36

Day- and night-time movementsof radiomarkedRed Knots stagingin the westernWadden Sea in July-August 1995

Jan van Gils & Theunis Piersma

Van Gils, J. & Piersma,T. 1999. Day- andnight-time movementsof radio-markedRed Knotsstaging in the westernWadden Sea in July-August 1995. WaderStudy Group Bull. 89:36 - 44.

Fourteenindividually radio-marked Red KnotsCalidris canutusstaging in the westernWadden Sea in July-August1995 oftenwandered considerable distances in the courseof a singletidal cycle,which confirmedprevious ideas based on movementsof flocksobserved. The birdscontinued this tidal feedingrhythm during nighttime darkness. There was a tendencyfor Red Knotsto remainfor shorter periodson thehigh-tide roost at nightthan during the day. Individual birds with bodymasses > 140 g when radio-marked(which may havebeen close to departurefor WestAfrica), were lessitinerant than light-weight individualsand were more likely to feed in an area closeto the roostwhere relatively soil-shelled shorecrabsmade up muchof the diet. Suchmass-related differences in foraging movementsmay be explainedby migration-relatedphysiological changes, different needs to track changesin local food stocksand to find suitableflock-mates to take-off with andbody mass related predationand starvationrisks and flight costs.

Jan van Gils & TheunisPiersma, Institute for Sea Research(NIOZ), P.O. Box 59, 1790 AB Den Burg, ,The Netherlands, and Centrefor Ecologicaland EvolutionaryStudies, University of Groningen,P.O. Box 14, 9750 AA Haren, The Netherlands

INTRODUCTION at the individuallevel duringday and duringnight. We aimed Red Knots Calidris canutusbreed in the High Arctic and to testwhether: (1) individualRed Knotsstaging in the spendthe non-breedingseason on intertidalmudflats in westernWadden Sea in late summer/earlyautumn can be temperateand tropical zones, feeding mainly on buried confirmedto covera large areaof intertidalflats duringsingle bivalveprey. In the westernWadden Sea, The Netherlands, low waterperiods, and (2) whetherthis rangingpattern is where this studytook place, two subspeciesoccur. Members maintainedat night. We haveused radiotelemetry as a means of the islandicasubspecies, breeding in Greenlandand to achieve this aim. For the benefit of readers, references on NortheastCanada, stay t¾om August to April, anduse the area the useof radiotelemetrym studiesof waderbehaviour have as their moulting and wintering site (Davidson& Wilson beenassembled m an Appendix. 1992). The canutussubspecies, breeding in north-central Siberia,only stopsover in July-Augustand in May, on the MATERIAL AND METHODS way to andfrom their West-African winter quarters(Pierstoa At ,one of the mostimportant wader roosts m the et al. 1992). westernWadden Sea, we mistnetted52 Red Knots in late July 1995. We glued radio-transmitterson the backsof 14 Red In the westernWadden Sea bothpopulations make intensive Knots,using superglue rather than epoxy (Raim 1978), but use of the totertidal flats around the small uninhabited islands otherwise followed the restructions of Warnock & Wamock of and Richel for feeding. The two islets,which are (1993). Basedon the absenceof primarymoult, 10 of these free of mammalianpredators but not necessarilyof avian RedKnots presumably belonged to the canutussubspecies predators,are usedas roostingsites during high tide. In an breedingin Siberia. The otherfour birdsbelonged to the earlierstudy, Piersma et al. (1993a) providedevidence based islandicasubspecies, one being a one-yearold birdin on movementsof flocks observedin the day-time that Red advancedwing moultthat waslikely to havespent the summer Knotsmay cover an area as large as 800 km2 m a coupleof m theWadden Sea, the restbeing adult birds in wingmoult t•dal cyclesm their searchfor food and saferoosting sites. (Table 1). All birdswere molecularly sexed using small blood samplesstored in 70% ethanol (Baker et al. 1999). The birds The large-scalemovements described by Piersmaet al. wereweighed to the nearestgram on an electronicbalance, (1993a) were basedon observationsof flocks duringdaytime. theirbill length,total head, and tarsus plus toe length Here we reporton our first attemptto measurethese patterns measuredto thenearest 0.1 millimetrewith calipers,and wing 37

Richel "/.•- ..•...... • qemm.. ..- ß •, .'r_•'.. ,

- . Gn.'end. _

.,

ß .

Richel

Ballastplaat

Friesland

Richel

.

ß

,•,

Ballastplaat

ß ß

Figure 1. Examplesof movementsof individualRed Knots through the western . Filledsquares indicate positions during the mght,open squares are positions in daytime.[A]. Movementpattern of femalecanutus-Knot (#212), 1-4 August.In thefirst night,between 0 00-3:55 h, the birdis roostingat Richel,whereafter she feeds south of Richeluntil 7 h. Duringthe nextlow tideperiod she feeds west of Griendfor a shorttime, beforemoving to the flats eastof Griendin the evening. Next morningshe is foundnortheast of Griendtill noon. That lateevening until the earlymorning she is foundon the mudflatsclose to the Frisiancoast. [B]. Almostthe wholeof 13August was spent by thesame female canutus-Knot #212 at andnear Richel, before moving on to theflats near during the night. Duringthe subsequent daytimelow tideperiod she was northeast of Griend,where she was recorded again at nightuntil late morning. That evening she was found to passwestward south of Griend,probably flying from feedinggrounds in the east. Sheroosted at Vlieland, whereaftershe fed on Posthuiswadat night. [C]. Thismap shows the movements of femaleislandica-Knot (#249), over a periodof almost100 hours, 11-16 August.In thefirst mghtthe bird is roostingat Griend,but flew to Richel(a distanceof 9 km) in the earlymorning where she probably continued to roost.Then shestarted to feedat theflats around Richel. At noonthat day, she was again recorded roosting at Richel. The nexthigh tide sheis roostingat Griend. That night sheflew to Richelwhere she continued roosting, to be recordedfeeding close to Richelthe next low tide. About half a day latershe is feedingsouth of Vlieland(7 km away),and at theend of thatday shefeeds east of Griend,implying another flight of 23 km. Next morningshe is foundthere once more, whereafter she roosts at Griendin the afternoon(a distanceof 7 km). That nightshe is recordedsouth of Vlielandagain, presumably feeding (16 km). Overthe period of observationthis bird has flown a minimumof 80 km, or 20 km/day. 38

Table 1. Summaryof biometrics,sex, age and subspeciesof the 14 Red Knotsradio-marked in late July 1995. All birdswere caughtat Richel, duringnight-time high tides. Radio frequencyat the 173 MHz bandwidthis given. (c.y.=calendaryear).

Radio Capture Body Bill Total Tarsus Wing Sex Age Putative frequency date mass length Head + toe length sub (kHz) (g) (mm) (mm) (mm) (mm) species

212 27 July 139 35.2 64.6 58 180 female adult islandica 220 27 July 176 34.8 64.4 59 173 female adult canutus 230 28 July 138 35.3 67.4 57 167 female adult canutus 235 28 July 132 33.7 63.4 56 171 female adult canutus • 240 29July 138 33.4 62.0 57 172 male adult islandica 249 29 July 140 32.4 63.2 57 180 female adult canutus 259 29 July 123 34.5 65.8 57 178 female adult canutus 280 29 July 186 36.5 65.0 61 175 female adult canutus 289 29 July 141 35.2 64.2 58 173 female adult canutus 299 29 July 142 35.6 65.3 58 175 female adult canutus 302 29 July 145 35.6 67.2 58 175 female adult canutus 314 29 July 112 32.2 63.6 56 167 male adult canutus 324 29 July 130 30.9 63.6 57 157 female 2nd c.y. islandica i 341 29 July 141 34.1 65.0 59 177 female adult islandica length (maximum chord) was measuredto the nearest Table2 (a).An analysisof varianceof thesignal strength of thefree millimetreusing a stoppedruler (Table 1). transmitterreveals the effects of (1) the heightof the transmitter,(2) the distancebetween receiver and transmitter, (3) theheight of the We used 1.4 g radio-transmittersfor the 173 MHz bandwidth receiver(4) an obstacle(a humanbody) just beforethe transmitter (Holohil SystemsLtd., Carp, Ontario,Canada). Individual and(5) theangle of thetransmitter antenna (tail awayor transmitterfrequencies differed by about 10 kHz. Battery-life perpendicular).Only distancewas treatedas a continuousvariable, time accordingto manufacturerwas 42 days,and was at least all othersas categoricalvariables. All variablescontributed 36 daysin the field. Signalswere listenedto by using significantlyto theexplained variance (p<0.0001; R2=0.60; n=380). hand-held three-element Yagi antennasand portablereceivers (TRX-2000S, Wildlife Materials Inc., Carbondale, Illinois, variance (%) USA). The antennaswere mountedat the end of long poles Variable Explainedp-value transmitterheight 29.1 and positionedapproximately 10 m aboveground level. The <0.0001 distance(km) 22.5 <0.0001 • signalwas detectedby manually turningthe pole 360ø . When a signalwas heard,the antennawas pointedin the direction receiverheight 4.2 <0.0001I giving the strongestsignal. As soonas this directionwas obstacle 2.3 <0.0001i found, backgroundnoise, amplitude of the signalas visible on the displayand directionwere registered.In caseswhere no transmitterangle____ 2.1 <0.0001• Table 2 (b). Parametervalues for the above model. signalwas detected,only the level of backgroundnoise was noted. Variable Parameter Effect constant +0.64 We made a detailedassessment of the signalstrength by transmitterheight 2 m +0.27 varyingthe positionsof both a receiverand a 'free'transmitter transmitterheight knot height -0.03 on a clear and sunnyday. This testrevealed strong effects on transmitterheight on mudflat -0.24 the strengthof the radio signal of transmitterheight, and of distance (km) continuousvariable -0.45 distancebetween transmitter and receiver (Table 2). Both receiverheight goodsite on bridgeship +0.07 variablestogether explained 52% of the variancein signal receiverheight hinddeckship +0.06 strength.The othertested variables (receiver height, the receiverheight fenceon bridgeship +0.04 presenceof an obstacleand the transmitterangle) had less,but receiverheight mudflat +0.02 still significant,impacts on signalstrength (together they receiverheight badsite on bridgeship -0.18 accountedfor another9% of explainedvariance). In practice, obstacle no obstacle +0.07 radiosignalscould be receivedat maximum distanceof obstacle obstacle -0.07 approximately3 km whenthe birdswere in the air, and 1.5 km transmitterangle perpendicular +0.05 when the birds were on the ground. transmitterangle tail away -0.05 39

From two receivingstations, one permanentlybased on Griend and one at variablelocations on boardthe NIOZ-research ship RV 'Navicula',we scannedall directionsfor radio-signalsat the appropriatefrequencies in theperiod 27 Julyand 5 6 September1995. The ship wasmostly based at Richel, where we took readingsfrom 27 July to 17 August,with a gapin the weekendof 4-6 August (Table 3). We also scannedRichel duringhigh tide on 25 Augustduring high tide. At Griend we made a continuousseries of measurementsfrom 1 Augustto 5 September.

During the sameperiod we followed flocks of feedingRed Knots at low water. We alwaystried to checkthese flocks for radiomarkedbirds. To ascertaintheir diet, droppingswere collectedand analysed in the laboratoryaccording to the methodsoutlined by Dekinga & Piersma(1993). Benthic samplingenabled us to determineprey densitiesfor different I I feedingareas. At the intertidalflats near Griendwe sampleda day night grid of 606 stations,with grid lines 250 m apart. At each stationwe took one coreof 1/56 m3 down to a depthof 20 cm Figure 2. The time spentat the Richelhigh-tide roost was shorter (Piersma et al. 1995, Piersma & Koolhaas 1997). At all other duringnight- thanduring daytime highwater periods, and differs on mtertidalflats we sampleda total of 384 stations,which were averageby 1 h 8 min (onesample t test;p=0.089). Birdswere alsospaced at intervalsof 250 m. In the field all bivalves, categorizedas night-time roosters when they arrived at Richel gastropodsand crustaceansretained on a sieve with a 1 mm between22:00 h and3:00 h. The datasetincludes 30 day-time meshwere collectedin plasticbags and stored frozen. observationsand 10 night-time observationson 8 individuals,all of Subsequentlywe measuredlengths of the individual thembeing collected during spring tides. invertebratesto the nearestmillimeter, whereafterthey were 250 •ncineratedat 550øCfor 2 hoursto determineash-free dry mass(see Piersmaet al. 1993a for further details of methods). ._o 200 RESULTS In total we made 1004 radioscans,each time checkingall possibleradiofrequencies. On average,an individualbird was o• 150 recordedon 206 occasions(21%, SD=i 11 occasions).In 707 .m of the 1004 scans(70%) we recordedat least one o radio-markedbird. On Griend the averageinterval between (• 100 scanswas 97 min (SD=155), andduring periods of o observationat RV 'Navicula'the intervalaveraged 45 min (SD=67). E 50

We were able to obtaindaily tracksof 11 individualsfor about 17 days,one bird for 9 days,and two individualsfor 35 days, )0 120 140 160 180 200 at whichpoint we stoppedour observations.The lattertwo brrds(#249 and#324) were the only birdsrecorded from 18 body mass (g) at catching Augustonwards. All the otherswere absentfrom aboutthat Figure3. Numberof telemetryrecordings of the 10 canutus-Knots tn-ne,at leastnear Griend and Richel. Exceptfor #249, the in theRichel area (i.e. roostand nearby intertidal flats) as a function d•sappearanceof the putativecanutus Knots was congruent of bodymass at catching(linear regression and its 95% confidence with the predictedtiming of their departurefrom the western interval are shown,f=female, m=male). Wadden Sea (Piersma et al. 1992, 1993a). on averagea linear distanceof 20.8 km (SD=4.6 km; n=15 more or lesscontinuous trackings). With an averageof 1.97 The estimated locations of the different individual birds hightides a day,this results in 10.6km duringa singletidal enabledus to derivethe linear distancemoved per day. For cycle. This estimatemay be biasedto the low distances,as our this analysiswe selectedcases in which we were able to track transmitterscould never be receivedat distanceslarger than 3 the birdsfrom at leastthree different positions during a single kin, andtherefore large distances could only be measured tidal cycle. Threeexamples of thiskind of space-useare when the research vessel also moved. plottedin Figure 1. In the courseof a singleday, birds moved 40

Table 3. Time scheduleof occupationand location of bothreceiving stationsduring our studyperiod (seeFigure 1 for locations). 1.0 light-weighed Period Station 1 (RV 'Navicula') Station 2 0.8 27 Jul - 2 Aug Richel no 1 observations 2 Aug - 3 Aug Ballastplaat Griend 0.6 (from 1 Aug) 3 Aug Frisiancoast Griend ,.,(D .: 4 Aug - 6 Aug no observations Griend 0.4 7 Aug - 13 Aug Richel Griend 14 Aug Posthuiswad,Vlieland Griend o 0.2 14 Aug - 15 Aug Ballastplaat Griend o 15 Aug - 17 Aug Posthuiswad,Vlieland Griend ,.,- 0.!3 17 Aug - 5 Sep no observations Griend o (at 25 Aug >, 1.0 also at o Richel) 0.8 There was a tendencyfor Red Knotsto spendshorter periods on the Richel-roost at night than during the day (Figure 2). 0.6 On average,they stayedat Richel for 4 hrs and 39 min during the day,compared with 3 hrs and 30 min duringthe night (p=0.089; one samplet-test). 0.4

As someof the 10 canutusbirds not only usedRichel as their 0.2 high tide roostbut the adjacentintertidal flats as their foraging site,it was interestingto seewhich individualswere so site-faithful for the entire tidal cycle. An analysisof the 0.0 variationin presenceat Richel, surprisingly,showed that about 0 5 10 15 20 half of the variancecould be explainedby variationin body massat marking (Table 4; Figure 3). In fact, most of the day in August 1995 heavy individuals(body mass>140 g; n=5) steeplyincreased Figure 4. The frequencyof visitsof the 10 canutus-Knotsto the their presencein the Richel area over time, whereasfor the lighterbirds (body mass,'E 140 g; n=5), the presencein this Richelarea increased over time. Someof theheavy-weighed individuals(> 140 g at catching,lower graph)reached an almost arearose slower. Around 12 August,3 of the 5 heavy continuouspresence around 12 August,a few daysbefore their individualswere ahnostalways present at or nearRichel (Figure 4). disappearancefrom the westernWadden Sea. The intensityof grey reflectsthe likelihoodof departurebased on literature-data. At the intertidalflats borderingRichel high densitiesof juvenile shorecrabsCarcinus maenas were found, and this overdistances of morethan 30 km per low tideperiod, but the prey categoryindeed contributed importantly to the diet of averagewas much lower due to many birdsremaining close to Red Knots feeding in this area (Figure 5). Other intertidal flats Richelthroughout the tidal cycle. were relatively poor in shorecrabs,but richer in harder-shelled bivalves such as Baltic tellins and Macoma balthica. When On the coarsescale of our measurements,the useof space transformedinto biomassvalues (Dekinga & Piersma 1993), duringthe nightdid not differfrom thatduring the day. Thisis the diet of birds foragingnear Griend and Vlieland contained consistentwith the finding that on intertidalflats Red Knots 97% molluscs,and that of birdsforaging near Richel find their prey on the basisof tactile stimuli(Piersma et al. contained51% crustaceansand only 49% molluscs. 1995, 1998),and thus do not necessarilyneed light for prey detection.In fact,roost duration was on averageroughly one DISCUSSION hourshorter during the night than during the day,an effectthat On the basis of observations on the movements of flocks in wasnot dueto differentialsampling during either spring or daytime,Piersma et al. (1993a) hypothesizedthat individual neaptides (all measurementswere made during spring tides). Red Knots stagingin the westernWadden Sea in late summer and autumnroam over considerabledistances during a tidal Thereis a whole suiteof possiblefactors influencing the cycle. The presentobservations on radiomarkedindividuals choicebetween different feeding areas, some of which relate confirmthat hypothesis.We observedindividuals that moved to distanceto the roostsite (Myers 1984). For example,there 41

At the sametime remaimngnear the high tide roostwould lead 1.0 I I to a reductionin the daily flight costs(Piersma et al. 1993a), n=13 n=25 especiallyin heavybirds. An abundanceof conspecificsmay O.8 ensurethat long distance-migrationflights can be initiated togetherwith sufficientnumbers of like-minded conspecifics (Piersmaet al. 1990), whetherduring high or during low tide. 0.6 - T Finally,body mass dependent predation and starvationrisks may influencetrade-offs in the choicebetween roost site 0.4 safety(e.g. Richel saferthan Griend;Piersma et al. 1993a) and proximityof goodfeeding areas (e.g. Griendbetter than Richel). Futurestudies should clarify the importanceof these 0.2 different factors.

0.0 ACKNOWLEDGEMENTS Many peoplehelped during this exploratorystudy, and were willing to get up at crazy midnighthours to checkmistnets or Figure5. Diet composition(in termsof biomass)of RedKnots to listento beepson a radio. We are very gratefulto Moniek feedingnear Richel, and in otherareas (mainly near Griend) in early de Boer, Anne Dekinga, Pier Duiven, Jan Drent, Andrea August1995 (mean percentages and standard errors). NearRichel Fischer, Karin Hermes, Lenze Hofstee, Anita Koolhaas, Rik half of the diet consistedof relativelysoft-bodied prey, mainly Kuiper,Karen Krijgsveld,Dick Schermer,Jeroen Smit, shorecrabs Carcinus maenas. The other half consisted of JannekeTomnga, Willem Renemaand PopkoWiersma. We hard-shelledmolluscs, mainly Baltic tellins and Macoma balthica. also like to thank the crews of the RV 'Navicula' (Kees van der Almostall preyitems fed uponelsewhere were of thehard-shelled Star,Johan Tuntelder and Peter Schagen)and the RV 'Phoca' kind. n indicatesthe numberof droppingsamples, each sample (Janvan Dijk andDirk Kuiper) for theirindispensable logistic containing10-300 droppings. help during the fieldwork. The molecularsexing of the birds was takencare of by AnnetteGreenslade in the laboratoryof maybe migration-related physiological changes that can play Allan J. Baker at the Royal OntarioMuseum, Toronto, Canada. a role. Differentindividuals may havedifferent needs to track JanDrent, Siike Nebel and an anonymousreferee helped with changesin localfood stocks and to find suitableflock-mates constructivecomments on the manuscript.During the analysis to take-off with. Relativerisks of predationand of starvation and writing up of this studywe were supportedby a maycritically depend on body mass, as will flight costs. PIONIER-grant to TP of the NetherlandsOrganization for ScientificResearch (NWO). This is NIOZ-publication number If heavyindividuals that are approachingtheir departure on a 3334. 4,000-5,000 km long flight to the winteringgrounds indeed showa weight-savingstrategy by reducingstomach mass (Piersmaet al. 1993b),such birds may be forcedto feed on REFERENCES relativelysoft-shelled prey such as shorecrabs. In a yearlike Baker, A.J., Piersma,T. & Greenslade,A.D. (1999). Molecular 1995, when shorecrabswere abundantnear Richel, it would versusphenotypic sexing in Red Knots. Condor 101' in press. thuspay off to staythere during the whole tidal cycle. Davidson,N.C. & Wilson,J.R. (1992). The migrationsystem Alternatively,or additionally,recently arrived birds with lower of European-winteringKnots Calidris canutusislandica. bodymasses may feel a greaterneed to exploreand WaderStudy Group Bull. 64, Suppl.:39-51. cognitivelymap the food abundance on different intertidal areasthan well-established heavy birds that are readyto go. Dekinga,A. & Piersma,T. (1993). Reconstructingdiet compositionon the basisof faecesin a mollusc-eatingwader, the Knot Calidris canutus.Bird Study40: 144-156. Table 4. Analysisof variancein the numberof recordingsof canutus Knotsin theRichel area,as explained by bodymass. In the model bodymass is treatedas a continuousvariable. Statistics are based on Myers, J.P.(1984). Spacingbehavior of nonbreeding 326 scansover a periodof 18 days(31 July- 17Aug.) nearRichel. shorebirds.In: Burger,J. & Olla, B.L. (eds.) Shorebirds. Bodymass explained significant variation (p < 0.03). Migration andForaging Behavior, pp. 271-321. PlenumPress, New York. Variables df SS Bodymass 1 22294 Piersma,T. & Koolhaas,A. (1997). Shorebirds,shellfish(eries) Error 8 23065 and sedimentsaround Griend, western Wadden Sea, R 2 0.49 1988-1996. NIOZ-report 1997-7, Texel. 42

Piersma,T., Zwarts, L. & Bruggemann,J.H. (1990). Piersma, T., van Aelst, R., Kurk, K., Berkhoudt, H. & Maas, Behaviouralaspects of the departureof wadersbefore L.R.M. (1998). A new pressuresensory mechanismm for prey long-distanceflights: flocking, vocalizations, flight pathsand detectionin birds:the useof principlesof seabeddynamics? diurnaltiming. Ardea 78: 157-184. Proc. R. Soc. Lond. B 265: 1377-1383.

Piersma,T., Prokosch,P. & Bredin, D. (1992). The migration Raim, A. (1978). A radio-transmitter attachmentfor small systemof Afro-Siberian Knots Calidris canutuscanutus. passerines.Bird-Banding 49: 326-332. WaderStudy Group Bull. 64, Suppl.:52-63. Warnock, N. & Wamock, S. (1993). Attachmentof Piersma,T., Hoekstra,R., Dekinga, A., Koolhaas,A. Wolf, P., radio-transmittersto sandpipers:review andmethods. Wader Battley,P. & Wiersma,P. (1993a). Scale and intensityof StudyGroup Bull. 70: 28-30. •ntertidalhabitat use by Knots Calidris canutusin the western Wadden Sea in relation to food, friends and foes. Neth. J. Sea Zwarts,L. & Wanink,J. (1993). How the foodsupply Res. 31: 331-357. harvestableby wadersin theWadden Sea depends on the variationin energydensity, body weight, biomass, burying Piersma,T., Koolhaas,A. & Dekinga, A. (1993b). Interactions depth and behaviourof tidal-flat invertebrates.Neth. J. Sea between stomach structure and diet choice in shorebirds. Auk Res. 31: 441-476. 110: 552-564.

Piersma,T, van Gils, J., de Goeij, P. & van der Meer, J. (1995). Holling's functionalresponse model as a tool to link the food findingmechanism of a probingshorebird with its spatialdistribution. J. Anim. Ecol. 64: 493-504. 43

Appendix 1. An overviewof radio-telemetrystudies on waders. The followinglist is orderedchronologically. Many studiesdeal with habitatchoice on the winteringgrounds, and the differencesbetween day andnight are oftenstressed (e.g. Dugan 1981, Smith 1987,Summers 1994, Wood 1986). Recently,migratory routes have beenexplored also (Bakeret al. 1998,Iverson et al. 1996,Warnock & Bishop1996, Warnock & Bishop1998). The largerwader species have been equipped with motion-sensitivetransmitters to recordactivity patterns(Exo 1992, Exo 1993a, Exo 1993b).

Species Phaseofannual cycle Research theme Reference

Grey PloverPluvialis squatarola wintering nocturnalfeeding Dugan (1981)

Long-billed Curlew Numeniusamericanus chicks movements,mortality Redmond & Jenni (1986)

Grey PloverPluvialis squatarola wintering diurnaland nocturnal territoriality Wood (1986)

Green SandpiperTringa ochropus wintering nocturnalroosting Smith (1987)

Wilson's PhalaropeSteganopus tricolor breeding matingbehaviour Colwell and Oring (1988)

Purple SandpiperCalidris maritima breeding incubativebehaviour Cresswell & Summers(1988)

Snowy Plover Charadriusalexandrinus breeding methods Hill & Talent (1990)

Bristle-thighedCurlew Numeniustahiriensis breeding breedingbehaviour Gill et al. (1991 )

GoldenPlover Pluvialis apricaria chicks behaviour Yalden (1991)

OystercatcherHaematopus ostralegus breeding time-energybudget Exo (1992)

OystercatcherHaematopus ostralegus wintering/breeding foragingpattern, activity,

time-energy budget Exo (1992), Exo (1993a),

Exo (1993b)

Dunlin Calidris alpina;

WesternSandpiper Calidris mauri wintering/migration methods Warnock & Warnock (1993)

PurpleSandpiper Calidris maritima wintering diurnaland nocturnal activity Summers (1994)

Mountain Plover Charadrius montanus wintering habitatchoice, activity Knopf & Rubert (1995)

Willet Catoptrophorussemipalmatus ;

Whimbrel Numeniusphaeopus wintering feedingterritoriality McNeil & Romprd(1995)

Dunlin Calidris alpina wintering habitat choice Warnock et al. (1995)

WesternSandpiper Calidris mauri migration use of stopoversites Iverson et al. (1996)

GoldenPlover Pluvialisapricaria staging habitat choice Ketzenberg& Exo (1996)

Willet Catoptrophorussemipalmatus wintering nocturnal habitat choice Romprd& McNeil (1996)

WesternSandpiper Calidris mauri migration use of stopoversites Wamock& Bishop(1996)

WesternSandpiper Calidris mauri wintering homerange Warnock & Takekawa (1996)

Red Knot Calidris canutus migration use of stopoversites Baker et al. (1998)

Red Knot Calidris canutus breeding breedingbiology Tulp et al. (1998)

WesternSandpiper Calidris mauri migration use of stopoversites Warnock& Bishop (1998 44

REFERENCES Iverson,G., Warnock,S., Butler, R., Bishop,M. & Warnock, Baker, A.J., Gonz•lez, P.M., Piersma, T., Minton, C.D.T, N. (1996). Springmigration of WesternSandpipers along the Wilson, J.R., Sitters,H., Graham, D., Jessop,R., Collins, P., de Pacific Coastof North America:A telemetrystudy. Condor 98: Goeij, P., Peck, M.K., Lini, R., Bala, L., Pagnoni,G., Vila, A., 10-21. Bremer, E., Bastida, R., Ieno, E., Blanco, D., de Lima do Nascimento, I., Scherer, S.S., Schneider, M.P., Silva, A. & Ketzenberg,C. & Exo, K.-M. (1996). Habitat choice of Rodrigues,A.A.F. (1999). Northboundmigration of Red migratingGolden Plovers(Pluvialis apricaria). Verb.Dtsch. Knots Calidris canutusrufa in Argentinaand Brazil. Wader Zool. Ges. 89.1: 309. StudyGroup Bull. 88: 64-75. Knopf, EL & Rupert,J.R. (1995). Habits andhabitats of Colwell, M.A. & Oring, L.W. (1988). Variablefemale mating Mountain Plovers in California. Condor 97: 743-751. tacticsin a sex-role-reversedshorebird, Wilson's Phalarope (Phalaropustricolor). National GeographicResearch 4: McNeil, R. & Rompr&G. (1995). Day andnight feeding 408-415. territorialityin Willets Catophorussemipalmatus and WhimbrelNumenius phaeopus during the non-breeding Cresswell,B.H. & Summers,R.W. (1988). A study of seasonin the tropics.Ibis 137: 169-176. breedingPurple Sandpipers Calidris maritima on the Hardangerviddausing radio-telemetry. Fauna norv.Ser. C., Redmond,R.L. & Jenni,D.A. (1986). Populationecology of Cinclus 11: 1-6. the Long-billed Curlew (Numeniusamericanus) in western Idaho. Auk 103: 755-767. Dugan,P.J. (1981). The importanceof nocturnalforaging in shorebirds:a consequenceof increasedinvertebrate prey Rompr&G. & McNeil, R. (1996).Variability in day andnight activity. In: N.V. Jones& W.J. Wolff (eds.). Feedingand feedinghabitat use in theWillet Catoptrophorussemipalmatus survival strategiesof estuarineorganisms. Plenum Press, duringthe non-breedingseason in northeasternVenezuela. New York. p. 251-260. WaderStudy Group Bull. 81: 82-87.

Exo, K.-M. (1992). Methoden zur Aufnahme von Smith,K.W. (1987).What do GreenSandpipers do at night? Raum-Zeit-Budgetsbei V6geln, dargestelltam Beispieldes AbstractsWSG AnnualMeeting, Gdansk, Poland, 1987. Austernfischers(Haematopus ostralegus). Vogelwarte36: WaderStudy Group Bull. 51: 22-23. 311-325. Summers,R. (1994). Diurnal and nocturnal activities of a Exo, K.-M. (1993a). Methodsto monitortime and energy PurpleSandpiper Calidris maritima. Wader Study Group Bull. budgetsof birds,especially waders (Charadriiformes). 72: 33-34. Biotelemetry XII: 224-231. Tulp,I., Schekkerman,H., Piersma,T, Jukema,J., de Goeij,P. Exo, K.-M. (1993b). Zeitbudgetsvon Wattenmeer- und & vande Kam, J. (1998).Breeding waders at CapeSterlegova, Binnenlandbriiterndes Austernfischers (Haematopus northernTaimyr, in 1994. WIWO-report 61, Zeist. ostralegus).Jahresber. Instit. Vogelforsch.1: 11. Wamock,N. & Bishop,M.A. (1996). Springmigration of Gill, R.E., Lancot, R.B., Mason, J.D. & Handel, C.M. (1991). radiomarkedWestern Sandpipers along the Pacific Flyway: Observationson habitatuse, breeding chronology and parental 1995. WaderStudy Group Bull. 79: 30. care in Bristle-thighed Curlews on the SewardPeninsula, Alaska. WaderStudy Group Bull. 61: 28-36. Warnock,N. & Bishop,M.A. (1998).Spring stopover ecology of WesternSandpipers. Condor 100: 456-467. Hill, L.A. & Talent,L.G. (1990). Effectsof capture,handling, bandingand radio-marking on breedingLeast Terns and Warnock,N., Page,G. & Stenzel,L. (1995).Non-migratory Snowy Plovers.J. Field Ornithol. 61:310-319. movementsof Dunlinson theirCalifornia wintering grounds. Wilson Bull. 107: 131-139.