leisler et al. may confoundanalyses at the communitylevel 1989,Price 1991, Landmann and Winding 1993, (Miles et al. 1987). Stiles1995). Such work is neededto corroborate To strike a balance between the difficulties premisesof ecomorphologyand to providethe noted above, we studied the diurnal birds of necessarylink between resourceuse, perfor- prey of the Philippines.This group is ecologi- mance,and morphologydemanded for a deep- cally and phylogeneticallywell definedbut is er understandingof the relationshipbetween heterogeneousenough to mediate between studiesconfined to closelyrelated species and thoseof guildsand communities.So far, no in- • Presentaddress: Museum of Natural History, De- partment of Vertebrate Zoology, Bird Collection, tegrativeinvestigations are availablefor birds Burgring 7, A-1014 Vienna, Austria. of prey, althoughsome studies on size differ- 2Address correspondence to this author.E-mail: ences(Schoener 1984) and morphology(Ro- h.winkler@klivv. oeaw. ac.at chon-Duvigneaud1952, Voous 1969, Nieboer 713 714 GAMAUF,PRELEUTHNER, AND WINKLER [Auk, Vol. 115

1973, Brown 1976, Bierregaard1978, Jaksi• Historie (Leiden, The Netherlands), Universitets 1985,Kemp and Crowe 1994,Hertel 1995,Jen- ZoologiskeMuseum (Koberthavn,Denmark), Zool- kins 1995) exist in which morphologicalpat- ogischesMuseum der Humboldt Universit•it(Ber- terns were relatedto someaspects of ecology. lin), StaatlichesNaturhistorisches Museum Braun- schweig(Brunswick, Germany), Naturhistorisches However,studies on raptorsthat combinedata Museum Wien (Vienna), American Museum of Nat- on hunting modes and habitat use have not ural History (New York), SmithsonianInstitution beenattempted. The Philippinesis an excellent (Washington,D.C.), Field Museum of Natural His- area for this kind of investigationbecause a tory (Chicago),Museum of Natural History (Cincin- large variety of raptor speciescan be observed nati, USA), Delaware Museum of Natural History in an area of less than 300,000 km 2. Moreover, (Wilmington,USA), National Museumof the Phil- habitatsin thePhilippines span distinctive eco- ippines(), Wildlife BiologyLaboratory at the logical gradientsfrom tropical primary rain Universityof the Philippines(Los Barios),and the forest to deforestedregions and coastlines. ZoologicalGarden (Manila). Originally, the Philippineswere almostcom- Up to 39 study skinsof adult specimenswere an- alyzed for commonspecies, whereas for pletelycovered by tropicalrain forest.Because and ,the number of individualswas much the proportion of forested area was reduced smaller.Sex ratios within samplesof speciesvaried from 58 to 17% between 1932 and 1991, several between0.45 and 0.55. Externalmorphological fea- speciesof raptors currently are threatenedby tureswere measured mostly as defined in Leislerand extinction (Collins et al. 1991, Dickinson et al. Winkler (1985,1991). The flight apparatuswas rep- 1991, ICBP 1992, Collar et al. 1994). resentedwith 23 variables.These included length of Our objectiveswere to: (1) examine the all primaries;length of alula;lengths of the first,cen- strength,consistency, and functionalbasis of tral, and innermostsecondaries; lengths of outerand the relationshipsamong foraging mode, habitat central rectrices;and wing length. Also used were use,and morphologyin this assemblageof rap- the primaryprojection, or Kipp'sdistance, measured asthe distancefrom the wing tip to the first second- tors; and (2) integratethese findings with re- ary; and tail gradation,the differencein lengthbe- spect to the questionof morphologicalcon- tween the innermostand outermostrectrices (Leisler straints on behavior and habitat use. We also and Winkler 1985, 1991). The mean correlation(ab- discussthe consequencesof our findingsfor the solutevalues) within this data set was 0.525 (range future of thesespecies in the faceof continued 0.007to 0.991).Thirteen characters represented mor- habitat loss. phologyof the hind limb. They comprisedall toe lengths,talon chords, and diametersof talonsat the METHODS base,and lengthof the tarsus.The meancorrelation among these variableswas 0.395 (range 0.005 to Speciesand study areas.--Members of three of the 0.977).The length,width, and depth of the bill were five falconiformfamilies (del Hoyo et al. 1994)occur measured:(1) includingthe cereat the baseof the in the Philippines(Dickinson et al. 1991).We were bill, and (2) on the bill proper at the distal edge of able to observe21 speciesof 14 genera(Appendix), the cere.The meancorrelation among these six char- includingthree endemicspecies and nine endemic acterswas 0.532 (range 0.006 to 0.935). subspecies. Two additionalcharacters, aspect ratio (wing span Habitatanalyses and behavioral observations were squareddivided by wing area) and wing loading made during a field study over a period of 9.5 (body massdivided by wing area),were calculated months(January to April 1993,November to Febru- fromphotographs of soaringbirds. Data for the Phil- ary 1994, and March to July 1994). Investigations ippineFalconet (Microhierax erythrogenys) were taken were carried out in 19 study areasat elevationsrang- from a freshlykilled specimen.No suitablephoto- ing from sealevel to 2,500m on the islandsof graphswere availablefor the Philippinesubspecies (Sierra Madre, and ;Mt. Makiling, of Jerdon'sBaza (Avicedajerdoni magnirostris), so we Laguna), (Mt. Kitanglad,; Car- usedphotographs of its closestequivalent, the Pacif- men-Cantilan,; Mt. Apo, DavaoCity ic Baza (A. subcristata)from the Australian region and North ;Initao, ), and (Marchantand Higgins1993). We alsohad no pho- (El Nido and BacuitArchipel, northern Pa- tographsof the EasternMarsh Harrier (Circusspilon- lawan). Observationsin eachparticular area lasted otus).Photographs were scannedusing the computer from a few daysto threeweeks. programImagein 3.0, and contrastof the silhouettes Morphometry.--Studyskins were measuredusing wasenhanced with programCoral Photopaint3.0 to 384 specimensfrom various museum collections: optimize image analysiswith program Lucia 2.11. British Museum (Tring), National Museumof Scot- All measurementsof soaringbirds refer to fully out- land (Edinburgh),Rijks Museum van Natuurlijke stretchedwings. Becausethe tail can be fanned to July1998] EcomorphologyofPhilippine Raptors 715

TABLE1. Characteristicsof the flightapparatus of 16Philippine raptors and one ecological equivalent from Australia (in brackets).

Linear- Wing Wing ized loading loading wing Bodymass Bodylength w/o tail w/tail load- (g) (cm) Aspect ratio (N m 2) (N m 2) ing Species M F M F M F M F M F F [Avicedasubcristata] 307 347 40.0 5.64 5.95 20.6 25.0 17.6 20.1 0.209 Pernisptilorhyncus 1,000 58.0 65.0 5.68 5.61 34.4 30.8 30.0 23.4 0.179 Pernis celebensis 679 738 53.5 55.4 5.32 5.41 26.0 26.0 22.4 22.4 0.175 Haliastur indus 450 581 47.1 48.9 6.26 6.45 17.2 21.3 15.6 19.6 0.171 Haliaeetusleucogaster 2,570 3,150 70.0 77.0 7.67 7.25 44.4 46.3 43.0 42.6 0.209 Spilornischeela 688 853 52.4 54.5 5.26 5.29 25.5 28.9 22.5 25.6 0.185 Accipitervirgatus 95 154 25.7 28.1 4.72 4.34 21.1 28.4 16.5 22.2 0.247 Accipitertrivirgatus 199 353 33.2 37.5 5.75 5.77 25.4 35.9 19.7 27.7 0.241 Accipitersoloensis 156 204 27.8 29.0 5.68 6.14 27.3 33.1 22.1 26.9 0.256 Butastur indicus 375 433 42.6 42.9 6.34 6.44 27.2 30.7 22.0 25.8 0.216 Pithecophagajefferyi 4,464 6,000 95.2 105.2 3.89 3.83 48.7 51.0 42.2 44.3 0.178 Hieraaetus kienerii 733 800 46.8 52.6 5.61 5.68 33.2 31.6 27.1 26.1 0.200 Spizaetuscirrhatus 1,360 1,600 58.4 64.9 5.48 5.35 44.9 41.9 37.2 33.5 0.214 Spizaetusphilippensis -- 1,225 56.6 58.2 4.98 4.55 -- 46.5 -- 38.5 0.203 Microhieraxerythrogenys 46 52 15.9 17.2 5.74 5.66 25.4 26.4 21.9 22.9 0.217 Falco tinnunculus 186 217 33.8 36.2 7.07 6.92 24.1 24.5 18.0 18.4 0.268 Falcoperegrinus 650 1,000 48.9 52.8 5.61 6.13 47.5 57.2 39.1 46.8 0.266

variousdegrees, we used60 ø as the standardtail-fan- were carried out primarily for the study of birds ning anglefor measurementsof all species,and the within the forest interior. To maximize the number silhouetteswere modified accordingly. This value is of different individuals, large areas(30 to 50 km2) the approximateaverage angle shownby soaring were investigatedusing both methods.These two birds. Relevant values were calculated as described methodshave been used successfullyin other stud- in Pennycuick(1975), Kerlinger (1989), and Norberg iesof tropicalforest raptors (Thiollay 1989, Whiracre (1990). Wing loading (N m 2)was calculatedaccord- et al. 1992). Sample sizes ranged from 2 to 219 ob- ing to Norberg(1990), either with the tail excluded servationsper species.Only specieswith morethan or included.The two measuresof wing loadingdiffer five observationswere included in subsequentanal- widely in long-tailedspecies (Table 1). We also cal- yses. culatedlinearized wing loading(Jaksi• and Caroth- Behavioral and habitat variables were noted si- ers 1985),except that we usedthe sum of wing and multaneouslyfor eachundisturbed hunting raptor at body area instead of wing area alone. Body-mass the first sighting.To assureas much statisticalin- data were taken from Bennet (1986), Goodman and dependenceas possible (see Hejl et al. 1990),the be- Gonzales(1989), Dunning (1993), Marchant and havior of raptorson the wing was recordedagain Higgins (1993),and del Hoyo et al. (1994),and from only afterfive minuteshad elapsedand, for perched labelsattached to museumspecimens. individuals, additional data were taken only after All measurements were taken as indices relative to the birdshad changedtheir perches.These second- bodylength (total body length minus tail length)be- ary observationscomprise only 1.1% of the total of causewe intendedto analyzeaspects of shaperather 896 observations. than size (Mosimann1970), and all measurements Five behavioral traits associatedwith hunting were log-transformed.Even in raptors with pro- were chosen:perching, powered flight (continuous nouncedsexual size dimorphism,morphological flapping),flap-gliding, gliding, and soaring(Kerlin- variationbetween the sexesis low comparedwith ger 1989).Perching denotes a searchmode during that amongspecies (see Leisler and Winkler 1991). whichthe bird scansits surroundingsfrom a perch. Therefore,we usedspecies' means for all analyses. Whengliding, the wingsare held stretchedout from Fielddata.--Point observations (>2 h per observa- the body in a fixed positionwithout flapping, and tion) were carried out at exposedsites, e.g. cliffs, the flight path is more or lessstraight. Soaring is a clearings,and prominenttrees. Through recurrent circulargliding mode used to gain altitudein ther- visitsto eachpoint at differenttimes of the day,the mals or slope updrafts. Poweredflight comprises observationscovered the full daylightperiod (0600 two forms, continuousflapping and flap-gliding to 1800). Observationsmade along line transects (powerglide),a flightmode during which flapping is 716 GAMAUF,PRELEUTHNER, AND WINKLER [Auk, Vol. 115 interspersedwith gliding.The data were analyzed as EPe ptilorhyncus arcsine square-root transformed percentagesex- Pe celebensis pressingthe proportionof thesebehavioral modes in Av jerdoni the observations. To characterizehabitat use by raptors,we estimat- Sp cheela ed forestcanopy cover and the proportion(in 5% in- crements)of 16 habitat types (primary rain forest, Ac soloensis secondaryrain forest, degraded secondaryforest, • Ac virgatustrivlrgatus tree plantations,clearings, fallow land, grassland, pasture,banana, rice, other cultivation,road, settle- Pi jefferyi ment, water, coconuts,cliffs) within a 250-m radius Sp cirrhatus of the locationof everybird that we observed.Data were averagedfor each speciesand then arcsine Sp philippensis square-roottransformed for analyses. Hi kienedi

Data analysis.--Thedata were evaluated using Ha indus principal componentsanalysis (PCA) and stepwise multivariate regressionanalysis. Principal compo- Ha leucogaster nents were based on correlation matrices. Particular- ly when many charactersare used, there may be EZ'ø,Z2 many relevant componentsjudged by eigenvalues >1. In orderto avoidover-interpretation of the data, Bu indicus however,we adoptedthe followingcriterion: a com- El caeruleus ponentwas deemedto be relevantif its correspond- ing eigenvaluewas greaterthan 1 in 95% of 10,000 bootstrapsamples and explainedmore than 10%of Fa severus the total variance.By applyingthis rule,we avoided Fa peregrinus discussing"significanW but biologically irrelevant FaMI orythrogenystinnunculus components.PCA was used solelyto describerela- tionshipswithin our dataset, which was not intend- FIG. 1. Classificationof Philippineraptors used ed to representa sampleof a large,unknown statis- to computeindependent contrasts. ticalpopulation. The results of thebootstrap analysis were alsohelpful in the interpretationof component loadings.Stepwise methods have been widely criti- analysisresults. The variableswere analyzedwith cized (seeJames and McCulloch 1990), mainly be- multiple linear regressionthrough the origin (Fel- causethey do not guaranteea selectionof the most senstein1985). The independentcontrasts were rath- influential variables or even the best correlations. er sensitiveto thebranch lengths. Therefore, in some Consequently,we used stepwisemultiple regression caseswe alsopresent results with correctionsthat as- analysismainly to showthat a particularset of data sume constantbranch lengthsbetween nodes.We canbe usedto predictthe criterionvariable; we have used independentcontrasts only as a meansof re- alsotried to point out the biologicalrelevance of the ducingbias, and not as estimatesfor correlatedevo- variablesselected in eachindividual case.Although lutionarychanges; that is, we did not necessarilyas- we cannotrule out the possibilitythat othervariable sume that characters evolved homogeneously combinationsmay produce better predictions,we throughoutthe phylogenyof the group.All results are confidentthat our resultsprovide good estimates of the regressionanalyses are presentedas plots of for the strengthof the associationamong ecological the observed values of the criterion variable based on attributes,behavior, and morphology. predictionsfrom the multipleregression equations. Similaritiesdue to phylogeneticinertia may cause To conservethe functionalrelationship, and to dis- statisticalbias in correlationalanalyses (Felsenstein playthe positionsof individualspecies in thescatter, 1985,Harvey and Pagel1991). Available phylogenet- we presentthe relationsof the originalvariables and ic analysesof raptorsare widely divergentand do not those of the contrasts. All calculations were car- not include all of the taxa treatedby us. Therefore, ried out with programswritten by us. we constructedour own phylogenetictree (Fig. 1) basedon studiesby De Boer and Sinoo(1984), Boyce RESULTS and White (1987), Olsen et al. (1989), Marchant and Higgins (1993), Seibold et al. (1993), Helbig et al. (1994),Holdaway (1994), Griffiths (1994),Wink and Habitat.--Amongthe 21 raptorsstudied, 13 Seibold(1995), and Wink et al. (in press). speciesoccurred in habitatswith more than Independentcontrasts were computed for the sta- 50% forest cover and therefore were defined as tistical evaluationof stepwisemultiple regression forest dwellers;the other 8 speciesoccupied July1998] EcomorphologyofPhilippine Raptors 717

mainly abovethe canopyin the secondcom- 1oo ponent (t = 1.68, P = 0.121). Behavior.--Twoprincipal components ex-

75 /• PPP•Hk• plained81% of the overallvariation in hunting mode (n = 18 species).PC1 explained48% of o the variation (eigenvalue= 2.57) and was as- sociated with the transition from sit-and-wait to flap-glidinghunting modes. PC2 explained 33% of the variation (eigenvalue= 1.26) and representedthe contrastbetween soaring and Fti /• 'e Ate the other flight modes.This suggeststhat in

o these birds, the difference between the use of 0 20 40 60 80 100 % foresl cover differentflight modeswas nearly as important as the transition from active-search to sit-and- FIC. 2. The relationshipbetween height above groundat whicha speciesforages and forestcover in wait hunting. Philippineraptors. Open circlesdenote species that Morphology.--Threeprincipal components hunt abovethe canopy,filled circlesdenote species accounted for 70.5% of the variation associated thatinhabit forest interior, and open triangles denote with flight and feeding apparatus.PC1 ex- speciesthat useopen habitats. See Appendix for the plained 36% of the variation (eigenvalue= abbreviationsused to designatespecies. 15.25)and arranged the 21 speciesalong a con- tinuum from specieswith narrow wings and less-pronouncednotches to thosewith broad, openhabitats (Fig. 2). All forestdwellers except deeplynotched wings. The width of the wings the ChineseGoshawk (Accipiter soloensis) are was reflectedin a positive correlationwith residents.Four speciesof the open and semi- lengthof the innerprimaries (P1 to P6),the sec- openhabitats are winter visitorsonly. The for- ondaries, and the scapulars.PC2 combined est dwellers fall into two distinct groups (Fig. charactersof the flight apparatuswith claw 2): (1) four speciesthat hunt insidethe forest measurementsand explained20% of the total below the canopy(below 40 to 50 m), and (2) variance(eigenvalue = 8.51).With respectto nine speciesthat hunt within and abovethe the wing, this axis denotesa decreasein wing canopy zone. lengththat wasmainly due to a reduceddistal Three principalcomponents accounted for sectionof the wing and thus reducedpoint- 68%of the total variationin habitat(n = 18 spe- ednessof the wing (Kipp'sdistance), and to an cies).The first component(PC1) explained 34% increasein the numberof wing slots.The claw of the variation (eigenvalue= 5.83) and de- measurementsreferred to increasingly large scribedthe contrastbetween densely forested (length,diameter) inner and hind claws.Spe- habitatsand open and extremely"disturbed" ciesscoring high on this axis are well equipped habitats consisting of grasslands and rice for killing comparativelylarge prey with their fields.PC2 explained21% of the variation(ei- feet. PC3 explained14% of the total variance genvalue= 3.60)and was relatedto an increas- (eigenvalue= 6.01)and wasrelated to the feet ing proportion of water (effectively,the sea), and the bill; this componentrepresented the coconutpalms, and rocky areasin the habitat major variationin the feedingapparatus to- versusdegraded and secondaryforest stands getherwith the "killing-grip variables."PC3 and banana cultivations.PC3 explained13% of denotedan overallincrease in the lengthof the the variation(eigenvalue = 2.18)and described toestogether with lengthenedouter and mid- variation within cultivated areas, from settle- dle claws.Bill size increasedalong this axis mentsand neighboringfarming areas to aban- with a relativelysmaller increase of the distal doned fields. Much of the variation in habitat sectionand an almostparallel increaseof bill use concernedthe open countrybirds, as de- width and height.This axisthus represents an fined above.Forest species formed a tight clus- increasein the relative size of the captureap- ter, and those of the interior scoredlower on the paratus(feet) and bill that togetherare well first principal component(t = 3.06, P = 0.011) suited for killing avian or insectprey. but were not separatedfrom those hunting The sixthprimary (P6) canbe consideredas 718 GAMAUF,PRELEUTHNER, AND WINKLER [Auk, Vol. 115

sesssquare-cut tails and round, broad wings. They alsopossess hind limbsthat are typicalof raptorsthat prey on vertebrates. Stepwise multiple regression analysis of habitat using PC2 (forest interior vs. coastal) Sp.• Pj yieldeda high multiplecorrelation (R = 0.900, P < 0.0001)with three morphologicalpredic- •'c.) _.•AtoP• (•'oSC'sch Oppp tors. Wing length and tail gradationwere pos- itively correlated,and length of outer rectrices was negativelycorrelated, with the tail becom- ing morewedge-shaped with increasinguse of coastal habitats. When the clearly outlying White-belliedSea- (Haliaeetus leucogaster) -3 B was excludedfrom analysis,the multiple cor- •F• relation between the same variables and PC2 -6 -3 0 3 6 was still substantial(R = 0.785, P < 0.005), and Predictionfrom morphology the regressioncoefficients were similar. The F]•. 3. Morphologicalcorrelates of habitatuse in difference between the observed PC2 score of Philippineraptors. Results are from a multiple re- the sea-eagleand that calculatedfrom the re- gressionof morphologicalvariables as predictorsof gressionequation is well within acceptableer- habitat data basedon PC1 scores.Values predicted ror limits (deviation <90% of overall standard from the regressionequation are plotted on the X- deviation of observationsaround the regres- axis, and observedscores are plotted on the Y-axis. sion). The R-value was 0.596 (P > 0.05) when Of the five morphologicalvariables extracted, Kipp's distanceand length of central rectricesnegatively computedfrom standardizedindependent con- correlatedwith predictedhabitat use, and diameter trastsand 0.845 (P < 0.001) when computed of hina claw,length of inner toe, and lengthof in- with branchlengths set to equal. hermostseconda• positivelycorrelated with pre- The most important structuralhabitat vari- dicted habitat use (see text). ablewas canopycover (cf. Thiollay 1996). Step- wise multiple regressionanalysis with canopy a key structurefor the form of the wing. If P6 coveras the criterionvariable produced a mul- is long, the outer primaries (P7 to P10) are tiple correlationof R = 0.906(P < 0.0001),with short,giving the wing a roundedappearance. Kipp's distanceand lengthof centralrectrices If P6 is short,the outer primariesbecome lon- correlatingnegatively, and inner toe length and ger, and the wing is more slenderand pointed. bill heightcorrelating positively, with the pre- The lengthof P6 correlateswell with PC1 (r = diction(Fig. 4). Thecorresponding R-value was 0.89), and the lengths of P7 to P10 correlate 0.644 (P > 0.05; P < 0.05 using Kipp's distance negativelywith PC2 (r = -0.47 to -0.79). and tail length alone)for the standardizedin- Integration.--Toidentify morphologicalcor- dependentcontrasts and 0.901 (P < 0.0005)for relatesof habitatuse, we conducteda stepwise the independent contrasts calculated with multiple regressionanalysis using PC1 of the branchesset to equallength. As in the preced- habitat data against 42 morphologicalvari- ing analysis,these results indicate that raptors ables.The five morphologicalvariables extract- living in forestedareas tend to possessround- ed explained 87% of the total variance (R = ed wings. 0.934;Fig. 3). Two characters(Kipp's distance, Speciesof the forest interior differed from lengthof centralrectrices) were negatively cor- thosehunting within or abovethe canopyby related with predicted habitat use, whereas beingsmaller (t = 3.30,P = 0.007;log-values of length of the inner toe, diameterof the hind femalebody mass).No significantsize differ- claw, and length of the innermostsecondary enceswere found between the forest species were positivelycorrelated with predictedhab- and the opencountry species. itat use.The multiple R for the corresponding We expectedthat the most importantstruc- independent contrastswas 0.811 (P < 0.05). tural habitat variable, canopy cover, would Thus, speciesthat occurredin habitatswith a show the strongest associationwith flight higherpercentage of forestcover tend to pos- mode. Stepwise multiple regressionanalysis July1998] Ecomorphologyof Philippine Raptors 719

Pc.•_ppp •Sp o Aim_ / Ate 2

1 Bi ..

0 1 2 3 0 1 2 3 4 Predictionfrom morphology FIG.4. Morphologicalcorrelates of useof canopy coverby Philippineraptors. Results are from a mul- tiple regressionof morphologicalvariables as pre- dictorsof habitat canopycover. Values predicted from the regressionequation are plottedon the X- axis,and observedscores are plottedon the Y-axis. Of thefour morphological variables extracted, Kipp's distance,and length of innerremiges were negative- /-•6 Asø ly correlatedwith predictedcanopy cover, and inner toe lengthand bill depth(without cere) were posi- tively correlatedwith predictedcanopy cover (see text).

(backward variable selection)showed that the 0 I 2 3 4 searchmode used in foragingpredicted habitat Prediction from behavior use with respectto canopycover very well. Perching,gliding, and soaringaccounted for FIG. 5. Behavioralcorrelates of use of canopy 81%of thevariance in canopycover (R = 0.900, coverby Philippineraptors. Results are from a mul- P < 0.0001; R = 0.765, P < 0.01 for the stan- tiple regressionof behavioralvariables as predictors dardized independent contrasts).All coeffi- of habitatcanopy cover. Values predicted from the regressionequation are plotted on the X-axis, and cientswere positive;perching, however, was observedscores are plotted on the Y-axis.Three be- negativelycorrelated with theregression score. havioralvariables were extracted: perching, gliding, Basically,the resultsmean that soaringand andsoaring (see text). (A) Analysisbased on all spe- gliding occurred mainly in connectionwith cies. (B) Analysisbased on all speciesexcept Eur- closedhabitats. The plot of predictedversus asian Kestrel and Eastern Marsh Harrier. observedvalues (Fig. 5A) showsthat the spe- ciesobserved in totally openhabitats, Eurasian Kestrel (Falcotinnunculus) and EasternMarsh we obtainedR = 0.783 (P < 0.01; R = 0.760, P Harrier, may have determined the results. < 0.025for the independentcontrasts), and the Thus,we repeatedthe analysis excluding these predictedscores for the two omittedspecies speciesin order to corroboratethe results.The werevery closeto the observations(Fig. 5B). same variableswere selectedin the stepwise Stepwise multiple regressionanalysis was multiple regressionanalysis; the signs and applied to test the correlationbetween modes magnitudesof the coefficients,as well as the of locomotionand morphologicalcharacters, correlationswith the regressionscores, were includingaspect ratio and wing loading(Table similarto the foregoinganalysis. In particular, 1). First,we analyzedthe relationshipbetween 720 GAMAUF,PRELEUTHNER, AND WINKLER [Auk, Vol. 115

56

$ch 0 0 )._.S/Pcs24,5 e 40 Hii/NH(• Ppp

19.5

17.0 19.5 22.0 24.5 27,0 8 24 40 56 Predictionfrom behavior(PC) Predictionfrom morphology FIG. 7. Behariota!corre!ates of winõ ]oadi• i• FIG. 6. Morpholoõica!correlates of soarinõ be- ?h•Hppi•e •apto•s. Eesultsa•e •om a multiple •e- haviorLn Philippine raptors. Results are from a mul- tiple •e•essio• o• morphological•a•iables as ea•ed w• ]oad•. Valuesp•ed•cted •mm the •e- dicto•s o• p•opo•tio• o• time soa•i•. Values •ess•o• equafio• a•e plotted o• the X-ax•s,a•d ob- d•cted&ore the •e•essio• equatio• a•e plotted se•ed sco•esa•e plottedo• the •-ax•s. The two •a•- the X-axis,a•d obse•ed sco•esa•e plottedo• the ables extracted were scores o• •C] a•d •C2 o• the axis.A]] threeo• the morphological•a•iables extract- behavioraldata. The •ad•c Ba•a (Asu) was used as ed (bill width without cede,tail •aduatio•, a•d tar- a su•o•ate •o• •e•do•'s Ba•a i• th•s a•a]ys•s (see suslength) were •e•ati•ely correlatedwith text). fio• o• time soafi• (seetext).

morphologyand soaring.A strongcorrelation foragingbehavior is dominatedby soaringin (R = 0.878, P < 0.0001; R = 0.849, P < 0.001 for combinationwith a moderateproportion of sit- the independentcontrasts) was found with and-waithunting. three characters(all of them entered with a negativesign): (1) width of bill (withoutcere), DISCUSSION (2) tail gradation,and (3) lengthof tarsus(Fig. 6). Raptorsthat soar frequentlyhave a short Our analyses revealed consistentcompo- tarsus,narrow bill, and a square-cuttail. With nentsof morphologicalcovariation with for- respectto the flight apparatusalone, the num- aging habitat and behavior.We also showed ber of primary notcheswas positively correlat- that the relationshipsamong foraging behav- ed with soaring(r = 0.599,P < 0.01;r = 0.570, ior, habitat,and morphologyto a large extent P < 0.05 for the correspondingindependent are independentof phylogeneticrelationships. contrasts).Wing loading and aspectratio to- The shapevariables that werethe mostimpor- getherexplained only 21% (P > 0.05) of the tant componentsof morphologicalvariation variancein soaringfrequency. pertainto charactersthat usuallyare not mea- We alsoexamined the claimby Jaksieand Ca- suredat all--wing shapeand the feet.Features rothers(1985) that linearizedwing loadingis of the bill figuredonly marginally in thisvari- relatedto the sit-and-waitversus active-flight ation. One of the most popular charactersin continuumof huntingmode. We used ordinary ecomorphologicalstudies, tarsus length, did multipleregression, with thefirst two principal not contributesubstantially to the threemajor componentsderived from the behavioraldata componentsof morphologicalvariation, and as predictors(Fig. 7). The correlation(R = evenwing lengthwas not very importantas a 0.801, P < 0.001; R = 0.536, P > 0.05 for stan- shapevariable. The correlationanalyses yield- dardized contrasts; R = 0.744, P < 0.01 for con- ed similarresults, although tarsus length was trastswith equalbranch lengths) indicated that relevantfor predictingthe frequency of soaring wing loadingis low in large speciesin which (seebelow). Our findingsstress how important July1998] EcomorphologyofPhilippine Raptors 721

it is to workwith sufficientlylarge morpholog- foragingmode may be consideredindependent ical charactersets (Leisler and Winkler 1985, nichedimensions (Price 1991), or they maybe 1997),and they should be consideredwhen dis- seenas completelycongruent with eachother cussingresults obtained in studiesbased on AlthoughRosenzweig (1985) adheres to thelat- character sets restricted in number or on the ter view,Price (1991) showed that within Phyl- functionalcomplexes to whichthey belong (e.g. loscopuswarblers, foraging behavior and habi- Schoener1984, Hertel 1995). tat use largely are independent.Janes (1985) Severalstudies have discussedthe flight foundno strongor consistentrelationships be- style of raptorswith respectto wing loading tweenhabitat structure and the foragingbe- and aspect ratio (Pennycuick1975, Rayner haviorof hawks.In our study,hunting behav- 1988, Jaksi• and Carothers 1985, Janes 1985, ior correlated well with habitat use, and the Kerlinger1989, Norberg1981, 1990). These morphologicalpredictors for habitatuse and characterswere not the bestpredictors of the locomotionobtained with stepwise multiple frequencyof certainflight modesin our study. regressionrevealed the complexinteractions Soaring,for instance,was best predicted by the amongthese functions. We concludethat hab- numberof notchedprimaries, and its closere- itat use and foragingare neithercompletely lationshipwith featuresof the feedingappa- equivalentnor uncorrelatedwith oneanother ratushints at the complexweb of factorsthat This is due, at leastin part, to morphological may influencethe evolutionof behavioraland constraintsposed by conflictingdemands of morphologicaltraits. Wing loadingand aspect hunting, migration,and habitatuse (Winkler ratio were not correlatedsignificantly with and Leisler 1985, 1992). soaring frequency.Although Rayner (1988) Forest-dwellingraptors are small and they found it surprisingthat soaringhawks have haveshort, rounded wings as a generaladap- low aspectratios, subsequent discussions of the tationto flightin densevegetation. This results subjectstressed that long wingsmay be dis- in a low aspectratio and moderately high wing advantageousfor takingoff from perchesand loading,and thereforea ratherenergetically ex- that thermalsoaring requires a small turning pensiveflight mode (Jaksi6 and Carothers 1985, radius (see Norberg 1990). Our findings con- Kerlinger 1989, Norberg 1990). High-speed firm the notionthat for raptorsthat are limited poweredflight canbe attainedonly by flying at in wing span(and hence have low aspectratio a speedthat is a large multipleof minimum- androunded wings), notched primaries are the power speed(Pennycuick et al. 1994).Thus, a appropriatealternative to reduceinduced drag sit-and-waitstrategy combined with shortpur- (Pennycuick1972, Withers 1981, Kerlinger suitsis the mosteconomical hunting mode for 1989,Norberg 1990). This, and the fact that low raptorsin the forestinterior but is notpossible wing loadingalso is relatedto otheraspects of in openareas that lack suitableperches, even if flight performance(i.e. slow flight; Norberg prey are abundant(Preston 1990, Widen 1994). 1990),may be responsiblefor the poor predic- The accipitersare typical representativesof tions derivedfrom aspectratio and wing load- this group;only the migratoryChinese Gos- ing alone.The hypothesisthat raptors with hawk, with the longestwing tip of the high wing loadingtypically use sit-and-wait (Wattel1973), hunts most frequently above the huntingmodes, whereas species with lowwing forest. loadingare active-searchforagers (Jaksi• and Largerspecies are not able to hunt within Carothers1985), was supportedby our data. denselyvegetated areas. Therefore, they rely on However,light wing loadingalso was charac- the soaringmode of hunting, and they often teristicof mostspecies for whichsit-and-wait perchin treetops from which they launch their hunting was an importantcomponent of for- attacks.Their flight apparatuscan be consid- aging. ered a compromiseamong various constraints. Our correlative results concur with ideas de- The wingsare not too long,because these rap- velopedby Rochon-Duvigneaud(1952) and tors need to dive into the canopy (see also Voous(1969) on the functionaland ecological Brown1976). Among the speciesthat inhabitat importanceof talonlength, and they also stress openand semiopenhabitats, the four winter that associatedfeatures, such as talon diameter visitors are completelyindependent of forest and toe length,are relevant.Habitat, diet, and habitats.Species of openhabitats, particularly 722 GAMAUF,PRELEUTHNER, AND WINKLER [Auk, Vol. 115 migrants,are characterizedby high aspectra- ippineEagle Conservation Program Foundation, the tios and long, pointed wings. Thesemorpho- Haribon Foundation,Green Mindanao,N. Ingle (Da- logicalspecializations support, among other vao), and the TechnicalAid Agencyof the Federal things, efficientlong-distance flight (Winkler Republicof Germanyfor their cooperationon the Philippines.We alsoexpress thanks to the industrial and Leisler 1992,Yong and Moore 1994,M6nk- concerns in Carmen (Puyat Logging) and k6nen 1995) and prevent these speciesfrom (PRI), as well asto the localstaff and our Philippine overlappingwith speciesof the forestinterior guides.The morphologicalportion of the studywas in morphology,behavior, and habitatrequire- made possiblethrough the excellentcooperation of ments(Thiollay 1985). the museums and curators of the collections listed In the Philippines,13 speciesoccur primarily above.We are greatlyindebted to A. Schuster,S. Teb- in tropical rain forest,including the most en- bich,and M. Zeiler for their supportin the field,to J. dangered speciesobserved during our field Kickertfor her adviceon the computer-basedimage work, the (Pithecophagajeffer- analysis,and to W. Pinskerfor his supportduring yi; Kennedy1977). Eight of thesespecies are ob- many stagesof the study.We alsothank W. Bock,R. Dudley,and an anonymousreviewer for criticalcom- ligate inhabitantsof mature rain forest.Their mentson the manuscript. main prey,relatively large mammalsand birds, also are restricted to these forest habitats. Some LITERATURE CITED of thesespecies also use secondaryrain forests to some extent. These areas, however, are rath- BENNET,P.M. 1986. Comparative studies of mor- er small and short-lived, and because of exten- phology,life history and ecologyamong birds. siveexploitation, these forest remnants usually Ph.D. dissertation,University of Sussex,Brigh- are convertedwithin a few years into grass- ton, United Kingdom. lands.Owing to the deteriorationof the envi- BIERREGAARD,g. O. 1978.Morphological analysis of communitystructure in birdsof prey.Ph.D. the- ronmentthrough activities(e.g. Salva- sis,University of Pennsylvania,Philadelphia. dor 1994,Thiollay 1994, 1996), all forestspecies BOYCE,D. A., AND C. g. WHITE. 1987. Evolutionary arenearing extinction. Those residents needing aspectsof kestrelsystematics: A scenario.Pages only a minimum of forest have similar mor- 1-21 in The ancestralkestrel (D. M. Bird and R. phologicalcharacteristics developed as adap- Bowman,Eds.). Raptor Research Report No. 6. tations for hunting over open surfaces,e.g. BROWN,L. H. 1976.Birds of prey,their biologyand lakes, shores,or the air spacehigh abovethe ecology.Hamlyn PublishingGroup, Feltham, forest canopy.After ,these spe- United Kingdom. cies were able, to some extent, to exploit new BROWNL. H., ANDD. AMADON.1968. , hawks and falconsof the world. Country Life Books, habitat types suchas grasslandsor rice fields. London. Not actuallythreatened are the winter visitors. CADE,t. J., AND g. D. DIGBY.1982. The falcons of the Membersof thesespecies find sufficienthabitat world. Collins, London. in whichthey appearto thrive.That speciesof COLLAR,N.J., M. J. CROSBY,AND A. J. STATTERSFIELD. primary forests are the most threatenedhas 1994. Birds to watch 2: The world list of threat- been statedfor ,involving in part the ened birds. BirdLife International Conservation sameor closelyrelated species,and for other SeriesNo. 4, Cambridge,United Kingdom. nearbytropical countries(Thiollay 1996).Our COLLINS, N.M., J. A. SAYER, AND T. C. WHITMORE. study shedssome light on the ecologicalrela- 1991.The conservationatlas of tropical forests: and the Pacific. Macmillan, London. tionshipsunderlying the conservationof these DE BOER,L. E. M., AND R. P. SINOO.1984. A karyo- raptor speciesand how they were shapedby logical study of (Aves: Falconifor- ecomorphologicalconstraints. mes),with karyotypicdescriptions of 16 species new to cytology.Genetica (Dordrecht) 65:89- ACKNOWLEDGMENTS 107. DEL HOYO, J., A. ELLIOT%AND J. SARGATAL(Eds.). The studywas supportedby the AustrianScience 1994. Handbook of the birds of the world, vol. 2. Foundation(Fonds zur F6rderungder wissenschaft- New World vultures to guineafowl. Lynx Edi- lichenForschung, Project P8889-BIO) and by the In- cions,Barcelona, Spain. stitute for Wildlife Biology and Game Management DICKINSON, E. C., R. S. KENNEDY, AND K. C. PARKES. (Agricultural University,Vienna). We are indebtedto 1991.The birdsof the Philippines.An annotated the Departmentfor Environmentand Natural Re- checklist.British Ornithologists'Union Check- sourcesof the Republicof the Philippines,the Phil- list No. 12, London. July1998] EcomorphologyofPhilippine Raptors 723

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APPENDIX.Species treated in this paperand their diets.Our observationsaugmented by datafrom Brown and Amadon (1969),Wattel (1973),Kennedy (1977), Cade and Digby (1982),H. Miranda (pers.comm.), Marchantand Higgins(1993), and del Hoyo et al. (1994).Diet: (?) = possibly,(o) = occasionally,(+) = regularly, (+ + ) = frequently,(+ + + ) = very frequently.

Code Species Diet Hunting above the forest Ppp Pernisptilorhyncus philippensis Oriental Honey-Buzzard Wasplarvae (+ + + ), frogs (+), (+), small nestlings (+) Pcs Perniscelebensis steerei BarredHoney-Buzzard Wasplarvae (+ + +), frogs(?), Pernis celebensis winkleri lizards (+), small nestlings (+) Sch Spilornischeda holospilus CrestedSerpent Eagle (+ + + ), small birds (+), small mammals (+ +) As Accipitersoloensis ChineseGoshawk Insects(+), frogs (+ +), lizards (+), small birds (+), small mammals (+) Pj Pithecophagajefferyi PhilippineEagle Reptiles(+), medium and large birds (+ +), medium and large mammals (+++) Hkf Hieraaetuskieneriiformosus Rufous-belliedEagle Small and medium birds (+ +) Scl Spizaetuscirrhatus limnaetus ChangeableHawk-Eagle Reptiles(+), medium and large birds (+ +), small to large mammals (+) Sp Spizaetusp.philippensis PhilippineHawk-Eagle Reptiles(o), smallbirds (+), me- Spizaetusp. pinskeri dium birds (+ + + ), small mammals (+) Fpe Falcoperegrinus ernesti PeregrineFalcon Small birds (+ +), medium birds (+++) Hunting in the forest interior Ajn Avicedajerdoni magnirostris Jerdon'sBaza Insects(+ + + ), frogs (+), liz- ards (+) Av Accipitervirgatus confusus Besra Small birds (+ + +), small mam- Accipitervirgatus quagga mals (+) Ate Accipitertrivirgatus extimus CrestedGoshawk Lizards (+), small birds (++), medium birds (+ +), small mammals (+) Me Microhieraxe. erythrogenys PhilippineFalconer Insects(+ + + ), especiallydrag- Microhierax e. meridionalis onflies, butterflies and cicadas; small birds (o) Hunting outside the forest Ech Elanuscaeruleus hypoleucus Black-shoulderedKite Insects(+ + +), lizards (+), small mammals (+ + + ) Hii Haliasturindus intermedius BrahminyKite Carrion(+ +), grasshoppers(+), fish (+), frogs (+), reptiles(+), small birds and mammals (+) H1 Haliaeetusleucogaster White-belliedSea-Eagle Carion (o), fish (+ + +), reptiles (+), medium and large mama- mals (o) Cs Circusspilonotus EasternMarsh Harrier Carrion (o), insects(+), fish (o), frogs (++), lizards (+), small birds (+), small mammals(+ +) Cm Circus melanoleucos Pied Harrier Insects (++), frogs (+), lizards (+), small birds (+), small mam- mals (+++) Bi Butasturindicus Grey-facedBuzzard Fish (o), frogs (++), reptiles (+ + ), small mammals (+ + ) Fti Falco tinnunculus interstinctus Eurasian Kestrel Insects(++), reptiles (+), small birds (o), small mammals (+ + +) Fss Falcoseverus severus Oriental Hobby Insects (+++), small birds (+ + +), bats (+ +)