Habitat Partitioning and the Distribution and Seasonalabundances Migratory Plovers and Sandpipers in Los Alamos, Rio Negro, Argentina

Gonzalez:Plovers and sandpipersin Argentina

Habitat partitioning and the distribution and seasonalabundances migratory plovers and sandpipers in Los Alamos, Rio Negro, Argentina

Patricia M. Gonzalez

Gonzalez,P.M. 1996. Habitat partitioningand the distributionand seasonalabundances of migratoryplovers and sandpipersin LosAlamos, Rio Negro,Argentina. InternationalWader Studies 8: 93-102.

BetweenSeptember 1989 and December1990, field studieswere conductedon the population fluctuationsof migratoryplovers and sandpipersand on their useof foraginghabitats along 4 km of coastlinenear Los Alamos, San Antonio Oeste, Rio Negro,in Argentina.Eight species were observed,of which four breedin northernNorth America. The largestflocks (up to 2,550birds) arrivedfrom the NorthernHemisphere in the secondhalf of Novemberand werepresent in significantnumbers until early April. The greatestnumber of birds was recordedin March (8,500 birds),when Calidriscanutus and C.fuscicollis were migratingnorthward. The first monthof the southernwinter was characterizedby the presenceof C. albaand Charadriusfalklandicus, common specieswhose numbers increased substantially thereafter. The mostcommonly used foraging habitatwas rockcovered with patchesof sandysediment and water up to 3 cm deep. Similaritiesin the useof microhabitatsare discussed.The mostsimilar species morphologically (C. albaand C. falklandicus)also showed a positivecorrelation in time. Nestingand the seasonalvariations in the numbersof people,dogs and vehicleswere recorded. The Los Alamoscoast is considereda 'vital site' (Clark1974) for the conservationof migratoryplovers and sandpipers.

Entre septiembre1989 y diciembre1990, se estudiaron la fluctuaci6npoblacional y el uso del h&bitatde alimentaci6n de chorlosy playerosmigratorios en 4 km de costacon restinga en las cercanlasde 'Los Alamos',San Antonio Oeste, Rio Negro, Argentina. Se observaron8 especiesde las cuales4 sereproducen en el nortedel continenteamericano. Los grupos rmts conspicuos provenientesdes Hemisferio Norte (2 550 ejs.)aparecieron en la 2da. mitad de noviembre registr;indoseabudancias importantes hasta los lros. dias de abril. E1rmtximo de avesocurri6 en marzo,cuando el sistemaalberg6 rmts de 8 500limicolos simult;ineamente: principalmente Calidris canutusy C.fuscicollis en pasomigratorio hacia el HemisferioNorte. E1ler. mesdel inviernoaustral secaracteriz6 por la presenciade C. albay Charadriusfalklandicus,especies frecuentes que entonces exhibieronsu mayor abudancia. El ambientede alimentaci6nrmts utilizado fue la roca cubiertacon peliculasde sedimentosarenosos en machonesy aguahasta 3 cm de profundidad. Se discuten similitudesen el usode microh;ibitats;las especies rmts parecidas estuvieron adem•is correlacionadaspositivamente en el tiempo(C. alba y C.falklandicus). Nidificaci6n y variaci6n temporalen el nfmero de personas,perros y vehiculos,fueron registrados. Se estirna que la costa de LosAlamos representa un sitiovital (Clark 1974)para la conservaci6nde chorlosy playeros migratorios.

Entreseptembre 1989 et dEcembre1990, on a •tudiE sur le terrainles fluctuationsde populationsde pluvierset de ScolopacidEsmigrateurs et leur utilisationdes habitats d'alimentation sur une portionlongue de 4 km du littoral du fleuveNegro dansla regionde LosAlamos, San Antonio Oeste,en Argentine.Huit esp•ces,dont quatrese reproduisenten AmEriquedu Nord, ont EtE observEes.Les vols les plus importants-- 2 550oiseaux -- sontarrives de l'hEmisph•reNord au coursdes deux dernitres semaines de novembreet y sontdemeur•s en grandnombre jusqu'au debutd'avril. La plus grandeconcentration a EtEenregistrEe en mars (8 500 oiseaux),au moment o• Calidriscanutus et C.fuscicollis migraient vers le Nord. Le premiermois de l'hiver australa EtE caractEris•par la presencede C. albaet de Charadriusfalklandicus,desespies communesdont le nombrea par la suiteaugmentE. L'habitat d'alimentation le plus frEquemmentutilis• Etait constituEde rochesrecouvertes de plaquesde s•dimentssableux et d'au plus 3 cm d'eau. Les auteurstraitent des similitudes dans l'utilisation des habitats. Lesesp•ces morphologiquement les plus semblables(C. albaet C.falklandicus) ont aussiprEsentE une correlationpositive dans le temps. On a aussienregistrE la densitEde nidificationet les variationssaisonni•res du nombrede personnes,de chienset de vEhicules.On consid•reque la c6te de Los Alamosest une ,,r•gion vitale,, (Clark 1974)pour la conservationdes pluviers et desScolopacidEs.

Casillade Correo 84, PedroMoron 384, 8520San Antonio Oeste, Provincial de Rio Negro, Argentina.

93 International Wader Studies 8:93-102

Introduction .exceptin front of ITMAS, whereit is about100 m wide. There are sedimentdeposits ranging from fine sandsto smooth rocks (20 cm diameter) and Despiteits interestingabundance and diversityof mollusc shells. birds,no studieshave yet beenconducted on the avifauna of the coastal area of Bahia de San Antonio and the coastalzone bordering the Gulf of San For moreinformation, see Angulo et al. (1981), Mafias,with the exceptionof censusescarried out GonzalezDiaz & Malagnino (1984),Piola & Scasso by Morrison& Ross(1989). (1988) and the San Antonio Oeste Environmental Charter (Underdirectorate of the Environment, Departmentof Economicsof Rio Negro). The objectivesof thisproject were as follows: With respectto continentalvegetation, the regionis (1) to provideinformation on the compositionand includedin the phytogeographicprovince of El abundancesof shorebirdsthroughout the year Monte (Cabrera1976); with respectto ornitho- alongthe coastnear the LosAlamos geographics,it falls under the coastalprovince TechnologicalInstitute of Mining and (Narosky& Yzurieta 1987). Groundwaters (ITMAS) in San Antonio Oeste, Rio Negro, and Material and methods (2) to describethe partitioningof foraginghabitats by the variousspecies of ploversand sand- Observationswere made every two weeksfrom pipersfor purposesof establishing(i) the September1989 to December1990, except for the importanceof thissite for migratoryshore- first two weeksof March,between 3 p.m. and 8 p.m. birds, (ii) the statusof shorebirdpopulations (later in the summer and earlier in the winter) on prior to the full functioningof a Solvay cleardays with wind speedsunder 40 km/h. I manufacturingplant, whose construction has observed the birds with 16 x 50 binoculars. beenunder way for sometime in Punta Delgado,and (iii) the biologicalgrounds for Patterns of distribution and seasonal seekingpolitical action to minimizethe impact abundance of large enterprisesand proposingmanagement plans. The coastwas studiedat high tide when the shoal was floodedand the species,numbers, behaviour and moultingstatus (where possible)of shorebirds Study area presentwere recorded.Pedestrians, dogs, vehicles and otherdisturbances were alsorecorded. Passing The Los Alamos coast is located on the Gulf of San airplaneswere not included. Mafias(64ø55'W, 40ø45'S), close to the city of San Antonio Oeste and the Las Grutas seaside resort in The reliability of the estimateswas substantiatedby the District of SanAntonio, Provinceof Rio Negro, recountingthe birds afterwardsor by using Argentina. It is the coastalsector that extendsfrom ITMAS to the entrance of the Antoine de Saint photographs.The specieswere groupedaccording to wherethey bred, as described in Myers& Myers ExuperyAirport (Figure1). (1979).

The zone is arid and mesothermic with a mean tidal amplitudeof between0.64 and 8.26m. On the coast Partitioning of foraging habitat of LosAlamos, the recedingtide uncoversa shoal Observations were made between 5 November 1989 (up to 1 km) perpendicularto the high-waterline. and 24 November 1990. The zone between the It is a horizontal,smooth, slightly convex, greenish- coastaldunes up to 100m of exposedShoal was yellow surface,which has fracture joints running in selectedfor observations,as the birdsgathered variousdirections in the limoliteof the Patagonia there to feed. Formation(marine Miocene) (Angulo et al. 1981). Threehomogeneous macrohabitats were The study area that was selectedowing to its recognized. Thesewere subdivided into micro- abundanceof birdsincluded the non-sloping habitatsthat were temporary because of draining coastalsector of the PatagoniaFormation. Its upper and dryingthrough the tidal cycle. Thespecies and limit is markedby fixed or shiftingdunes 1.5-3 m numbers of birds in each microhabitat were high, which are higher(10 m) and moreunstable in recordedunder differenttidal conditions(given by front of ITMAS. The intertidalcoastal strip, located roman numerals). When possible,notes were made betweenthe dunesand the exposedshoal, of the numberof birdsat rest(rest being considered correspondsto the area includedbetween the any activityother than foraging). high-tidelimits during spring and neap tides (Figure 2). It has a variablewidth of some50 m,

94 Gonzalez:Plovers and sandpipersin Argentina

MEDANC•,.•JI=RA I RE,.q'I'. MEDANO$......

SUPRAMAREAL

III III Figure1. Map of the Bahiade SanAntonio and Gulf of San Matias hinterland. The dotted area indicates the B IV A Los Alamos coast, and the dotted line shows the low-tide condition.• RESTINGA

The macrohabitats were identified with letters and Figure 2. (A) Diagram of the layout of sectionsin which the microhabitats with Arabic numerals. Habitats the habitatdivision project was carriedout. The large circlesindicate high, shiftingor plant-covereddunes. not usedby ploverswere markedwith a dash. The smallercircles indicate low, plant-covereddunes. The dottedlines showthe heightof the tide. (B) The specificaspects of the differentmicrohabitats Sketchof the outline of the coast (not to scale). encounteredin the study areaare shownin Table 1, rnedanos= sanddunes; supramareal = intertidal; and the macrohabitats are described below: restinga= shoal;pleamar alta = high tide; pleamar baja= neaptide. Intertidal (S): Describedin Studyarea and shown in Figure 2. The observationswere carriedout Fortnightlyvisits were carried out during low tides simultaneouslyalong the route usedfor censusing followinga routeperpendicular to the coast bird numbers. The tidal conditions were (I) towardsthe sea,and the presenceor absenceof incominghigh tide, high tide and slacktide and (II) shorebirdsand humanactivity was recorded. outgoinghigh tide without uncoveringthe shoal. Data processing Typical shoal (A): Representsmore than 90% of the uppershoal. Patchydeposits of sandand fine The SimpsonDiversity Index was usedto analyse sediments(0-3 cm deep). It faceslow duneswith diversity. I usedthe DominanceIndex to relatethe vegetation. The tidal conditionswere (III) outgoing highestnumber of birds for eachspecies to the total tide uncovering50 m of shoalperpendicular to the numberof birds seen(all speciescombined). The coastand (IV) outgoingtide uncovering100 m of Bucherand Herrera Index of RelativeImportance shoal. (Bucher & Herrera 1981) was used as an index to describethe relativenumbers of eachspecies in the Shoalwith sediment(B): The remainingsurface population. consistsof depositsof sandand fine sedimentsup to 30 cm thick and decreasingseaward for about The Spearmancoefficient (rs) (Southerwood1971) 50 m. This macrohabitatfaces high, shiftingor was usedto measurethe intensityof association plant-covereddunes (Figure 2A). The tidal betweenthe annualpatterns of differentspecies. conditionswere (III) outgoingtide uncovering50 m of shoalperpendicular to the coastand (IV) The following index,which is similar to the Bucher outgoingtide uncovering100 m of shoal. and HerreraIndex of RelativeImportance and whichrelates the relativeintensities of foragingand Censusdivisions consisting of 100m of shoreline resting,was usedto estimatethe feedingactivities reachingback 50 or 100m from the shorewere of eachspecies in the intertidalsector: relative establishedaccording to the heightof the tide. The importance(feeding/rest) or RI (f/r) -- (Nf/Nt) correspondingintertidal surface area of the census (Mf/Mt) 100, where Nf = the number of birds divisionswas determinedby projection.A census feedingin all the censuses;Nt = the number of birds was carried out on a total of four divisions shown in in all the censuses;Mf = the number of censusesin Table1 in the followingorder: BIII, Alii, BIV and which the speciesis feeding;and Mt -- the number AIV. Macrohabitat B was uncovered first (see of censusesin which the speciesis present. Figure2A). The frequencyof habitat useby a specieswas calculated as the number of observations of each

95 International Wader Studies 8:93-102

Table1. Designationofmicrohabitats. Different numbers for a microhabitatindicate a different spatial location ora different substrate.

Macrohabitats and tide

SI SII AlII-IV Bill-IV Microhabitats

1 1 1 1 DRY SEDIMENT 2 2 2 2 DRY BACKWATER(deposits of algaeand dry grass) 3 WET BACKWATER 4 8 15 20 BORDER1: zonealternatively covered and uncoveredby waves 5 9 16 21 BORDER2: deeperthan BORDER1, coveredby at least3 cm of water 6 SEMI-PERMANENT POOLS (>5 cm) 7 13 7 ALGAE recentlydeposited by the sea 10 10/11 17 WET SEDIMENT 12 18 SEDIMENT COVEREDIN WATER (0-5 cm deep) 14 19 ROCKcovered in film of sedimentsin patchesand waterup to 3 cm deep PATCHESOF MUSSELS10-30 cm wide with variablelengths LARGETIDE POOLS(up to approximately30 cm deep) HIGH ROCKFORMATIONS (up to 100cm high) ROOTED GREEN ALGAE

speciesin eachmicrohabitat divided by the total speciesin early fall and (3) the increasein early numberof observationsmade of thisspecies. The winter due to C. albaand Charadriusfalklandicus. chi-squaredtest (Z 2) wasused to analysefrequency. The SimpsonDiversity Index rangedbetween 0.0 The Mean Taxonomic Distance Index (MTD) (Sokal and 2.06on the northernmigration. The seasonal 1965)was used to identify similaritiesin foraging variation in dominanceshowed a definite pattern in habitatuse among species. The meanlinkage the successionof dominantspecies: C. fuscicollis technique(Sokal &Sneath 1963)was usedfor group dominatedfrom mid-Novemberto early April analysis.Graphic representation was doneusing (SimpsonDiversity Index > 0.93),interrupted only dendrograms;the copheneticcorrelation coefficient by the arrival of C. canutus,which thenbecame (r) of Sokal & Rohlf (1969) was used to measure dominant(Simpson Diversity Index = 0.79). distortionbetween the similaritymatrices (Crisci & Lopez Armengol 1983). Oncethe migrationof the Nearcticplovers had occurred,C. falklandicus became dominant until the The segregationof pairs of speciesthat were very next season.North Americansandpipers similar in their use of habitat and tide was carried (Scolopacidae)dominated from mid-springto early out usingthe Wilcoxonsigned-ranks test (Sokal & fall, when plovers(Charadriidae; Patagonian Rohlf 1980). species)exercised full dominance.

Results The annualbalance studied by meansof the relative importancevalues is consistentwith the results describedabove (Figure 4). Eightspecies of shorebirdsbelonging to the Charadriidae(4) and Scolopacidae(4) were identified. Overall, the Scolopacidaeoccurred in far larger numbersthan the Charadriidae (RI = 59.68)owing to themigration of largeflocks and not becauseof a Patterns of abundance and seasonal constantmovement of sandpipersinto the area. distributions

The highestnumbers of birdswere seenfrom A positivecorrelation was found betweenthe mid-Novemberto mid-July;there were no numbers seasonalpatterns of C. albaand C.falklandicus (rs = exceeding100 birds/census at othertimes of the 0.5937;p < 0.01). year (Figure3). Most of the observersalong this coastlinewere The annualpattern showed three phases: (1) the sportsfishermen. In the summer,there were larger sudden abundance of birds in November, due numbersof touristsduring high-tideperiods. At mainly to the arrival of Calidrisfuscicollisfrom low tide, thehuman presence decreased, and a North America,(2) the northernmigration of all the typicalactivity at that time was the collectionof

96 Gonzalez:Plovers and sandpipersin Argentina

Thousands of birds -2O

4 a •3 3 4 4 433 3 3 4 2 20113

O u ^ ouo Jo do ^ S o ,. o Diversityø,1

C,canutu$ C,fuscicolli$ C,falklanclicus Dominant species

Figure 3. Frequencydiagram: Seasonal variation in the total numberof ploversand sandpipers,showing the contributionof the dominantspecies. The numberon eachbar indicatesthe numberof speciespresent. Lines:Seasonal variation in the numberof peopleand vehicles.Lines were usedto indicatepossible trends, but the variablesare discrete.Points: Seasonalvariation in speciesdiversity (Simpson). Observations are for the periodbetween October 1989 and October 1990. small octopuses.The numberof dogsranged SanderlingCalidris alba between0 and 4; 50 goatsand 1 boat were also recorded. The groupsthat interactedmost with the Sanderlingsused the studyarea as a migratorystop birds werepassers-by, dogs and vehicles(Figure 3). on their way southin November and north in March, even though low numbers were often Speciesobservations observedin the summer(Figure 4). During the southern fall and winter, there were birds that did North American not migrate. Similarobservations involving Family Scolopacidae juvenile birds were made in Peru by Castro& Myers (1987). Contrary to observationsin Peru, the Ruddy TurnstoneArenaria interpres birdsdid not moult to breedingplumage in Los Alamos,except for or• bird sightedon 16 June1990. One bird in non-breedingplumage was observedon Thesecould be sexuallyimmature birds that, like 5 November 1989, and two birds with advanced their counterpartsin California,did not acquire transitionalplumage (verging on breeding breedingplumage, although the latter do migrate plumage)were observedon 15 February1990. (Myers et al. 1985a,cited in Castro& Myers 1987). The birdssighted in March were beginninga body moult.

97 International Wader Studies 8:93-102

In thousands

C. canutus

N I = 4.6% Freqalba = 51.4% RI = 2.4 NI- 28% Freq = 14.3% RI=4

! i : , : ß : , = I , I ß ,' ß ,' , ; , : . ß ß ß . ß ß ß ß ß ß ß ! ! ! ß o N 0 J F M A M J J A

In thousands

C. fuscicollis ' C.falklandicus = 2.9% [111 Feq = 74.3% IIII ,R1=9.6 m IIII NI = 54.4% Freq = 57.1% RI = 31.1

? n I-,IP' I , "!' ! • • n I I I I o •0 N D d F M A M d J A S o # o d F Id A M J J A S

Figure4. Seasonalvariation in the numberof individualsfor the specieswith the highestrelative importance (RI), indicatingnumerical importance (NI) and Frequency(Freq.) Observationsare for theperiod between October 1989 and October 1990.

On otherbeaches in the region,this specieswas White-rumpedSandpiper Calidrisfuscicollis presentfor a largepart of the annualcycle (pers. obs.). In January1982, Morrison & Ross(1989) The White-rumpedSandpiper used this coasfiine reported490 C. albaon the beachesof the eastcanal duringits northwardand southwardmigrations as that links the Bahia de San Antonio to the Gulf. well as duringthe australsummer (Figure 4). Althoughthe largegroups appeared in the second Red Knot Calidris canutus half of November (>2,400birds), the first flocks (7--61birds) were seenin early November 1989and The RedKnot was seen in largenumbers during the in late September1990. Onenon-migratory bird migrationto its breedinggrounds (Figure 4). Its was recorded in June. patternof seasonaldistribution is consistentwith that observedby otherresearchers (Harrington & Patagonian Morrison 1980;Blanco, Pugnali & RodrfguezGofii Family Charadriidae 1988),whereby the speciesuses different southward and northwardmigration routes. In Februaryand Tawny-throatedDotterel Oreopholus ruficollis November, the Red Knots were in breeding plumage. Birdsseen in Marchhad beguna body On 1 January1989, one bird fed for a few minutesin moult (approximately30% complete). In March, approximately30 RedKnots with colourbands the dry sandat high tide and thenflew away (pers. obs.). were sighted;these included birds with orange bandsfrom PuntaRasa, Argentina, birds with dark greenbands from the United States and some birds with light greenbands from an unknownlocation.

98 Gonzalez:Plovers and sandpipersin Argentina

Two-bandedPlover Charadriusfalklandicus quantifiedfor the intertidalregion at high tide (conditionI-II): P. socialisand C. albacomprised the Thisspecies was recorded in LosAlamos almost all highestproportion of feedingbirds (Riff/r) = 27.02 year(Figure 4). Widely fluctuatingnumbers from and 10.20,respectively). The index relatingresting the end of Januaryto March and May suggestthat and feedingin C. canutuswas only 1.50(very low at leastpart of the populationconsisted of birds despitehaving the highestnumber of foraging migratingnorth. By contrast,no springpeaks were individuals)owing to their lessersignificance; at observed.The winter residentpopulation showed tide condition IV, no more than 360 birds out of the highestnumbers of the year (1,100birds). The 4,800(7.5%) were fe4ding. Most of the C.fuscicollis lowestpopulation densities were during the remained at rest (Riff/r) = 0.19). breedingseason. Two chickswere observed:one on 31 December1989 and anotheron 16 January1990 On 16June and 13 July1990, C. albaand C. (possiblythe samebird), confirmingthat the species falklandicusremained at rest,even when tidal waters was nestingin this area. exposedabout 400 m of shoal.

Observationswere made in Septemberof birds with Frequency of feeding habitat use breedingplumage, which they wore until January, Intertidal habitat when moultingbegan. In March and until late April, mostbirds wore non-breedingplumage. This At high tide (SI), the microhabitatmost used agreeswith the observationsof Blanco,Pugnali & (p < 0.005)by all specieswas Border1 (35%),an RodrfguezGofii (1988)for PuntaRasa. In May, the environmentrepeatedly covered and uncoveredby ploversshowed very advancedtransitional waves(Figure 5). Calidrisalba used the greatest plumage,verging on breedingplumage, in contrast numberof resourcesfor the longesttime, whereas with that observedon the previousvisit. This C.fuscicollis and C. canutusfed only at Border1. possiblelack of synchronyin moultcould be related to the geneticvariability of populationsthat may Whenthe tide beganto ebb (SII), the diversityof alternate in their use of the same site. foraginghabitats increased. The Charadriidaeand C. albaboth significantlypreferred to forageon wet MagellanicPlover Pluvianellussocialis sediment(p < 0.005).In similarfashion, C. fuscicollis preferredBorder 1 (p < 0.005),and C. canutus waded acrossthe borderat greaterdepths A speciesfrom the south,it is a residentof the (p < 0.005). studyarea during the non-breedingseason. Althoughlocal records show little latitude in its The shoal knownrange of non-breedingdispersion up to the Valdes Peninsula(Jehl 1975), I have receivedmore When the shoalwas uncovered,the plovers recentreports from the southernpart of the dispersed.For a certainperiod of time, the water drained from the rock in a laminar flow. As the provinceof BuenosAires (GrupoBecasa, San AntoniaOuest, unpubl. data). Threespecimens slopewas not steep,the borderenvironments were observedon 18 September1989; 2 were seen becamequite wide and shallow,with small waves. on 18April, 13 on 16 and28 Juneand 9 on 13July With the shoreabout 50 m away (conditionAIII), C. 1990. Out of 13 birds,7 had yellowfeet and whitish fuscicollischose algal deposits on the shoal(p < spotson the back(juveniles), 2 had reddish-orange 0.005),which were in variablesupply. Charadrius feet (olderjuveniles?) and 4 had red feet (adults). falklandicuspreferred algae deposited by the sea, sediment with water and rock covered in sediment and water (p < 0.005),although no significant Brazilian-Paraguayan differences were found in the use of these three FamilyCharadriidae environments. Pluvianellus socialis used the low border. Collared Plover Charadrius collaris In conditionAIV (seaat 100m), the species One bird was seen in the wet sand of the intertidal preferredrock partly covered(>62%) in a film of regionon 25 September1990, close to four C. fine sedimentand waterup to 3 cm deep(micro- falklandicusat rest. habitat 14) (p < 0.005for the sum of individuals of all speciesand for eachindividual species). Relationship between foraging and resting birds As the typicalshoal was the mostavailable environ- mentand the greatestfood supply was in this Exceptfor the RedKnots, the shorebirdsnormally macrohabitat(microhabitat 14), it was obvious that restedin groupsat high tide and fed on the shoal thiswas the mostimportant feeding environment in whenit was uncoveredby the sea. The knots the upper intertidalzone. would rest even with 100-150 m of the shoal still exposed.The proportionof feedingbirds was

99 International Wader Studies 8:93-102

IdI•qOHABI TAT8 0,4 0,2 0 tim m , a!•lnnB I ! 7 8 O lO Cf.O: 11 12 18 14 18 18 17 18 10 •0

i S ZZ r-0,12 Chf • 1/1• Of "%\111111111111lIIIIF/J ••'J 1/2 Gc

2/10Chf / o iJ 0,3 qFI!11111111111111111111/A ZZ! r= 0,-97 Cf $1 $ II

ß , I I v Vl'Vi • v VL/,10/14 8/14______•• •1%':::'Iß . A ZV r- 0, g6 Cc-Ps E• _v•v vvlI 0/16 Cf 10/1õ•,•__,.___ --.,_ !, •f L 0/2 Cc

[:-- ! .....:: e/lO Chf 0,6 0,3 7/10'I • ; i i I i I•:: •:::: :J1/2 Ps 1/2• B ZZZ r-Z A III A IV I •ccf I •V !

Figure 6. Dendrogramsof Similarity(MTD) of feeding habitat use betweenspecies for various macrohabitats (capital letters)and tide conditions(Roman numerals). r = copheneticcorrelation coefficient; names of species listed by initials;macrohabitats and tide conditions listed in Methods. Figure5. Relativeannual use -- by species-- of feeding microhabitats (Arabic numerals) in various macro- environments(capital letters) and tide conditions In general,C. albaused a greaternumber of (Romannumerals). The fractionspoint out the microenvironments(17); C. fuscicollis and C. relationshipbetween the number of samplesin which falklandicusused 15 and 14,respectively; C. canutus the speciesused that habitat and tide condition and P. socialiswere presentin the regionfor less (numerator)and the total samplesin which it was time, foragingin only 7 environments.Plovers and represented(denominator). The speciesare indicated sandpiperswere always presentat low tide. by the initials of their names;macrohabitats, micro- Feedingareas were locatedin the upper, middle habitats and tide as in Methods. Observations are for and lower intertidal zones. the periodbetween 5 November1989 and 24 November 1990 (from Southerwood1971; Jeh11975; Myers & Myers 1979;Harrington & Morrison 1980; Similarities between species Sokal& Rohlf 1980;Myers et al. 1987;Narosky & Yzurieta 1987; Piola & Scasso 1988; Morrison & Ross The analysisof similaritiesbetween pairs of species 1989). (Figure6), which includedall the experimental conditionssimultaneously, was significantfor the followingdistance relationships (MTD) (note:the In conditionBIII, C. albaand C.fuscicollis fed more speciesare identifiedby the initials corresponding on sediment covered with water (microhabitat 18) to their names): than on rocks(microhabitat 19) (p < 0.005);as the sea went out farther (BIV), the latter microhabitat Ca-Chf < Ca-Ps (*) becamemore available,and its frequencyof use-- Ca-Chf < Ps-Chf includingC. falklandicus and P. socialis(which did Ca-Cf < Cc-Chf not use BIII) -- increased to levels of over 95%. Ca-Chf < Ca-Cc Only C. canutusshowed a markedpreference for the Ca-Chf < Cc-Chf (*) low border(p < 0.005). Ps-Chf < Ca-Cc

100 Gonzalez:Plovers and sandpipersin Argentina

Ca-Cf < Ca-Cc The figuresobtained from the recountstended Cf-Chf < Cc-Chf towardsunderestimations, but they offer reliable Cf-Chf < Ca-Cc figureson the minimumnumbers of birdsusing this area. p < 0.05except where marked (*), wherep < 0.025. The resultsshow the importanceof the sitefor the Calidrisalba was similarto C.falklandicus; C. canutus speciesobserved: at least3,050 C.fuscicollis, 6,000 C. and P. socialiswere furtherapart. As therewere no canutus,600 C. albaand 1,100C. falklandicus used the significantdifferences between Ca-Chf and Ca-Cf LosAlamos coast during the 1989-1990winter. and no similaritycould be drawnbetween P. socialis and C. canutus,it is proposedthat the speciesbe Feedinghabitats segregatedin the followingthree groupings that bestdescribe associated and independentspecies In thecourse of thesefield studies,it appearedto that usethe foraginghabitat at LosAlamos. These me that mostbirds at restfed later in the upper are (1) Ca, Chf and Cf, (2) Ps and (3) Cc. intertidalzone. The time during which the birds used this zone, and whether or not shorebirds comingfrom otherroosting sites used it, could not Discussion alwaysbe determined.

Patterns of abundance and seasonal Therewere similaritiesin feedinghabitat use distribution betweenthe mostcommon species (C. fuscicollis, C. albaand C.falklandicus) and the lesscommon species The LosAlamos coast is onlyone of the various sites of shorebird concentrations in the Bahia de San (C. canutusand P. socialis),although they remained widely apart. The correlationin the patternsof Antonio and the Gulf of San Matias. Could the abundance and seasonal distributions between C. patternsobtained here be extrapolatedto the restof albaand C.falklandicus is interesting,because these the region? specieswere not only similar in their use of habitat but alsonot segregatedin time. This leadsto the Thisstudy showed that largenumbers of plovers assumptionthat the habitatand feedingresources arrived from the north until the second half of were not limiting and that there would thus be no November. However, at othersites, peak numbers competition; however, it is still unknown whether werereached at the end of Septemberin 1990(pers. theywere segregatedon the feedingaxis. obs.).These observations suggest that ploversused the habitats at different times. Conclusions can Trophic dynamics thereforenot be drawn on habitatuse by the ploversbased exclusively on the resultsobtained Thegreatest numbers of ploversand sandpipers from Los Alamos. were observedduring the monthsof Februaryto April. This is especiallyrelevant, because the On 20 and 29 October1988, about 2,400 C. fuscicollis highestvalues of chlorophyll'a' in the coastal and 400 C. albawere recorded at Los Alamos, and watersof LasGrutas were obtained during that similar concentrations were observed near Punta periodbased on samplingcarried out by G.B. Delgado(pers. obs.). This indicates that patterns DomecqChantry in 1986(unpubl. data). Sincethe maychange from yearto year. The variationmay period during which the systemmaintains the most be due to causes that are internal or external to the migratoryshorebirds coincides with the systemor to the schedulingof the censuses,which phytoplanktonbloom, this indicates a positive may not reflectthe actualpattern, as significant relationshipbetween primary marine productivity numbersof ploversand sandpipers may come and and the availabilityof bottom-dwellingprey for go between censuses. birds.

How many birds depend on the site? Conservation The informationobtained suggests that therewas In orderto ensurethe conservationof migratory some turnover in the numbers of North American shorebirdsat thehemispheric level and the critical species(although it wasnot quantified)during the habitatsthey require,it is importantto determine non-breedingseason. By contrast,the similar the significanceof this sitein Argentina. These numbersof C. alba,C. falklandicus and P. socialis birds gatherin specificareas at timesthat are throughoutthe threeconsecutive censuses and the relatedto the seasonalavailability of resources. distinguishableplumages of shorebirdspresumably Plovers make maximum use of the food available at on their way north indicatedthat thesespecies were thesesites (Evans 1979, cited in Myerset al. 1987; residentduring the southernwinter. Goss-Custard1979; Schneider & Harrington1981), whichmeans that birdsdisplaced by habitat degradationwill be in a desperatesituation by beingforced to usesites already used to capacity.

lol International Wader Studies 8:93-102

The conservationstrategy set out by Myerset al. Cabrera,A.L. 1976. RegionesFitogeograficas Argentianas. (1987)calls for the protectionof importantsites [Argentinianphytogeographical regions.] Acme Editorial usedsequentially by shorebirds,thus forming S.A., BuenosAires. 85 pp. critical links in the international chain. The data Castro,G. & Myers,J.P. 1987. Ecologiay Conservacion del playeroblanco Calidris alba en el Peru. [Ecology presentedin thispaper demonstrate the significance and conservationof the SanderlingCalidris alba in of this coastline to shorebirds in Los Alamos and Peru.] Boletinde Lima 52: 47-61. the need for the implementationof protection Clark,J. 1974. Coastalecosystems. The Conservation measures in the future. Foundation,Washington, DC. 178pp. Crisci,J.V. & Lopez Armengol,M.F. 1983. Introducciona la Conclusions teoriay proacticade la taxonomianumerica. [Introduction to thetheory and practice of numericaltaxonomy.] Organizationof AmericanStates, Washington, DC. This studydemonstrated the importanceof the Los 127 pp. Alamoscoastline for migratoryshorebirds. GonzalezDiaz, E.F. & Malagnino,E.C. 1984. Accordingto the guidelinesin Clark (1974) Geomorfologiadela Provinciade Rio Negro. regardingthe managementof coastalareas, it is a [Geomorphologyof the Province of RioNegro.] IX ArgentinianGeological Congress, San Carlos de 'vital' coastalarea, i.e. it shouldbe protected Bariloche.159 pp. becauseof its role in maintainingthe essential Goss-Custard,J.D. 1979. Predictingthe effectof lossof ecologicalprocesses of thisecosystem. The overall feedinggrounds on wading birds.In: B. Knights& J. role of the SanAntonio Oeste region in the Philips(eds.), Estuarine and coastal land reclamation and migratorycycles of shorebirdsremains to be waterstorage. Faroborough, London. 245pp. determined. Harrington, B.A. & Morrison, R.I.G. 1980. An investigation ofwintering areas of RedKnots Calidris canutus and HudsonianGodwits Limosa haemastica in Argentina. Acknowledgements Reportto the World Wildlife Fund,Washington, DC, and Toronto, Ontario. I wish to acknowledgethe Ornithological Jehl,J.R., Jr. 1975. Pluvianellussocialis: biology, ecology Associationof El Plata (AOP), which awaided me and relationshipof an enigmaticPatagonian shorebird. Trans.San Diego Soc. Nat. Hist. 18(3):25--74. the OlrogScholarship to carryout thisproject, and Morrison,R.I.G. & Ross,R.K. 1989. Atlasof Nearctic AlparamisS.A., which financed it. Partialsupport shorebirdson thecoast of SouthAmerica. 2 vols. was alsoprovided by La Red Hemisfericade CanadianWildlife ServiceSpecial Publication, Reservaspara AvesPlayeros (RHRAP) and the EnvironmentCanada, Ottawa, Ontario. 325 pp. Groupode AvesLimicolas (GAL). Specialthanks Myers,J.P. & Myers,L.P. 1979. Shorebirdsof coastal go to MontserratCarbonell, whose suggestions and BuenosAires Province,Argentina. Ibis 121:186-200. supportwere invaluable,and to the following Myers,J.P., Morrison, R.I.G., Antas,P.Z., Harrington,B.A., individualsand institutions:Eliseo Sepulveda and Lovejoy,T.E., Sallaberry,M., Senner,S.E. & Tarak,A. staff of ITMAS, Luis Curtolo, Daniel Paz and 1987. Conservationstrategy for migratory species. Am. Sci. 75: 18-26. GuillermoDomecq Chantry. Lastly,my special Narosky,T. & Yzurieta,D. 1987. Guiapara la identificacion thanksgo to Paul Pedersenand Daniel Blanco. delas aves de Argentina y Uruguay.[Field guide to the birdsof Argentina and Uruguay.]Vasquez Mazzini, References BuenosAires. 340 pp. Piola, A.R. & Scasso,L.M. 1988. Circulacion en el Golfo San Matias. [Traffic in the San Mafias Gulf.] Geoacta Angulo, R.J.,Fidalgo, F. & G6mez Peraly Schnack,E.J. 15(1): 33-45. 1981. Geologiay Geomorfologiadel BajoSan Antonio Schneider,D.C. & Harrington,B.A. 1981. Timingof y alrededores,Provincia de Rio Negro. [Geologyand shorebirdmigration in relationto prey depletion.Auk geomorphologyof BajoSan Antonio and surrounding 98: 801-811. areas,Province of Rio Negro.] CIC deRio Negro, Serie Sokal,R.R. 1965. Statisticalmethods in systematics.Biol. Estudiosy DocumentosNo. 8 (1981):1-25, Viedma. Rev.(Cambridge) 40: 337-391. Blanco,D., Pugnali,G. & RodriguezGofii, H. 1988. Punta Sokal,R.R. &Sneath, P.H.A. 1963. Principlesof numeric Rasasu importanciaen la conservaci6nde lasaves taxonomy.W.H. Freemanand Co., SanFrancisco, migratorias.Unpublished report, Ornithological California. 359pp. Associationof El Plata (AOP), BuenosAires. Sokal,R.R. & Rohlf, F.J. 1969. Biometry.W.H. Freeman Bucher, E.H. & Herrera, G. 1981. Comunidades de aves and Co., SanFrandsco, California. 776pp. acuaticasde la LagunaMar Chiquita(Cordoba, Sokal, R.R. and Rohlf, F.J. 1980. Introducciona la Argentina).[Communities of aquaticbirds in the Mar bioestadistica.[Introduction to biostatistics.]S.A. Reverte, ChiquitaLagoon (Cordoba, Argentina).] Ecosur8(15): Barcelona,Spain. 362 pp. 91-120. Southerwood,T.R.œ. 1971. Ecologicalmethods. Chapman and Hall, London. 391 pp.

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