CHARACTERISTICS
OF CLIFFS
BY BREEDING
D.E.
AND
PRAIRIE
RUNDE AND S.H.
NEST
SITES
USED
FALCONS
ANDERSON
ABSTRACT
- Datafromover400PrairieFalcon(Falco
mexicanus)
eyriesin 8 states
showa consistent
patternof eyrie
placement
relativeto heightand aspectof nestcliffs.Meaneyrieheightaveraged
63% of meancliff height.Mean
exposure
of eyriesandnestcliffstendedtobesoutherly
withnosignificant
differencebetween
eyrieandcliffexposures.
Potholes
werethemostfrequently
usednestsites.Patterns
of occupancy
andnestsuccess
in Wyomingwerestatistically
independent
of physical
habitatvariables
measured.
However,eyriesontallexposed
buttesconsistently
hadhighfailure
ratesthatappearedweatherrelated.Attributes
of Wyomingeyriesarepresented
andsuggestions
madefor creatingnew
eyriesfor Prairie Falconsasa managementtool.
We summarized and compared data on nest each cliff was estimatedwith a large protractor and was either
cliffs and eyries used by the Prairie Falcon(Falco vertical(85-95ø),overhung(<80 ø)or underhung( >100% Cliffs
are dataavailablein the literatureand originaldata
from eyries active between 1982 and 1984 in
Wyoming. Our objectivewasto documentthe variation in nestcliffs and eyriesusedby thesefalcons
and to identify consistentpatterns of use. In our
study,we examinedthe association
betweenphysicalnestinghabitatand patternsof eyrieoccupancy
were classedas: canyonwalls,buttes or mountains,rimrock or
ridges,and isolatedrock outcrops.
Standardstatistics
are presentedfor mostvariables.Statistics
from other studies,if not reported, were calculatedfrom frequencytablesor raw data. We analyzedour data usingone-way
ANOVA and Chi-square(X2) to examinerelationshipsbetween
physicalvariablesand historiesof nest success
and occupancy
within and among years.In among-yearanalyses,we only includedsiteswith complete3-yr histories.
Data suitablefor circularstatisticalanalysis(Batschelet1981;
and nest success. We discuss attributes
Zar 1984) were available for Montana, Utah, New Mexico, Idaho,
mexicanus)in the western United States. Included
of Prairie
Colorado and Wyoming. Grouped data were analyzed as
suggestedby Batschelet(1981); 954 confidenceintervalswere
estimatedby interpolation(Batschelet(1981: Fig. 5.2 1). We used
usedRayleigh'stestto determinestatisticalsignificanceof mean
exposuresto infer nonrandomorientations(Zar 1984). Concentration (r), or lengthof the meanvectorascalculatedby circular
methods,rangesfrom 0 to 1andisaffectedbyvariationin circular
data, samplesize,and grouping.Valuesof r near 1indicatedata
pointscloselyconcentrated
aboutthe meanangle.
Falconnestcliffsand eyries,and suggestguidelines
for creatingnew falcon eyries.
STUDY AREA AND METHODS
Data from 8 stateswere considered:Washington(Decker
1931), Wyoming-Colorado(Enderson1964), Montana (Leedy
1972), Utah (Porter and White 1973), New Mexico(Platt 1974),
Oregon (Denton 1975), Idaho (Ogden 1973; Ogden and Hornocker 1977), and Colorado (Williams 1981).
We collecteddata from eyriesand associated
cliffsin southern
RESULTS
Wyoming known to have been activebetween 1982 and 1984. We
defineeyrieastheareain andimmediately
aroundthenestscrape.
Eyries. -- Dimensionsof eyriesfrom the present
Nestcliff wasthe rock formationaboveand belowthe eyrie. A
study
were summarized(Table 1), and comparable
singlenestingterritorymaycontainseveralseparatenestcliffsand
eyriesthat are occupiedand defendedin different years.We to Williams (1981) and Porter and White (1973).
climbedto eyriesby ladderor rope;nestcliff measurements
were Williams(1981) reported eyrie lengthsand widths
taken from
below.
Variablesmeasuredat eyriescenteredon the nestscrape,if
recognizable,
or on the approximatecenterof the eyrie. These
includedroof (or overhang)height,width,length,and percent
coverage
of nestscrapebyroof or overhang.We measuredareaof
bothentranceand floorwitha transparent25 cm2grid. Slopeof
both floor and ceilingwere measuredwith a clinometer.Eyrie
exposurewasmeasuredby placinga compass
in the nestscrape
and taking readingsalong a horizontalplane to both outside
edges.From theseazimuths(correctedfor declination)we calculatedmeanandextentof horizontalexposure.Finally,eyrieswere
classedas either potholes,horizontalledgesor shelves,vertical
cracks or crevices, and stick nests.
Nest cliff measurements
focusedon that portionof the cliff
directlyaboveand belowthe eyrie.Variablesincludedcliff and
eyrieheight,inclination
of thetoeslopebelowcliff(determined
by
clinometer),
and aspectperpendicular
to the cliff. Verticalityof
whichaveraged78.9 cm (SE -- 7.63) and 81.1 cm
(SE = 9.52), respectively.Both meanswere significantly less than measurementsfrom Wyoming (tTest; P<0.01). Roof heights of Colorado eyries
(Williams 1981)averaged83.2 cm (SE = 12.04), and
weresignificantlygreater(t-Test; P < 0.01) than we
found. The Coloradodatayieldedan averagefloor
area of 6821 cm2 (SE = 1198.22). Area within 8
eyries averaged 15,000 cm2 in Utah (Porter and
White 1973). Our estimate of area lies between
these,but statistical
comparisons
couldnotbe made.
Floorsof most (80%) Wyomingeyries sloped
downwardstowardsthe front at 5-10ø.Conversely,
most(84%) eyrie roofsor overhangsslopedto the
21
RAPTORRESEARC•20 (1):21-28
22
RUNDE
ANDANDERSON
VOL.20, No. 1
Table 1. Attributesof Prairie Falconeyriesin southernWyoming,1982 to 1984.
VARIABLE
MEAN
Height (cm)
Width (cm)
SE
RANGE
N
47.9
3.62
11-193
68
91.2
7.45
18.313
70
Length(cm)
135.4
8.82
43-400+
71
Floor (cm2)
9325
769.83
1600-29275
70
Entrance (cm2)
5375
975.12
875-53500
56
Floor Slope(o)
7.4
0.78
-10-35
67
Roof Slope(o)
- 12.3
2.23
-65-45
56
rear at a wide range of angles(Table 1). All eyries
we examined,exceptfor 2 (3%), had overhanging
rock or ceilingsprotectingthe nestscrape.Percent
coverageof nestscrapeswasfrequently 100%,and
averaged93%.
Acrosstheir range, Prairie Falconsnestedmost
frequently in potholesor on cliff ledges.Crevices
and sticknestswereusedlessfrequently(Table2).
Nest cliffs. -- Heights of eyriesand nest cliffs
variedwidely.Relativeto meancliff heights,mean
eyrie heightsvaried from 60-70% (Table 3). Mean
heightsof eyriesfrom 8 studieswerehighlycorrelated with mean heightsof cliffs (R2 = 0.99; P <
0.001), and averaged 63% of mean cliff height.
Minimum cliff and eyrie heightsreportedin these
studieswere 2.1 m and 0.8 m, respectively.Signifi-
Table 2. Typesof eyriesusedby nestingprairie falcons.
STATE
POTHOLE 1
CREVICE2
LEDGEa
STIC KNEST
REFERENCE
n
(%)
n
(%)
n
(%)
n
(%)
WY
29
(41)
17
(24)
18
(25)
7
(10)
CO
2
(14)
9
(64)
3
(21)
....
24
(19)
26
14
(39)
7
(19)
....
4
(19)
9
Williams (1981)4
ID
76
(60)
OR
15
(42)
NM
8
(39)
UT
26
(36)
7
(10)
23
(32)
(16)
22
MT
18
(37)
18
(37)
9
(18)
4
(8)
CO-WY
20
(56)
16
(44)
6
(43)
1
(7)
7
(50)
200
(45)
105
(24)
69
(16)
WA
65
(15)
This study
(21)
Ogdenand Hornocker(1977)
(43)
Platt (1974)
Denton (1975)4
Porter and White (1973)
Leedy(1972)
Enderson (1964)
'Includes sites listed as caves, holes and cavities.
2Includes sites listed as vertical cracks.
aIncludessiteslistedashorizontalshelves.Includesa few siteswith sticknests
present.
4Datanot reported but sticknests
used.
Decker (1931)
SPRING
1986
PRAIRIE
FALCON
NESTCHARACTERISTICS
23
Table3. Meanheightsof PrairieFalconeyriesand nestcliffs.
CLIFF HEIGHT (m)
EYRIE HEIGHT (m)
PERCENT 1
MEAN
(n)
RANGE
14.6
(71)
53.7
(14)
4.3- 34.6
36.9
(49)
3.7- 122+
14.0
(21)
30.4
MEAN
(n)
RANGE
HEIGHT
REFERENCE
9.8
(71)
2.9- 30.6
67
This study
32.1
(14)
10 -90
60
Williams ( 1981)
22.9
(41)
2.1 - 61+
62
Denton (1975) 2
6- 35
8.6
(21)
3
61
Platt (1974)
(126)
2.3- 122+
19.8
(126)
2.4- 122+
65
Ogden(1973)2
31.0
(44)
2.1 - 154.4
19.6
(51)
0.8- 137.2
63
Porter and White (1973)
38.1
(57)
9.2- 92+
24.4
(57)
3.1- 76.2
64
Leedy (1972)a
15.8
(36)
7.7- 38.7
11.1
(36)
7O
Enderson (1964)
29.3
(418)
2.1 - 154.4
18.5
(417)
63
Grand
15 - 140
- 30
.....
0.8- 137.2
Mean
= Mean
x 100%
'Percent
height
eyrie
height
Mean cliff height
2Values
biased
lowassomeverytalleyriesandcliffswereexcluded.
SApproximatevalues.
canflymore Wyomingeyrieswere in the upper fidence intervals could be calculated, intervals tbr
one-halfof thecliffsthanin thelowerone-half(X2; eyrieexposureand cliff aspectoverlappedexten-
P < 0.005).But the upperandmiddleone-thirdof sively(Appendix;Fig. 3) Overall,meaneyrie ascliffswereusedequally.
pectsaveraged161.2ø(r = 0.24);meancliff aspects
Inclination
of toeslopes
rangedfrom0-36ø. Most averaged158.3ø(r = 0.19).Due to largedisparities
(57%)cliffswerevertical(85-95ø),
thoughmany in samplesizes,thesegrand meansare biasedto-
(34%)sloped
backintothehill( > 100ø).
Only9% wardour datafrom Wyoming.
wereoverhung(< 80ø).
Aspectsof cliffsand eyriesin Wyomingranged
We found nestcliffsfairly evenlydistributed from 0 - 360ø(Fig.2). We lumpedeyrieexposures
among volcanicbuttes or mountains(34%), into2 groups(northeastandsouthwest
facing)and
sandstonecanyons(30%) and isolatedrock out- foundthat70.2%facedsouthwest;
closetothepercrops(25%).Fewoccurred
on lowrimrock(11%). centage(69.4%) of eyriesthat facedsouthwestin
In Oregon,Denton(1975)reportedeyriesonbluffs Utah (Porterand White 1973; Fig. 16). Extentof
(38%),ridges(29%),canyons
(24%)andoutcropshorizontalexposureof eyriesweexamined(Fig.3)
(9%).
Exposureof eyriesand cliffs. -- Exposuredata
rangedfrom 5 - 160ø,and averaged54 __+
12ø (r =
0.83). Williams(1981) reported"anglesof view"
rangingfrom 30 - 170øandaveraging122--+3ø(r =
0.74).
from6 of the8 westernstates
areshownin Figure1
NeitherANOVA nor X2 testsrevealedany sig-
(Appendix). Except for Utah and New Mexico, as-
nificant(P>0.05) relationships
amongphysical
pectsof bothcliffsandeyrieswasreported.In no traits,includingexposures,
of Wyomingeyriesand
casedid the distributions
of eyrieandcliff aspects historiesof nestoccupancy
and success.
This held
differ significantly(X2;P > 10). When 95% confi- true bothwithinand amongyears.
24
RusI•, ^si• Asi•,]•sos
560*
270*
VOL. 20, No. 1
560*
01
o
5
270
5
04
0.5
o
Figure1. Meanaspectof PrairieFalconeyries(A) or nestcliffs(B) in Montana,Colorado,Wyoming,Utah,Oregonand
New Mexico.Vectorlengthsare proportionalto degreeof concentration
(r) aboutmeanaspect(Appendix).
560ø
360*
Figure2. Frequency
histograms
of eyrieexposure(A) andcliff aspect(B) for PrairieFalcons
in southernWyoming,
1982-1984.
SPRING 1986
PRAIRIE FALCON NEST CHARACTERISTICS
25
360 ø
360 ø
27
90 ø
27
90 ø
214ø/,.,..
'•' I•
•' "--.....
....
•168
ø
Figure3. Meansand 95% confidenceintervalsfor (A) extentof exposureand (B) cliff aspect(brokenline) and eyrie
exposure(solidline),for PrairieFalcons
in southernWyoming,1982-1984.
DISCUSSION
Comparedto other westernraptors,Prairie Falconshavenarrow nestsiterequirements.They nest
almostexclusively
on rockcliffs(cf., MacLarenet al.
1984). Nest cliffs used vary widely in height, location andaspect.Yet in the studiesexamined,Prairie
Falconsdemonstratedsome consistentpatterns in
their useof eyries.Mean eyrieand cliff heightswere
stronglycorrelatedand distributionsof eyrie and
cliff aspectswere similar. We do not infer habitat
selectivitybecausedata on availabilityof potential
eyriesand nestcliffshaveneitherbeencollectedby
us nor presentedin the studieswe cite.
Eyries. -- Potholes,reported most frequently,
provide excellent shelter from both inclement
weather and direct sunlight, but are not always
available.In our experience,potholesoccurmost
frequentlyin sandstone,
whileledgesand vertical
cracksaremorecommonin granite,basaltand conglomeratecliffs.Verticalcracksand crevicesalso
provideexcellentshelterand shade,but may be
subjectedto chillingdrafts.Nestsin creviceswere
reportedinfrequentlyin the literaturebut were
commonin our studyarea.
Nest cliffs. -- Mean eyrie heights, as percentage
of mean cliff heights,were surprisinglyconsistent
and indicateextensiveuseof nestsites60 - 70% up
cliff faces.Further studyis neededto explain this
narrowrangeof eyrieheightsrelativeto cliff heights.
By nestingin the upper reachesof verticalcliffs,
Prairie
Falcons
should
be safe from
mammalian
predators. Such a location also provides a commandingview of the territory and of potentialprey
or predators.Dependingon aspectand prevailing
winds,updraftsalongcliffsmayaid the falconswhen
leavingthe nestto hunt or defend territory. Convective updrafts may form more frequentlyon southfacingcliffsastheyradiatemore heatthan cliffswith
other aspects.
Exposure. -- Prairie Falconshave long been
known to neston cliffs with southerlyaspects(e.g.,
Dawson 1913). Sixty-oneand 42% of the eyries
studied by Enderson (1964) and Ogden (1973)
facedsouth.But their data, asreported, could not
beincludedin our circularstatistics
analyses.With 2
exceptions(Platt 1974; Denton 1975), the studies
examinedindicatedsoutherlymeanaspects(Fig. 1).
Although cliff and eyrie exposurevaried widelyin
26
RUNDEANDANDERSON
VOL.20, NO. 1
most studies,Rayleigh'stest indicated significant
nonrandomnessin most cases(Appendix). Mean
exposureswere often only weaklysignificant(P •
0.10) due to wide rangesof exposuresand because
most data t¾omthe literature were grouped into
broad exposureclasses.
Aspectsof nestcliffsin New
Mexico and eyries in Oregon were random
(Rayleigh'stest;P > 0.10). Excludingthese,mean
cliff aspectranged t¾om144 - 288ø, and mean aspect of eyriesranged from 143 - 226ø. Prairie Falconsdo use north-lacingcliffs and eyries(Figs. 1
and 2). In fact, Tyler (1923) reported that most
Prairie Falcon eyries in southern California had
northerly aspectsand none were southerly.He attributed thisto a scarcityof south-facingcliffs and
an abundanceof north-facing cliffs. Our results
demonstratea tendencyfor Prairie Falconsto use
southerly aspects,but do not demonstrateany
benefit in termsof nestsuccess.
Eyrie configuration
and locationon the cliff mayoverrideeffortsof cliff
aspect(Ellis 1982).Data on availabilityof potential
cliffsandeyrieswith differingaspects
areneededto
concludethat falconsactivelyselectsouth-lacing
lower shelteredcanyons,rims and outcrops(18 38%). However,X2 testsfailed to confirm a signifi-
southwest-lacing
eyriesfailed in 1980. Williamsattributed this to localweatherpatterns.
Bioticthctorslikelyplaya larger role than physicalhabitatin determiningoccupancy
and nestsuccessin Prairie Falcons.Though not confirmedby
statisticalanalyses(X2; P>0.10), nesting Greathorned Owls (Bubo virginianus)were often associatedwith unoccupiedand unsuccessful
falcon
territoriesin our studyarea. Although we did not
quantifyaccessibility
of eyriesto mammalianpredators,thismaybean importantfactor(Ogdenand
Hornocker 1977). Abundanceof prey clearlyall
fectsPrairie Falconproductivityand nestsuccess.
Townsend's Ground Squirrel (Spermophilus
cliffs.
townsendi)densities in Idaho accounted for over
The microclimatewithinan eyrieisaffectedbyits
exposure and cliff aspect; southerly exposures
likely help to moderatecold temperaturesduring
incubationand brooding. Solar heating of nest
scrapesmay lessenthe energy requirementsof incubatingandbroodingfalcons.The majority(97%)
of eyries we examined had overhead protection.
Most eyriesexaminedby Enderson(1964), Leedy
(1972), Platt(1974), Ogdenand Hornocker(1977)
and Williams (1981) were similarly sheltered.
Overheadshademay be important during midday
sincenestlingsexposedto direct sunwhen temperaturesare near 32øC may die (Nelson 1969). Such
temperatures are unusual during the nestling
period in our studyarea, but useof shadedeyries
may increasenestlingsurvival at lower elevations
98% of the annualvariationin Prairie Falconproductivity(USD1-BLM 1979).
Managementimplications.-- Mitigationfor loss
of suitablenestingcliffs due to energy,urban, or
recreationaldevelopmentmay be neededin some
nest sites. Such sites were rapidly colonizedin
California(Boyceet al. 1980)and Alberta(Fyfeand
Armbruster 1977). Becausethe size of the nonbreedingpopulationof Prairie Falconsmay be as
high as 25% of the breeding population(Runde in
prep.) substantial
populationincreases
seempossible, but will dependupon the localavailabilityof
prey and foraginghabitat.
The data presentedhere suggestlocatingnew
nestsiteson south-lacingcliffsabouttwo-thirdsup
and latitudes.
the cliff. Area of the floor should be at least 7,000
We believeshelterfrom late springstormsto be
more important than protectionfrom heat stressin
our Wyoming study area. Such stormswere associatedwith a high rate (64%) of nestingfailure on
buttesin 1983. A springsnowstormthissameyear
was followed by desertion of all 5 active nestson
buttesin a smallarea of northeasternWyoming(J.
Squirespers.comm.).In our studyarea, territories
on tall exposedbuttesconsistently
sufferedhigher
cmz,and slopegently(5-10ø)to the front. Overhead
covershouldbe present,and horizontalexposure
shouldbe about 54ø (Fig. 3A). If eyriesare to be
createdon mine highwallsas part of habitatreclamationor mitigation,their legal,hydrological,and
physical constraints must first be addressed
(Tessman1984). The data in Table 3 suggestthat
cliffs,or highwalls,selectedfor eyrie creationbe at
rates of nestfailure (43 - 64%) than thoselocated on
We suggestthat newlycreatedeyriesbe clustered
cant association(P > 0.10) between nest successand
cliff location.
In our study, neither cliff nor eyrie aspectappearedto determinepatternsof eyrieoccupancyor
nestsuccess
(seealsoOgdenand Hornocker 1977).
Eyrie, but not cliff, aspectapparentlyaffectednest
successin Colorado (Williams 1981) where all 5
areas. An obvious solution is the creation
of new
least 2.1 m tall.
SPRING 1986
PRAIRIE FALCONNEST CHARACTERISTICS
27
together to mimic nesting territories with several NELSON,M.W. 1969. Statusof the peregrine falcon in
alternate
nest sites. These
new territories
could be
spacedapproximately1-2 km apart unlessvisual
barriersare presentto separatethem. In this situation, we have seen successful nests as close as 150 m.
the Northwest.Chp. 4 In J.J. Hickey (Ed.). Peregrine
FalconPopulations: Their biologyand decline. Univ.
of WisconsinPress,Madison. 596 pp.
OGDEN,V.T. 1973. Nesting density and reproductive
success
of prairie falconsin southwesternIdaho. M.S.
Thesis.Univ. of Idaho, Moscow.39 pp.
OGDEN, V.T. AND M.G. HORNOCKER.
1977. Nesting
Our data showthat in a 3-yr period overone-half of
the eyrieswere only occupied1 yr, and 23% were
occupied2 yrs. Similar findingswere reported by
densityand reproductivesuccess
of prairiefalconsin
ELderson(1904) and Ogden (1973). We suggest
southwestern
Idaho.J. Wildl.Manage.41:1-11.
that 2 or 3 nest sitesbe provided per cliff. The PLATT,S.W. 1974. Breeding statusand distribution of
the prairie falcon in northern New Mexico. M.S.
abilityto usealternateeyrieswithin a nestingterriThesis.
Oklahoma State Univ., Stillwater. 68 pp.
tory may help to reducedirect competitionfor nest
siteswith owls,and may decreasethe frequencyof PORTER,R.D. AND C.M. WHITE. 1973. The peregrine
falconin Utah, emphasizingecologyand competition
parasiticinfestations.
with the prairie falcon.BrighamYoungUniv. Sci.Bull.
28:1-74.
ACKNOWLEDGMENTS
TESSMAN,S. 1984. Habitat reclamation proceduresfor
Tricia MacLaren helped locate and collect data from the
surface mines in Wyoming. Pages 185-195. In R.D.
Wyoming eyries. Richard Guenzel programmedthe circular
Comer etal. (Eds.). Proc. of the Symposium:Issues
statistics
calculations.
JamesELderson,GraingerHunt, Larry Irand Technology in the Management of Impacted
win,JamesMosherand KarenSteenhofreviewedearlierversions
Western Wildlife. Steamboat Springs, Colo. Nov.
of thispaper.This studywassupportedby theBLM, the Wyoming
CooperativeFishand Wildlife ResearchUnit, USFWS,National
Wildlife Federation, and the late Robert Runde.
LITERTURE
CITED
BATSCHELET,E. 1981. Circular statistics in biology.
AcademicPress.New York. 366 pp.
BOYCE,D.A., JR., L. FISHER,W.E. LEHMAN,B. HIPP ANDJ.
PETERSON. 1980.
Prairie
falcons nest on an artificial
15-17, 1982. Thorne Ecol. Inst. Tech. Pub. 14. Boulder,
Colo. 250 pp.
TYLER,J.G. 1923. Observationson the habits of the
prairie falcon.Condor25:95-97.
U.S.D.I. - B.L.M. 1979. SnakeRiver Birds of Prey Special ResearchReport to the Secretary of Interior.
Boise,Idaho. 142 pp.
WILLIAMS,R.N. 1981. Breeding ecologyof prairie falcons at high elevationsin central Colorado. M.S.
Thesis.Brigham Young Univ. Provo, Utah. 44 pp.
ZAR,J.H. 1984. BiostatisticalAnalysis.SecondEdition.
PrenticeHall. EnglewoodCliffs, NJ. 736 pp.
ledge.RaptorRes.14:46-50.
DAWSON,
W.L. 1913. The nestingof the prairie falconin
San Luis ObispoCounty. Condor15:56-62.
Wyoming Cooperative Fisheries and Wildlife Research Unit,
DECKER,F.R. 1931. Prairie falcon's nest. The Oologist
48:96.
DENTON,S.J. 1975. Statusof prairie falconsbreedingin
Oregon.M.S.Thesis.OregonStateUniv., Corvallis.58
Received1 May 1985;Accepted20 September1985
PP.
ELLIS, D.H. 1982. The
peregrine
falcon
in
Arizona: Habitat utilization and management
recommendations.
Inst. Raptor Stud.Res.Pap. No. 1.
ENDERSON,J.H.1964. A studyof the prairiefalconin the
centralRockyMountain region.Auk 81:332-352.
FYFE,R.W. ANDH.I. ARMBRUSTER.
1977. Raptor managementin Canada.Pages282-293.In R.D. Chancellor (Ed.). Proc. of the World Conferenceon Birds of
Prey. Vienna, 1975.ICBP. 442 pp.
LEEDY,R.R. 1972. The statusof the prairie falcon in
western Montana: specialemphasison possibleeffects of chlorinated hydrocarboninsecticides.M.S.
Thesis. Univ. of Montana, Missoula.96 pp.
MAcLAREN,
Department of Zoology and Physiology, University of
Wyoming, Box 3166, University Station, Laramie, Wyoming 82071.
P.A.,
D.E.
RUNDE AND S.H.
ANDER-
SON. 1984. A recordof tree-nestingprairie falconsin
Wyoming.Condor86:487.
28
RUNDEANDANDERSON
VOL. 20, No. 1
Appendix: Mean aspectof Prairie Falconeyriesand Prairie Falconnestcliffs.
MEAN
STATE
SIGNIFICANCE
ASPECT 1
r VALUE
LEVEL 2
N
Wyoming
180ø_31ø
0.41
P< 0.001
67
Presentstudy
Colorado
200 ø+ 60 ø
0.44
P < O. 10
Oregon
255ø
O.18
P >0.10
Utah
2260-+ 34 ø
0.36
P < 0.01
14
36
49
Williams (1981)
Denton (! 975)
Porter and White (1973)
Montana
143ø-+ 33 ø
0.34
P< 0.001
49
Leedy (1972)
REFERENCE
Eyries
Cliffs
Wyoming
191+ 23ø
0.40
P< 0.001
71
Presentstudy
Colorado
200ø+ 60 ø
0.44
P<0.10
Oregon
288ø+ 51ø
0.28
P < 0.10
New Mexico
Montana
353 ø
144 ø+ 35 ø
0.07
0.34
P >0.10
P< 0.01
15
36
21
Williams (1981)
Denton (1975)
Platt (1974)
45
Leedy(1972)
•With 95% confidence interval, when calculable.
ZRayleigh's
test.