International Studies 8:114-121

Nocturnal foraging in shorebirds

RaymondMcNeil & Jos Ram6n RodriguezS.

McNeil, R. & RodriguezS., J.R. 1996. Nocturnalforaging in shorebirds.International Wader Studies 8: 114-121.

Membersof sevenfamih'es of shorebirdsforage both by day and by night in tropicaland temperate latitudes. In somespecies, foraging takes place principally at duskand at night. Somespecies appearto usetheir daytimeterritory at night. Somevisually guided peckers and somelong-billed tactileprobers forage by the samepreferred method both during the day and duringthe night. However,some long-billed species change from visualto tactileforaging between day and night. The rolesof moonlightand bioluminescencein prey detectionare discussed.Two main hypotheses canexplain why shorebirdsforage at night:(1) nightfeeding occurs only when the daytimefeeding hasbeen inadequate to meet the ' energeticrequirements; this is calledthe 'supplementary hypothesis';and (2) birdsprefer to feedat night becauseit providesthe mostprofitable (most availableprey), or safest,feeding opportunities. Day and night habitat segregationhas been reportedfor winteringshorebirds.

Miembrosde unassiete familias de chorlosy playeros,tanto de regionestropicales como templadas,se alimentan de nochey de dia. En ciertasespecies, el forrajeoocurre principalmente al atardecery de noche. Unasespecies parecen usar de nochesus territorios de alimentaci6ndiurna. Ciertoscazadores visuales y ciertoscazadores t/lctiles de pico largo sealimentan de la misma manerade nochecomo de d/a. Sin embargo,otras especies de pico largo,cazadores visuales de dia, cambiansu estrategia y sealimentan tactilmente de noche.Se discute el papeljugado por las mareas,el alumbradolunar y la bioluminescencia.Dos hip6teses principales permiten explicar porquelas aves lirn/colas se alimentan de noche:(1) la alimentaci6nnocturna ocurre finicamente cuando,al alimentarsesolo de dia, el ave no 1ograsatisfacer sus exigencias energ•ticas, y asi necesitade una alimentaci6nsuplementaria de noche;(2) la nochepresenta las condiciones alimenticiasmas provechosas (mayor disponibilidad o actividadde presas)y masseguras y asflas avesse alimentan de nochepot preferencia.En lugaresde invernadaen regi6ntropical, ciertas especiesparecen alimentarse de nocheen lugaresdiferentes de losque frecuentande dla.

Lesmembres de quelquesept families d'oiseaux de rivage,tant desrdgions tropicales que temp•r•es,s'alimentent de nuit et de jour. Chezcertaines esp•ces, la chassede proiesse fait surtout au crdpusculeet la nuit. Quelquesesp•ces semblent utiliser de nuit lesterritoires d'alimentation qu'ilsexploitent de jour. Certainschasseurs visuels et quelqueschasseurs tactties a longbec s'alimententde nuit de la m•me faconque durant le jour. Cependant,d'autres espc•es a longbec, chasseursvisuels de jour, changentleur strategieet s'alimententtactilement de nuit. Le cyclede la marde,l'dclairage lunaire et la bioluminescencejouent un certtainr/•le. Deuxhypoth/•ses principalespermettent d'expliquer pourquoi les oiseaux de rivages'alimentent de nuit: (1) l'alimentationnocturne a lieu uniquementquand, a s'alimenterseulement de jour,l'oiseau ne r•ussitpas a satisfaireses besoins energ•tiques, et ainsia besoind'une alimentation suppl•mentaire de nuit; (2) la nuit offredes conditions plus avantageuses (plus grande disponibilit• ou activit• des proies)et pluss•curitaires et ainsiles oiseaux s'alimentent de nuit par preference.Sur les aires d'hivernageen rdgionstropicale, certaines esp•ces semblent utiliser de nuitsdes sites differents de ceuxqu'ils fr•quentent de jour. R. McNeil,D•partement de sciences biologiques, Universit• de Montrfal, CP 6128,Succ. 'A', Montreal, QufbecH3C 3J7,Canada. J.R.Rodriguez $.,Departamento deBiologia, Universidad deOriente, Cumarui, Sucre, Venezuela.

Introduction ,members of sevenfamilies forage regularlyor mainly at night. The habit of beingactive during darknesshas been viewed ascharacteristic of a minorityof The behaviourof shorebirdsduring darknessis species,with mostconsidered entirely diurnal. largelyunknown. Night activitiesin shorebirds Primaryexamples of activityin minimallight have beendocumented by direct observationonly conditionsare found in the Apterygiformes, on rare occasions(Wood 1986;McNeil & Robert Strigiformes,Caprimulgiformes and Apodiformes 1988;Robert & McNeil 1989; Robert, McNeil & (Martin 1990). In shorebirdsof the order Leduc1989; Burger & Gochfeld1991). This is due particularlyto the difficultyof makingobservations

114 McNeil & RodriguezS.: Nocturnal foraging duringdarkness; however, with the recent Latitude and seasons developmentof night-visionlight intensifiers, nocturnal observation of has become Exceptfor the PaintedSnipe, Crab , possible(see McNeil & Robert1988; Robert & Burhinidae,Glareolidae, lapwings and otherspecies McNeil 1989; Robert, McNeil & Leduc 1989). that resideyear-round in the tropics,nocturnal activitiesin shorebirdshave been reported almost exclusivelyfor birdsstaging or winteringin coastal Becausethe main nocturnalactivity reportedto and estuarinehabitats in temperatelatitudes. occurregularly in shorebirdsis foraging,the Recent studies in Venezuela and Mauritania have importantquestions are: why forageat night?and shownthat some Neotropical residents and what are the causesof selectionfor night activityin Holarcticwinter migrantsfeed at night in tropical shorebirds?This paper overviews published environments (McNeil & Robert 1988; Robert & informationon (1) the occurrenceof nocturnal McNeil 1989; Robert, McNeil & Leduc 1989; Zwarts foragingin shorebirds,(2) the specialadaptations & Dirksen 1990;Zwarts, Blomert & Hupkes 1990; favouringsuch habits and (3) the suspectedbenefits Morrier & McNeil 1991). There seemto be only a thesebirds may get fromforaging at night. few exceptions,and sometimes there are regional variations. For example,the Curlew Sandpiper Nocturnal foraging activity Calidrisferrugineaforages at night in Australia (Dann 1981)but not in South Africa (Puttick 1979). Who forages at night? Most accountsof nocturnalfeeding in northern Thereare no reportsthat any shorebirdforages Europereport that it is mostintense during winter exclusivelyat night. Yet thereare manyreports of and lessintense or absentin the early autumn and speciesregularly foraging both during the day and the spring(Goss-Custard 1969; Heppleston 1971; duringthe night (Table1). Suchspecies include Pienkowski 1981a, 1982;Puttick 1984). In southern oystercatchers(Haematopus), (Pluvialis, Portugal,Batty (1991) found that nocturnalfeeding ),many Calidrisspecies and mostother is thenorm duringthe migrationperiods but much Scolopacidae,the majorfamily of shorebirds,and less common from November to March. In stilts(Himantopus). Other shorebirdspecies are less addition, the woodcocks are known to switch from likely to foragein full daylightbut restricttheir their winterpattern of feedingat night to feeding activityto twilight and night-time(Table 1). Such only duringthe day in summer(Dunford & Owen speciesinclude Painted Snipe Rostratula 1973; Hirons 1988). benghalensis,Crab Plover Dromas ardeola, Burhinidae (Esacus,Burhinus), coursers (Rhinoptilus), a few Almostnothing is known aboutthe occurrenceof lapwingspecies (Vanellus), Inland Dotterel Peltohyas nocturnalforaging in breedingshorebirds. australis,woodcocks (Scolopax), a few snipespecies However,in the tropics,Two-banded Coursers (Lymnocryptes,Gallinago, Coenocorypha) and Ruff Rhinoptilusafricanus are known to feedchicks Philomachuspugnax. Pratincoles(Glareola ) and the mainlyat night (MacLean1967). In the northern AustralianCourser Stiltia isabella are activemainly latitudes,breeding Eurasian Dotterels Charadrius at dawn and dusk; the latter and the Common rnorinellusand PipingPlovers Charadrius rnelodus PratincoleGlareola pratincola continue foraging at forageboth during darkness and duringdaylight night undermoonlight conditions (Ali & Ripley (Kalas1986; K.J. Staine & J. Burger,pers. commun.). 1981;Cramp & Simmons1983). Shorebirdmist- nettingdone on stagingor winteringareas with betterprofit at night-timeis anotherindication that Foragingbehaviour somespecies are very activeat night. Shorebirdsuse two basictypes of foraging techniques(Table 1): visual searching (e.g. plovers) Night-time foraging territories for prey items,or indicationsof their presence,on or near the surface;and probing(e.g. Short-billed During the non-breedingseason, many species of DowitcherLirnnodromus griseus) with the bill for shorebirdsdefend foraging territories (Myers, buriedprey, which are detectedby tactileand taste Connors& Pitelka 1979). Wood (1986) has shown cues. While somespecies may feedexclusively that someGrey PloversPluvialis squatarola continue with oneof thesetechniques (e.g. visual searching to usetheir feedingterritories at night. Further- by mostplovers, or tactileprobing by Short-billed more, there are indications that territories defended Dowitchers),other species (e.g. Semipalmated by EurasianCurlews Numenius arquata, Willets SandpipersCalidris pusilla) use both techniques, Catoptrophorussemipalmatus and Whimbrels beingvisual in someconditions and tactilein Numeniusphaeopus during daylightwere occupied others,according to food items and feedinghabitats by individualsof the samespecies during darkness (seeGoss-Custard 1970; Evans 1979;Schneider (Cramp& Simmons1983; R. McNeil, unpubl.data). 1983). Pratincolesare a specialgroup; they feed extensivelyby aerialhawking for flying insects (Brosset1979; Hayman, Marchant & Prater1986).

115 International Wader Studies 8:114-121

Table1. Daytimeand night-time foraging habits and strategies ofshorebirds. DIU = diurnal;CRE = crepuscular; blOC= nocturnal;VIS = visual;TAC = tactile;(+) partly; (++) largely; (-) occasionally.Sequence of genera and nomenclaturefollow Hayman, Marchant& Prater (1986).

Foragingpattern Foragingstrategy

Day Night Principal Principal Famih'es& genera DIU CRE NOC referencesa VIS TAC VIS TAC referencesa

ROSTRATULIDAE Rostratula - ++ + 1,2,3,4 + + 1,4

DROMADIDAE Dromas - ++ ++ 2,3 + ? 5

HAEMATOPODIDAE Haematopus + + + 4,5,6,7,8,9 + + 7,8,9

RECURVIROSTRIDAE Hirnantopus + + + 2,10,11,12 ++ + + + 10,11,13 Recurvirostra + + + 2,4,13,14 + + 13

BURHINIDAE Burhinus + ++ ++ 1,2,3,4,15,16 Esacus + ++ ++ 1,2,16,17 ++ - 17

GLAREOLIDAE Rhinoptilus - + ++ 3,4,18 + 3,18 $tiltia - ++ + 3,16 Glareola + ++ 2,3,4,16,19 (text)

CHARADRIIDAE Vanellus + + + 1,2,3,4,20,21 Pluvialis + + + 2,4,22,23,24,25 ++ ++ 26,27 Charadrius + + + 10,11,12,26,28 ++ ++ 1,26,27,28 + + + 3,29 Peltohyas + + ++ 3,30,31 Eudromias + + + 4,32,33

SCOLOPACIDAE Lirnosa + + + 2,22,26 ++ ++ 26 Nurnenius + + + 2,22,26,34,35 ++ ++ 35 Tringa + + + 2,10,11,12,36,37 ++ ++ Catoptrophorus + + + 12,38 ++ + + + 38,46 Actitis + + + 2 Arenaria + + ? 22,39,40 Scolopax + ++ ++ 2,41,42,43 Coenocorypha - ++ ++ 3,44 Gallinago - ++ ++ 1,2,4,45 Lyrnnocryptes + ++ ++ 2 Lirnnodromus + + + 12,13 ++ ++ 12,13 Calidris + + + 2,12,22,26,40,47 + + + ++ 26,38 Micropalarna + + + 12 ++ ++ 38 Philomachus + + ++ 1,2,4

1, Ali & Ripley(1980-1981); 2, Cramp& Simmons(1983); 3, Hayman,Marchant & Prater(1986); 4, Urban,Fry & Keith(1986); 5, Swennen etal. (1987);6, Heppleston(1971); 7, Hulscher(1976); 8, Sutherland(1982); 9, Goss-Custard(1983); 10, McNeil & Robert(1988); 11,Robert & McNeil(1989); 12, Robert, McNeil & Leduc(1989); 13, Hamilton (1975); 14, Gibson (1978); 15, Glue & Morgan(1974); 16,Pringle (1987); 17, Woodall & Woodall(1989); 18, MacLean (1967); 19, Brosset (1979); 20, Spencer (1953); 21, Milson (1984); 22,Evans (1976); 23, Dugan (1981); 24, Pienkowski (1981a); 25, Wood (1983); 26, Pienkowski (1982); 27, Pienkowski (1983a); 28,Pienkowski (19&ø,b); 29, Phillips (1977); 30, MacLean (1976); 31, McNamara (1980); 32, Kalas (1986); 33, Nethersole-Thompson (1973);,'M, Hale (1980);35, Zwarts (1990); •, Goss-Custard(1969); 37, Goss-Custard (1970); 38, R. McNeil,unpubl. data; 39, Schneider (1985);40, Zwarts, Blomert & Hupkes(1990); 41, Hirons & Bickford-Smith(19&3); 42, Sheldon (1961); 43, Hirons (1988); 44, Miskelly (1990);45, Grisser (1988); 46, McNeil & RodrfguezS. (1990);47, Manseau& Ferron(1991).

Someshorebirds may modify their foraging daylightbut switchto tactileforaging at night. techniquesbetween night and day. Thus,oyster- During daylight and on bright moonlit nights, catchers(Hulscher 1976) and Tringa species Black-wingedStilts Himantopus himantopus are (Goss-Custard1970; McNeil & Robert 1988;Robert usuallyvisual peckers, but theyuse scythe-like & McNeil 1989)are normallysight feeders during sweepsof the bill (a tactiletechnique) on moonless

116 McNeil & RodrfguezS.: Nocturnal foraging

nightsor underlower moonlightconditions suggestedthat ploversmay alsouse acoustic cues to (McNeil & Robert 1988;Robert & McNeil 1989). locateprey (Failer1962).

Foragingsuccess Pienkowski(1982, 1983a) concluded that plovers usesight as the main meansof prey detection,even Comparedwith visual'plover strategists', on dark nights,and showedthat, comparedwith shorebirdsthat feedby touchboth by day and by daylight,Grey Plovershave lower pecking rates on night shouldbe relativelyunaffected by darkness dark moonlessnights but not on moonlitnights. In (Dugan 1981;Pienkowski 1981b; Goss-Custard addition, Double-banded Plovers Charadrius 1983). It is very difficultto find out the proportion bicinctusin Australiaroost for longerperiods (and of attemptsto captureprey that are successfulat thus feed for shorterperiods) during daysthat night. Some,but not all, authorshave observedor followmoonlit nights, suggesting that their energy assumedthat the rate of prey intakeis lessat night intakeswere greateron the moonlitnights (Dann than by day. For example,Heppleston (1971) and 1981). Althoughthe moonseems to influence Goss-Custard& Durell (1987)found oystercatchers nocturnalforaging activity for somespecies, it does to be feedingless during darkness,but Hulscher not appearthat moonlightper se is the proximate (1976),Swennen, Leopold & De Bruijn(1989) and factor. Thus, for most of the lunar month, Northern Swennen(1990) found no differencein averagefood Lapwingsand EurasianCurlews forage by day and consumptionbetween hours of daylightand roostat night. For a few daysaround the full moon darkness.The caseof someplover-like species is period,the situationis reversed,even if the moonis surprising.For example,Wood (1984)measured not visible(Spencer 1953; Hale 1980). The the time budgetof a Grey Ploveron its territoryby significanceof thisis not known,but it may reflect day and by nightand foundno significant an increasedactivity of prey itemsinfluenced by the differencein the total time spentforaging and in the lunar cycle. bird's peckrate in thesetwo periods. Ingestion ratesof Northern LapwingsVanellus vanellus at night canbe doublethose achieved during the day Pienkowski(1983a, 1983b) suggested that shore- (McLennan 1979). birdsmight take advantageof luminescent organismsat night. In a coastallagoon of northern Venezuela,no relationshipwas found betweenthe Sensoryadaptations, moonlight and presenceor absenceof bioluminescenceand the bioluminescence typesof nocturnalforaging methods of shorebirds (McNeil & Robert 1988;Robert & McNeil 1989). The relationshipcould be indirect,if it were shownthat Shorebirdshave visual or tactileadaptations that prey (e.g.fishes) on which Tringaand Himantopus may enhanceforaging at night. Accordingto Dugan (1981)and Pienkowski(1983a, 1983b), the speciesfeed at night (Robert& McNeil 1989)are largeeye in relationto headsize of plovers, attractedby luminescentorganisms. comparedwith that of sandpipers,is assumedto be an advantagefor low light intensity. The Crab Why forage at night? Plover, Burhinidae,coursers (Rhinoptilus) and woodcocksalso have large eyes. In addition,the There are two main hypotheses:(1) the actualvisual receptors of birds,as in other 'supplementaryhypothesis', suggesting that night vertebrates, are rods and cones. Nocturnal birds feedingoccurs only when the daytimefeeding has havea greatpreponderance of rodsin their retinae beeninadequate to meetthe birds' energy (Tansley& Erichsen1985). The Grey Plover,a requirements;and (2) the 'preferencehypothesis', diurnal and nocturnalsight feeder, has more rods, a suggestingthat birdsprefer to feed at night because greaterrod/cone ratio and longerrod outer it providesthe mostprofitable, or safest,feeding segmentsthan the GreaterYellowlegs Tringa opportunities. melanoleuca,a daylight sight feeder that mostof the timeswitches to tactileforaging at night(Rojas de Azuaje 1991). The Short-billedDowitcher, a tactile Supplementaryhypothesis foragerduring both day and night, is intermediate. Tidesmay limit accessto feedingsites regardless of prey abundance(Burger 1984), and thusshorebirds The presenceof many touch-sensitivenerve might be limited in their diurnal feedingtime and endings(e.g. Herbst's corpuscles) in the bill tip needto feedat night to satisfytheir energeticneeds. favourstouch feeding by many scolopacidspecies However,even species not affectedby tidesmay (Limnodromus,Gallinago, Calidris, etc.) (Bolze 1968; sometimesfeed at night. For example,shorebirds Schwartzkopff1973, 1985). In addition,taste or feedingin coastallagoons in northernVenezuela chemoreception(presence of tastebuds in the tip of canfeed all of the time, even during mosthigh the beak)may play a role in locatingareas rich in tides,yet many speciesfeed by both night and day. prey(Gerritsen, Heezik & Swennen1983; Heezik, Gerritsen& Swennen1983). Finally,it hasbeen

117 International Wader Studies 8:114-121

Activitypatterns of birdsare related to energetic Nocturnal activitiesin shorebirdsmay be related to needs,which vary during the annualcycle, and the avoidanceof diurnal predatorsor other kinds of nocturnalfeeding in temperatezones was first diurnal disturbance.Although the effectof human interpretedas a strategyto 'top up' an inadequate disturbancehas been little studied,Sanderlings daytimeenergy intake. In temperatelatitudes, Calidrisalba avoid disturbanceby peopleon Florida energyrequirements are generallyhigher during beaches,and thus increasethe time they feed at low winter, and mostaccounts of nocturnalfeeding by tide, by feedingat night (Burger& Gochfeld1991). shorebirdsin northernEurope report that it is most In the ChacopataLagoon (Venezuela), small bays intenseduring winter and lessintense or absentin surroundedby mangrovewoodlands are usedfor early autumnand spring(Goss-Custard 1969; feedingby shorebirdsmuch less frequently by day Heppleston1971; Goss-Custard et al. 1977; than by night. This is in spiteof the fact that they Pienkowski 1981a, 1982; Puttick 1984). In winter, are very rich in prey at all times. During the day, thereis lessdaylight time availableto searchfor the birds congregateon vast,open mudflats, food, and prey availabilitymay decreasebecause apparentlyto avoid predationby PeregrineFalcons intertidalinvertebrates move deeperwithin the Falcoperegrinus (Robert, McNeil & Leduc1989). sediment (and sometimes are less active) as Also in the samelagoon, Wilson's Plovers temperaturefalls (Goss-Custardet al. 1977; Charadriuswilsonia, in spiteof the Ucacrab Pienkowski1982). In the tropics,these factors do abundance,forage very little during daytime; not apply,yet severalshorebirds feed regularly at daylightprey intake alone is insufficientto balance night (Robert& McNeil 1989). In sometropical theirenergy budget, and the factthat they forage situations,e.g. mudflats in Mauritania,daytime mainly at night appearsrelated to predator prey abundanceis low, and feedingin daylight avoidanceduring daylight (Morrier & McNeil alone is sometimes insufficient for shorebirds to 1991). In north-easternAfrica, PaintedSnipes feed achievetheir daily energeticneeds (Engelmoer et al. at timesduring the day if the areais undisturbedby 1984). humansand othermammals, although only where coveris plentiful (A.J.Tree,fide Cramp & Simmons Finally,we suspectthat, even in thetropics, the 1983). occurrenceof nocturnalfeeding may be greater when migratoryspecies have higherenergetic During the winter in northernlatitudes, Common demands(Myers & McCaffery1984) -- for instance, SnipesGallinago gallinago (Grisser 1988) and during the time of pre-migratoryfattening, when woodcocks(Dunford & Owen 1973;Hirons 1988) refuellingat a stop-overplace or when landingafter roostin woodlandin daytimebut feedon pastures a long overseaflight. The higher incidenceof at night. The switchto night feedingin the open nocturnalfeeding during pre-migratoryor habitatsmay reflectincreased vulnerability to migrationperiods in southernPortugal (Batty 1991), predatorsin thesesituations during the day. Mauritania (Zwarts, Blomert& Hupkes 1990)and Accordingto Cramp& Simmons(1983), Pintail northern South America (Morrier & McNeil 1991) SnipesGallinago stenura feed mainly at nightbut providessupport to the supplementaryhypothesis. may feed during daytime,if undisturbed.

Preferencehypothesis Conclusions Somespecies may take advantageof increased availabilityand activity of prey at night (Dugan Nocturnalforaging in shorebirdsmay be consid- 1981;Pienkowski 1983a, 1983b; Townshend, Dugan ered as a behaviourthat evolvedin different groups & Pienkowski 1984; Evans 1987; Robert & McNeil of speciesfor differentreasons and whose 1989). It may evenbe advantageousfor shorebirds occurrenceis governedby a variety of factors.For to feedat night at sitesand on prey that are not the more terrestrialspecies, nocturnal foraging usedduring the day (Evans& Dugan1984; occursregularly and seemsto be preferred to Townshend,Dugan & Pienkowski1984; Robert & feedingby day. For the majorityof speciesand McNeil 1989; Robert, McNeil & Leduc 1989). At populations,however, foraging at night seemsless somesites, the abundanceor activityof prey is preferredand probablyless efficient than foraging higherat night than during daylight(Evans 1987; by day. However,the useof openhabitats by these Robert& McNeil 1989). Black-wingedStilts and species,and theirability to locateprey by tactile Tringaspecies use such sites principally at night cues,have given them the option of feedingat night and seem to feed then on food items (fishes, shouldenergetic demands not be satisfiedby Pelecypodaand Hemiptera) at leastpartly different daytimefeeding. Thus,these birds have a from thosethey foragedfor during daylight(Robert flexibilityin foragingstrategy that few otheravian & McNeil 1989). The useof differentday and night groupspossess. Nocturnal feeding is importantfor habitatsmight be a fundamentalrequirement for the successfulcompletion of the annualcycle in winteringshorebirds, at leastin someregions. manypopulations of shorebirdsand soshould be takeninto accountin anyconservation measures. The indication that some shorebirds feed nocturnallyat sitesand onprey that arenot used

118 McNefi & RodriguezS.: Nocturnal foraging

duringthe day coulddemand the protectionof Evans,P.R. 1976. Energybalance and optimal foraging somewintering habitats less densely populated by strategiesin shorebirds:some implications for their shorebirdsduring the daybut moreintensively distributionsand movementsin the non-breeding season. Ardea 64: 117-139. usedat night. Many authorshave dealt with time-activity or energybudgets of shorebirds. Evans,P.R. 1979. Adaptationsshown by foraging shorebirdsto cyclicvariations in the activityand However,nobody seems to havetaken nocturnal availabilityof their intertidalinvertebrate prey. In: E. activities into account. Most information on the Naylot & R.G. Hartnoll (eds.),Cyclic phenomena in time and energybudgets of shorebirdsneeds to be marineplants and animals, pp. 357-366.Pergamon revised,bearing in mind their nocturnalactivities. Press, Oxford. Evans,P.R. & Dugan, P.J. 1984. Coastalbirds: numbers in relation to food resources.In: P.R. Evans,J.D. Acknowledgements Goss-Custard& W.G. Hale (eds.), Coastalwaders and wildfowlin winter,pp. 8-28. CambridgeUniversity Thisstudy is part of ecologicalresearch supported Press,Cambridge. by the Natural Sciencesand EngineeringResearch Fallet,M. 1962. Uber Bodenvogelund ihre terricole Council of Canada, the Universit6 de Montr6al and Beutetiere.Technik der Nahrungssuch- Population Universidad de Oriente. dynamik. Zool.Anz. 168:187-212. Gerritsen, A.F.C., Heezik, Y.M. van & Swennen, C. 1983. Chemoreceptionin two furtherCalidris species (C. References maritimaand C. canutus).Neth. J. Zool.33: 485-496. Gibson,F. 1978. Ecologicalaspects of the time budgetof the American Avocet. Am. Midi. Nat. 99: 65-82. Ali, S. & Ripley,S.D. 1980. Handbookof thebirds of India Glue, D. & Morgan, R. 1974. Breedingstatistics and andPakistan. Vol. 2. Megapodesto CrabPlover. Oxford movementsof the StoneCurlew. BirdStudy 21: 21-28. University Press,London. Goss-Custard,J.D. 1969. The winter feedingecology of All, S.& Ripley,S.D. 1981. Handbookofthe birds of India the RedshankTringa totanus. Ibis 111:338-356. and Pakistan. Vol. 3. Stone Curlews to owls. Oxford Goss-Custard,J.D. 1970. Feedingdispersion in some University Press,London. overwinteringwading birds. In: J.H. Crook (ed.), Batty,L. 1991. Aspectsof the phenology ofwaders (Charadrii) Socialbehaviour in birdsand mammals, pp. 3-35. onthe Ria Formosa, Portugal. PhM Thesis,University of Academic Press, London. Wales, UK. Goss-Custard,J.D. 1983. Spatialand seasonalvariations Bolze,G. yon. 1968. Anordnung und Bau der in the foodsupply of wadersCharadrii wintering in HerbstschenK6rperchen in Limicolenschn•belnim the BritishIsles. Proc.Third Nordic Congr. Ornithol. Zusammenhangmit der Nahrungsfindung.Zool. Anz. 1981: 85-96. 181: 313-343. Goss-Custard,J.D. & Durell, S.E.A. Le V. Dit. 1987. Brosset,A. 1979. 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