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
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Chickadees
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AUSTIN,G. T. 1974. Nestingsuccess
of the Cactus
Wren in relation to nest orientation.
Condor 76:
216-217.
BecauseGilded Flickersare relatively large
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E. 1981. Circular statisticsin biology.
woodpeckers,
they may have difficultylosing
Academic Press, London.
excessheat. Thus, their thermoregulatoryret. M. 1991.A comparisonof goodness-of-fit
quirementsarelikelyto havea stronginfluence BERGIN,
testsfor analysisof nest orientationin Western
on cavityorientation.Heat stressin the region
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ities in cactiare subjectto greaterheatstress BORG,J. 1956. Cacti. Blanford Press,London.
than in other substrates
becauseof the larger BURGER,
J. 1974. Breedingadaptationsof Franklin's
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sue (Howe et al. 1987). Avoidanceof direct ex-
Behaviour
22:521-567.
P. J. 1956. The territory of the Wheatear
posureto the sun and possiblytakingadvan- CONDER,
(Oenantheoenanthe).Ibis 98:453-459.
tageof prevailingwindsmaybe adaptiveif the
highertemperatures
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