V74 P286 Rocklage and Ratti.PDF
Ann M. Rocklageand John I Rattii, Departmentof F sh and W d fe ResourcesUnverstVofldaho N,toscow. daho 83844-1136
AvianUse of RecentlyEvolved Riparian Habitat on the LowerSnake River,Washington
Abstract
Since I 975 |he U. S. Armv Corps of Enginccrshas managedand inigatcd 440 h.r along the lo\\'er S. akc River in $ishi ngron as miiigalion lbr ibur dams constructed 1962 1975. \!e investigatedavian use of irrigated Habirat \{anagenenr Units (H\'{Us). comparedto non-i|rigated sitcs and streamsthirt entered the ri\'cr \\t conductedbird sur|cys al25 siresin sumnrerand fall 1997 and in sprinS 1998. \le compared alian abundance.spccics richness.and sfecies dilcrsitv among hrbitats a.d scrsons.we detectedan averagcof 169 birds and 33 speciesat HMUS. 120 birds and 28 specicsal non inigated sires.and 6l birds .rnd 2l speciesalong strcamsin a1l thee \eason\. We delcctcd an averageof 29 species/sitcin summer, 31 in fall. and 22 in spfing. Speciesdi\'ersil!. as mcasuredby the Shannon Wicncr lunclion, was higher jn summer. irdicaling that largc ilocks of a felv specieswefe common in lall and spring. These data dcmonsrated thai the lower Snakc Ri\er is an imporranr slopo!er site for migrating birds.$e derectcd an alerage of 30 more bird spccicsthan a study conduciedon thc samearea in I 97,1.Thc increasein speciesrichnes\ is attributed!o thc delelopment ofHtr{Us and to naturalsuccession ofpalustrine vegetatim sinceda connruc- tion. Fuiure potential changcsin reseNoir lelels, iuch as brcachingofdams. r'illundoubredly ulect bird comrNnities along the lo**er Sn.rkeRi|er in all scasons.However. our data demonsratedthat habitatpenurbations can be panially mitigatcd b] habitat enhrncementand managelneni.
Introduction Severalstudies have been conducted to evalu ate wildlife communitiesand habitatsalong the The importanceoI riparian zonesfor birds in thc lowerSnake River (e.g.. Asherin and arid andsemi-arid West has been well documcnted Claar1976. Lewkeand Buss 1977, Monda and Reichel (Szaro1980. Knopf and Samson1988, Johnson 1989, Corps199 19E9.Schulz and Leininger 1991. Douglas et al. J, Downset al. 1996);however, nonc lqq2. Cl:rr) .rnLlVedin I q93). Wr..lirn ripirridn have specifically addressedthe wildlife value of zonesgenerally have a higher structuraland veg- irrigrtedHMUs. Our objectir e. u er..ru e.rimare etativediversity than uplands. This leadsto a higher and compareavian abundance,species richness, numberofniches andhigher species density, rich- andspecies diversity among inigated HMUS. non- ness.and diversity (Jolnson 1989. Clary and Medin inigatcd riparian sites.and strcamsthat entered 1993).However, many westcrn streams and riv the river. These data were part of a repofi sub- ershave been altcred fbr hydropowerproduction. mitted to the U. S. Army Corps of Engincers resultingin the loss of riparianhabitat (Lewke (Rocklageand Ratti 1998). andBuss 1977). Four d;uls werebuilt on the lower SnakeRiver StudyArea betweenl962- 1975. These impoundments rcsuked The lower SnakeRiver study areaextended 209 in theloss of approximatelvl.200haofriverine knr trom Ice HarborDam nearKenne$'ick. Wash- habitat(Corps 1991).In 197-5,thc U. S. Army ingtiu. upriverto the conf'luenceofthe Snakeand Corpsof Engineers(Corps) initiated the Lower Clearwaterrivcrs at Clarkston.Washington. The SnakeRiver FishandWildlife CompensationPlan study arca included fou| reservoirs:Ice Harbor, 1()analyze and mitigate impactsto t'ishand wild- Lower Monumental.Littlc Goose,and Lowcr life resultingfiom thesedarns. The Corpsacquired Granite.SeeAsherin and Claar (1976) and Lewke and/ordesignated 1,702 ha of land for wildlile andBuss (l977) for a dctaileddescription of the habitat(Corps l99l). Approximatclv440 ha have studyarea. becndeveloped as 10 intensivelvmanaged and irigated HabitatManagement Units (HMUs). Twenty-live study siteswere selcctedtbr bird surucysin 1997and 1998.Study sites were di- videdrunong three habitat types:7 irrigated HMUs. rAu$orto $honl corespondenceshould beaddrcsscdt email: [email protected] 7 non idgated sites,and ll streams.Irrigated
286 Nothu'est Science,VoI.7,1, No.,1.2000
Ol00()hy rheN.(rrenS.renrilic,\i\irLrhon AlLrr:h$E!erred HMUS wcrc locatedon barsor benchesalong the non-irrigatedsitcs, stalions werc locatedapproxi- SnakeRiver and werc intensivelymanagcd and mately equidistantbetween shoreline and inland irrigated.Thcy were characterizedby patchesof edge of the bench. Stationsalong sfeams were trees and shmbs interspersedwith upland habi placed on the edgeof riparian vegetation.There tats and crops planted for u ildlile such as hay. were 44 stationson irigated HMUs. 43 on non corn. sunflower.and millet. Trees commonly irigated sites,and 46 along streams. planted on irrigated HMUs wcrc Russianolive The variable circular plot (VCP) rnethod (EL.te.tgnusa gustilblia), poplars (Popultrsspe- (Reynoldset al. 1980)u,as used to surveybirds. cics),dogwood (Corzus species) and black lo- We surveyedbirds in threeseasons: summer (i.e.. cust (RoDlrla pseudo-acacia).Shrubs included thebreeding season),1all, and spring. Breeding- Siberianpea ( Carrr,qarrna r&orescers). bufthloberry bird survcys took place from mid May thfough (.Shephediaspecics). rose (Ro.r.rspecles), and mid July 1997.Fall surveysoccurred during Sep- Himalayanblackberry (Rubusdiscolor). Un- temherrnll O,.toher of 1997.lnd springrurr ey. managedupland habitat was largely composed from mid-March through April 1998. Each sur of lbrbs and grasses.cspccially of cheatgrass vey stationwas visited four times in summerand (B rLtm u s te ct o nn t). bluebunchwheatgrass (Agro- three times in tall and spring. Observersrotatcd plron spicatunt),and Srndberg blucgrass(Po.i amongstations to distdbutepotential differences sard6ergll).Rubberrabbrtbrush(Chn^sothamnu.t in observerability. To distributc dil'ferencesdue nduseosus)and big sagcbrush(Artemisio tri to time of day, we also rotatedthe order stations dentata) \\de also common in upland habitats. \\"erevisited (Robbins 1981). Surveys bcgan at Shorelinehabitat included white alder (Ahrs or nearoft'icial sunriseand continueduntil 1000. rhonbifoli a), scrub-willowcomnunities (Sa1lr Surveysdid not take place during rain or when species),and palustrine-emergent vegetatiol. such wind interleredwitb observer'shearing ability. as cattail (Irplrrr species),bullrush (Sciryrasspe- EachVCP surveywas 10 minutes.Observers cies). and rccd-canarygrass (Phdaris urun- recordedspecies of all individualbirds detected di\u&d). and distancein meters to each bird. Birds that Non-irrigatedsites rverc also located along the tlushed asthe obserr,'erapproached the station were river Thcy t_r'-picallyhad na.now strips of palustrine countedas if they were detectedduring the sur- .hruh-.cmbcnd prltrstrine-emergent \ egetJrion vey.All flocks and family groupswere recorded along the shore,vhich developednaturally since as such.Birds or flocks flying over the sampling damconstruction and subsequent formation ofres- area were recordedseparately because it could er\oirslDo\\ n\ tl rl. lao6).Prlustrinc !..gclalion not be determinedwhether thcsc birds were us- was irnrncdiatclybordercd b)' uplandvegetation. ing the sampling area:however birds that flew Study streamsor drainagesentered the Snake within sampling area vegetationwere recorded Rivel, and rangedin sizefiom the rclativcly large asdetections within theVCP Birds that flew from TucannonRiver to small.nafow canyonswith anotherarea aDd landed in the samplingarea af ephemeralstrcarrs. All drainageshad woody veg- ter lhe suney beganrvele recordedas flyovers. quantity etation,although type and of vcgctatior'] Density cstimates(birds/10 ha) for each site often varicd dramaticallydepending otr seasonal in eachseason were calculatedwith the ordered- precipitation.and slopeof watersupply, annur) distancemethod atter Roeder et al. (1987).We walls.Riparian vegetation rvas immedi- canyon chosethis nonparametricmethod for its lower atelybordered by uplandvegetation. Most strcams varianceestimate and robustnilture under a vari- had u'hite alder, but in various sizcs and densi etyofsituations (Roeder et al. 1987).The method ties. Himala),anblackberry was also common. ci,Llculatedan ellective surve)' arca for cach Palustrinewillow and emergentvegetrtion oftcn species.At least30 dctectionsof a specieswere occurred llong strcams, particularly at the neededto calculate a reliable effectir,earea confluencewith the SnakeRiver. (Burnhamet al. l9E l). Civen that one ssunrp- tion ofthe methodis thatcach detection is inde- Methods pendent(Roeder et al. 1987).wc calculatedden- We placedbird-survcy s{ations ,+00 m apartalong sity of tlocks if greaterthan 207. of a species il transectat each site. On irrigated HMUs and detectionswere of flocks. Flyovers wcrc not
Avian Use of SnakeRiver Riparian Habitat 287 includedin densityestimate calculations. All de- Its theoreticalnaxirnum is logr(S).u,here S is tection distanceswere truncatedto 200 m at each mlrimunrnumher o[ specie.in lhL'cornnrunitv. stationto eliminatethose outsidc the targethabi- However,in biologicalcommunities H'r'arely tats. Effective arcas were calculated separately exceeds5.0 (Krebs1989). fbr eachseason since species' detectability may Variableswcre checked lbr univariatenomtality vary amongseasons (Gutzwiller l99l). Becausc prior to analyseswith probabilityand quantile plots. observer-hearingability can changein different Many specieshad non-normal plots due to zero habitats (Schieck 1997), an ef1'ectivei{ea was entricsat somesites. Because the rcsearchques, 'r calculaleJli eachhabitat tl pe lor thosespccies tion is multivariate, speciesdensities could not with more than 30 detectionsin eachtype. be usedin the analyses.Therefore, data were col- SwallowseLre difficult to accuratelysurvey with lapsedinto overall avian abundance;i.e., the av- the VCP method.Their switi, d;fting flight make eragenumberofbirds detectedat eachsite. Avian it difllcult to count and measurcdistances to all abundance,species richness. and speciesdivcr- individuals.Furthermore, it is uncertainwhether sity lnet the nomality assumptionand wereused they classity as tlyovers. Therefore, observers asdependent vadables in a multivariateanalysis countedthe numberof individualswallows ob of variance(MANOVA). The main effects were scryedat the beginning of the survey.We calcu- habititttypes (irigated HMUs, non-itrigatedsites, lated relative abundanceof swallows (average and streams).seasons (summer, fall, spring),and numbcr observed)fbr eachsite in eachseason. their interaction.We usedunivariate F-tests and Becausefall birdsare less vocal andmore cryp- canonicalcorrelations to examinewhich dcpen- tic, we also uscd an area-searchrnethod in fall. dent vadablescontributed to significantmain el'- "bird This methodis similar to watching" in that fects. Fisher's LSD was then used fbr multiple thc observerwanders through an areaand records comparisonswithin treatments. numbersof each speciessccn or heard during a specilicdtime period(Ralphet al. 1993).Observcrs Results wereinstmcted to paypaflicular attention to dense- We detccted92 speciesduring the brecding sea- riparianvegetation and fruiting plants al all sites sonon the lower SnakeRiver Includingflyolers, and cropsat irrigatedHMUs. They were allowed thetive mostfrequendydetected species were bank to take as much time as neededto identif,vbirds. sw^llow (.RipariLtriprrrio; n = 1,185).clif'f swal The searchperiod occurredbetween sunrise and low (Hiruntloptthoaora; r = 1,078).red-winged noon. The arca-searchmethod $'as only used to blackbird(Agelalls phoeniceus. n = 881),west obtain a more completespecies list for cach site. ern meadowlark (.Stunrcllaneglecta. n = 5731, Survcydata were used to calculatespecies rich- and Bullock's oriole (lcterus buLktckii.n = 489). nessand diversity.Spccies richness was total Absolutedensitics were calculated for 30 spccies. number of speciesdetected al each site in each Red-winged blackbird (13.131birds/10 ha), scason.Both VCP andarea sealchdala werc used Bullock'soriole (10.63birds/10 ha), American for calculationofspecies richness in fall. We used goldfinch (.Ca rduel i s t i sti s, 7 .72 birds/1 0 ha). averagenumber of eachspecies dctccted at each brown-headedcowbird, (M olot lt rus at e r; 7.8 | bids/ siteto calculatedivcrsity in eachseason. Diver l0 ha).lnJ Amcriir n ro\in tTtrrJu.tntt lrotoritr': sity indices measurethe number of specicsand 5.63 birds/IOha) had the highestdensities. See evennessof specicsrepresentation in a commu Rocklageand Ratti ( 1998)lbr additionalresults. nity. We chosethe Shannon-WienerFunction (H') Duringlall n,1 specieswere detccted using hccru:eit is sensitirelo chrngesin rlrc spe.ies both VCP and area-searchmethods. Including in thecommunity. ll) u\ er..the mosl lrcquentl; ,J. teL ted spec ies were Shannon-Wiencrt'unction: red-wingcdblackbird (,? = 1.906.),white-crowned sparrow (Zonotrichitt leucopltrys; r = 1,635). H,=I(pr)flog.p,) Amelican goldfinch (r = 832), Canadagoose \Brant.l canadeflsis.r = 7,12).and Europeanstar $,herep = proportion of eachspecies in the ling (.tlr.1r.,ii.rrvul garis; n = 737). Starlings.bow- total sanple. ever,were only abundantat one irri€ratedHMU.
288 Rocklagc and Rrtti Seventeenspecies had a sufficientnumber ofde- types(F = 5.7,14;df = 6,136;P ( 0.001)and sca- tectionsto calculatedensity, and we calculatcd sons(F = 8.57,1:df - 6,l36: P ( 0.001)were sig- densityof flocks for I I of thesespecies. White- nificant. Univariate F tests and canonicalcorre crownedsparrow (17.69 flocks/l0 ha,mean flock lationsshowcd that avianabundance (F = 2.1.685; size = 5.10), song spanow (Melospizamelodict: df = 2,'70tP < 0.001)and speciesrichness (F = 14.50flocks/l0 ha,mean t'lock size = 1.32),sa- 11.206:dl = 2.70; P ! 0.001 ) weredifferent among vannahsparrow (Passert ulus sandw ic hensis; 6.29 habitat types in all three seasons.Mean avian flocks/I0 ha, meanflock size= 2.31),yellow abundancewas higher at inigated HMUs (168.84 rumped warbler (Deadroica contnata; 2.30 tlocks/ I 22.9I birds)than both non-irigated sites ( I 20.47 10 ha, mean flock size = 3.20), and American + 10.30birds) and strcams(62.55 I 5.5,1birds) goldfinch(3.22 tlocks/10 ha, meanflock size= (Table1). Species richness showed the sametend, 2.56) had the highestdensities. with more speciesfound at inigatedHMUs (33.14 Wedetected 9l speciesduring spring. The most t 1.52 species),followed by non-irrigatcd sites frequentlydetected species were white-crowned (27.91t L64 species)and streams (23.18 t I .48 sprmow(n = 1,344),Americangoldfinch (,? = 862), species)(Table 1). red-wingedblackbird (n = 809).westem mead- For the eflectof scasons,species richness (F owlark (r = 802). and Canadagoose (r = ,107). = 13.817;df = 2.?0;P ( 0.001)and diversity (F = Of the 21 speciesfor which density was calcn 2.808;df = 2,70;P = 0.067)contributed to the lated,white-crowned sparrow (4.28 flocks/10 ha, significantMANOVA, andwere dift'erent among meanflock size= 5.86),song sparow (6.90bilds/ scasons.Species richness was higher in tall (30.96 l0 ha),westem meadowlark (6.62 birds/10 ha), t 1.8,1species), tbllowed by surnmer(29.32 t red-wingedblackbird (5.30 birds/10 ha), and 1.52spccics), and spring(21.60 t 1.31species) Americanrobin (,1.62birds/10 ha) had the high- (Table2). Spccicsdiversity. however, \\,as high- estestimates. est in summer(summer. Shannon-Wiener Func- Therewa! no signilicantinteraction between tion= 3.651t 0.157,spring = 3.291t 0.110,fall habitatsand seasorsin the MANOVA model (F = 3.2271 0.I 33)(Table 2). Although the average = 0.772, TABLE L Mean numberofbirds. number ofspecies,and speciesdiversit) (Shannon-Wienerfunciion ) a! imgated Habi!a! lvlan agementUnits (HNIU). non-inigated sites,and stfeans. lower SnakeRiler, $rashington.I997- I998 Meanscombinc sunnncr.tall. and spring cnjnr atc\. Diffcrcnllc(crs lbllowingmeans indicale signilicanrdiilerences (Fisher's LSD;P < 0.100r. Non-irrigated Strcanr df P Mean SE Mean SE Nlean SE Nnmber of Bifds 2:1.685 2.10 < 0.001 168.837a22.905 120.,168b10.302 62.5,15c 5.511 Number of Species 1,1.206 l.tt) < 0.001 ll.I.1la 1.517 21.905b 1.636 :3.182c 1.,183 SpeciesDiversit) 0.206 1.10 0.81,1 3.'156a 0.163 1.106a 0.111 3.336a 0.112 TABLE 2. Mern number ol birds. nunber ol species. nd \pecies ditersit) (Shannon-wienerfunction) in \ummer. fall. and spring. lo\ier Smke River. [ashingtoD, 1997 1998.Nleans combine estimatesfionl irrigated Habitrt Management Uni6 (H!lU ). non imgalcd sircs. and streams. Dillerent letlersfollowing neans indicatesignificant difterences (Fisher s LSI);P< 0.i001. Summer I"all Spring N{ean SE Mean SE Mean SE Numbcrof llirds 0.19,{ 2.10 0.676 91.870a 9.075 121.880all.00.1 1(15.827a1'1..119 Numbefof Species 13.817 1.70 < 0.001 29.320a 1.516 30.960a 1.8,13 21.600b 1.311 SpeciesDivefsity 2.808 2.70 0.067 3.651a 0.157 3.22tb 0.133 3.291b 0.110 AvianUse ofSnake River Riparian Habitat 289 121.88t 21.00birds in fall. 105.83t 14.43 flyovers were of largeflocks that may havebeen birdsin spring,and 97.87 t 9.08birds in sum- disturbedby the obsen'erWe thereforesffess that mer (Table2). our numbersmay underestimatethe value of the louerSnule Rir er asr mi!ritli.)n.lopo\er.ile. Discussion we demonstratedthat more speciesand more birds werepresent at irigated HMUs than at non- stopoversitcs that ofler safeand plenti- Quality irrigated sites and streamsin all three seasons. ful food sourcesare critical for migrating birds To further examine the impodance of irrigated (Moore et al. 1995).Such sites are probably most HMUs and other lower SnakeRiver habltats.wc available in riparian areasin the arid and semi- comparcd our lesults r'"'iththose from a study addwest (Mooreet al. 1995).Our numbersindi- conductedin1974 (Asherin and Claar 1976).They catedthat all lowcr SnakeRiver riparianhabitats the lowerSnake River into two reaches: were impofiant stopoverareas during fall migra divided Ice Harbor reservoirand from Lower Monumen- tion. Asherinand Claar (1976)observed more dam to Clarkston,Washington. We divided our specieson the lowcr SnakeRiver in spring.Ri- tal In tce Harbor,we detected39 more parianhabitats on the Umatilla National Wildlife datasimilarly. 49 more in fall, and 16 more Relugealong the ColumbiaRivernear Hemiston, speciesin summer, (Figure sccondreach. we de- Olegon, also appearedto have higher numbers in spring l). In the in summer,40more in of birds during tall migration than sunrmer (S. tected2,+ nore specics (Figurc 2). Although Hudson,University of ldaho,Dept. of BioSci., tall. and 1.1nrore in spring suNey loca- Moscow.lD,pers. comm.). Because this was only sun'ey intensity ditfered and actual $'e method- a onc-yearstudy, we do not have dataon annual tions occasionallydiffered, bclieve vadation in numbersor weatherpattems. Unfor- olog1' alone cannot accoult tbr these dramatic tunately,wedid not studyavian communities along differences.Thc increasein nurnberof bird spe- the lower SnakeRiver during winter. and *e feel cie5dete(1,:dlikel) ua\utlrihulrble loan inrrer:.' this is an impofiant areafor future research. in quality habitatsince the first lower Snakedam was constructedin 1962and the developmentof Even thougbour methodsdetected more birds irrigatedHMUs in 1975.In 1974there was little and speciesduring fall, we feel that abundance or no shorelineregetation, as previous vegeta- estinates tbr fall u,ere conservativefor several tion was llooded and new vegetationhad little reasons.First. bird songis decreasedin fall; thus, timeto develop.Monda and Reichel ( 1989)com- wc probably missedbirds with the VCP method. paredavian ;rbundance and species richness along Even though u'e detectcdmore specicswith the Lower GraniteReservoir pre- andpost-irnpound- areasearch (106 speciesrvith areasearch, 9,1 with ment.They found that riparian-associatedpasse VCP). this methodwas not standardizedand abun- rincsdecreased tiom 1973to 1981,and that up- dancescould not accuratelybc conpared with land-associatedspccies correspondingly increased. thosefrom thc VCP Second.317o of all detec This changewas attributed to lossin riparianveg- tions in tall were of flocks, comparedto 20c1,it etation.A study conductedin 1996 showed an spring and 27c in summer.We believe there $'as increasein palustrineemergent and palustrjne oftenserious underestimation when counting birds shmb-scrubvegetation along the lower Snake Rivcr in flocks, particularly when mixed flocks werc since 1987.particularl), at slack water areasand foraging in dense-shrubpatches. Species diver- at dcltasof maiortributaries (Downs et al. 1996). sity waslowest in fall. which alsoindicated that Thcrefore, birds have respondedpositively to largeflocks ola 1'ewspecies. such as white-crowned habitatsoffered at HMUS and to the naturalsuc- sparrow and red winged blackbird, werc super- of riparianvegetatlon. abundant.Third, l ii% ofall detectionsin fall were cession of flyovers, comparedto 1I 7. in spdng, and 7%' Future potential changesin reservoir levels, in sunll-Iler.Beclusc it could not be accurately suchas breaching of dams.will undoubtedlyal- determinedwhether tlyovcrs werc using the sul' f'cctbild comnrunitiesalong the lo$'erSnake River vey area.flyovers were not included in any sta- in all seasons.If the SnakeRiver is allowedto tistical tests.Birds that were flying over thc area return to pre-illlpoundmentlevels. effects on the during surveysmay havc been using thc Snake aviancommunity will be a complicatedlnterac- Rjver corridor tbr migration. In addition, many tior anong natulal and managementresponsesl 290 Rocklageand Ratti 80 60 'o o tt) a19lI 40 E1997-98 e 30 z= 10 Summer Fall Spring Figurc l. Number of bird specicsobserved in three seasonsalong lcc Harbor Reservoir,Washingon in l9l'1 (Asherin andClaar 1976) and in 1997-1998. a '^ o o .i974 E 1997-98 o E z Summer Fall Spring Figufe 2 Number ofbird specie\ ob\eNed in threescasons from Lo\er Ntonunenlal Dan to Clarkston.\Vashingftrn in 197,1(Asherin and Claar 1976) and in l99l 1998. Avian Use of SnakeRiver Riparian Habitat 291 thus.predictions ofchanges in bird communities also observedin crop fields ar ilrigated HMUS u ill bed ilfieult. Cuncnt ripurian \ cgcralion may duringf;rll (A. Rocklagepers. obs.). Migrating senesccas the watcr table drops.Upland vegeta- white-crownedsparows appearedto have ben- tion will likell replrcescne.,.ing riprrian reg efitedfrom the gradualexpansion ofriparian veg etation.Natural revegetationnlay take decadcs. etation.Lewke and Buss (1977) derecred 320 white- Breeding birds that may be immediately af- crowncd sparows prior to the construction of fectedby lower water lcvels would be thosethat LowerGnnite Dam, Mondaand Reichel (1989) dependon willow shrub-scrubvegetation. Breeding observed1,1 six yearsafter its construction,and birds,such lu Americangoldfinch, Bullock's oriole. oursruJ) delcclcd 224. A longJII tour reserr oirr. song sparow, willow flycatcher (Empidonax we estimatedan averageof 156 white crowned traillli), yellow-breastedchat (L ter.iafircrr), and sparifowsper 10 ha at irrigatcd HMUs. This spe- yellow $'arbler (Dendroi.a petechia), fiay tem cieshas exhibited a significantpopulation decline porarily decreasein numbers(Monda andReichel since 1966in the westem U.S. (DeGraafand 1989,Knopf and Sedgwick1992). Monda and Rappole1995); thus, Snake River habitatsmay ReiLhelr lq8qr notedr llrge decrea:ein num- be vital to current populations.Little is known beIS in Amedcan goldfinch and lazuli bunting about other quality stopoversites and nigration (Passerinaamoena) six yearsafter construction pattems in the inland Nofihwest (Moore et al. of Lo*,er Granite Dam. Although our data dem- 1995). onstratedthat American goldtinch numbershave Thecomparison between ourdata and that trom rebounded,lazuli buntings were still rare. Some Asherinand Claar (1976) and Monda andReichel birds will moveinto drainages,but drainagesmay (1989)clearly indicated that bird populationshave be too small and narrow to suppofi large num- reboundedtiom impoundmentof the lower Snake bels ofnesting birds.Upland birds. howevcr may River. This reboundwas undoubtedlydue to the benefitfrom the gradualexpaursion ofupland veg- developmentand management of irrigatedHMUs, etalion(Stauffer and Best 1980, MondaandReichel as well as to the natuml successionof shorcline 19891.Grasshopper sparrow (Amnodranus vegetation.Howevet we emphasizethat it is un- savanna rum), homed,latk( Ere mophila alpestris). known how annual vadation, competition, pre- Iark sparrow (.Chond e st e s g rdnunqc Lt s ), ril]tg- dation, and cowbird parasitismaffect bird popu- neckedpheasant(Pfu rid,?rl.rcolc/ri.an), and west- lations on the lower Snake River. Our data em meadowlarkmay increaseon benchesalong demonstlatedthat futurehabitat perturbations can the lower SnakeRiver. be partiallymitigated by habitatenhancernent and Migratingbirds will alsobe affecredby changes managemcnt. in watcr levels.Migrating birds needan adequate lbod supply and proteclive cover (Moorc et al. Acknowledgements 199-5).These resources were readily availableat The U. S. Arny Corps of Engineers provided iaigatcdHMUs. somenon-fuigated sites and along tunding for this project. Lonnie Metleq Cl;rk largel strcamsdudng fall and spring. Migrating Derdeyn. and Scott Ackerman from the Corps sparro\\"sconcentrated in weedy fields that of provided technical and logistical assistance.We f-ereda plentiful seedsupply adjacentto protcc- particularly thank our field assistants,Suzanne tivc cover suchas blackbeny and willows (Strolrg Tomassi.Gene Onh, andKaren Kriesel.We thant and Bock 1990,A. RockJagepers. obs.). Large MarkUlliman andJohn Giudice for contributions flocksofred-winged blackbirds and sparrows were duringthe earl) Lle.ignphare oI rhisnrojecr. LiteratureCited Burnhan.K. P. D. R. Andcrson.and J. l-. Laake.I98LLine transeciestimalion of bird population densjry using Asherin. D. A . and J. J. Ciaar. 1976. lnlcnlory of fiparian a Foufierserics. Pages.166 4821, C. J. Ralphand J. habilat\ and associatedu ildliie along the Columbia NL Scox (edirors)Eslimaring rhe Nudber ofTerrcs and Snakcrilers. !blumc lll,{. U. S. Amr} Corps of tnal Birds. Sludies in Avian Biology 6. pres\. Flngineers,North Pacilic Di\'ision. Allen La$rcnce. Krn\as. USA. 292 Rocklageand Ratti 7 Clary. $'. P, and D. I Nlcdin. 1993.Vegetation. ne\ting bird. Moo.c, Fl R.. S. A. Gauthfeaux,JL. P Kerlingcr. and T. R. andsmall mammal characlerislicsi\\ttCreek. ldaho. \rmun\ lao\. HaL.r'atreqJi-e nen.',ludnr' mi!r-lirn USDAForcst Serr'jceGeneral Technical Rcpor| INT ilnporanl li*s in conscrlalion. Pages121-111 InT. 193. 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Dennis. and E. O. Carton. 1987.Estimating E62. dcnsily froin variable circular plot censuses.Jlrumal John\on,A. S. 1989.The thin green line. Pages 35 ,161rPrc of wildliie N{anagemenr51( l)r22,1 230. serving cor nunities .rnd corridors. Defenders of Schicck. J. 1991. Biaseddeteciion ofbird vocalizalionsai: wildlife. wa\hingtdr.D. C., USA. lecrsconparisons ofbird abundanceamong lbrested Knopf, F. L.. .rndF B. Sa son. 1988.Ecological patleming habitats.Condor 99:179 190. of riparian tilaunas. Pagcs77 7E /, K. J. Rredeke SchulT.T. t. and \\i C. Leininger. 1991.Nonganc wildliii (cditor) StreamsideN{.rn.rgenent: Riparian wildlife communiliesin grazcdandungrazed mountarn ripar- and Foreslry'lnteraclions. Conribution 59. Univer ian rites.Gfeat Basin Natur.rlist 51:286 292. sir,"-of washington Institute of Foreslrr"Rcsourccs, Struffer D. F. and L. B. Best. 1980.Habitat selection by Seattle.USA. birds of ripadan coDrnnrnities:e!aluating cffccls of Kropl. F L.. andJ. A. Sedgwick.1991. AD erperimcnul sludy habitat allenlions. Joumal of Wildlife Nlanagenent of nest sile sclcclionh,v,vello$ $arblers. Culdor ,ll(1):l-14. 91:131-112. Suong.T. R..and C. B.Bock. 1990.Bird speciesdisdbudon Iccbs. C. J. 1989.Ecological Nlethodolosy. HarpcrCollins, pauems in riparian habitatsin \outheasternArizona. New York. USA. Condof92:866'885. Lcwkc.R. 8.. andL O. Bu\s. 1977.llnpacis ofinrpoundment Sraro, R. Cl. 1980. Factors influencing bnd populations in to venebrateaiimals and theif habit.rt\ in the Snak. southr estemripaiar lbres|s.Pages ,103 ,1 | 8 /r R . M. Rivcr canlon, wtlshingtor. Norlh$cs! Science Decralfand N. G. Tilghan (editots)Man.tgement |)1 5.1(1):2I9270. westem Fofestsand Grasshndsibr Nonga e uirds. \4ord..\.4 .1..xnd J. D. R.r.h Received30 Decenber 1999 Auepred 3 April, 2000 AvianUse of SnakeRivcr RipadanHabitat 293