TheAuk 115(3):713-726,1998 PHILIPPINE BIRDS 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 Philippines.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 species 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 bird 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(Manila), 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 rare species pletelycovered by tropicalrain forest.Because and subspecies,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 Habitat analysesand behavioralobservations 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 ippine Falconet(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 Luzon graphswere availablefor the Philippinesubspecies (Sierra Madre, Quirino and Isabela;Mt. Makiling, of Jerdon'sBaza (Avicedajerdoni magnirostris), so we Laguna),Mindanao (Mt. Kitanglad,Bukidnon; Car- usedphotographs of its closestequivalent, the Pacif- men-Cantilan,Surigao del Sur; Mt. Apo, DavaoCity ic Baza (A. subcristata)from the Australian region and North Cotabato;Initao, Misamis Oriental), and (Marchantand Higgins1993). We alsohad no pho- Palawan(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 Museum of 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