counts, particularly from Alaska, where Rock Sandpiper abundance may change as ... (Cordova, Juneau, Sitka; Table 1), although the trend for the first two was.
RECENT CHANGES IN THE WINTER DISTRIBUTION AND ABUNDANCE OF ROCK SANDPIPERS IN NORTH AMERICA JOSEPHB. BUCHANAN,Cascadia Research Collective, 2181/2W. FourthAvenue, Olympia,Washington 98501 andWashington Departmentof FishandWildlife,600 CapitolWay North•Olympia,Washington98501
The North American population of the Rock Sandpiper (Calidris ptilocnemis)wintersalongthe Pacificcoastfromthe BeringSeato northern California(AOU 1998). In Alaska,where it is the most abundantwinter residentshorebird(GillandTibbitts1999), the speciesusessubstrates of soft or coarsesediment(GillandTibbitts1999), whereasrockyshorelines are the primary habitat in the southernpart of its range (Paulson1993). Rock Sandpipersare rarelyencounteredaway from the coast(Campbellet al. 1990). Perhapsbecauseof their closeassociation with ruggedor isolated coasts,little is known abouttheir winter populationstatus. Paulson(1993) suggested that winter populationshave declinedin the PacificNorthwestbutwasuncertainwhetherthe apparentdeclineis limited to that regionor reflectsa more widespreadchangein populationabundance.In this paper, ! usedata from annualChristmasBird Counts(CBC) throughoutthe winter range of the Rock Sandpiperto assessthe winter populationstatusof thisspecies. METHODS
To evaluaterecent trendsin winter populationsof Rock Sandpipers,I tallied results from CBCs conducted in Alaska (9 count sites), British
Columbia(6 sites),Washington(4 sites),Oregon(6 sites),and California(5 sites)where RockSandpipershave been detectedon at least 10% of the countssince1968-69 (seebelowand Table 1). The CBC isan annualsingleday eventinvolvingvolunteerswho countas many birdsas they can within a 12-km radiuscircle(seeBockand Root [1981] for additionaldetailsabout the CBC).
A numberof researchers havesuggested methodsfor standardizing CBC datapriorto analysis(e.g., Bockand Root 1981). Standardization of count data is an importantconsideration for many speciesbecausethe levelof observereffortmaybe correlatedwith a species'abundance(Bockand Root 1981). In thisanalysis,however,I usedthe actualcountdataratherthan an indexvalue(i.e., birds/partyhour)becauseI foundno positiverelationships betweenobservereffortand the abundanceof RockSandpipers(Spearman rank correlation;rs < 0.26, P > 0.25 in all cases). ! originallyintendedto useregression analysis(Neteret al. 1990) to assess relationships betweenabundanceof RockSandpipersand year of count.In
many cases,however,I was unableto performadequatedatatransformations (to normalize data distributions) becauseof high variabilityin the counts,particularlyfrom Alaska, where Rock Sandpiperabundancemay changeas birdsmove within or among estuaries(Gill and Tibbitts1999). WesternBirds30:193-199, 1999
193
DISTRIBUTION
AND ABUNDANCE
AVVAV
OF ROCK SANDPIPERS IN NORTH AMERICA
A
V
V
V
VVV
o
o
o
o
75% of the yearsbetween1968 and 1997. In addition,I usedregression analysis for NarrowCape/KalsinBay(Alaska) andSkidegate(BritishColumbia)databecauseeither1og•0or polynomialtransformations werepossible andthe numberof yearswith CBC datapriorto 1982-83 wastoo smallfor a two-sample analysis; thesetworegression analyses coveredperiodsending in 1996-97 and beginningin 1981-82 and 1983-84, respectively. RESULTS
RockSandpiperswere recordedregularlyin 19 CBC circles,throughout most of their winter distribution (Table 1). WinteringRock Sandpipers reachedtheir greatestabundancein three countcirclesin Alaska:Homer (highof 3400 in 1995-96; sixcounts>1000), GlacierBay(1708 in 198788; three counts>1000), and Valdez(1100 in 1989-90). Their abundance varied substantially from year to year in these and other count circles, particularlyin Alaska.Rock Sandpipersoccurredin lower numbersin all other count circles;their scarcityin many circlesin Washington(i.e., Bellingham,Seattle,San JuanIslandsArchipelago;all means
