ABUNDANCE OF SHOREBIRDS AT WILLAPA BAY, WASHINGTON

JOSEPH B. BUCHANAN and JOSEPH R. EVENSON, Cascadia Research Collective,218•/• W. FourthAvenue, Olympia, Washington 98501

There is a growingbody of literaturedocumenting large concentrations of shorebirdsat winteringsites or migratorystaging areas along the Pacificcoast of North America. In the PacificNorthwest, such areas include the Fraser River delta (Butler 1994, Vermeer et al. 1994), Puget Sound (Buchanan 1988a, Evensonand Buchanan1995), GraysHarbor (Herman and Bulger 1981), WillapaBay (Widrig 1979), andbeaches of the outercoast (Buchanan 1992). Someof thesesites support numbers of shorebirdsthat qualify them as regionallyor internationallyimportant sites in the Western Hemisphere ShorebirdReserve Network (I. Davidsonpers. comm.). Others comprise clustersof smallersites that togethersupport substantial numbers of birds (Evensonand Buchanan1995). Identifyingthe role these sites play in supportingwintering and migrantshorebirds is an importantstep in develop- ing conservationstrategies to protectshorebirds and their habitats. Prior researchon shorebirduse of Willapa Bay has been limited.At LeadbetterPoint, Widrig (1979) conductedmultiple shorebird surveys but only over a singleyear. Becauseshorebird abundance can vary both from year to year (Buchanan1988a) and within a year (Evensonand Buchanan 1995), both intensiveand long-termstudies are essentialfor assessing populationtrends. The objectiveof thisstudy was to estimatethe abundance of shorebirdsat WillapaBay, Washington,to identifyimportant candidate siteswithin Willapa Bay for future monitoringefforts. Here we present resultsof ground-and aerial-basedcounts of shorebirdsduring winter, spring,and autumnfrom 1991 to 1995 that documentthis site as among the mostimportant to shorebirdson the westcoast of North America.

STUDY AREA

WillapaBay is on the outer coast of Washingtonstate between Grays Harbor andthe Columbia River mouth. It coversabout 420 kmz and is fed by the Cedar, North,Willapa, and Palixrivers in the northand the Nemah,Naselle, and Bear riversin the south(Figure 1). A long,narrow peninsula (North Beach Peninsula) dominatedby lowdunes, pastures, and woodlands separates the mainbody of thebay from the Pacific Ocean. Of theseveral salt marshes around the bay, the largestare at the mouthsof the WillapaRiver to the northand the Bear River to thesouth. Low tide (0.0 m)exposes about 200 kmz of mudfiats. Numerous sandshoals are exposedduring all but the highesttides; there are no dredge- spoilislands in the bay.Two areas,Leadbetter Point and the BearRiver/Lewis Unit fiat, are withinWillapa National Wildlife Refuge.

METHODS

Our countsinvolved a combinationof aerial and ground-basedefforts. BecauseWillapa Bay is largeand accessto manyareas is limited,surveying

158 WesternBirds 28:158-168, 1997 ABUNDANCE OF SHOREBIRDS AT WILLAPA BAY, WASHINGTON

+ •+

0 1 2 3 4 5 6 7 Pacific Kilometers

Ocean

Figure1 WillapaBay, showingthe locationof sitescovered by groundand aerial surveysfor shorebirdsbetween 1991 and 1995. Lightstippling, intertidal foraging and roostinghabitats.

shorebirdsadequately from the groundis difficult.For thisreason, on each surveywe madecounts from a smallairplane flying at a heightof about60 to 70 m. These aerial countswere the basisof our primaryestimates of shorebirdabundance in the estuary.We also made aerial countsof birds (primarilySanderlings) on outerNorth Beachon five occasions;the beach coveredby the countswas 37 km long.

159 ABUNDANCE OF SHOREBIRDSAT WILLAPA BAY,WASHINGTON

Groundcounts were madeby a total of 18 observers(median 5 per seasonalcount) who countedshorebirds at eightprimary sites: Tokeland, CedarRiver, North River, Willapa River, Palix River, Bear River/Lewis Unit, East North Beach Peninsula,and LeadbetterPoint. Ground countswere usedto estimatethe proportionsof speciesnot identifiedfrom the air.Thus, dependingon theseason, ground observers determined the species compo- sition of groupsof look-alikespecies, including the Greater and Lesser yellowlegs;Whimbrel, Marbled Godwit, and Long-billedCurlew; Western Sandpiper,Least Sandpiper,and Dunlin; and Red Knot and dowitchers. Proportionsderived from ground counts of particularsites or regionsof the bay were appliedto the correspondingunidentified species groups from aerialcounts of theseregions, then regional totals were summed to provide baywideestimates. Aerial counts alone were used to estimatepopulations of the Black-bellied Plover. Ground counts alone were used for all other species,which consequently were underestimated because of partialcover- age of the bay by this method. Becausethe mainobjective of thesecounts was to identifyimportant sites forfuture monitoring efforts, they were usually made only once each season (Table1). Countswere made during rising or fallingtides generally within four hoursof hightide. The logisticalconstraints noted above necessitated conductingthe groundcounts at siteswhere shorebirds aggregated immedi- atelyprior to and/or afterhigh tide. Consequently, aerial counts covered the entireshoreline whereas ground counts covered only the areasof major concentrationsof birds.Our scheduledflights were occasionallypostponed

Table 1 Dates of Shorebird Counts at WillapaBay, Washington,1991-1995

Aerial Ground

Winreft 28 Nov 1992 21-22 Nov 1992 4 Dec 1993 22 Nov-4 Dec 1993 31 Dec 1993 28-29 Dec 1993 21 Dec 1994 21-30 Dec 1994 9 Feb 1995 28 Jan-9 Feb 1995 Spring• 27 Apr 1991 27 Apr 1991 27, 30 Apr 1993 25 Apr-1 May 1993 26 Apr, 1 May 1994 28, 30 Apr 1994 Autumn 30 Aug 1993 15-20 Aug 1993

•Two complete(aerial and ground)counts were con- ducted in the winters of 1993-94 and 1994-95. •Twoflights were made in the springsof I993 and I994; each pair of flightscoincided with a single groundcount.

160 ABUNDANCE OF SHOREBIRDS AT WlLLAPA BAY, WASHINGTON becauseof adverseweather conditions, and thereforesome ground counts duringwinter and springwere not made on the sameday as the aerial counts.Nonetheless, we believethat the estimatesof the proportionsof speciesderived from these counts are reliablebecause the numberof species duringwinter was low and did not vary appreciably within the bay,and most groundcounts in springwere made on or withintwo daysof the aerial counts.

RESULTS AND DISCUSSION

SpeciesAccounts Black-belliedPlover (Pluvialis squatarola). This was the secondmost numerous speciesin winterin all threeyears and generallythe fourthmost numerous species duringmigration (Tables 2 and3). The totalof 4049 countedon 21 December1994 included3848 roostingon outerNorth Beach at hightide, the highestknown winter countat a singlesite in Washingtonstate (Paulson 1993). SemipalmatedPlover (Charadrius semipalmatus). The irregularityof thisspecies in Washingtonin winter(Buchanan 1992) is reflectedin our results(Table 3). The SemipalmatedPlover is locallydistributed in all seasons. Killdeer(Charadrius vociferus). The Killdeerwas observedin low numbersin all seasons(Table 3). Widrig(1979) sawvery few Killdeersat LeadbetterPoint during any season. GreaterYellowlegs (Tringa melanoleuca).The GreaterYellowlegs is a regularly occurringwinter residentin estuarinehabitats in the PacificNorthwest (Buchanan

Table 2 SeasonalHigh Countsof Black-belliedPlovers, Dunlins, Western Sandpipers,and Short-billedDowitchers at PrimaryCensus Sites in Willapa Bay, 1991-1995

Winter Spring

Black- Black- Short- bellied bellled Western billed Site Plover Dunlin Plover Dunlin Sandpiper Dowitcher

Tokeland 415 2,320 35 832 3,603 300 Cedar River 67 450 8 756 4,844 1,780 North River 240 3,915 100 1,890 12,110 5,190 WillapaRiver 5 13,510 100 2,970 16,830 12,460 BetweenWillapa R. and Palix R. 6 3,120 180 2,481 14,059 2,345 PalixRiver 35 8,800 84 1,191 6,749 4,380 Between Palix R. and Nemah R. 15 2,160 85 2,586 10,344 1,465 NemahRiver 205 8,150 300 2,400 9,600 4,000 BearRiver 210 27,260 300 12,300 36,900 5,000 E. North Beach peninsula 50 5,115 65 2,554 3,831 680 LeadbetterPoint 54 3,935 125 7,930 5,070 4,425

161 ABUNDANCE OF SHOREBIRDS AT WILLAPA BAY, WASHINGTON

Table •3 Numbersof ShorebirdsCounted or Estimatedat WillapaBay, Washington, 1991-1995

Winter Spring Autumn Species 1992-93 1993-94 1994-95 1991 1993 1994 1993

Black-belliedPlover • 415 881 4,049 918 653 245 205 SemipalmatedPlover b 12 0 0 27 122 264 98 KilldeeP 0 6 1 0 0 2 4 GreaterYellowlegs • 84 42 97 40 160 275 65 LesserYellowlegs a 0 0 0 0 1 0 2 Willetb 0 0 0 0 0 0 5 SpottedSandpiper • 0 0 3 0 0 1 1 Whimbrela 4 9 3 0 82 27 229 Long-billedCurlew d 0 67 70 0 8 1 0 Marbled Godwitd 0 303 462 0 115 51 70 Largesandpiper spp. 0 0 0 150 0 0 0 RuddyTurnstone • 0 2 0 0 2 2 0 Black Turnstone• 28 26 29 1 0 7 1 Red Knot• 0 0 0 0 177 1 0 Sanderlingd 372 135 16 0 0 6 2 WesternSandpiper • 80 e 258 82,575 55,195 49,615 8,976 LeastSandpiper • 0 22 235 1 e 150 374 Dunlina 47,017 69,850 27,120 7,525 29,720 41,640 0 Long-billedDowitcher • 50 94 61 0 0 0 0 Short-billedDowitcher • 0 0 0 23,865 8,900 16,595 153 Dowitcherspp? 0 0 0 0 0 0 31 CommonSnipe b 10 2 0 0 1 1 0

øDirectaerial count of the entirebay. bNumbercounted from the groundonly; total for somespecies may under-represent actual number of birds present. CDirectaerial count of the entire bay unless ground count revealed Lesser Yellowlegs, in which case proportionalcounts were used. dNumberprojected from proportions of similarspecies counted during surveys on theground (see Methods). ePresent but not counted.

1988b). The countfrom winter 1994-95 appearsto be the highestwinter count yet made in the region(Table 3; Paulson1993, Buchananunpubl. data). LesserYellowlegs (Tringa flavipes). The onlysurvey observations were of one bird in spring1993 and two in autumn1993 (Table3). Widrig(1979) notedthis species at LeadbetterPoint only duringautumn migration, whereas (Herman and Bulger 1981) found smallnumbers at GraysHarbor duringspring. Willet(Catoptrophorus sernipalrnatus). The fiveWillets at CedarRiver in autumn 1993 were the onlyones recorded on our surveys(Table 3). By contrast,Willets were observedfairly regularlyat WfilapaBay duringwinter in yearsprior to our counts (Paulson1993), thoughWidrig (1979) notedthis speciesat LeadbetterPoint only duringautumn migration. SpottedSandpiper (Actitis rnacularia).Spotted Sandpipers were observedon singlewinter, spring, and autumncounts (Table 3), a patternsimilar to that notedby

162 ABUNDANCE OF SHOREBIRDS AT WILLAPA BAY, WASHINGTON

Talkie •, SeasonalHigh Countsof all ShorebirdSpecies at PrimaryCensus Sites in WillapaBay, 1991-1995

Site Winter Spring Autumn

Tokeland 2,447 4,530 494 CedarRiver 450 6,360 150 North River 4,099 19,200 2 WillapaRiver 13,510 22,665 60 betweenWillapa R. and PalixR. 3,122 16,540 0 PalixRiver 8,800 9,000 2,099 betweenPalix R. and NemahR. 2,307 14,495 1,690 NemahRiver 8,358 16,000 -- Bear River/LewisUnit 27,470 54,450 2,403 EastNorth BeachPeninsula 5,119 6,465 57 LeadbetterPoint 3,971 13,000 6,270

Widrig(1979) at LeadbetterPoint and by Herman andBulger (1981) at GraysHarbor duringspring migration. Whimbrel(Numenius phaeopus). The Whimbreloccurred primarily as a spring and autumnmigrant with smallernumbers overwintering (Table 3). Widrig (1979) likewisereported it as a migrantat LeadbetterPoint but did not recordthe species duringwinter. We observedWhimbrels only in the northernpart of Willapa Bay (includingLeadbetter Point), mostly at siteson the westernshore. Herman and Bulger (1981) foundWhimbrels most numerous in GraysHarbor in mid-May. Long-billedCurlew (Numenius americanus). The Long-billedCurlew was observed duringtwo winter and two springcounts (Table 3). In all seasons,it was generally found only in the northernmostpart of WillapaBay. At LeadbetterPoint, Widrig (1979) recordedonly a few Long-billedCurlews in spring. MarbledGodwit (Limosa fedoa). We observedlarger flocks of MarbledGodwits in the wintersof 1993-94 and 1994-95 than duringmigration periods (Table 3). In all seasons,nearly all godwitswere seen at Cedar River, North River,Tokeland, and Willapa River. We have no informationto explain this localizeddistribution. At LeadbetterPoint, Widrig (1979) observedno MarbledGodwits in winterand verylow numbersin other seasons.Wintering numbersof Marbled Godwits in northern WillapaBay may haveincreased between the early 1980s and the 1990s; countsof >100 were unusualduring the earlierperiod (C. Chappellpers. comm.). RuddyTurnstone (Arenaria interpres).Two RuddyTurnstones were found on a singlewinter and on two springsurveys (Table 3). Springnumbers may have been low becauseour surveyswere conductedprior to the early May peak of movementof RuddyTurnstones in this region(Paulson 1993). BlackTurnstone (Arenaria melanocephala).We noted very similarnumbers of BlackTurnstones during each of the three winters,lower countsduring migration (Table3). BlackTurnstones were observedat the town of Nahcottaon the EastNorth BeachPeninsula. Herman and Bulger(1981) recoredvery few BlackTurnstones at GraysHarbor duringspring migration. RedKnot (Calidriscanutus). The Red Knot occurredonly in springmigration and the number of birdscounted annually was quite variable(Table 3). The countsat WillapaBay were much lower than those from Grays Harbor, where several thousand

163 ABUNDANCE OF SHOREBIRDS AT WlLLAPA BAY, WASHINGTON birdswere noted by Herman and Bulger(1981). However,our springcounts there were conductedprior to the primarypassage of Red Knotsin thisregion (Paulson 1993). Sanderling(Caliclris alba). We regularlyrecorded Sanderlings each winter within the bay, but few duringmigration (Table 3). On outerNorth Beachwe madethree aerialcounts in winter[mean 50.1 birds/krn,standard deviation (SD) 6.5] and single countsduring spring(78.6/krn) and autumn (213.5/krn). Our countsthere were comparableto thosemade on the samebeach in the wintersof 1982 to 1990 (mean 46.6, SD = 14.5; Buchanan1992) and in spring1983 (94 birds/krn.;Myers et al. 1984). Western Sandpiper(Calidris mauri). Western Sandpiperswere recordedeach winter,although they were far moreabundant during migration (Table 3). Therewas considerablevariation among spring counts, possibly related to the timingof our countsrelative to the actualpeak passage. LeastSandpiper (Calidris minutilla). We recordedsmall numbers of this species on nearly all counts(Table 3). The Least Sandpiperhas a local distributionin Washin,on duringwinter. Dunlin(Calidris alpina). The Dunlinwas by far the mostnumerous species during winter(Table 3), when it constituted85.6% to 97.9% of all shorebirdsand 98.7% to 99.8% of all Calidrissandpipers. This is within the rangeof dominancenoted in the greaterPuget Sound region (Evenson and Buchanan 1995, Buchanan1988a) and in an earlierstudy on North Beach(adjacent to WillapaBay; Buchanan1992). The Dunlin was the secondmost abundantspecies during spring migration (Table 3), a patternobserved at LeadbetterPoint (Widrig1979) and at GraysHarbor (Herman and Bulger1981). Short-billedDowitcher (Limnodromus griseus). The Short-billedDowitcher oc- curredprimarily in spring,when it wasthe thirdmost numerous species (Table 3). It was alsoobserved during autumn but not in winter. Long-billedDowitcher (Limnodromus scolopaceus). We recordedthe Long-billed Dowitcherby vocalizationsin all threewinters (Table 3), when it is generallythe only speciesof dowitcherfound in Washington(Buchanan 1992, Paulson1993). We did not recordthis species in spring,although it is likelythat it waspresent then each year. Similarly,Widrig (1979) foundthat L. scolopaceusconstituted only about1% of all dowitchersat LeadbetterPoint in May. Common Snipe (Gallinagogallinago). Recorded on only two winter and two springcounts (Table 3).

Seasonal Abundance of Shorebirds The total abundanceof shorebirdsvaried considerablyfrom winter to winter.The variationin countslargely reflected variation in the abundanceof the Dunlin(mean 47,996, SD = 21,382; Table3). This approximaterange of annual variation in abundance has been documented in other studies in coastalWashington (Buchanan 1992) and PugetSound (Buchanan 1988a, Evensonand Buchanan1995). It is currentlyunclear whether the variation in wintercounts was related to factorsin breedingareas, nonbreeding areas, or both. Among the springcounts, we noted similarvariation that was primarily relatedto the abundanceof WesternSandpipers (Table 3). We believeit is likelythat differencesamong spring counts may havebeen due to the timing of surveysrelative to the peak passageof springmigrants.

164 ABUNDANCE OF SHOREBIRDS AT WILLAPA BAY, WASHINGTON

We observed within-season variation in total shorebird numbers in one of the two yearsin whichwe conductedmultiple counts; our aerialcount of 49,400 on 4 December1993 wasmuch lower than the estimateof 70,650 on 31 December1993. Substantialchanges in the within-seasonabundance of shorebirdsalso have been noted at severalmajor sitesin Puget Sound (Evensonand Buchanan1995) but not at two smallersites there (Buchanan 1988a). At PugetSound sites the changesin abundancewere thought to be primarilyrelated to both regularmovement among a networkof sitesand larger-scalemovements in responseto adverseweather (Evensonand Buchanan1995). It is possiblethat shorebirdsregularly move between WillapaBay and GraysHarbor (16 km to the north)or the ColumbiaRiver estuary(6.5 km to the south).Although we were unableto documentsuch movements, shorebirdsare known to travel these distancesin western Washington(Evenson and Buchanan1995) and elsewhere(Warnock et al. 1995). Adverse weather conditions are known to influence the seasonal distribu- tion and abundanceof shorebirds0garnock et al. 1995). it is possiblethat the relativelylow countsin winter 1994-95 were a responseto mid-winter floodingat WillapaBay. Both countsthat yearwere madeduring a periodof severestorms. We noticedthat certainchannels and fiatsin the bay were visiblyaltered between counts by scouring.in addition,flood tides inundated many foraõingand roostingareas for longerthan usual. important Areas The importanceto shorebirdsof varioussites in an area can be measured by the abi]iWof sitesto meet the energeticdemands of overwinteringor migrantbirds (Goss-Custard 1984) or to supportlarge numbers of individu- als.This studywas not designedto determinethe energeticsof shorebirds, butdid providepreliminary data on the seasonalabundance of shorebirdsat varioussites within Willapa Bay. Our resultsindicate greater total abundance of shorebirdsat the Bear River/ LewisUnit andWillapa River in the winterand spring (Tables 9., 4). Fromthe air, however,we noted that shorebirdsused much of the intertidalarea of the baybefore congregating at the majorsites when less than about 5% of themud fiatsin the bay were still exposed.Emphasizing concentrations of birdsat specificsites is appropriatebut it is crudalto recognizethe importanceof the otherareas used by shorebirdsat otherstages of the tidalcycle. Our censusefforts indicated that in all seasonssome shorebirdspecies were concentratedat specificsites or withincertain regions of the bay. For example,in all seasonsthe Willet, Long-billedCurlew, and MarbledGodwit were observedonly at sites in the northern part of the bay, primarily Tokeland,Cedar River, and North River. Other specieswith very local distributionsincluded the Whimbrel(in all seasonsmostly at Tokeland,North Cove, LeadbetterPoint), Black Turnstone (in all seasonsat Nabcottaon East North BeachPeninsula), Red Knot (in springin the northernportion of the bay), Least Sandpiper(in winter primarilyat East North BeachPeninsula, LeadbetterPoint, Tokeland),Long-billed Dowitcher (in winter primarilyat Bear River/LewisUnit), and Common Snipe (in winter at Bear River/Lewis Unit, WillapaRiver).

165 ABUNDANCE OF SHOREBIRDS AT WlLLAPA BAY, WASHINGTON

Among the sites important to shorebirdsare those used for roosting, where they preen and rest during high tides. At Willapa Bay shorebirds roostedprimarily in saltmarsh, pastures, on islands,and on the outerbeach. Our highestcount of roostingbirds was from the outer North Beach in spring(about 28,500 shorebirds,including several thousand Sanderlings, on 30 April 1993). Largenumbers of shorebirdsroost there in winteras well (about34,600, not includingSanderlings; Buchanan 1992). We also ob- servedseveral thousand spring migrant shorebirds roosting in pasturesand agreewith Colwelland Dodd(1995) that pasturesmay be importanthabitats for roostingshorebirds. WillapaBay and the PacificFlyway The Western Hemisphere ShorebirdReserve Network has proposed standardsfor ranking the importance of sites to shorebirds.Sites that support>20,000 shorebirdsor 5% of a flywaypopulation are considered regionallyimportant, whereas sites that support>100,000 shorebirdsor 15% of a flyway populationare consideredinternationally important (I. Davidsonpers. comm.).Willapa Bay meetsthe criteriaof an internation- ally importantsite becauseit supportsup to 15.5% of the Pacificflyway populationof winteringDunlins (derived from Page and Gill 1994) and an averageof over 100,000 total shorebirdsin spring.Willapa Bay's impor- tance indicatesit is a prime site for future shorebirdmonitoring and conservation efforts in the Pacific Northwest.

Conservation Issues A currentissue of conservationsignificance at WillapaBay is the occur- rence of the exoticand invasivecordgrass Spartina alterniflora. This salt- marshplant appearsto have spreadrapidly in recent years,and in 1992 coveredabout 809 ha of the intertidalarea of the bay (Washington Departmentof Agricultureet al. 1993). Thisspecies colonizes bare tidefiats, traps sediments,and displaceslow intertidalsalt-marsh plants. Conse- quently,the invasionof $partina will likely have a negativeeffect on shorebirdpopulations by reducing foraging habitat (Goss-Custard and Moser 1988). Effortsare currentlyunderway to controlthe spreadof, and eventu- ally eliminate,this exoticspecies.

SUMMARY

We conductedseasonal censuses of shorebirdsat WillapaBay, Washing- ton, between 1991 and 1995. The censuswas designedto identifythe locationof potentiallyimportant sites for futuremonitoring efforts. The Dunlin was the most abundantspecies in winter, with annualtotal counts rangingbetween 27,120 and 69,850 birds.The WesternSandpiper was the mostabundant species during spring; our annual counts ranged between 49,615 and 82,575. Dunlinsand Short-billedDowitchers were also abun- dant duringspring and contributedto annualspring counts that exceeded 100,000 totalshorebirds. Two estuarineareas within the bay, WillapaRiver and Bear River-LewisUnit, typicallysupported the highestseasonal counts at highertides, but shorebirdswere well distributedalong much of the

166 ABUNDANCE OF SHOREBIRDS AT WILLAPA BAY, WASHINGTON shorelineof the bay on risingand fallingtides. Willapa Bay is an internation- allyimportant site for overwinteringand migratingshorebirds.

ACKNOWLEDGMENTS

We thank the followingvolunteers who conductedcounts at WillapaBay from 1991 to 1995: Will Beatty, MargaretBertram, Lanny Carpenter,Linda Carpenter, Malpina Chan, Hector Douglas,Henry Gilmore, Bob Hughes, David Jennings, Ruth McCausland,Harry Nehls, Mike Patterson,Alan Richards,Susan Sandwick, Nat Seavy, Bob Sundstrom,Bill Tweit, and Terry Wahl. Jim Cubbage, "Hawk" Greenway,and Eric Nystuenwere our excellentpilots. We thank everyoneat PearsonAir, TumwaterFlight Service, and Lighthawk for their assistance.Bill Tweit helpedwith one of the aerialcounts. This projectwas funded by PointReyes Bird Observatoryand CascadiaResearch Collective. This is contributionnumber 814 of Point ReyesBird Observatory.Dennis Paulson and Dave Shufordprovided con- stmctivecomments that improvedthe manuscript.

LITERATURE CITED

Brennan, L. A., Buchanan, J. B., Herman, S. G., and Johnson, T. M. 1985. Interhabitatmovements of winteringDunlins in westernWashington. Murrelet 66:11-16. Buchanan,J. B. 1988a. The abundanceand migrationof shorebirdsat two Puget Sound estuaries. W. Birds 19:69-78. Buchanan,J. B. 1988b. Migrationand winter populationsof GreaterYellowlegs, Tringa melanoleuca,in westernWashington. Can. Field-Nat.I02:611-616. Buchanan, J. B. 1992. Winter abundanceof shorebirdsat coastal beaches of Washington.Wash. Birds 2:12-19. Butler,R. W. 1994. Distributionand abundance of WesternSandpipers, Dunlins, and Black-belliedPlovers in the FraserRiver delta, in The abundanceand distribution of estuarinebirds in the Straitof Georgia,British Columbia (R. W. Butlerand K. Vermeer,eds.), pp. 18-23. Can. WildlifeServ. Occas.Paper 83. Colwell,M. A., and Dodd, S. L. 1995. Waterbirdcommunities and habitatrelation- shipsin coastalpastures of northern California.Conserv. Biol. 9:827-834. Evenson,J. R., and Buchanan,J. B. 1995. Winter shorebirdabundance at greater Puget Sound estuaries:Recent censusresults and identificationof potential monitoringsites, in Proceedingsof PugetSound Research '95 (E. Robichaud, ed.),pp. 647-654. PugetSound Water Quality Authority, Olympia, WA. Goss-Custard,J. D. 1984. Intakerate and foodsupply in migratingand wintering shorebirds,in Shorebirds:Migration and ForagingBehavior (J. Burgerand B. L. Olla, eds.),pp. 233-270. Plenum,New York. Goss-Custard,J. D., and Moser,M. E. 1988. Ratesof changein the numbersof Dunlin,Caliclris alpina, wintering in Britishestuaries in relationto the spreadof Spatrina anglica.J. Appl. Ecol.25:95-109. Herman, S. G., andBulger, J. B. 1981. The distributionand abundance of shorebirds duringthe 1981 springmigration at GraysHarbor, Washington. Contract report DACW67-81-M-0936, U.S. Army Corps of Engineers,P.O. Box C-3755, Seattle, WA 98124. Myers, J.P., Schick,C. T., and Hohenberger,C. J. 1984. Notes on the 1983 distributionof Sanderlingsalong the UnitedStates' Pacific coast. Wader Study Group Bull. 40:22-26.

167 ABUNDANCE OF SHOREBIRDS AT WlLLAPA BAY, WASHINGTON

Page, G. W., and Gill, R. E. Jr. 1994. Shorebirdsof western North America: Late 1800s to late 1900s. Studies Avian Biol. 15:285-309. Paulson,D. 1993. Shorebirdsof the PacificNorthwest. Univ. Wash. Press,Seattle. Vermeer, K., Butler, R. W., and Morgan, K. H. 1994. Comparisonof seasonal shorebirdand waterbirddensities within FraserRiver delta intertidal regions, in The abundanceand distribution of estuarinebirds in the Straitof Georgia,British Columbia(R. W. Butlerand K. Vermeer,eds.), pp. 6-17. Can. WildlifeServ. Occas.Paper 83. Warnock,N., Page, G. W., and Stenzel,L. E. 1995. Non-migratorymovements of Dunlinson their Californiawintering grounds. Wilson Bull. 107:131-139. WashingtonDepartment of Agriculture,Washington Department of Ecology,Wash- ingtonDepartment of NaturalResources, Washington Department of Fisheries, WashingtonDepartment of Wildlife,and NoxiousWeed ControlBoard. 1993. Noxiousemergent plant management.Final environmentalimpact statement. Wash.Dept. Fishand Wildlife,600 CapitolWay North, Olympia,WA 98501. Widrig, R. S. 1979. The shorebirdsof LeadbetterPoint. Independentlypublished; availableat The EvergreenState Collegelibrary, Olympia, WA 98505.

Accepted 17 June 1997

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