Soloviev& Tomkovich:Brood aggregations and their structure in wadersin northernTaimyr

The phenomenonof brood aggregationsand their structurein waders in northern Taimyr M.Y. Soloviev & P.S. Tomkovich

Soloviev,M.Y. & TomkovichP.S. 1998.The phenomenon of broodaggregations and theirstructure in wadersin northernTaimyr. International Wader Studies 10: 201-206.

Observationsof thespatial distribution of thebroods of five waderspecies Grey Plover Pluvialis squatarola,Curlew Sandpiper Calidris ferruginea, Tumstone Arenaria interpres, Knot Calidriscanutus, and SanderlingCalidris alba were carried out in 1991in thenorthern Central Taimyr, near Knipovich Bay. Thesespecies were found to form looseaggregations in whichthe adultswere never out of earshotof eachother. Statistical analysis demonstrated associations between Grey Plover and Knot, Grey Plover and CurlewSandpiper, and CurlewSandpiper and Turnstone.This attraction of broodsto eachother canbe explainedby theprotection provided by theaggressive and vocal Grey Plovers and Tumstones to theweaker Knot andCurlew Sandpiper against avian predators. The formerare usually found alone andrarel)• if ever,join conspecifics.Of the "weak"species, Curlew Sandpiper is themost gregarious: 85.1%of itsbroods were recorded in aggregations,75.4% of broodswere associated with broodsof other speciesand only 14.9%of broodswere found to wandersolitarily. Therefore inter- and intra-specific aggregationsare equally important for CurlewSandpipers. Broods of Knotand Sanderlingare found significantlyless often in associations.Sanderling showed no inclinationto aggregatewith any other species.The probability of encounteringa solitary brood was highest (52.8%) and can be explainedby thecomparatively small scale of broodmovements in thisspecies. The probability of findingat leasttwo broodsin an aggregationdecreased in the orderCurlew Sandpiper, Turnstone, Grey Plover, Knot, Sanderling.Chick exchange between broods in aggregationsis brieflydiscussed as a probablenegative consequenceof theformation of aggregations.The phenomenon described is probablya resultof complexinteractions between species, each adopting brood-rearing strategies which will increasetheir reproductivesuccess.

M.Y. Soloviev,Dept. of Vertebrate Zoology & GeneralEcology, Moscow State University, Moscow 119899, Russia. P.S.Tomkovich, Zoological Museum, Moscow State University, Bolskaya Nikitskaya Str. 6, Moscow103009, Russia.

CoaoBbeB,M. IO., TOMI•OB•q, I1. C.t998. (l)euoMeu • ½?pyI•?ypaarperatl•fi BmBOAKOB y Kya•KOB ua CenepUOMTafiM•,Ipe. International Wader Studies 10: 205-206.

201 International Wader Studies 10: 201-206

Introduction PloverPluvialis fulva and GreyPhalarope Phalaropus The existenceof nestingaggregations is well known fulicariuswere uncommon. They and the very common Little Stint Calidris minuta inhabited tundra for differentbird species,including waders (Mayo 1974;Dyrcz et al. 1981;Pattison & Erckmann1985; marshesduring the brood-rearingperiod, areas whichwere rarely visited by otherwaders with Newman 1992),the usualexplanation for which has broods. beenthe relativesafety of the nestsof small "weak" speciesin thevicinity of larger"strong" species, Mono- or polyspecificconcentrations of adult whichactively chase predators which come near their nests.The attractionof certainspecies to wadersdisplaying the alarmbehaviour typical otherscan be consideredto haveevolved as a way duringthe brood-rearingperiod (in our casemostly a reactionto the appearanceof an observer)were of increasingreproductive success. One would thereforealso expect that therewould be similar consideredas brood aggregations. We includedall activelyalarming adult wadersthat couldbe heard interspecificaggregations later in the brood-rearing period. However,we know of only one referenceto in normalwind conditionsin a singleaggregation. interspecificassociations, where broods of Buff- Large-scaleindividual colour-marking of adult waderson nestsand with broods(except Curlew Sandpiperand Turnstone)has enabledus to a) excludebirds with nests,and b) confirm the existenceof a brood,as indicatedby the behaviour of the adult birds.

We treatedeach encounter with an aggregationas a separaterecord, regardless of whetherit was:a) a groupof broodsrecorded on differentdays, or in differentplaces; b) an identifiablydifferent group of broods;or c) all recordsof solitarybroods.

The year of this study (1991)was favourablewith a combinationof an absenceof ArcticFoxes Alopex lagopusand an averagenumber of letomingswhich resultedin highnesting success for tundrabirds. As a result,in the secondhalf of July,the studyarea containeda relativelyhigh numberof waderswith broods. In total, we obtained data on the occurrence and compositionof 66 aggregationsand 86 solitary broods.

breastedSandpipers Tryngites subruficollis were seen The term "monospecific"is hereused for to associatewith Grey PloversPluvialis squatarola aggregationsformed by birdsbelonging to the same (Paulson& Erckmann1985), the only otherreference species.There were two categoriesof "polyspecific" to groupingof broodsbeing intraspecific, in Bristle- aggregations(i.e. including broods of morethan one thighedCurlew Numeniustahitiensis (Gill et al. 1991). species):interspecific and combined.The former During our studiesin the NorthernTaimyr, we wasused when a speciesin an aggregationwas noticed that the occurrence of the broods of certain representedby a singlebrood, the latterwhen there specieswas highly clumped. Moreover,in onecase, was morethan onebrood of a particularspecies. resightingsof colour-markedbirds in 1990showed Fromthe statisticalpoint of view, brood that CurlewSandpipers Calidrisferruginea alarming aggregationscan be regardedas observations nearbroods associated for at leastsix to sevendays characterisedby a setof variablescorresponding to with a pair of TurnstonesArenaria interpres and that the speciesrecorded within them. Thesevariables the two speciesmoved several kilometres together. havea limited rangeof values(presence or absence In orderto studythe compositionof these of speciesin an aggregation,or numberof broodsin aggregationsand to find possiblereasons for their it) and thusthey are categorical.The data setcan be formation, we undertook research in 1991 in the representedas a contigencytable, with the number vicinitiesof KnipovichBay (76øN;98ø30'E) in the of factorsequal to the numberof variables(species), northernCentral Taimyr. This paperpresents the and a numberof categoriesequal to the numberof resultsof the study. observedvalues. To study the interactionsin such tables,we decidedto apply the methodof log-linear Methods models(Upton 1978). The amountof availabledata Within the studyarea, five speciesof waderswere determined the choice of table, with no more than regularlyrecorded in broodaggregations: Grey two categoriesfor eachspecies, allowing easier Plover, Tumstone, Knot Calidris canutus,Curlew interpretationof the results.The simplesttable had Sandpiper,and SanderlingCalidris alba. Only these two categoriesfor eachspecies: 1 - if a specieswas wereincluded in the analysis.Among other presentin an aggregation;2 - if it wasabsent. The information in this table was used to model the breedingwader speciesin the region,Pacific Golden communaloccurence of species(model-O).

202 Soloviev& Tornkovich:Brood aggregations and their structurein wadersin northernTaimyr

The presenceof morethan onebrood of Curlew Sandpipers,Knots and Sanderlingsin many aggregationsis of specialinterest when compared with GreyPlover or Tumstone,where more than SQU• onebrood in an aggregationwas recorded less than CAN FER five times. To studythis phenomenon, we added three more variables to the model. In each of them, the speciescategories of Curlew Sandpiper(model- ALB• ARN 1), Knot(model-2) and Sanderling (model-3) were giventhe value 2 whenone brood was present in an la. Model-0 aggregationand the value 1 when therewas more than onebrood (we recordedup to 10 broodsof Curlew Sandpiperin oneaggregation). Categories 1 and 2 of another four variables in each of these modelsreflected the presence or absenceof other speciesin an aggregation,in a similarway to model-0. SQU ARN

The tablefor model-0was incomplete because the cell2 x 2 x 2 x 2 x 2, correspondingto an absenceof CAN ALB broodsof any speciesin an aggregation,cannot containfrequencies other than zero. The lb. Model-1 significanceof any interactionbetween variables, but not its value,was calculatedusing the statistical packageSystat 3.0. Othermodels were fitted using ARN the statisticalpackage Statgraphics 3.0, with a subsequentestimate of the degreeof interactionand standarderror in eachmodel. In all casesonly hierarchicalmodels were fitted. A smallfrequency FER (0.5) was added to all cellsof the tables,as 1.99 suggestedby Upton (1978).The adequacyof a ALB model after the removal of one of the variables was checkedby estimatingthe difference between the 2'.72•SQU maximumlikelihood chi-square values for models lc. Model-2 with andwithout the variable being considered. If this difference exceeded the critical level of chi- squaredistribution for onedegree of freedomand 95%significance level (equalto 3.84),then an CAN FER exclusion of the variable was considered to be unjustified.All log-linearmodels included no more than two variables, which allowed an illustration of the resultsby diagrams. 1.89•/.24 SQU • ARN In orderto givea bettergraphical presentation of 2.24 the results,correspondence analysis was used on the table,in whicheach of five columnsrepresented a ld. Model-3 differentwader species, rows - aggregations,cells - numberof broodsobserved in eachaggregation. The algorithmfor the analysiswas takenfrom Davis ALB Sandefiing (1986),and appropriate programs were written and CAN Knot run in BASIC,apart from the estimateof eigen- ARN Tumstone valuesand eigenvectors of the chi-squaredistance FER Curlew Sandpiper matrix, which was calculatedin the Systat3.0 SQU Grey Plover Dependenceof numberof broods package. r'•-[• onpresence ofother broods analysed

Results .' • Significantinteractions

The generalmodel of communaloccurrence .•. tendencytooccur together in (model-O),demonstrates pairwise mutual attraction aggregations of broodsof GreyPlover and Knot,Grey Ploverand 1.75 Normalizedeffect coefficient If value >1.96 then p< 0.05 CurlewSandpiper, Curlew Sandpiper and Tumstone(Figure la). Sanderlingshows no Figure1. Pathdiagrams for the modelsof species relationshipwith broodsof otherspecies, neither in interactionsin waderbrood aggregations. respectof attractionor avoidance.

203 International Wader Studies 10: 201-206

Model-1(in whichCurlew Sandpiperis represented 2. Broodsof GreyPlover and CurlewSandpiper by categorieswith one and morethan onebrood in havea tendencyto occurin aggregationstogether, an aggregation)shows that the numberof Curlew aswell asin thepresence of broodsof Knot. Sandpiperbroods is higherin thepresence of Turnstonebroods (Figure lb). The presenceof any 3. Broodsof Knot and Grey Ploverare attractedto numberof Curlew Sandpiperbroods in an eachother, as well as occurringin aggregationswith aggregationmakes the presenceor absenceof both Curlew Sandpiperor Sanderling. Grey Ploverand Knot moreprobable than if they occur alone. 4. The numberof broodsof Knot is largerin aggregationswith CurlewSandpiper (or, put Model-2(in whichKnot is representedby categories anotherway, broods of CurlewSandpiper prefer to with one and more than one brood in an associate with two or more broods of Knot - aggregation)shows a positiveinteraction between statisticalmethods cannot distinguish between the thepresence of CurlewSandpiper and thenumber two). of Knot broods. It also demonstrates mutual pairwiseattraction of bothCurlew Sandpiper with 5. The presenceand numberof broodsof Sanderling Grey Plover,and Sanderlingwith Turnstone,in the are unrelatedto the presenceof broodsof other presenceof Knotbroods (Figure lc). However,in species. the caseof Sanderlingand Turnstone,an analysisof Table 1. Distributionof broodsin differenttypes of aggregations.

Species % Solitary % in aggregations No. of broods monospecific interspecific apecies*,• combined*** total ß ,:•pecies* ...... =,..=.=.• ...... o ...... y ...... •,.•,...•,.- v ...... , ...... •.,.•.== ...... • • .... .

Calidris alba 52.8 18.9 20.8 7.6 47.2 53 Calidris canutus 38.8 13.4 22.4 25.4 61.2 67 Calidrisferruginea 4.9 9.7 16.7 58.8 85.1 114 Arenariainterpres 17.4 21.7 43.5 17.4 82.6 23 Pluvialissquatarola 28.2 0.0 71.8 0.0 71.8 39

* aggregationis representedby broodsof onespecies ** aggregationis representedby onebrood of consideredspecies and one or morebroods of otherspecies *** aggregationis representedby morethan one brood of consideredspecies and one or morebroods of otherspecies

cross-tabulationtables suggests that their apparent An analysisof the compositionof brood association is in fact due to the absence of both in aggregationsshows that the probabilityof aggregationswith Knot. encounteringa solitarybrood decreases in the

Model-3(in whichSanderling is representedby categorieswith oneand morethan onebrood in an aggregation)shows that the presenceof broodsof any otherspecies do not influencethe numberof

Sanderlingbroods (Figure ld). Nevertheless,there ARN are somepairwise interactions between other speciesparticipating in aggregationswith Sanderling.These are between Knot and Grey 1 Plover,Turnstone and Curlew Sandpiper,and Grey Plover and Turnstone. The interactions between the ALB two firstpairs correspond well with the resultsof the generalmodel (model-O), but the attractionof Turnstoneand Grey Plover appearsin the model ! I • I due to the almostcomplete absence of both from -2 -1 SQU I aggregationswith Sanderling. ALB Sanderling Theseresults can be summarisedas the following ARN Turnstone key points: CAN Knot FER Curlew Sandpiper 1. Broodsof Curlew Sandpiperare attractedby SQU Grey Plover lCAN broodsof Tumstone,up to thepoint at whichthe numberof broodsof eachspecies become equal. Figure2. The positionof eachwader specieson the first and secondcorrespondence axes.

2O4 Soloviev& Tomkovich:Brood aggregations and their structure in wadersin northernTaimyr followingsequence: Sanderling - Knot - Grey Plover The results show that there is an association of - Tumstone- Curlew Sandpiper(Table 1). In other "timid"Knot and Curlew Sandpiperbroods with words,broods of Sanderlingshow the least "bold"Grey Ploverand Tumstone.There can be tendency,and broodsof Curlew Sandpipershow the little doubt about the role of "bold" waders as the greatesttendency to aggregate. focusof aggregations,because some early broods of Curlew Sandpiperand Knot were evenattracted by As to participationin differenttypes of aggregation, pairsof GreyPlover which were still at the the absenceof Grey Ploverbrood aggregations with incubationstage (these aggregations were not conspecificsand the relative rarity (only9.7%) of includedin the analysis). recordsof monospecificgroups of Curlew Sandpiperbroods were of particularnote. Theincrease in theprobability of the appearanceof The resultsof the correspondenceanalysis are Curlew Sandpiperbroods in aggregationswith presentedin Figure2. The firsttwo correspondence morethan onebrood of Knot may be a resultof axesare responsible for 60.7%of the totalvariance. complexinteractions between broods of Grey Plover,Knot and Curlew Sandpiper,which were not These results were extracted from the table shownstatistically because of the generalshortage containingall theinformation on thenumber of of data. However,Green et al. (1990)suggested that broodsparticipating in certainaggregations, and communal nest defence is recorded more often in theyseem to confirmpretty well the conclusions birds of intermediatesize, because they are less drawnconcerning species interactions listed above. successfulat it, than largebirds. In our case,Grey In particular,the largeseparation of Sanderlingfrom Ploversdid not permit conspecificsto remainin the the otherspecies on the first axisdemonstrates its vicinityof theirbroods. Aggregations of up to four relative lack of association with them. broodsof Knotprobably have someability to The datawe haveat our disposalare not sufficient protecttheir broodsand may be attractiveto Curlew to identifythe reasons for the changesin structureof Sandpipersin the absenceof Grey Ploversor individualaggregations. It is only possibleto say Tumstones.The rarity of monospecificaggregations that, accordingto recordsof colour-markedbirds, of Curlew Sandpiperbroods can be explainedin the the structureof someaggregations hardly varies at sameway, because even the communalefforts of all over a periodof severaldays, while othersare severalCurlew Sandpiper females would hardlybe more variable. sufficientto stopa predator.

Discussion The lackof any relationshipbetween Sanderling and otherspecies can be explainedby the noticeably Of the wader speciesinhabiting the Northern smaller-scale movements of its broods in Taimyr,only Grey Plover and Tumstone are "bold" comparisonwith otherwader species.It may speciesas defined by Dyrczet al. (1981)i.e. they are thereforebe difficultfor a Sanderlingbrood to ableactively to protecttheir nests and broods by follow an aggregationcomposed of moremobile attackingapproaching avian predators with alarm wader species.The fact that Sanderlingsare more calls(Cramp & Simmons1983; our observations). Knot also, on rare occasions,attack skuas "settled"than other species may be due to the fact that Sanderlingbroods do not needto move very far Stercorariusspp. which gettoo closeto a brood to meettheir food requirements. (Whitfield & Brade 1991;our observations). Other wadersare "timid"and reactto avian predators Aggregationsexist until the fledgingperiod or even eitherby adoptinga motionless,crouching posture a bit later, in other words, until the moment that the precededby an alarmcall, initiating the same tiesbetween adult birdsand juveniles are lostand reactionin chicks,or by mobbingthe predatorwith the brooddisperses. Later, the aggregationsform alarmcalls produced in flight or from the ground, flock-likegroups from which adult birds disappear whilstkeeping themselves aloof. In thisrespect, our becausethey leavethe breedinggrounds earlier, resultsfit well the conceptof a "protectiveumbrella" while juvenilesin many casesaccompany late- providedby largespecies of wadersthat will chase hatchedbroods of conspecifics,or broodsof Grey predatorsto smallerones (Paulson & Erckmann Ploversand Tumstones,which staytogether longer. 1985),however there are probably also other reasons. This phenomenonneeds further study.

Somenegative consequences are also possible for at The interspecificwader brood aggregations that we observed have little in common with the "creche- leastsome of the speciesthat form aggregations.It is possible,for example,that theremay be intense type"brood associations recorded in Bristle-thighed competitionfor foodin associationsof Golden Curlew (Gill et al. 1991). The former are loose PloversPluvialis apricaria with DunlinsCalidris associationswhich move around together, which are alpina(Byrkjedal & Kt•lt•s1983), but thisis unlikely formedand maintainedby the greaterantagonistic in the Siberian tundra which is so rich in food tendenciesof onespecies over another, the mutual resources(Ryabitsev 1992). Moreover,the Golden aggressionof adult birdsin the brood-rearing Ploverand Dunlin observedin the earlierstudy period,and the apparentdesire of at leastsome of them to be close to other birds with broods. were separatedfrom eachother by shortdistances of up to about10 metres.The broods in the wader

205 International Wader Studies 10: 201-206

aggregationswe observedon the Tairnyr,on the References otherhand, were distributedover quitea largearea Byrkjedal,I. & K•l•s, J.A. 1983. Plover'spage turns into of tundra, often several hectares. plover'sparasite: a look at the Dunlin/Golden Plover association. Ornis Fennica 60: 10-15. Chickexchange between broods in aggregationsas Davis,J.C. 1986.Statistics and data analysis in geology.John a resultof chickdispersal when a predatorappears Wiley & Sons,New York. is likely to be a moreserious problem. When a Dyrcz,A., Witkowski,J. & Okulewicz,J. 1981.Nesting of broodconsists of chicksof significantlydifferent "timid"waders in the vicinityof "bold"ones as an ages,one might expectthat the smallerchicks antipredatoradaptation. Ibis 123: 542-545. would get left behindand die. We recordedan Cramp,S. & Simmons,K.E.L. (eds.) 1983. The birds of the exchangeof chicksbetween several broods of Knot, WesternPalearctic, Vol. 3. Wadersto Gulls. themost commonly observed species, in OxfordUniversity Press, Oxford. monospecificand combinedaggregations (Table 1). Gill, R.E. Jr.,Lanctot, R.B., Mason, J.D. & Handel, C.M. Thiscould only havehappened as a resultof chick 1991.Observations on habitatuse, breeding dispersal. chronologyand parental care in Bristle-thighed Curlew on the Seward Peninsula,Alaska. Formationof polyspecificbrood aggregations in WaderStudy Group Bull. 61: 28-36. wadersis probablya resultof a complexinteraction Green,R.E., Hirons, G.J.M. & Kirby,J.S. 1990.The of species,optirnising their brood-rearing strategies. effectivenessof nestdefence by Black-tailed Featuresof aggregationparticipants such as size, Godwits Limosa limosa. Ardea 78: 405-413. aggressiveness,territoriality, fidelity and chick Mayo,A.L.W. 1974. Wadernesting associations. mobility,as well as,probably, synchronisation of British Birds 67: 82. reproductionand a degreeof overlapin thebroods' Newman, O.M.G. 1992. Nestingassociation between habitats,may influencethe structureof an HoodedPlover and Pied Oystercatcher. aggregation.In this study,we found Curlew The Stilt 21: 26-27. Sandpiperto be themost social species, for which Paulson,D.K. & Erckrnann,W.J. 1985. Buff-breasted participationin aggregationsseems to be an Sandpipersnesting in associationwith Black- importantreproductive strategy. Further studies of bellled Plovers. Condor 87: 429-430. thephenomenon of broodaggregation would Ryabitsev,V.K. 1992.Trophic relations among the birds providea deeperunderstanding of thebehavioural and nichestructure of Subarcticecosystems. adaptationsof wadersfor increasingtheir In: Y.I. Chernov (ed), Cenoticinteractions in tundra reproductivesuccess. ecosystems,pp. 60- 70. Nauka, Moscow. In Russian. Acknowledgements Upton,G.J.G. 1978. TheAnalysis of Cross-tabulated Data. Thestudy was carried out in a field camp,with the JohnWiley & Sons,New York. financialsupport of the InternationalArctic Whitfield,D.P. & Brade,J.J. 1991. The breeding behaviour Expeditionof the Instituteof Evolutionary of the Knot Calidris canutus. Ibis 133: 246-255. Morphologyand Animal Ecology of the Russian Academyof Sciences,and with thesupport of ProfessorE.E. Syroechkovsky. Our fieldcamp was ableto functionbecause of theamount of effortput into organisingit by E.E. SyroechkovskyJnr., M.M. Zabelinand members of staffof theTaimyr nature reserve.We are extremelythankful to them. We are alsograteful to Dr. O. Hilden, V. Yakovlevand S. Palatovfor their help in the field.

206