WESTEBN

Volume 30, Number 3, 1999

THE BR!STLE-THIGHED CUial_/LANDFALL OF 1998: CLIMATIC FACTORS AND NO'!T,S ON IDENTIFICATION

STEVEN G. MLODINOW, 4819 GardnerAvenue, Everett, Washington 98203 STEVEN FELDSTEIN, Earth SystemScience Center, The PennsylvaniaState University,248 Deike Building,University Park, Pennsylvania16802 BILL TWEIT, P.O. Box 1271, Olympia,Washington 98507

The Bristle-thighedCurlew (Nu men ius tah it iensis)undertakes one of the longestknown transoceanic migrations of any shorebj•:d,commuting be- tweenits breedingrange in westernAlaska and itswintering grounds in the tropicalPacific. Its world population is likelyless than 10,000 (Marks1996), and its breedingpopulation consists of approximately3500 pairs(Gill and Redmond1992). Prior to 1998, there were only four North American recordsof the Bristle-thighedCurlew south of Alaska,which is not surprising giventhe species'small numbers and expectedmigratory route. DuringMay 1998, however,between 13 and 17 Bristle-thighedCurlews were recordedon the Pacificcoast between Point Reyes,California, and TatooshIsland, Washington. Notably, vagrants of three other trans-Pacific migrantswere alsofound along the samestretch of coastline that May, the Gray-tailedTattler (Heteroscelusbrevipes), Eurasian Whimbrel (Numenius phaeopusvariegatus or N. p. phaeopus),and Bar-tailedGodwit (Limosa lapponica).At the sametime, weatherpatterns over the North Pacificwere stronglyinfluenced by both the well-publicized1997/1998 E1Nifio and a muchless publicized but equallyinfluential positive phase of the WestPacific Oscillation(WPO). We hypothesizethat, in general,the occurrenceof a largenumber of long- distancetransoceanic vagrants is relatedto extremeweather, whereas the occurrenceof a singlevagrant may be causedby a number of factors, includingunusual weather, a defectiveinternal compass (Berthold 1993), and shipassistance. Consequently, we examinedwind and cloudpatterns in the North Pacificto searchfor anomaliesthat mighthave contributed to the Bristle-thighedCurlew landfall. We alsolooked at broaderclimatic phenom- ena (El Nifio and the WPO) for their part in any unusualconditions.

WesternBirds 30:133-155, 1999 133 THE BRISTLE-THIGHED LANDFALL OF 1998

Evaluationof the May 1998 Bristle-thighedCurlew reportsrequired a thoroughunderstanding of this species'identification. Therefore, we re- viewedpreviously published identification criteria and assessedthese further by examiningthe specimensin the BurkeMuseum, University of Washing- ton, Seattle.

METHODS

We locatedand assessedpast recordsof the Brisfie-thighedCurlew and other speciesby reviewingregional texts (see Literature Cited), reviewing AmericanBirds/Field Notes,and contacting state and provincial records committees.Sightings from the 1998 invasionwere first compiled by a review of MichaelPatterson's Bristle-thighed Curlew World Wide Web page and from discussionswith active birders. We assessedthe reportsby examiningdescrip- tions, photographs,and in one case, a wing of the bird involved.The photographswere gleanedmostly from Patterson'sWeb page, the descrip- tionswere obtainedfrom the observers,and the wing was inspectedat the Burke Museum (UWBM 59322). We evaluatedidentification criteria for the Bristle-thighedCurlew by reviewingpreviously published analyses and photo- graphs(Johnsgard 1981, Hayman et al. 1986, Paulson1993, Rosairand Cottridge1995, Higginsand Davies1996), by studyingspecimens at the Burke Museum, and through discussionwith observersfamiliar with this species(David James, Dennis Paulson, Peter Pyle, and SievertRohwer). KevinAanerud and Mlodinowcompared the eightfull specimens and five spreadwings of the Bristle-thighedCurlew with 39 full specimensand 25 spreadwings of the Whimbrel,mostly N. p. hudsonicus, but including some variega tus from eastern Asia. Three of the Bristle-thighedswere in relatively freshplumage, two from April and one from August.The remainingfive whole specimenswere somewhatworn adultscollected in October.All Bristle-thighedwings were from fall. We measuredthickness of tarsi 2 cm belowthe tibiotarsaljoint. Our estimatesfor the total numberof Bristle-thighedCurlews making landfallsouth of Alaskawere basedon the numberof birdsseen, the amount of sandybeach habitatbetween Tatoosh Island and Point Reyes, and the extentto whichthis habitatthat was surveyed.Linear milesof sandybeach habitatwere estimatedfrom geologicalmaps for California,Oregon, and Washington.This habitatwas denotedas Quaternarysand or Quaternary beachand dune sands on thesemaps. Estimates of the amountof thishabitat searched were based on interviews with active birders. Estimates of total birds found were made on both most conservative and least conservative criteria. For the mostconservative estimate, all sightingswithin a 12-dayperiod and a 10-mileradius were consideredto be of the sameindividual(s). The 12-day periodwas basedon the stayof the birdsat the southjetty of the Columbia River,the longestwe know of. The leastconservative estimate supposed that all nonconsecutivesightings at least1 mileapart were of differentindividuals. We arrived at the most conservative estimate of total involved in the 1998 eventby expandingthe mostconservative estimate of birdsby the most conservativeestimate of sandybeach habitat surveyed. Similarly, we derivedthe leastconservative estimate by expandingthe leastconservative

134 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 estimateof birdsby the leastconservative estimate of habitat.We did not extrapolatebeyond the northernand southern edges of the observedarea of the curlew's occurrence. The monthlyaverage WPO index and the SouthernOscillation index (SOl)were both madeavailable by the NationalOceanic and Atmospheric Administration(NOAA)/Climate PredictionCenter in Washington,D.C. Theseindices are expressedby a positiveor negativenumber that measures the strengthof the WPO and E1Nifio/Southern Oscillation, respectively. To searchfor anomalouswinds between 15 April and 15 May 1998, we used dailyaveraged data from the NationalCenters for EnvironmentalPredic- tion/National Center for AtmosphericResearch Reanalysis (Kalnay et al. 1996), whichwere obtainedfrom the NOAA ClimateDiagnostics Center in Boulder, Colorado. We calculatedmodel trajectories to estimatethe pathtaken by the migrating Brisfie-thighedCurlews, using the windsat the 600-mb pressurelevel. This level,which approximately corresponds to an altitudeof 4 km abovesea level, is selectedbecause that is the typicalelevation for shorebirdsmigrating over water (Richardson1976, Williamset al. 1977, Elkins1988, Kerlingerand Moore 1989, Berthold1996). We calculatedthe trajectoriesfor sixconsecu- tive daysbeginning 26 April 1998. The initiallocation of the curlewsis specifiedas the southernmostend of the 20 m/s northerlywind contour (the dashedcontours in Figure 2) in the north-centralNorth Pacific.We then assumedthat the curlewsflew parallelto the localwind vector,i.e., drifted downwind,at an air speedof 25 m/s (similargeneral conclusions are obtained with otherrealistic air speeds).Mathematically, this can be writtenas V = Vw + ar, where the vector V is the bird's groundspeed, V•v is the observedwind vector,a = 25 m/s (the bird'sair speed,Marks and Redmond1994a), and r is a unit vector parallelto V•v. The equationsfor the longitudinaland latitudinaldisplacement of a birdundergoing downwind drift are dx = U(t)dt; dy = V(t)dt, where dx is the eastwarddisplacement and dy is the northwarddisplace- ment of a bird movingwith an eastwardground speed at time t of U(t) and a northwardground speed at time t of V(t) over a time intervaldt. The appropriatespherical representations are usedfor dx and dy (seeHolton 1992), andthe time stepdt is specifiedas one hour.With thisapproach, the temporalchanges to the observedwind patternthroughout downwind drift are taken into account.Also, temporal and spatial mathematicallinear interpolationis performedas the observedwind vectorsare obtainedfrom NOAA Climate DiagnosticsCenter as daily averageson a 2.5 ø latitude/ longitudegrid.

RESULTS AND DISCUSSION

Status and Distribution Bristle-thighedCurlews are knownto breed only in Alaska,where they havebeen found in the NulatoHills (the low mountainousregion just north and east of the lower Yukon River) and acrossthe northern half of the

135 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

Seward Peninsula(Handel and Dau 1988, Kessel 1989). They typically arrive at their breedinggrounds in mid-May but have been found there as earlyas 5 May (Kesse11989);a recordfrom Attu Islandon 2 June1993 (AB 47:444) waslikely of a •atenorthbound migrant. After nesting, much of the populationstages in Alaska'sYukon-Kuskokwim delta before migrating south, with smallernumbers staging along the Seward Peninsulacoast (Hande•and Dau 1988, Kesse11989).The firstsouthbound adults appear at thesestaging areas as earlyas late June. A largerinflux of adultsoccurs in late July, followedby adultswith juvenilesin early August(Handel and Dau 1988). By mid-to-lateAugust most adultsand juveniles are gone. The latest date from Alaskais 18 October1994 on St. LawrenceIsland (FN 49:85). In both the up•andbreeding areas and the coastalstaging areas, dwarf shrub habitatis preferred(Kessel 1989). Little is known of Bristle-thighedCurlews during migration.The first possiblestop for southboundbirds is the northwesternHawaiian Islands, some4000 km away.These islands serve as the winteringground for 700 to 800 individuals,but few if any passagemigrants stop there duringeither fall or spring(Marks and Redmond1994a,b). Consequently,those curlews winteringfarther south in the Pacificlikely travel at least6000 km without restingduring both fall and springmigration. Bristle-thighed Curlews have beenknown to migratein the companyof PacificGolden-Plovers (l•luvialis fulva) (Marks and Redmond 1994a) but rarely associatewith Whimbrels, even at mutualstaging sites in Alaska(Handel and Dau 1988). The Bristle-thighedCurlew winterscommonly in the northwesternHa- waiian Islands,eastern Micronesia, and easternPolynesia. It is lesscommon in central Polynesiaand Fiji and rare in the main Hawaiian Islandsand western Micronesia(Pratt et al. 1987, Marks and Redmond 1994b). The bulkof the winterrange is, therefore,between 135 ø W and 175 ø E. There are four records from farther south or east in the Pacific: two from the KermadecIslands during September 1972 (Veitch1974), one fromNorfolk Islandduring January 1968 (Turbott 1990), and one from EasterIsland (Vilina et al. 1992). Bristle-thighedCurlews can be found year round on their wintering groundsbut are most numerousbetween Septemberand April (Gill and Redmond 1992). Birds remainingthrough the australwinter are largely immatures,which do not migrateback north until they are approximately34 months old (Marks 1993, Marks and Redmond 1996). The favoredwinter habitatsinclude open dry grasslands,saltpans, edges of tidalchannels, and sandybeaches (Pratt et al. 1987, Gill and Redmond1992), but somebirds alsoventure into brushlandand open woodlands(P. Pyle pers. comm.). On the northwesternHawaiian Islands, returning adults arrive from mid- Julyto late August,juveniles mostly between mid-August and earlySeptem- ber (Marks and Redmond 1994a), though some appear as late as early October (P. Pyre pers. comm.). Spring departuresoccur almostentirely duringvery late April and early May (Marksand Redmond1994a, P. Pyle pers. comm.). Brisfie-thighedCurlews wintering in Hawaii mosfiyinhabit open dry grasslandsbut congregateon sandybeaches, mudfiats, airplane runways,and similarareas just after fall migrationand just prior to spring migration(J. Marks, P. Pyle pers. comm.).

136 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

On the main Hawaiian Islands,Bristle-thighed Curlews are quite scarce. Historically,only one or two birdswere seen,usually between late August and early October,and usuallynear Kahuku,Oahu (R. Pyle pers. comm.). Startingabout 1990, individualsbegan wintering, and the numbersduring fallincreased. During the winterof 1997-98, therewere at least13 birdsat Kahuku,and, for the first time, a few may be summering(R. Pyle pers.

Records Prior to 1998 Prior to 1998, there were only four acceptedrecords of the Bristle- thighedCurlew from North Americaoutside of Alaska.The firstof theseis of a birdcollected at Grant Bay at the northwesternend of VancouverIsland, BritishColumbia, on 31 May 1969 (Richardson1970). The secondis of two photographedat Bandon, Oregon, on 16 September1981 (Gilliganet al. 1994). The third is of one seenat LeadbetterPoint, Washington,on 1 May 1982 (Widrig 1983), and the fourth was recordedat BlackieSpit along BoundaryBay, BritishColumbia, 13-14 May 1983 (Campbellet al. 1990). Severalbirds reported and publishedas Bristle-thighedCurlews were later rejectedby localauthorities. One photographedat Cox Bay, near Torino, alongthe westernshore of VancouverIsland on 1 September1982 was initiallyidentified as a Bristle-thighed(AB 37:904), butlater evaluation of the photographsuggests that it maywell have been a Whimbrel(Campbell et al. 1990, D. Paulson,pers. comm.).A report from Victoria,British Columbia, on 11 September1986 is consideredhypothetical (K. Taylorpers. comm.). Widrig (1983) referred to two Bristle-thighedCurlews seen flying past LeadbetterPoint on 18 May 1980--two years prior to his sighting. Unfortunately,the descriptionof thesebirds, seen only in flight,is very brief, and the reportmust be left as hypothetical. Notably, recordsof vagrantsin Asia are also quite unusualand are apparentlylimited to Japan. Brazil(1991) listed13 Japaneserecords, few with actualdates. Multiple records have come from May and September, with singlerecords from Marchand July.

Records from 1998 The 1998 Bristle-thighedCurlew invasion started quietly on 6 May when David Lauten and Kathy Casteleintentatively announced a Bristle-thighed Curlew at FlorasLake, Curry County, Oregon. Regionalbirders' interest grew dramaticallywhen two more were seen on 8 May flyingpast Ocean Shores,Grays Harbor, Washington(R. Sundstrom,H. Opperman pers. comm.).The ensuingthree weeksled to 13 more reportsthat couldhave involvedas many as 22 additionalbirds, giving a total of 15 reports consistingof up to 25 individuals(Appendix 1). Of these 15 reports,we foundthree (involving a totalof eightbirds) to be lackingdetails sufficient to be includedin our analysis. On the basisof the most and least conservativecriteria under Methods, between13 and 17 Bristle-thighedCurlews were seen,all between6 and 25 May (contra Patterson1998). Initial detectionranged from 6 May to 19 May, with a median of 13 May. All but two recordscame from sandy beaches,the birdsat TatooshIsland and BatteryPoint occurringon marine

137 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 terraces(Tertiary conglomerate). The discrepancybetween the upper and lowerestimates comes mostly from OceanShores/Westport, Grays Harbor County,Washington. At this location,one or two Bristle-thighedCurlews were reportedonly intermittentlybetween 8 and 25 May, despitenearly continuouscoverage, implying that severalindividuals or pairs may have passedthrough. The actualnumber of birdsseen at Westport/OceanShores is somewherebetween two and six, probablycloser to six. Between 40 and 65 miles of the 309 miles of beaches between Point Reyesand Tatoosh Island was surveyed by birders.Extrapolation by the most and least conservative methods leads to an estimate of 60 to 150 Bristle- thighedCurlews making landfall on the PacificCoast of the contiguous United States.If the breedingpopulation is roughly3500 pairs(Gill and Redmond 1992), the 1998 invasioninvolved between 0.9 and 2.1% of breedingBristle-thighed Curlews. If additionalbirds were lost at sea,an even greaterproportion of the populationwas affected.

Parallel Vagrants The Bristle-thighedCurlew is not the only shorebirdthat breeds in Beringia,winters on tropicalPacific islands, and is a vagrantalong the coast of North America south of Alaska. Other suchtaxa are the Gray-tailed Tattler,Asiatic Whimbrel (N. p. variegatus),Bar-tailed , Red-necked Stint( ruficollis), and Sharp-tailedSandpiper (Calidris acuminata). Of these,the Gray-tailedTattler, Asiatic Whimbrel, and Bar-tailedGodwit were reportedsouth of Alaskaduring May 1998 (Appendix2)--the first time three of these specieswere reportedduring the same spring,an unprecedentedevent that seemslikely related to the sameweather factors that misplacedthe Bristle-thighedCurlews. Surprisingly, Pacific Golden- Ploversdid not occurin unusualnumbers during the springof 1998 (contra Patterson1998), despitehaving a migratoryroute similarto that of the Bristle-thighedCurlew.

The Role of Weather Giventhat Brisfie-thighedCurlews migrate long distancesover the open oceanand infrequenfiystray off course,one mightpresume that theyhave extraordinarynavigational skills and are able to cope well with adverse weather.Williams and Williams (1990), however,suggested that transoceanic migrantsdo not haveexceptional navigational skills. Current theory presents a pictureof overwatermigration of threestages: (1) when departing the tropics in spring,birds tend not to departinto strong headwinds--a trait of theBristle- thighedCurlew (Marks and Redmond1994a); (2) thereis littleor no compen- sationfor lateralwind drift during overwater migration, with birds appearing to maintaina constantcompass heading (Richardson 1976, 1991, Alerstam 1981, Williamsand Williams 1988, Berthold 1996); (3) as birdsapproach theirdestination, they use additional navigational skills, such as compensating for winddrift and usinglandmarks (e.g., Williams et al. 1986). There are three main causesof weather-relatedvagrancy among birds: stronghead winds, strong lateral winds, and deep and horizontally extensive cloudcover. Unusually strong head winds rapidly deplete the fat reservesof migrantbirds, particularly dangerous to thoseflying over the ocean.Exces-

138 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 sivelateral winds can causeoverwater migrants to driftfar off course,while deep cloudslead to a reductionin visibilitythat can lead to disorientation (Lack and Eastwood1962, Able 1982a, Elkins 1988, Richardson1990, Berthold1993, Moss 1995). Both headwindsand heavycloud cover can sometimesresult in downwindorientation (Williamson 1959, Able 1982a,b, Able et al. 1982, Elkins1988, Moss 1995), as this strategyincreases the likelihoodof reachingland.

E1 Nifio and the West Pacific Oscillation The occurrenceof the Bristle-thighedCurlews coincided with both a large El Nifio and a large positivephase of the WPO. The well-known[] Nifio phenomenonis characterizedby anomalouslywarm surfacewater in the easternequatorial Pacific Ocean and is accompaniedby a strengtheningof the westerlywinds in the easternsubtropical Pacific. This change in the wind patterncan be seenby comparingthe average300-mb windvectors off the westcoast of Mexicofrom 15 April to 15 May 1998 (Figurela) to the 10- year averagewind vectorsfor the same period (Figurelb). (The 300-mb pressurelevel is about 8.5 km above sea level, well above the elevationof migratingshorebirds, as discussedearlier. However, we examinethe 300- mbwinds because midlatitude storm systems are to a largedegree steered by the windsat this level.)The WPO, identifiedthrough the applicationof a rotatedprincipal-component analysis (Barnston and Livezey1987), involves changesto the wind pattern in the northwesternand north-centralNorth Pacific.In the north-centralNorth Pacific,where Bristle-thighedCurlew migrationnormally takes place, the positivephase of the WPO is character- izedby a strengtheningof the northerlycomponent of the winds(compare Figuresla and lb). The extraordinarycircumstances of the springof 1998 are determinedby comparingthe SOl and WPO indiceswith thoseof previousyears. The SOl hasbeen measuredas far back as 1882, the WPO indexto 1950. The SOl for April 1998 istied with that for 1987 for the secondmost negative value since1882 (a largenegative SOl valuedenotes El Nifio).The WPO indexfor the springof 1998 hadthe secondlargest positive value during the pasthalf century.

Wind Patterns As noted above,shorebirds in generalmigrate over water at aboutthe 600-mb level.Therefore, we searcheddates between 15 April and 15 May 1998 for stronganomalous northerly or stronganomalous westerly winds (speedsat leasttwo standarddeviations greater than average)at 600 mb in the tropicaland midlatitude North Pacific west of 140øW.Analyses at other pressurelevels, from sea level to 250 mb, yieldedessentially the sameresults as those at 600 mb. We confinedthe searchto this region becauseit encompassesthe Bristle-thighedCurlew's normal migratory route. For this analysis,we define the anomalouswind vectorsas the differencebetween the observedvector wind fieldon a givenday and the averagevector wind fieldon the samecalendar day, averagedfrom 1988 to 1998. We empha- sizeexceptional winds because curlews have presumablyevolved to com- pensatefor normal winds.

139 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

...., a) A•_ril16 I .... to MayI• _ . 16 f j• • 1998• .I. . . I

ZZ_• ...... LZ.Li ......

140•E 180• 140•W 100•W

Figure1. The 300-mbtime-average wind vectors for (a) 15 April-15May 1998; (b) 15 April-15 May 1988-1998. The maximumvector length, in unitsof m/s, is indicatedat the top rightcorner of eachframe.

140 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

We foundanomalies of greaterthan two standarddeviations only between 26 April and 2 May 1998. We illustratethe daily averagedwinds on alternatedays beginning on 25 April 1998 in Figure2, whichshows two regionsof largeanomalies, one between30 ø and 50 ø N, the other between 5 ø and 15 ø S, both in the centralPacific. The former regioninvolved both anomalousnortherly and westerlywinds, the latterjust anomalouswesterly winds. At 40øN, 160 ø W on 25 April 1998, there was a weak trough(note that the winds rotate counter clockwisein a trough) that rapidly deepened (extendingfar to the south) over the followingfour days. This trough deepening,which is very unusual,is consistentwith the influenceof the positivephase of the WPO, with itsanomalous northerly winds between 25 ø and 50 ø N and between170 ø and 130 ø W (compareFigures la and lb). Such anomalouswinds correspondto an enhancementof the so-called stretchingdeformation field (Dutton 1995), which resultsin troughsbeing "stretched"southward and leadingto substantialtrough deepening(Lee 1995, Whitaker and Dole 1995; Figure 2). Coincidingwith this trough deepeningis a strengtheningof northerlywinds, reinforced by the positive phaseof the WPO. Furtheramplification of thistrough was likelydue to a weak cyclone(denoted by an X in Fig. 2) at the oceansurface on 27 April 1998. The location of this cyclone, east of the 600-mb trough, was appropriatefor a mutualinteraction with the trough,resulting in a rapidly amplifyingstorm and strongerwinds at all levelsvia baroclinicgrowth (Hoskinset al. 1985, Holton 1992). In the other region of interest,the tropical Southern Hemisphere, analysesat various pressurelevels (not shown)revealed an extensionof anomalouswesterlies down to sea levelbut a declinein the amplitudeof the anomaliesat higherlevels. Such character- isticsare consistentwith westerlywind bursts(e.g., Kiladiset al. 1994). If the northerly headwindswere sufficientlystrong, they could have depleteda curlew'senergy reserves before it reachedAlaska. Furthermore, theseheadwinds covered a longitudinalrange broad enough that they could have affectedbirds headingnorth from anywhere in the species'winter range. For westerlywinds, anomalous, not total, windsare relevant,because Bristle-thighedCurlews have presumably evolved to compensatefor lateral driftby the averagewind. The solidcontours in the centralPacific in Figure 2 indicatethat the anomalouswesterly winds in both hemispherescould havealso caused lateral wind drift, particularly for birdswintering in eastern Polynesia. We firstconsidered the influencesof the anomalouswesterly winds in the SouthernHemisphere, whose maximum speed was approximately15 m/s (Figure2c). If migratingcurlews in thisregion are flyingdue north at an air speedof 25 m/s and encounteranomalous crosswinds of 10 m/s over 10 degreeslatitude, they will drift eastwardby a distanceof approximately4 degreeslongitude. Clearly, this amount of eastwarddrift couldnot, by itself, accountfor the Brisfie-thighedCurlew landfall. However, it may have contributedto the landfallindirectly if thisdrift was sufficient to leadthe birds into the strongheadwinds in the North Pacific. The anomalouswesterlies in the NorthernHemisphere, just to the south of the surfacecyclone, were strongerthan those in the SouthernHemi-

141 50øN..

30øI,,I.

10øN

10ø•

140øE 180ø 140øW 100øW Figure2. Total600-mb windvectors for (a)25 April 1998. (b)27 April 1998, (c)29 April 1998, (d) 1 May 1998. Solidcontours, anomalous westerly winds: dashed contours,anomalous northerly winds. The contour interval is 5 m/s. Shading indicatesthose regions where the anomalyexceeds two standarddeviations, and the "X" denotesthe locationof the surfacelow. The maximumvector length, in unitsof m/s, is indicatedat the top rightcorner of eachframe.

142 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

143 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 sphere.If we assumean averageanomalous crosswind of 15 m/s over 10 degreeslatitude, the eastwarddrift would be 6 degreeslongitude, again, insufficient to account for the 1998 landfall. On the other hand, an examinationof the northerlywinds in the North Pacific quicklyreveals that they were sufficienfiystrong to be a major impedimentto any northboundBristle-thighed Curlew. The maximumnorth- erlywind speed in thisregion was in excessof 25 m/s, aboutthe airspeedof a migratingcurlew. Thus, birds flying into thiswind wouldhave made little headwayand might have even been pushedbackward. Since these strong headwindsspanned as much as 20 degreesof latitude,the birds likely depleted their fat reservesfor littlegain. To try to avoidthese adverse headwinds, the migratingcurlews could have dropped to a loweraltitude, a responseknown in other species(see references in Richardson1990). In this case,however, such an adjustmentwould have been of limitedbenefit. For example, at 850 mb (approximately1.5 km abovesea level), the strongestheadwinds (not shown)were still in excessof 20 m/s, and at the surface,the maximum headwinds(not shown) varied between 10 and 15m/s. Furthermore, a reductionin flight elevationto well below 850 mb would have been an unattractivealternative, obliging the birdsto flythrough a fairlyextensive cloud cover(see below), which can seriously impair a bird'sability to orientcorrecfiy (Richardson1990). Therefore,the Bristle-thighedCurlews could not have avoidedthe widespreadanomalous northerlies in the North Pacific,and it is thesewinds more than the anomalouslateral winds that likelyaccounted for the curlew landfall.

Role of Clouds As discussedearlier, extensive cloud cover can seriouslydisorient migrat- ing birds.During the lastfew daysof April 1998, therewas fairly extensive cloudcover over muchof the North Pacific.All of the cloudtops, however, were at a low elevation,except for high cloudsseveral hundred kilometers from the storm centernortheast of Hawaii (for example,see the infrared satelliteimage from NationalClimatic Data Centerfor 29 April at the World Wide Web site http://www.ncdc.noaa.gov/pub/data/goesbrowse/1998/ g9ir29APR199800.jpg). Thus,except for anybirds that mightbe insidethe storm,curlews migrating at their usualaltitude should have been well above the clouds,so cloudcover was unlikely to haveplayed a significantrole in the 1998 landfall.

Model TrajectoryCalculations As stated earlier, there is some evidencethat migratory birds orient downwindwhen encounteringstrong headwinds.Indeed, when a bird is facedwith headwindssufficient to matchits airspeed,flying downwind may be its only survivalstrategy. Therefore, we addressedthe questionof whether downwinddrift couldhave broughtthe migratingBristle-thighed Curlewsto the west coastof the contiguousUnited Statesby means of a seriesof modeltrajectory calculations. We calculatedmodel trajectories for the 600-mb pressurelevel, one for eachof the sevenconsecutive days beginning on 26 April 1998. Thosefor the firstfour daysare shownin Figure3. The trajectoriesfor 30 April to 2

144 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

140øE 180ø 140øW 100øW

Figure3. Modeltrajectories calculated for Bristle-thighedCurlews reorienting down- wind in the face of insuperableheadwinds. The thin solidcurve corresponds to downwinddrift beginning on 26 April1998, thethick dashed curve to thatbeginning on 27 April 1998, the thindashed to thatbeginning on 28 April 1998, andthe thick solidcurve to thatbeginning on 29 April 1998. The trajectoryterminates when the theoretical bird reaches the North American west coast.

May 1998 are not shownbecause they predictthat the curlewswould have arrivedin BajaCalifornia, inconsistent with actual observation. The trajecto- ries' startingpoint is the westernendpoint on the curvesin Figure3 and correspondsto the southernmostend of the 20 m/s northerlywind contour. Thesepoints, which correspond to the positionof strongestheadwinds at that latitude,represent possible locations where the curlewsswitched to flyingdownwind. The trajectoriesimply the birdsreached the westcoast betweensouthern California and southernBritish Columbia, a pattern ratherclose to that observed.The modelssuggest that birdsbeginning downwinddrift on 26 and 27 April 1998 flew to the PacificNorthwest, thosestarting downwind drift on 28 and 29 April 1998 to California.This southwardshift in thearrival location for the latter two dates is explained by Figure2, whichshows that as the trough moved eastward, curlews undergo- ingdownwind drift were increasingly under the influenceof westerlyrather that southerlywinds. According to thesecalculations, the amountof time a bird took to reachland was 40, 36, 38, and 26 hoursfor the initialdates of 26, 27, 28, and29 April 1998, respectively.During a typicalyear, curlews takebetween 25 and37 hoursto reachthe Alaska coast from the starting pointof the modeltrajectories. These results suggest that reaching the west coastof the U.S. waswell within the curlews'capabilities. Accordingto ourmodel, the curlewsactually touched ground between 28 Apriland 1 May. The discrepancybetween this prediction and field observa- tionsmay be dueto the species'rarity and the similarityto the Whimbrel.

145 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

Indeed,David Lauten (pers. comm.) almost wrote the firstbird off as an odd Whimbrel.Furthermore, during the aftermathof the landfallseveral birders in centraland northernCalifornia reported early May Bristle-thighedCur- lewsidentified in retrospect,initially passed off as unusualWhimbrels (M. Rogerspers. comm.). Many of the birds were found in part because observerswere actuallylooking for them and may not havebeen encoun- teredor identifiedotherwise. Thus the lagbetween arrival and identification seems somewhat reasonable. We alsoused the modeltrajectory to evaluatethe contributionof El Nifio to the downwinddrift to the contiguousU.S. For thiscalculation, we used the observedwind pattern at 300 mb rather than that at 600 mb. This is becauseit is at the 300-mb levelthat E1Nifio hasa stronginfluence; at 600 mb the effectof E1Nifio is substantiallysmaller (Pan and Oort 1983, Wang 1992). Thusif El Nifio affectedthe migratingcurlews, the birdswould have had to moveupward to a muchhigher elevation, an unlikelyscenario. The resultsof thiscalculation, using the samefour initial dates and locations as in Figure3, bringthe birdsto thewest coast of centraland southern Mexico, far to the southof any observedcurlews. Consequently, if strongheadwinds followedby downwinddrift accountedfor the Bristle-thighedCurlew land- fall, E1Nifio did not playa role.

Identification The Bristle-thighedCurlew most closely resembles the Whimbrel,particu- larlythe North Americanrace hi. p. huclsonicus.Characteristics considered usefulhave includedbill shapeand color,underpart color, chest markings, flankbarring, undertail-covert barring, bristled thighs, upperpart coloration, rump pattern and color, tail pattern and color, under-primarypattern, underwing-covertcolor, leg shape, and call. We found some previously proposeddistinctions to be lacking,while otherswere useful.In addition, apparentlyconsistent differences in upper-primarypattern, underwing primary covert pattern, leg thickness,and behavior were uncoveredby observersof the 1998 invasionor duringour reviewof photographsand specimens.Of previouslypublished discussions, we foundPaulson (1993) to be the mostaccurate and informative, though the drawingsin Haymanet al. (1986) and the photosin Rosairand Cottridge(1995) andPatterson (1998) are veryuseful. Bill Color. When compared with the Whimbrel, the Bristle-thighed Curlewtypically has more extensivepink-flesh color in the baseof the bill, but there is muchoverlap in thismark, and its usefulnessin the fieldis likely marginal(Paulson 1993). Also,the bill colorof the Bristle-thighedCurlew varieswith age,sex, and season.Females, winter adults, and immatures tend to have more extensivelypale bills (J. Marks pers. comm.). On Laysan Island,during the springof 1991, 70ø-/0of adultBristle-thighed Curlews had attainedcompletely black bills before migrating north, whereas less than 4ø-/0 of subadultshad doneso (Marks1995). Many of the spring1998 vagrants had blackor nearlyblack bills, but somehad extensivepink. Bill Shape.Differences in billlength, thickness, and curvaturehave been proposed,with the Bristle-thighedCurlew having the longer,thicker, and more decurvedbill. These do not seemto hold up to the scrutinyof actual

146 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 measurement(Johnsgard 1981, Haymanet al. 1986, Higginsand Davies 1996, A. Jaramilloin litt.) and reviewof photographs. Underpart Coloration. The Bristle-thighedCurlew is often reportedto have more richlycolored underparts than the Whimbrel.However, both hudsonicusand the Bristle-thighedCurlew can be rather orange-buff underneath(variegatus lacks these warm tones).While the brightestBristle- thighedsare more colorfulthan the brightestadult or juvenilehudsonicus, someoverlap does exist between juvenile hudsonicus and the adultBristle- thighed,especially those in worn plumage.Some Bristle-thigheds are more brightlycolored on the flanksand undertailcoverts than on the centralbelly (see photos in Patterson 1998), whereas hudsonicusdoes not show contrastinglybrighter flanks or undertailcoverts. Underpart Markings.The presenceor absenceof flankbarring can be a helpfuladjunct in Bristle-thighedCurlew identification. Bristle-thighed Cur- lews typicallyhave unbarredflanks or have the barringlimited to the far anteriorflanks, though one specimenshows barring well into the rearflanks, asdoes a photoin Gill et al. (1988). In contrast,all Whimbrelshave barring well onto their rear flanksand, in some,all the way to the undertailcoverts. Thus,a birdwith unbarredflanks is verylikely a Bristle-thighedCurlew with one caveat:both speciessometimes droop their wings, hidingany flank barring. The presenceof markingson the undertailcoverts is saidto be diagnostic for the Whimbrel,the lackof themdiagnostic for the Bristle-thighedCurlew (Paulson1993). Some Whimbrel specimens,however, have very few markingshere and in the field couldeasily appear unmarkedeven under excellentconditions. None of the Bristle-thighedCurlew specimens had any undertailcovert bars, streaks,or spots.Thus, in the field, plain undertail covertsare not diagnosticfor the Bristle-thighed,but marked undertail coverts eliminate it. The breaststreaking on the Bristle-thighedoften appearslike that of a PectoralSandpiper (Calidris melanotos),with fine verticalstreaks cut off sharplyat the lower breastedge. Whimbrelsusually do not look this way becauseof cross-barringon the lower breastfeathers (in many but not all birds)and their barredflanks. Bristle-thigheds lack the chestcross-bars and often lack the flank barring.The Pectoral-likeappearance is only mildly suggestiveof the Bristle-thighedCurlew, but cross-barson the cheststreak- ing are likelydiagnostic for the Whimbrel. Bristled Thighs. The thigh bristleshave often been regardedas nearly undetectablein the field,yet in spring1998 manyobservers found them to be readilyvisible. Jeff Marks(pers. comm.) finds that theyare oftenvisible at 75 meters,if one is usinga goodscope under good lighting conditions. Also, the thighsof Bristle-thighedCurlews often look shaggy, an aspectlacking in the Whimbrel. Back, Scapula r, and Wing Covert Markings.In Bristle-thighedCurlews, the backfeathers, scapulars, and wing covertsare roughlyhalf dark brown and half orange-buff(excepting adults in worn plumageduring the fall). In adultWhimbrels, these feathers are mostlydark brown, with only 10 to 25% of the surfacearea consisting of palegrayish-brown (not orange-buff) feather edgingand spotting.

147 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

JuvenileWhimbrels, however, are muchmore brightlypatterned, with at leastone specimenin the BurkeMuseum approaching a fresh-plumaged Bristle-thighedCurlew in the size and color of its markings.Also, the October Bristle-thighedCurlew specimensin the Burke Museum are far dullerthan the springbirds, and the upperpartmarkings on theseindividuals arewell within the rangefound on juvenileWhimbrels. Thus, while the back/ scapular/wing-covertpattern is veryuseful in spring,it is of muchless value for juveniles. Rump and Uppertail Coverts. The pattern and color of the rump and uppertailcoverts are two of the mostreliable marks for the Bristle-thighed Curlew.In the Bristle-thighed,the rump and uppertailcoverts are typically orange-buff(varying from rustyto pale buff), often with a few long fine streaks,whereas in hudsonicusthey are brownwith heavybrown markings. This givesthe appearanceof a plain,brightly colored rump patch,while in hudsonicusthe rump is concolorouswith the back. The Asian variegatus has a paler and whiter rump and uppertailcoverts than hudsonicuswith fewer markingsbut is still more heavily marked than a Bristle-thighed Curlew. We did find one Bristle-thighedCurlew specimenwith a fairly heavilymarked rump, the relativelyunmarked region limited to the uppertail covertsonly. Tail Pattern and Color. Tail patternand colorare alsoamong the most reliable charactersfor separationof the Whimbrel and Bristle-thighed Curlew.In the Bristle-thighed,the tail isbrightly colored (like the rump)with dark brown bars, whereas in hudsonicusthe tail is medium brown with dark brownbars. Consequently,the contrastbetween the pale and dark barsis muchgreater in the Bristle-thighed. The Whimbrelhas seven to nine dark barsabout 6 mm apart, the Bristle- thighedonly six to sevendark bars about 7 mm apart. Variegatusshows the same numberof dark bars as hudsonicus,but its pale bars are paler than those of hudsonicus,thus showingmore contrast.These pale bars, how- ever,are whitish,with no warm buff huesas in the Bristle-thighed. Primary Pattern. Paulson (1993) stated that in the Whimbrel the undersurfacesof the inner web of the outerfour primaries(p7-p10) show distinct,large, pale notches,whereas in the Bristle-thighedCurlew there is only diffusemottling. This mark mostlyheld up to specimenexamination. Unfortunately,3 of 64 Whimbrelsin the BurkeMuseum collection showed the mottled pattern of a Bristle-thighed,and one of the thirteen Bristle- thighedshad a Whimbrel-likepattern. A more usefulmark may be foundin the upper primarypattern. In the Bristle-thighed,the uppersurfaceof the inner five primaries(p l-p5) shows a bold whitish rear border that cuts acrossthe feather tip to form a prominenttriangle of whitish.In the Whimbrel,the rear borderis lackingon somebirds and narrowon others,often extending only from pl to p3. No Whimbrelspecimens showed the white terminaltriangles. For field observers,these two markswill rarely prove useful,though in somephotos and specimensthey couldbe valuable. Underwing Coverts. A differencein underwingcovert colorationhas been previouslysuggested (Johnsgard 1981, Hayman et al 1986, Rosair and Cottridge1995), with the Bristle-thigheddescribed as more brightly

148 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 colored.We foundno differencebetween the Bristle-thighedCurlew and hudsonicus, in agreement with Paulson (1993). Variegatus has quite differentgrayish underwing coverts. On the other hand, the pattern of markingson the underwingcoverts doesappear to differentiatethe Bristle-thighedCurlew from the Whimbrel. SievertRohwer noted that in all wing preparationsin the Burke Museum, the underwing'sgreater primary coverts are barredheavily in the Whimbrel but are spotted or notched in the Bristle-thighedCurlew. The greater secondarycoverts are heavilybarred in both species,but Whimbrelshave more bars. Leg Shape. Many observersof the vagrantscommented that the Bristle- thighedappeared to have shorterthicker legsand longer thicker toes. In many photos,Bristle-thigheds appear distinctlythicker legged, and at the BurkeMuseum Brisfie-thighed Curlew tarsi averaged 6.9 mm in diameter, those of the Whimbrel 6.0 mm (thesemeasurements may be affected somewhatby shrinkage).There was, however,a smallamount of overlap. Leg length,however, is not significantlydifferent (K. Garrettin litt, Higgins and Davies 1996). The shorter-leggedappearance of the Bristle-thighed Curlewmay be dueto the increasedthickness of the tarsior to the tibiabeing obscuredby shaggythigh feathers. Toe thicknessand lengthare lesswell known. Specimensof the Bristle- thighedCurlews do appear to have thickertoes, owing mostlyto more pronouncedfleshy extensions at the sidesof toes. Call. The callsof the Whimbreland Bristle-thighedCurlew are remarkably different.Whimbrels utter a seriesof sharpwhistles, typically five to seven. Bristle-thighedCurlews usually give a two- or three-notedwhistle variously describedas "too-ee, tee-oo-whit,and wheet-o-weet"by Paulson(1993), "chiu-eet"by Marksand Redmond (1994a), and "chi-u-itand whee-wheeoo" by Haymanet al. (1986). The patternof the Bristle-thighed'scall resembles that of a Black-belliedPlover, but the qualityis more stridentand less plaintive.Many havenoted that thesewhistles sound humanlike (D. Paulson pers. comm.).Marks and Redmond(1994a) alsodescribed a singlenoted "klee"call, and PeterPyle (pers. comm.) remarked on a "jureeeee-jureeeee- jureee"call that resembles,in quality,the vocalizationsof Long-billedCurlew (Numenius americanus).Many of the spring 1998 vagrantsvocalized frequently,though some were quiet. Habits. Witnessesof the 1998 spring invasionoften commentedon apparent differencesin habitat and behaviorbetween Whimbrelsand the vagrantBristle-thighed Curlews. One particularlydramatic behavior was that of whipping .Some Bristle-thighedsseized crabs by the leg, then smashedthem repeatedlyinto rocksor hard-packedsand with a whipping motion of the bird's head and neck. Some felt that this was to subdue the crabfor accessto itseggs (A. Jaramillopers. comm.). The birdsat the south jetty of the Columbia,however, grabbed crabs 2-5 cm in diameterand beat them until their carapaceswere broken into smallpieces and the interior fleshwas well exposed,then eatingit. This behavioris commonamong Bristle-thighedswith food itemsthat are too largeto be swallowedwhole (Marksand Hall 1992). Remarkably,some Bristle-thigheds have learned to crack open albatrosseggs by whippingstones into them with a similar

149 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998 motion (Marksand Hall 1992). Whimbrels,on the other hand, seem rarely to engage in such head and neck whipping, though Higgins and Davies (1996) describedit. Anothercomment was that the Bristle-thighedoften walked in a crouched manner, somewhatlike a rail (H. Nehls, M. Pattersonpers. comm.). This actionappears quite different from the usualmovements of a Whimbrel. There alsoappeared to be habitatdifferences. Whimbrels favor tidal fiats alongthe coast,whereas the Bristle-thighedsshunned these and were most oftenfound on beaches,at thebase of jetties,and on grassysand dunes. The birds along jetties walked among the rocks in searchof prey. Though Whimbrelscan sometimesbe seen at these same locations,the difference betweenthe two species'preferences seemed distinct. Althoughthese habitat and behavioraldifferences are not suitablefor identification,they might servewell as a red flag, drawingattention to a vagrant. We foundseveral marks to be stronglysuggestive but not fullyconclusive. In spring,a brightlycolored back and wingseliminate the Whimbrel,but the reverseis not necessarilytrue. A dullerbacked bird could be a Bristle-thighed in worn plumage.Flank barringand undertailcovert markings typically are quite different but in the field may be difficult to discern and are not definitive.If the underpartsare brighteston the flanksand undertail coverts, the bird is likelya Bristle-thighedCurlew, but the reverseis definitelynot true. Upper primarypattern is quiteuseful in specimensand somephotos, and may even be diagnostic,but field use is limited.Similarly, the under greaterprimary covert pattern also appears to be diagnosticbut difficultto use in the field.The underprimarypattern will identifya Bristle-thighedor Whimbrel with about 90 to 95% accuracyand is also best assessedin specimensor fortuitousphotographs. The Bristle-thighed'sprey-slamming behaviorappears to be quiteunusual in Whimbreland, if observed,would alsopoint stronglybut not absolutelyto the Bristle-thighed. Further featuresthat may be useful but are only suggestiveinclude underpartcoloration, leg thickness,and toe thickness.Bill sizeand curva- ture, bill color,leg length,and underwing coloration are likelynot useful.

SUMMARY

Between26 April and 30 April 1998, at an elevationtypical for migrating curlews,a highlyunusual weather pattern prevailed over the centralNorth Pacific--an anomaly associatedwith the West Pacific Oscillation,not El Niao. Shortlythereafter, between 13 and 17 Bristle-thighedCurlews were recordedfrom Point Reyes, California, to TatooshIsland, Washington. These two eventswere likelylinked. Any Bristle-thighedCurlews heading north between 26 April and 30 April 1998 would have encountered extremelystrong headwinds, giving them the choiceof continuingonward andfacing the riskof runningout of fuelor reorientingdownwind in search of land. Such reorientationwould have placedthese birdson the North American coast between southern California and southernmost British Columbiawith an arrivaldate between 28 April and 1 May.

150 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

The number of Bristle-thighedsthat landed on the West Coast was undoubtedlygreater than the number seen. Our estimatessuggest that between60 and 150 birdsactually made landfall.Not unlikely,additional birdsnever made it to land, either by failingto reachthe westcoast or by continuingon into the storm. A significantportion of the small world populationmay well have been placedat risk by this anomalousweather. Identificationof the Bristle-thighedCurlew is complex.Few marksare absolutelyreliable for identification,and previouslypublished discussions havenot beenentirely accurate. The tail and rumpremain the key, as in all plumages,the patternand colorationof theseareas consistently distinguish the Bristle-thighedCurlew from the Whimbrel.Even when the birdis on the ground, the tail pattern and color can usuallybe seen. The call of each speciesis diagnostic.The thighbristles, if seen,eliminate the Whimbrel.The 1998 invasionproved to be a fineopportunity for birdersto becomefamiliar with Bristle-thighedCurlew identification. The prospectof futureaccurate reportsof this specieshas certainlybeen enhanced.

ACKNOWLEDGMENTS

We are deeplyindebted to DavidJames, Jeffrey Marks, Dennis Paulson, and Peter Pyle,all of whomwere kind enough to reviewthe manuscriptand sharewith ustheir knowledgeand insight.We also thank the NOAA Climate DiagnosticsCenter for providingus with the NationalCenters for EnvironmentalPrediction/National Center for AtmosphericResearch Reanalysis dataset. We are alsovery thankful for informa- tion and assistanceprovided by KevinAanerud, Sharon Birks, Kathy Castelein,John Hunter, Alvaro Jaramillo,David Lauten, Betsy Mallow, Bob Morse, Harry Nehls, MichaelPatterson, Robert Pyle, MichaelRogers, Sievert Rohwer, Ruth Rudesill,Bill Shelmerdine,P. WilliamSmith, and Keith Taylor.Finally, many thanksto University of Washington'sBurke Museum for useof its facilitiesand accessto its collection.

LITERATURE CITED

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Campbell,R. W., Dawe, N. K., McTaggart-Cowan,I., Cooper,J. M., Kaiser,G. W., and McNall, M. C. E. 1990. The Birds of BritishColumbia, vol. 2. Univ. of Br. Columbia Press,Vancouver. Dutton, J. A. 1995. Dynamicsof AtmosphericMotion. Dover,New York. Elkins,N. 1988. Weatherand Bird Behavior.T. & A.D. Poyser,Calton, England. Gill, R. E., Jr., McCaffery,B. J., andTobish, T. G. Bristle-thighedCurlews, biologists and bird tours--a placefor all. Birding20:148-155. Gill, R. E., Jr., and Redmond, R. L. 1992. Distribution,numbers, and habitat of Bristle-thighedCurlews (Numenius tahitiensis)on RangiroaAtoll. Notomis 39:17-26. Gilligan,J., Smith, M., Rogers,D., and Contreras,A., eds. 1994. Birdsof Oregon. Cinclus,McMinnville, OR. Handel,C. M., andDau, C. P. 1988. Seasonaloccurrence of migrantWhimbrels and Bristle-thighedCurlews on the Yukon-KuskokwimDelta, Alaska. Condor 90:782-790. Harris, S. W. 1996. NorthwesternCalifornia Birds, 2nd ed. Humboldt State Univ. Press,Arcata, CA. Hayman, P., Marchant, J., and Prater, T. 1986. Shorebirds.Houghton Mifflin, Boston. Higgins,P. J., and Davies,S. J. J. F., eds. 1996. Handbookof Australian,New Zealand,and AntarcticBirds. Oxford Univ. Press,Melbourne. Holton, J. R. 1992. An Introductionto DynamicMeteorology. Academic Press, San Diego. Hoskins, B. J., Mcintyre, M. E., and Robertson.A. W. 1985. On the use and significanceof isentropicpotential vorticity maps. Q. J. RoyalMeteorol. Soc. 111:877-946. Johnsgard,P. A. 1981. The Plovers,, and Snipesof the World.Univ. of Nebr. Press,Lincoln. Kalnay,E., Kanamitsu,M., Kisfier,R., Collins,W., Deaven, D., Gandin,L., Iredell, M., Saha, S., White, G., Woolien, J., Zhu, Y., Chelliah, M., Ebisuzaki,W., Higgins,W., Janowiak,J., Mo, K. C., Ropelewski,C., Wang, J., Leetmaa,A., Reynolds,R., Jenne, R., and Joseph, D. 1996. The NCEP/NCAR 40-Year ReanalysisProject. Bull. Am. Meteorol.Soc. 77:437-471. Kerlinger,P., and Moore, F. R. 1989. Atmosphericstructure and avianmigration, in CurrentOrnithology (D. M. Power,ed.), pp. 109-142. Plenum,New York. Kessel, B. 1989. Birds of the Seward Peninsula,Alaska. Univ. of Alaska Press, Fairbanks. Kiladis,G. N., Meehl, G. A., and Weickmann,K. M. 1994. Large-scalecirculation associatedwith westerlywind burstsand deep convectionover the western equatorialPacific. J. Geophys.Res. 99 (D9):18,527-18,544. Lack,D., andEastwood, E. 1962. Radarfilms of migrationover eastern England. Br. Birds 55:388-414. Lee, S. 1995. Localizedstorm tracksin the absenceof local instability.J. Atmo- sphericSci. 52:977-989. Marks, J. S. 1993. Molt of Bristle-thighedCurlews in the northwesternHawaiian Islands. Auk 110:573-587. Marks,J. S. 1995. Migratorybehaviour of curlewswith brokenwings. Study Group Bull. 76:37-38.

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Marks,J. S. 1996. Reddata bird: Brisfie-thighed Curlew. World Birdwatch 18(2):20-21. Marks, J. S., and Hall, C. S. 1992. Tool use by Bristle-thighedCurlews feeding on albatrosseggs. Condor 94:1032-1034. Marks,J. S., and Redmond,R. L. 1994a. Migrationof Bristle-thighedCurlews on LaysanIsland: Timing, behaviorand estimatedflight range. Condor 96:316- 330. Marks,J. S., and Redmond,R. L. 1994b. Conservationproblems and researchneeds for Bristle-thighedCurlews Numenius tahitiensison their winteringgrounds. Bird Cons. Int. 4:329-341. Marks, J. S., and Redmond,R. L. 1996. Demographyof Bristle-thighedCurlews Numenius tahitiensiswintering on LaysanIsland. Ibis 138:438-447. McCaffery,B. J., andGill, R. E., Jr. 1992. Antipredatorstrategies in breedingBristle- thighedCurlews. Am. Birds46:378-383. Mlodinow,S. G., and O'Brien, M. 1996. America's100 Most Wanted Birds.Falcon Press, Helena, MT. Moss,S. 1995. Birdsand Weather,a Birdwatcher'sGuide. Hamlyn, London. Pan, Y.-H., and Oort, A. B. 1983. Global climate variationsconnected with sea surfacetemperature anomalies in the easternequatorial Pacific Ocean for the 1958-73 period. MonthlyWeather Rev. 111:1244-1258. Patterson,M. The greatcurlew fallout of 1998. FieldNotes 52:150-155. Paulson,D. 1993. Shorebirdsof the PacificNorthwest. Univ. of Wash. Press,Seattle. Pratt, H. D., Bruner, P. L., and Berrett, D. G. 1987. The Birds of Hawaii and the TropicalPacific. Princeton Univ. Press,Princeton, N.J. Richardson,F. 1970. A North Americanrecord of the Bristle-thighedCurlew outside Alaska. Auk 87:815. Richardson,W. J. 1976. Autumn migration over Puerto Rico and the western Atlantic: A radar study.Ibis 118:309-332. Richardson,W. J. 1990. Timing of bird migrationin relationto weather:Updated review,in BirdMigration (E. Gwinner,ed.), pp. 78-101. Springer-Verlag,Berlin. Richardson,W. J. 1991. Wind and orientationof migratingbirds: A review, in Orientationin Birds(P. Berthold,ed.), pp. 226-249. BirkhauserVerlag, Basel, Switzerland. Rosair,D., andCottridge, D. 1995. PhotographicGuide to the Wadersof the World. Hamlyn, London. Turbott, E.G. 1990. Checklistof the Birds of New Zealand and the RossDepen- dency,Antarctica, 3rd ed. Ornithol.Soc. N. Z., Wellington. Veitch, C. R. 1974. Bristle-thighedCurlew recordsfrom the KermadecIslands. Notornis 21:83-84. Vilina, Y. A., Larrea,A., and Gibbons,J. E. 1992. Firstrecord of the Bristle-thighed CurlewNumenius tahitiensisin EasterIsland, Chile. Wader StudyGroup Bull. 66:43-44. Wang, B. 1992. The verticalstructure and developmentof the ENSO anomalymode during 1979-1989. J. AtmosphericSci. 49:698-712. Whitaker,J. S., andDole, R. M. 1995. Organizationof stormtracks in zonallyvarying flows.J. AtmosphericSci. 52:1178-1191. Widrig, R. S. 1983. A Bristle-thighedCurlew at LeadbetterPoint, Washington.W. Birds 14:203-204.

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Williams,T. C., and Williams,J. M. 1988. Radarand visualobservations of autumnal (southward)shorebird migration on Guam. Auk 105:460-466. Williams,T. C., and Williams,J. M. 1990. The orientationof transoceanicmigrants, in Bird Migration(E. Gwinner,ed.), pp. 7-21. Springer-Verlag,Berlin. Williams,T. C., Williams,J. M., ,L. C., and Teal, J. M. 1977. Bird migration over the western North Atlantic Ocean. Am. Birds 31:251-267. Williamson,K. 1959. The Septemberdrift-movements of 1956 and 1958. Br. Birds 52:334-377.

Accepted30 August 1999

APPENDIX 1. Recordsof VagrantBristle-thighed Curlews in North America

Spring1998: AdequatelySupported FlorasLake, Curry Co., Ore. (1); 6 May (D. Lauten, K. Castelein) OceanShores, Grays Harbor Co., Wash.(2); 8 May (B. Sundstrom,H. Opperman) SouthJetty ColumbiaRiver, Clatsop Co., Ore. (3, photographed);9-21 May (H. Nehls) Ocean Shores,Grays Harbor Co., Wash. (1, photographed);12-14 May (P. W. Smith) TatooshIsland, Clallam Co., Wash. (1); 13-15 May (R. Paine, T. Wooton) Newport, LincolnCo., Ore. (2, photographed);13-15 May (E. Horvath) TatooshIsland, Clallam Co., Wash.(1, specimen);14 May (R. Paine,T. Wooton) BatteryPoint, Del Norte Co., Calif. (1, photographed);14-16 May (A. Barron) PointReyes, Marin Co., Calif.(1, photographed);16-25 May (C. andL. Lieurance, G. Griffeth) Westport,Grays Harbor Co., Wash. (1); 18 May (G. Revelas) BandonMarsh/New River mouth, Coos Co., Ore. (1); 19-23 May (D. Lauten, K. Castelein,S. Brown) Ocean Shores,Grays Harbor Co., Wash. (1-2, photographed);20-24 May (D. Paulson) Spring 1998: InadequatelySupported Point Reyes,Marin Co., Calif. (2); 6 May HumboldtCo., Calif. (1); 9 May South Jetty ColumbiaRiver, Clatsop Co., Ore. (5); 14 May Before 1998: AdequatelySupported Grant Bay, VancouverI., B.C.; 30-31 May 1969 (Richardson1970) Bandon,Coos Co., Ore. (2); 16 September1981 (Gilliganet al. 1994) LeadbetterPoint, PacificCo., Wash.; 1 May 1982 (Widrig1983) BlackieSpit, alongBoundary Bay, B.C.; 13-14 May 1983 (Campbellet al. 1990) Before 1998: InadequatelySupported Near Torino, VancouverI., B.C.; 1 September1982 (Campbellet al. 1990) Victoria,Vancouver I., B.C.; 11 September1986 (K. Taylorpers. comm.) LeadbetterPoint, PacificCo., Wash. (2); 18 May 1980 (Widrig1983)

154 THE BRISTLE-THIGHED CURLEW LANDFALL OF 1998

APPENDIX 2. Recordsof VagrantShorebirds from WesternNorth AmericaSouth of Alaskaand Parallelingthe Spring1998 Irruptionof the Bristle-thighedCurlew

The 1998 reportsfrom Californiaare all under reviewby the CaliforniaBird RecordsCommittee; some may not be accepted.We, however,feel these reports are correct. Gray-tailedTattler Point Reyes,Marin Co., Calif.; 24-26 May 1998 (K. Hansen,S. N. G. Howell) BodegaHead, SonomaCo., Calif.; 30 May 1998 (R. Rudesill) PrincetonHarbor, San Mateo Co., Calif.; 6 June 1998 (A. Jaramillo) Asiatic Whimbrel OceanShores, Grays Harbor Co., Wash.; 16 May 1987 (Paulson1993) OceanShores, Grays Harbor Co., Wash.; 16 May 1998 (P. W. Smith) Bar-tailed Godwit Ten previousspring records extending from 21 April to 10 June (Mlodinowand O'Brien 1996, NASFN 50:323). Ocean Shores,Grays Harbor Co., Wash.; 27 May 1998 (B. Shelmerdine) Red-necked Stint Arcata, HumboldtCo., Calif.; 5 May 1969 (Harris1996) Iona Island,Vancouver area, B.C.; 20 May 1997 (NASFN 51:914) Sharp-tailedSandpiper LeadbetterPoint, Pacific Co., Wash.;26 April 1979 (Mlodinowand O'Brien 1996) Lancaster,Los Angeles Co., Calif.; 5-9 May 1982 (Mlodinowand O'Brien 1996) Kern Nafi. WildlifeRef., Kern Co., Calif.;8-10 May 1984 (Mlodinowand O'Brien 1996) Pescadero,San Mateo Co., Calif.; 14 May 1994 (Mlodinowand O'Brien 1996)

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