TheAuk 115(1):119-126,1998 PATTERNS OF CAVITY-ENTRANCE ORIENTATION BY GILDED FLICKERS (COLAPTES CHRYSOIDES)IN CARDONCACTUS PATRICK W. ZWARTJES • AND SHAWN E. NORDELL2 Department of Biology,Universityof NewMexico,Albuquerque, NewMexico$7131,USA ABSTRACT.--We studiedpatternsof cavityplacementandorientationby theGildedFlicker (Colapres chrysoides) in the card6ncactus(Pachycereus pringlei)of Mexico,a columnarcactus characterized by a complexbranchingpattern.Overall,GildedFlickercavityentranceswere orientedsignificantlytoward the north-northwest,and they tendedto faceawayfrom the restof the cactusstructure.Thereweremorecavitiesproportionalto the numberof armsin the northwestquadrant,and thesecavitieshad the strongesttendencyto be orientedto the northwestand to faceawayfrom otherarms.Cavitiesin the northeastquadrantwere orientedslightlyeastof north,maintaininga strongpatternof orientationawayfrom other cactusarms.Southwest quadrantcavityorientations weresimilarto thosein thenorthwest quadrantbut deviatedfrom the trendof facingdirectlyawayfrom the bulk of the cactus structure.The fewestcavitiesproportionalto numberof armswerein the southeast quadrant, and theseshowedno significantorientations, insteadhavingthe greatestvariationin directionalorientationaswell as orientationwith respectto othercactusarms.Received 24 March1997,accepted 20 June1997. THE EXCAVATIONS OF PRIMARY CAVITY-NEST- INGBIRDS providea recordfromwhichtheecologicalfactorsthat influencecavityplacement may be inferred.Severalstudieshaveusedthis historical recordto examine thepatterns ofcavity locationand/or holeorientationin a variety of bird species(e.g.Conner1975,Connerand andSmith1990).Thesaguarois oneof several long-livedspecies of columnarcactiwithinthe subfamily Cactoideae (Gibson and Nobel 1986).It has a relativelysimplemorphological structure,remaininga singleunbranchedcolumn until approximately40 to 50 yearsof age, after whichit may developoneto five lateral Adkisson1977, Staufferand Best 1982). Previ- branches thatgrowupward(GibsonandNobel ousanalyseshaveexaminedverticaldistribu- 1986).Farthersouthin BajaCaliforniaandSotion,nestheight(e.g.Nilsson1984,Li andMar- nora,Mexico,the card6n(Pachycereus pringlei) tin 1991, Albano 1992), and nest orientationfor becomesthe dominantcolumnarcactus(Wigthermoregulation, eitherin termsof facingto- gins1980).The structureof the card6non the ward the sun in cold environments,or away eastern coast of the Gulf of California is more from the sun and/or towardprevailingwinds complexthan that of the saguaro.Card6ns in hotter environments(Ricklefsand Hains- commonly havemanybranches thatgrowfrom worth 1969,Austin 1974,Inouye1976,Inouye a centraltrunk at thebase,oftenwith no single et al. 1981, Finch 1983, Facemire et al. 1990, Rendell and Robertson 1994). Severalstudieshaveexaminedcavitydimensions,nestplacement,and entranceorientation by GildedFlickers(Colaptes chrysoides) andGila Woodpeckers (Melanerpes uropygialis) in thesaguaro cactus(Carnegiea gigantea)in southern Arizona (Inouye et al. 1981, Korol and Hutto 1984, McAuliffe and Hendricks1988, Kerpez •Present address:Department of BiologicalSciences,HumboldtStateUniversity,Arcata,California 95521,USA. E-mail:zwartjes@humboldtl.com 2Presentaddress:Departmentof Biology,California StateUniversityNorthridge,Northridge,California 91330, USA. 119 centralstem,andtheyexhibitpronounced secondary branching on the longer primary branches(Borg1956,Earle1980,Wiggins1980). Theregionof theSonoran Desertdominated by thecard6nalsomakesup a majorportionof the breeding range of both woodpeckerspecies thatpreviouslyhavebeenstudiedin saguaros in Arizona. Studiesof woodpecker nest-entrance holesin saguarocactihave revealedthat woodpeckers tend to orient their cavities toward the north and northwest(e.g. Inouye et al. 1981,Korol and Hutto 1984;but seeKerpezandSmith1990).In addition,Koroland Hutto (1984)reportedthat cavityorientationwasinfluencedin part by cac- 120 ZWARTJES ANDNORDELL [Auk, Vol. 115 tus architecture.Specifically,when adjacent Mexico.We randomly selected35 card6n cactiin secharacterbranches werepresenton a saguarostem,cavi- quenceandrecordedtheirmorphological ties were oriented in the direction of least ob- istics. Linear measurements were made with a series polesthat weremarkedwith red struction.If a specificdirectionand avoidanceof of interconnecting tape at 1.0-mintervalsand white tape at 0.1-minobstructionsare important factorsinfluencing tervals.Height and length of eachcactusarm (Fig. cavityplacement andorientation, thenthegreat- 1A) weredeterminedby havingonepersonholdthe er architectural complexity of thecard6ncactus poleverticallyagainstthearmwhilea secondperson relative to the saguaromay force tradeoffs notedthe measurements from a distance.Thelength amongpreferredorientation characteristics. The of an arm was determined to be the vertical distance variouslocationsof the card6n arms, radially betweenthepointwherethearmoriginatedfromthe distributedaround a centerpoint, will not be main trunk of the cactus(or a secondarm) and the equallysuitablefor a woodpeckerattemptingto apexof the arm. A compasswasusedto determine achievean optimal cavity orientation.For ex- the orientationof eacharm (+ 1ø)with respectto the ample,in the northwestregionof a card6ncac- centralaxis(Fig.lB). All anglesweremeasuredwith respect tomagnetic northandcorrected totruenorth tus with respectto its center,orientationof the using a magneticdeclinationof 11ø east (Defense cavitytowardthe northwestautomatically plac- MappingAgency1991).The distanceof eacharm es the bulk of the cactusarchitectureopposite from the centralaxiswasdeterminedby measuring the entranceto the cavity.In partsof thecard6n the horizontal distance from the midline of the trunk that do not correspond to a preferredcompass to the farthestlateralextensionof the arm (Fig. 1A). Cavitiesconstructedby Gilded Flickerscanbe disdirection,woodpeckers mustmaketradeoffsbetween maintaining a preferred directionand tinguishedfrom thosemade by other piciformsin (Gilorientingthe cavityentranceto avoid obstruc- thisregionby theirlargerentrancedimensions tion by the surroundingstructureof the cactus man 1915, Harrison 1979, Korol and Hutto 1984, McAuliffe and Hendricks1988).Cavitysize,shape,and depthwereassessed from the groundwith binocuWe quantifiedthe architectureof card6ncac- lars. We recordedonly thosecavitiesthat both inti in Sonora,Mexico,and examinedthe pattern vestigatorsagreed were fully excavatedand could (sensuKorol and Hutto 1984). of distribution and orientation of nest cavities of Gilded Flickers within the structure of these cacti.We testedthe hypothesisthat compass orientationof cavity entrancesand orientation with respectto cactusstructurediffer among cavitieslocatedin the four quadrantsdefined by north-southand east-westaxesthroughthe centerof the cactus.We predictedthat these quadrantsare apt to differ in ecologicalinfluencesbecause:(1) significantmean entrance orientationsto the northwest reported for woodpeckercavitiesin saguarossuggestecologicalconstraintson compassorientation;and (2) the locationof the studysiteat 30øNlatitude precludessunlightfromshiningdirectlyonthe northsideof the plant,thus creatinga difference in thermal conditions between northern quadrantsand southernquadrants.The combinationof theseecologicaland architectural constraintson orientation of cavity entrances shouldresult in differentorientationpatterns amongdifferentquadrantsof the cactus. METHODS Data collectionand organization.--Fieldwork was conducted duringspring1991in a card6nforestapproximately20 km north of Bahia Kino in Sonora, serveasfunctional cavities, basedonapparent depth and evenness in the circularityof the entrancehole. Each recordedcavity was designated"flicker" or "woodpecker"based on the size of the hole as judgedby both investigators.Cavity placementand orientationwere recordedby measuringthe height of eachcavityentranceand the compassorientation of eachhole(Figs.lA,B). Eachcactusarm andcavitywasassignedto oneof four quadrants(i.e.NW, NE, SE,and SW) delineated by the north-southand east-westaxesthroughthe cactuscenterA cavitywasplacedin a specificquadrant by the orientationangleof the arm containing the cavity(Fig. lB); armsand cavitieslocatedin the absolutecenterwere not includedin quadrantanalyses. Geometric equations incorporated asalgorithms of a Fortrancomputerprogramwereusedto calculate additionalgeometricrelationships fromdatacollected in the field (Fig. 1C). To examinethe orientation of a holewith respectto the positionof all the other armson a cactus,the programcomputedthe angle hb(Fig. 1C). Foreveryarm (A), the programcalculatedthe directdistancein a horizontalplane(line AB) to a secondarm on the cactus(B) and the angle (AOB)formedby thetwo radial distancesof eacharm from the centralaxis,O.Forany arm A, thesevalues werecalculatedfor everyotherarm on the cactus. Statistical analysis.--Characteristics of card6ncacti werefirstanalyzedby testingthedistributionof cac- January 1998] CavityOrientation in Flickers 121 tus armsin the four quadrantsusing a chi-squared goodness-of-fittest (Zar 1996).Analysisof variance (ANOVA) was used to test for differencesin mean arm heightsand lengthsin the differentquadrants usingthe SASstatisticalsoftwarepackage(SASInstitute 1988). The distributionof cavitiesthroughoutthe four quadrantswasanalyzedby testingfor differencesin the ratio of holes to total number of arms in each quadrant.The overall test usesa chi-squaredcomparisonof multipleproportions; rejectionof thenull hypothesisof no significantdifferencesis followed by a pairwiseanalysisamongquadrantsusing the Freemanand Tukeyarcsinetransformation and the Tukeymultiplecomparisontestfor proportions(Zar 1996). Cavity-holeorientationsand the arm positions with respectto the holes(anglehb)were testedfor nonrandom distribution using Rayleigh'sz-test; comparisonsof mean anglesin the four different quadrantswere conductedusing the Watson-Williamstest(Batschelet 1981).Fora sampleof n angles, theRayleightestcalculates a meanangleanda mean angulardeviationand thenteststhe null hypothesis that the angulardataare randomlydistributedwith respectto the mean angle.It also calculatesthe index,r, of the dispersionaroundthe calculatedmean angle.A value of r = 1.0 indicatesthat all angular measuresare oriented in the same direction, and r = 0.0 indicatesmaximumdispersionfrom the mean angle.The z-statisticis calculatedby the equation: z = (n)r2 A (1) In a comparisonof severalstatisticaltestsfor circular data, Bergin (1991) determinedthat this test wassubjectto TypeII errors(failureto rejectthenull hypothesis of randomdispersion) for significant polymodaldistributions. Forthis reason,we examined plotsof the raw datafor patternsof polymodality(P > 0.05)to confirmthatthenull hypothesis shouldbe accepted. In addition,the data for anglehb alsowere analyzedusingthe V-test,whichexamines whetheran- 0 gles are clusteredaround an expectedmean direc- tion (Batschelet 1981).In this case,we testedthehypothesisthat the hole is orientedoutward,away from the armsof the cactus(anglehb = 180ø).Fora B FiG. 1. (A) Field measurementsof cactus dimen- tationangleof entrancehole(arrow).(C) Data computedfrom fieldmeasurements: anglehb,anglefrom to point of arm attachmentto cactus;c, vertical dis- entranceorientationto other arms of cactus;angle tance to apex of arm; d, vertical distanceto bottom AOB,angleformedat the cactuscenter(O) by arm of the nesthole.(B) Field measurements of orienta- with cavity,A, and secondaryarm, B;line AB, horition anglesfrom true north (N): e,angleof arm with zontal distancebetweenarm with cavityand secrespectto trunk center(circlewith cross);f, orien- ondary arm. sionsand cavity-entrance height:a, horizontaldis- tance of arm from center of trunk; b, vertical distance 122 ZWARTJES ANDNORDELL TABLE1. Location(by quadrant) of Gilded Flicker nest holes relative to card6n cactus arms. [Auk,Vol. 115 = 1.62,df = 3 and585,P = 0.197;length:F = 0.092, df = 3 and 585, P = 0.913). Cavitydistribution.--Werecorded109 cavity Ratio of No. of No. of holes to Quadrant holes armsa armsb Northwest (NW) Northeast(NE) 28 29 0.304 0.197 Southwest(SW) Southeast(SE) 28 24 92 147 156 176 holes attributable to Gilded Flickers in 30 cacti. Five cacti (14%) had no cavitiesof any kind. GildedFlickercavityholeshad a meanheight of 5.6 + 1.64 m and a mean distance from the 0.179 0.136 top of the arm of 2.2 --- 1.39 m. McAuliffe and Hendricks(1988)reportedthat Gilded Flicker 'X 2 = 27.14, df = 3, P < 0.0001 (NW < [NE = SW] < SE). bX2= 11.22,df = 3, P < 0.02 (NW > [NE - SW] > [Sw = SE]). calculatedmean angle(/2)and an expectedangle(8), the V-statisticis calculatedby: V = (n)(r) cos(a- •2) (2) holesin saguarocactiwere almostexclusively restrictedto the upper3 m of the stems.In card6ns,this effectdid not appearto be asstrong in that 33 of the Gilded Flickerholes(30%)were morethan3 m belowthetop of thestem(three holeswere morethan 5 m belowthe top).This may indicatedifferencesin internal structure In thiscase,angle• = 180ø.Because of the additional betweensaguarosand card6ns. informationof theexpectedmeanangle,the V-testis The proportionof holesrelativeto the numconsideredto be more powerfulthan the Rayleigh ber of cactusarmsdifferedsignificantlyamong test alone (Batschelet1981). the four quadrants(Table1). Pairwisecomparisonsrevealedthatthenorthwestquadranthad RESULTS a greaterratio of holesto armsthan the other three quadrants. Thenortheastquadranthad a Cactusmorphology.--We recorded a total of higher ratio than the southeast, and the rela589 armson 35 card6ncacti(œ= 16.8,range 3 tionship of the southwest quadrant to thesetwo to 67 armsper cactus).The meanarm height was 4.62 -+ SD of 1.62m, approximately1.5 m quadrantswas unclear (i.e. NW > [NE = SW] greaterthanthemeanarmlengthof 3.03--_1.68 > [sw = SE]). Cavity-entranceorientation.--Cavity-entrance m. The mean distance of the arms from the cenholes exhibitedsignificantnonrandomorienter of the cactus was 1.15 --- 0.71 m. The maximum height of each cactus,defined as the tation to the north-northwest(342.5ø;Table2). The influenceof quadrantlocationof a cavity heightof the highestarm, was7.1 ___ 1.52m. on the orientation of the entrance hole was anAnalysisof the distributionof armsaround alyzedby dividingtheorientationdataintoone the centers of the cacti indicated that the arms are not evenly distributedaroundthe cactus of the four quadrants,revealing significant based on an expectedproportionof 0.25 per nonrandompatternsand strong quadrant efquadrant(Table1).Therewerefewerarmsthan fects (Table2). Patternsof significantnonranexpectedin thenorthwestquadrant(95%CI for dom orientationwere evident in all quadrants proportion0.12to 0.20)andmorearmsthanex- exceptthe SE quadrant.Gilded Flickerholes pectedin the southeast quadrant(95%CI 0.26 were significantlyorientedtoward the northto 0.36).Arm heightsandlengthswerenot sig~ west in the NW and SW quadrants(meanannificantlydifferentamongquadrants(height:F gles = 329.5ø and 298.5ø,respectively),and toTABLE 2. Orientation statistics • of Gilded Flicker nest-entrance holes in card6n cactus. Mean All holes Northwest Northeast Southwest Southeast Mean angular angle deviation z r P 342.5 329.5 23.5 298.5 74.4 80.6 52.1 55.7 73.8 148.3 15.05 12.26 11.27 5.33 0.03 0.37 0.66 0.62 0.44 0.04 •0.001 •0.001 •0.001 0.004 0.75 • From true north; meananglesand angulardeviationsin degrees. Rayleigh's January1998] CavityOrientation in Flickers 123 TABLE3. Orientationof Gilded Flickernest-entrance holesain card6ncactusrelativeto positionof cactus arms (anglehb.;seeFig. 1C). Data are testedwith the Rayleightest (whichtestswhetherorientationis nonrandom) andtheV-test(whichtestswhetherorientation is clustered aroundanexpected angleof180ø). Mean Angle hb All holes Northwest Northeast Southwest Southeast 154.5 177.5 171.5 115.5 101.5 angular deviation 85.6 64.0 74.1 75.8 141.7 Rayleigh test V-test z r P V 11.58 8.03 5.45 4.87 0.05 0.33 0.54 0.43 0.42 0.05 <0.001 <0.001 0.004 0.007 >0.500 32.22 14.97 12.45 5.03 0.24 P <0.001 <0.001 <0.001 0.090 >0.500 From true north;mean anglehb and angulardeviationsin degrees. wardthenorthin theNE quadrant(meanangle = 23.5ø).The amountof dispersionwaslowest in the NW and NE quadrants(r = 0.66 and 0.62, respectively).High levels of dispersion from thecalculated meananglewereindicated for theSEquadrant(r = 0.04).Comparisons of the quadrantswith significantmean orientation anglesshowedequivalentorientations in the NW and SW quadrants(F = 2.84,df = 1 DISCUSSION The orientationof an arm with respectto the centerof thecactusappearsto be animportant factor in cavity placementby Gilded Flickers. Thepatternof armgrowthimpliesthatclimatic or other ecologicalfactorsinfluencegrowth patterns,with more armsin the southeastand fewer in the northwest. Nevertheless, on the basis of the number of available arms, Gilded and 54, P = 0.10), with the orientationsin the NE quadrantsignificantlydifferentfrom both Flickersplacemoreholesthan expectedin the theNW quadrant(F = 13.76,df = 1 and55, P northwestquadrantand fewerholesthan expectedin the southeast quadrant.This cannot < 0.001)andtheSW quadrant(F = 22.16,df = be accountedfor by differencesin arm dimen1 and 55, P < 0.001). sionsbetweenquadrants,becausecactusarms Holeorientation versusposition of arms.--The did not differ in meanheightor length. overall distribution of arms from the directions of hole orientations(anglehb in Fig. 1C) was significantly nonrandom. The calculated mean anglesandthe V-tests(with an expectedangle of 180ø)bothsuggested a generalpreference for facingtheopeningof thecavitiesawayfromthe otherarmson the cactus(Table3). The positionof the cactusarms relative to hole orientationwas significantlynonrandom for cavitiesin all quadrantsexceptthe SE(Fig. 2).TheNW andNE quadrants hadmeanangles hb closestto being directlyoppositethe hole orientations(NW, 177.5ø;NE, 171.5ø);this was confirmed by thehighlysignificant P-values for the expected180øunder the V-test.The mean anglehbfromtheSWquadrant,alsosignificant underthe Rayleightest,waspositionedto the right of themeanholeorientation(meanangle hb = 115.5ø).In addition,the V-test for an expectedangleof 180ø was not significant.The analysesof the calculatedmeananglehbin the SEquadrantwerenot significant for eithertest (Table 3). The Gilded Flickers we studied oriented their holes to the north-northwest, which concurs with findingsfor GilaWoodpeckers in saguaro cactus (Inouye et al. 1981, Korol and Hutto 1984;but seeKerpezand Smith 1990).The rvalues(Rayleightest)we calculated wereintermediate between those reported for Gila Woodpeckersby Inouye et al. (1981) and Korol and Hutto (1984).Althoughour r-valuesindicateda fair degreeof dispersionfrom the significantmeanorientation angle,webelievethey indicatea preferencefor a generaldirection,i.e. northwest. GildedFlickerstendedto avoidfacingtheir cavitiestowardthemajorityof thecactusarms. Placement of cavities in card6n was such that it createdan unobstructed regionin front of the entrance.Similarly, when pairs of adjacent brancheswere present on a saguaro,Gila Woodpeckers tendedto placetheirnestholesin the direction of least obstruction(Korol and Hutto 1984). Orientation of entrances to avoid obstructions would result in increased visibil- 124 ZWARTJES AND NORDELL 315 45 225 315 135 45 225 180 315 [Auk, Vol.115 135 180 NW NE SW SE 45 315 45 9O 225 135 180 225 135 180 FIG. 2. Gilded Flicker cavity-entrance hole orientations andsecondary armpositions analyzed byquad- rants.Arrowsdenote meanholeorientations significant forRayleigh testof nonrandom distribution. Bars denote mean angles fromorientation ofholes tosecondary cactus arms significant forRayleigh test orV-test using expected angle of180 ø. Noarrow orbarindicates thatthecalculated mean angle wasnotsignificant byeither Rayleigh orV-test. Shaded areas denote regions between mean angular deviations oneither side of means. ity fromandtowardthecavity.Visibilityhas Theanalysis of databy quadrants supports beenshownto affecttheabilityof animals to thehypothesis thatcompass orientation of cavdefendterritoriesand resources(Easonand ity entrances and orientation with respectto Stamps1992),and evidencesuggests thatter- cactusstructurevary with quadrantlocation. ritorialboundaries ofbirdsareaffected byvis- Thebestlocation forachieving thegoalsoffacibility (Conder1956,Burger1974,Reid and ing awayfrom the cactusarmsand in a northWeatherhead 1988). Analysesof Northern westerly directionwould be in the northwest Flicker (Colaptes auratus)nest-sitecharacteris- quadrantof the cactus,and it is here that we ticshaveshown thatthisspecies prefers open findthestrongest statistical supportforbotha areas versus dense forest (Conner and Adkis- meanorientation angleanda meananglefrom son1977).Visibilityatnestsalsomayinfluence the entranceorientationto the cactusarms.The predationrisk. For example,Li and Martin northwest quadrant alsocontained thehighest (1991)foundthat depredatednestsoftenwere ratio of holesto cactusarms,with the smallest close tolargetreesandconcealed byfoliage. In ratio occurringin the southeast quadrant(aladdition,if GildedFlickersplacetheirneststo thoughmanycavities werelocatedthere).In takeadvantage of the coolingeffectsof pre- thesoutheast quadrant, theorientation ofholes vailingwinds,thenfacinga nestintothebulk wasrandomwith respect to bothcompass diofthecard6nstructure maylessen theseeffects rectionand locationof the other arms,reflect- to an unacceptable degree. ingthefactthatin thisquadrant, thegoalsof January 1998] CavityOrientation inFlickers 125 ACKNOWLEDGMENTS northwesterlyorientation and facing away from nearbyarms are in completeconflict. We extendspecialthanksto RaymondE. Jellerson for developinga computerprogramthat generated westquadrantssuggestthattradeoffsarebeing geometricrelationshipsfrom the field measuremade between thermal and architectural conHole orientations in the northeast and south- straints(Fig.2). In thesouthwest quadrant,facing away from cactusarms would require a southerly exposure;instead, the northwest preferenceis maintained while sacrificing someof the visibilityaroundthe nestentrance by orientingthecavitysuchthatthebulk of the cactusarmsarelocatedto theright andslightly behind the cavity opening.This is supported by thenonsignificant resultsof theV-testforan expectedangleto thecactusarmsof 180ø. In the northeastquadrant,facingawayfrom the bulk of the armscanbe achievedwithoutexposure to directsun,and in this quadranta northerly orientationachieves this withoutstrayingtoo far from the overallpreferencefor orientation to the north-northwest. ments. James H. Brown and Astrid Kodric-Brown providedguidanceduring projectdevelopmentand made substantial comments on an earlier version of the manuscript.ThomasJ. Valoneprovidedhelpful statisticalsuggestions andcommented onthemanuscript,andJ.David LigonandMicheleMerola-Zwartjes alsocommentedon the manuscript.The final versionof themanuscriptwasimprovedby thecomments of Paul Hendricks, Richard Hutto, David In- ouye,and WallaceRendell. LITERATURE CITED ALBANO,D. J. 1992. Nestingmortality of Carolina Chickadees breedingin naturalcavities.Condor 94:371-382. AUSTIN,G. T. 1974. Nestingsuccess of the Cactus Wren in relation to nest orientation. Condor 76: 216-217. BecauseGilded Flickersare relatively large BATSCHELET, E. 1981. Circular statisticsin biology. woodpeckers, they may have difficultylosing Academic Press, London. excessheat. Thus, their thermoregulatoryret. 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