California bighorn sheep habitat evaluation : Jarbidge and Bruneau Rivers, Owyhee County, Idaho

46 Pages·1998·9.8 MB·English

by  Taylor, ElRoy

BLMLIBRARY
880549 6 IDAHOBUREAUOFLANDMANAGEMENT May1998
CALIFORNIABIGHORN SHEEP
HABITATEVALUATION
JarbidgeandBruneauRivers
Owyhee County, Idaho
^
Vv
by
ElRoyTaylor
WildlifeResearchBiologist
BureauofLandManagement
Boise,Idaho
JimHott
WildlifeManagementBiologist
BureauofLandManagement
TwinFalls,Idaho
RandallB.Smith
RegionalWildlifeManager
IdahoDepartmentofFishandGame
Jerome,Idaho
QL
84.2
.L352
no.98-06

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621
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CALIFORNIABIGHORNSHEEPHABITATEVALUATION
JARBIDGEANDBRUNEAURIVERS
OWYHEECOUNTY,IDAHO
by
EIRoyTaylor,WildlifeResearchBiologist,BureauofLandManagement. Boise,Idaho.
JimKlott,WildlifeManagementBiologist,BureauofLandManagement,TwinFalls,Idaho.
RandallB.Smith,RegionalWildlifeManager,IdahoDepartmentofFishandGame,Jerome,
Idaho
TECHNICALBULLETINNO.98-6
IDAHOBUREAUOFLANDMANAGEMENT
CHALLENGECOSTSHAREPROJECTD010-P4-0179
April1998
'
to
INTRODUCTION
TheobjectiveofthisstudywastoevaluatehabitatsuitabilityforCaliforniabighornsheep{Ovis
canadensiscaliforniana)alongtheBruneauandJarbidgeRiversinOwyheeCounty,Idaho.
Weinvestigatedthepotentialforaugmentingtheexistingbighornpopulationorreleasing
bighornsintosuitableunoccupiedhabitat.Thisbulletindiscussesthesuitabilityofavailable
habitats,describesthecurrentbighornsheepdistributionandprovidesrecommended
managementpractices.
ThishabitatevaluationistheresultofaChallengeCostShareprojectbyBLM,IdahoState
OfficeandIdahoDepartmentofFishandGame,MagicValleyRegion.
STUDYAREA
Thestudyareabeginsabout10milessoutheastofBruneauandextendssouthuprivertothe
NevadaStateLine. Elevationsrangefromapproximately900matthemouthofBruneauRiver
Canyontoabout1800mattheNevadastateline.Thestudyareaconsistsofsteep-walled
canyonsandadjacentplateausoutto300mfromthecanyonrim. Canyonsaretypicallyabout
200mdeep.Principalcanyonsareorientedinanorth-southdirection. Canyonslopesconsistof
alternatingcliffsandterracesformedintoastep-likeprofile. Cliffmaterialiseitherrhyoliteor
basalt. Therearenumeroussidecanyonsthatbranchfromthemajorcanyons. Clifffacesvary
fromstraighttoconvoluted. Theupperplateausareborderedbyabasaltrimrockaveraging
about3minheight.
Plantcommunitiesincludewillow(Salixsp.)inthecanyonbottomsandextensivesagebrush
(Artemisiatridentatatridentata,A.t.wyomingensis,andA.t.vaseyana)standsontheplateaus.
Thefewtreespresentarecottonwoods(Populusspp.),westernjuniper(Juniperusoccidentalis)
andquakingaspen{Populustremuloides).Grassesincludebluebunchwheatgrass
(Pseudoroegneriaspicatd),Sandbergbluegrass(Poasecunda),andwildrye{Elymuscinereus).
Theprincipallanduseislivestockgrazinginspringandsummer. Recreationusesinclude
hunting,Whitewaterrafting,hikingandfishing. Huntedspeciesarebighornsheep,muledeer
{Odocoiieushemionus),pronghorn{Antilocapraamericana),sagegrouse(Centrocercus
urophasianus)andchukars(Alectorischukar). Bobcat{Lynxrufus)trappingandpredator
huntingoccurduringwinter.
METHODS
ABell206BJetRangerhelicopterwasusedtocountbighornsheepandevaluatebighornsheep
habitats.FlightsweremadeonJune8,9,10,and11,1993andAugust26and27,1994. The
helicopterdoorswereremovedtoincreasevisibility.Twoorthreeobserverswereused
1
dependingonflyingconditions. Onlytwoobserverswereusedwhenhightemperaturesand
canyonwindsmadeflyingdifficult.Flightswereconductedwhentheweatherwasclearand
visibilitygood.
Habitatevaluationandpopulationdatawererecordedduringthesameflightwhenpossiblebut
populationdatawasthepriorityduringfirstflights. Additionalpasseswereflownasnecessary
tocollecthabitatevaluationdata.Populationsurveyflightswerelimitedtoareaswherebighorn
sheepwereknowntobepresent. Habitatevaluationscoveredtheentiredrainage. Observers
whoparticipatedbothyearswereRustyAnderson,RandySmith,DonStucker,andEIRoy
Taylor.Additionalobserversin1993wereTimCarrigan,JimClark,JimKlott,CraigKvale, .
LouisNelson,andLloydOldenburg.
ThecensusandhabitatevaluationswereconductedalongtheBruneauandJarbidgeRiversin
OwyheeCounty,Idaho.WesearchedareasnearcanyonsfromthemouthoftheBruneauRiver
upstreamalongtheBruneauandJarbidgeRiverstotheNevadastateline.Thereisarough
divisionbetweenoccupiedandunoccupiedhabitatsatabouttheconfluenceoftheBruneauand
JarbidgeRivers.Unoccupiedhabitatwasgenerallyfromtheconfluenceofthetworivers
downstreamtothemouthofBruneauCanyon.Occupiedhabitatextendedupstreamalongboth
riversfromtheirconfluencetothestateline.
Populationsurvey:
SurveyfollowedsightabilityprotocoldevelopedbyBodieetal.(1992). Thistechniqueconsists
ofselectingblocksofhabitatandflyingroutesalongcanyonwallsatabout200footelevation
intervalswithineachblock.Flightsbeginalongthecanyonbottomandendwithasweepout
overtheplateautofindanysheepthatmightbeoutofthecanyon. Typically, wemadethreeor
fourtransectsoneachsideofthecanyonfollowedbyatopsweep. Sightabilityconditionsare
recordedforeachbighornsheepobservation. Dataarerecordedfor:(1)terrainwhereanimalwas
seenincludingclifftype,(2)activity, standingormoving,and (3)lightconditions,sunorshade.
Weclassifiedeachobservedbighornsheepbysexandageclass(Giest,1971). Weclassified
ewesandlambswithnoattempttoseparateyearlingewes. Weclassified ramsintoclassI
(yearling),classII(>l/2curl),classIII(>3/4curl),andclassIV(>fullcurl). Population
estimateswereobtainedbycomputermodelmanipulationoffielddatatoadjustforsightability
conditions. Estimatesofthenumberofsheepineachageclassweremade.Populationestimates
arefollowedbythe90%confidenceintervalinparentheses.
HabitatEvaluations:
Abighornsheephabitatsuitabilitymodelwasdevelopedbasedonthe"HabitatSuitabilityRating
SystemforDesertBighornSheepintheBasinandRangeProvince"(ArmentroutandBrigham,
1988). CategoriesweremodifiedtofitCaliforniabighornsheepinsouthernIdahobasedonthe
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nearbyLittleJacksCreekstudy(E.Taylor,unpublisheddata).Basically,theirsystemwas
modifiedbymakingthecategoriesmoregenericandarbitrarysotheycouldbequicklyevaluated
fromahelicopter. Twoexampleswillillustratethedifferencesbetweenourmethodsandthose
ofArmentroutandBrigham. Weratedforageonacontinuousscalefrom pointsforexotic
annualswithoutshrubsupto10pointsfornativerangewithgoodshrubandbunchgrass
components. Theirratingsystemconsideredforageareas,seraistageorcondition,distanceto
escapecover,andvisualobstruction.Weratedwaterfrom fornowaterinanevaluationblock
to10fornumerousperennialsourcesandgavebonuspointsifthesourcewashighonacanyon
wall.Theyratedwateronamountandpermanence,distancefromescapecover,competition,
visualobstruction,anddistribution. Webroketopographyintoslopeandlambinghabitatbased
ontheLittleJacksCreekdata.Eachhabitatvariablewasratedonascalefrom forunsuitableto
10forexcellenthabitats. Ahabitatevaluationfieldformwasdevelopedforuseinthehelicopter
(Appendix).
Thestudyareawasdividedintoblocksofsimilarhabitats.Landmarkswereselectedattheendof
eachblockandlatitudeandlongitudecoordinatestakentoensuremappingaccuracy. Thesame
blockswereusedforthepopulationsurvey andhabitatevaluationpurposes.Allhabitatvariables
werescoredineachblock.Scoresforeachhabitatcategorywerediscussedbyobserversuntil
agreementwasreached.Totalscoresforeachhabitatblockwerecalculatedbyaddingthescores
ofallhabitatvariables.Habitatswerethenrankedbytotalscores.Habitatswiththehighest
scoreswerejudgedtobethebesthabitatforbighornsheep.
Thecharacteristicsofadjacenthabitatblockswerealsoconsideredduringtheevaluations.Blocks
withcomplimentaryscoreselevatedtherankofindividualblocks. Forexample,ablockwith
abundantlambingshelveslocatednexttoablockwithgoodforagewouldberankedaheadofa
similarlambingblockbutwithoutavailableforagingarea. Lowcategoryscoreswithinan
analysisblockwereusedtoidentifypotentiallimitingfactors.Thepotentialformanagementto
improveahabitatwasusedtobreaktiesinhabitatrankings.
Thenumberofsheepthatcouldbesupportedinsuitablehabitatswasestimatedtobefive
bighornspersquaremile. ThisestimateisbasedonworkinOregon(VanDykeetal.,1986)and
issimilartothefivetosixsheeppersquaremilepresentonthenearbyLittleJacksCreekarea.
Thenumberofacresusedincalculationsincludedcanyonsandplateauwithin300metersof
canyons. AtLittleJacksCreekabout95%ofalleweobservationswerewithin300metersofa
canyon.Thecapacitiesofadjacenthabitatswereconsideredtoidentifythepotentialforthe
combinedhabitattosupportaminimumviablepopulationofbighornsheep.
Thefollowingisabriefdescriptionofthecategoriesevaluatedandtheratingcriteriausedfor
eachcategory.
Slopeswerejudgedexcellentiftheywere>50%andincludedcliffsandledgessuitable
forsecurity/thermalcover. Slopesbecamelesssuitableastheyapproachedeitherflator
vertical.Slopesintermediatebetweenexcellentandunsuitablewerescoredaccordingto
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theirperceivedusefulnesstobighorns.
Lambinghabitatwasjudgedonpresenceandabundanceoflambingshelves. Lambing
shelveswereidentifiedasisolatedterraceswithdifficultaccess. Habitatratingswerelow
iffewormarginalterracesexistedandhighifanabundanceofsuitableterraceswas
present.
Accessibilitywasbasedonavailabilityoftravellanessuitableforbighornsheeptocross
slopesfromtoptobottom. Ahighratingwasgivenifcliffswerebrokenintosegments
bytravellanes. Lowratingsweregiventolongcontinuouscliffswhichlackedcrossing
routes.
Livestockusewasameasureofgrazingpressure.Excellentscoresweregivenifnosign
oflivestockwaspresent. Lowscoreswereawardedforthepresenceofnumerousdistinct
trailsandabundantsignsofcattlegrazing.Ifpartsofahabitatblockhadobviously
differentgrazingpressure,theywereevaluatedseparately.Typically,grazingpressure
wasmostevidentinriparianareasandonplateausadjacenttothecanyon.
Thevegetationcategoryratedplantcommunitycomposition. Nativerangewithagood
mixofshrubsandbunchgrassscoredhigh. Annualgrasses,weeds,andmonoculturesof
crestedwheatgrassscoredlow. Aswasthecasewithlivestockuse, insomecasesthe
plateau,slopesandriparianareaswereratedseparately.
Thewatercategoryscoredhighifwaterwasabundantandconvenient,especiallyif
locatedhighonacanyonwall. Lackofwaterorwaterlargelyinaccessiblescoredlow.
Ephemeralwateralsoscoredlow. Wheninformationwasavailable,notesweremade
regardingthepresenceofwaterduringdroughtyears.Goodwateravailableatthebottom
ofacanyonwasscoredasaneight. Ifthissourcewasaugmentedwithspringsonthe
canyonwall,thescorecouldbeashighas10.Waterwasconsideredavailableifitwas
within2milesofahabitat.
RESULTS
Populationsurvey:
Surveyanddistributionpatternsforthetwoyearsweresimilar(Table1). In1993,wesaw114
bighorns;51ewes,55rams,and8lambs.Therewere16legalrams(ramsthatcanbelegally
takenbyhuntersmusthavehorns_>3/4curlorexceed4yearsofage)and39sublegalrams.
Thepopulationestimatebasedonthecomputeradjustmentforsightabilitywas165(±37)
bighornsconsistingof79(±27)ewes,73rams(±18),and13(±6)lambs. In1994,weobserved
132bighorns;76ewes,32rams,and24lambs.Wesaw17legaland15sublegalrams.
Observationsadjustedbythesightabilitymodelgaveapopulationestimateof174(±31)bighorn
sheepconsistingof101(±22)ewes, 42(±13)rams,and31(±8)lambs. Weestimatedthatthere
were19(±6)sublegalramsand23(±8)legalramsinthepopulation.
BighornsweredistributedalongtheJarbidgeandBruneauRiversabovetheirconfluencenear
IndianHotSprings(Figs.1&2). SheepwereseenontheJarbidgeRiverfromtwomilesabove
DorseyCreekdownstreamtotheconfluence. SheepwereseenontheBruneauRiverfromBlack
RockCrossingtotheconfluencewiththeJarbidgeRiver.
Table1. CensusData. Countsarerawdatawhileestimatesarethecountsadjustedforthe
sightabilityofeachobservation.
Category 1993Count 1993Estimate 1994Count 1994Estimate
Total 114 165(±37) 132 174(±31)
Ewes 51 79(±27) 76 101(±22)
Rams 55 73(±18) 32 42 (±13)
Lambs 8 13(±6) 24 31(±8)
SublegalRams 39 53(±14) 15 19(±6)
LegalRams 16 20(±6) 17 23(±8)
ELKOCO R.6E.R.7E. R.7E.R.8E. NEVADA R.8E.R.9E. R.9E.R.10E.
0.51 2 3 4Miles
Scale
Fig.1. LocationofCaliforniabighornsheepseenduringtheJune1993census. Observation
numbersarekeyedtocountsandclassificationinTable3.