DISTURBANCE TO WATERFOWL ON ESTUARIES Edited by Nick Davidson & Phil Rothwell Wader Study Group Bulletin 68, Special Issue, August 1993 DISTURBANCE TO WATERFOWL ON ESTUARIES Edited by Nick Davidson & Phil Rothwell Wader Study Group Bulletin68, Special Issue, August 1993 This publicationcan be obtainedfrom The Royal Societyfor the Protectionof Birds(The Lodge, Sandy, BedfordshireSG19 2DL, U.K.) Price ½'15includesp & p This report should be cited as: Disturbance to waterfowlon estuaries Wader Study Group Bull 68 Special Issue Individualpapersshouldbe cited as: Wader Study GroupBull.68: These papers have been subjectto peer groupreview The statementsmade in individualpapers remainthe intellectualproperty of the authorsand not necessarilyrepresentthe views of the editorsor the sponsoringorganisations The editorsacknowledgeBev Whitten, Janice Harnett, Martin Nugent, Sylvia Sullivan,and all the workshopparticipants,withoutwhom the meeting and this volume would not have happened Copyright¸ 1993 by the Wader StudyGroup(WSG) Publishedby the RSPB and the Wader Study Group, w•th financial assistance Committee of the U.K Joint Nature Conservation Frontcover:by ChrisGomersall(RSPB) Back cover:by PatrickSutherland(RSPB) Typesettingby BedfordTypesettersLimited Printedby SterlingPress ISSN 0260-3799 RSPB Ref 22/749/93 Contents Introduction Nick Davidson Wader and Phil Rothwell disturbance: a theoretical overview John Cayford Effects of disturbance on shorebirds: a summary of existing knowledge from the Dutch Wadden Sea and Delta area Cor Smit and George J M Visser Disturbance of foraging knots by aircraft in the Dutch Wadden Sea in August-October 1992 Anita Koolhaas, Anne Dekinga and 'l-heunisPiersma 20 Experimental wildlife reserves in Denmark: a summary of results Jesper Madsen 23 Studies on the effects of disturbances on staging Brent Geese: a progress report Martin Stock The UK Shooting Disturbance Project Myrfyn Owen 29 35 Some effects of disturbance to waterfowl from bait-digging and wildfowling at Lindisfarne National Nature Reserve, north-east England David Townshend and David O'Connor 47 Impact and extent of recreational disturbance to wader roosts on the Dee estuary: some preliminary results Jeff Kirby, C Clee and V Seager 53 Disturbance and feeding shorebirds on the Exe estuary John Goss-Custard and N Verboven A preliminary study of the effects of disturbance on feeding Wigeon grazing on Eel-grass Zostera Tony Fox, D Bell and G Mudge 59 67 Disturbance on estuaries: RSPB nature reserve experience Graham Hirons and Gareth Thomas 72 Disturbance to estuarine birds: other reports and papers Nick Davidson 79 Kentish Plovers and tourists - competitors on sandy coasts? Rainer Schulz and Martin Stock 83 The impact of tourism on coastal breeding waders in Western and Southern Europe: an overview Mike Pienkowski 92 Human disturbance to waterfowl on estuaries: conservation and coastal management implications of current knowledge Nick Davidson and Phil Rothwell 97 Dawdson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge principlesfor coping with potentialrecreationaland waterfowl demands on estuaries in the future, and identifyresearch needs We concentrate here on issues of disturbance to waterfowlfeeding and roostingon estuarieswhilstthe birds are on their wintering grounds and during periods of springand autumn migrations.The effectsand •mplicationsof recreationaldisturbanceon breeding waterfowl have rather different patterns of effect and imphcation(see e.g Pienkowski1993; Schultz & Stock 1993) They are not consideredfurtherhere although the overall principleremains the same: people in too close proximityto birds have at least the potentialfor creating a disturbingeffect explanation) This is because most studies have so far relied on observationalor semi-experimentalways of recordingeffects of disturbanceand so cannot readily be used to deduce the extent of any impact of human disturbanceon the birds Conversely,it is just as difficult to use the available data to demonstrate that there is no impacton waterfowlof a particulardisturbingactivity Cayford (1993) suggeststhat future researchcould concentrateon more experimentalfield manipulations as a way of controllingfor confoundingvariables Coastal research is accustomedto dealing with two major sets of changingvariables First is the high dynamism of coastal systems, as seen throughthe physical,chemical and biologicalprocessesthat shape estuaries and open coasts Second is the ever-changingpatternof human uses of coastlines, characterisedby many differentactivitiesoften taking place simultaneouslybut independently.In studyingthe However,knowngeneralfeaturesof waterfowlecology and populationdynamicsdo help by providinga framework in which to judge disturbanceeffects Cayford(1993) pointsout that optimalforagingtheoryis a useful'basisfrom whichto understandlikelyeffectsof disturbanceon feeding Many studieshave shownthat birds concentratewhere feeding is best (often where there is best opportunityto maximisenet energy gain) If birdsare forcedtemporarilyor permanentlyto leave these places (by disturbance) then there is an increased risk that their energy balance will suffer However, the severity of this type of situationand ways in which birds respondagain vary in a complex way Responses depend on many factors such as whether there are alternativefeeding areas available Furthermoresome parts of a population,e.g juveniles,can be more disturbance affected STUDYING AND INTERPRETING DISTURBANCE of human activities to birds there is also a third major set of variables: inter- and intra-specific d•fferences in the responses shown by birds to even the same activityat differenttimes and/or in differentplaces (see e.g Smit & Visser 1993) Th•s multiplicityof variables underlyingthe observed •nteractionsbetween waterfowl and people makes it d•fficultto assess what is the cause and the implications of a particular instance of recreationaldisturbance.This is particularlythe case for observationalstudies Althoughthese can identifycorrelationallinksbetween human disturbance and the responses of the birds it is often difficultto isolate key variables, and to assess whether human disturbance adds to or replaces natural disturbancelevels from e.g birdsof prey Furthermore, the magnitudeof the disturbanceto waterfowlmay arise from synergisticeffects of more than one activity For example Townshend & O'Connor (1993) suggestthat waterfowl numbers and usage at Lindisfarnein northeast Englandwere affectedby wildfowlingactivity,but chieflywhen the presence of bait-diggersin just one part of the area prevented birds from usinga zone establishedas a non-shot refuge (see also Bell & Fox (1991) and Owen (1993) for furtherdiscussionof wildfowlingrefuges) than others Disturbancedoes not in itselfalways implythat it causes a serious problem to the birds, at least in the short-term.This is because waterfowlcan compensate for disruptionsto their natural behaviourpatternsin a variety of ways For example some species and individualsdo not always feed for all the available time during the tidal cycle These birds can extend their periodof feedingto compensatefor time lostduring disturbance,in a parallel with the extended feeding times that occurduringperiodsof high energy demand inducedby cold weather (e.g Davidson& Evans 1986) Some waders can accelerate food intake rates in responseto reductionsin time available for feeding (Swennen et al 1989) Hence even apparentlyhigh rates of disturbanceto feeding routinesdo not always lead to major reductionsin food intake or overall usage of feedingareas - an example for Oystercatchers Haematopus ostralegusis describedby Goss-Custard& Verboven (1993) But note that on the same estuary there is evidence that another waterfowl species (WigeonAnas penelope)may be seriouslyaffectedby even occasionaldisturbance during key parts of the feeding cycle (Fox et al 1993), emphasisingthe difficultyof extrapolatingeven from studiesin the same location Care also needs to be taken to ensure that Measuringand controllingfor the many variablesin dynamiccoastal systemsis a large task, and one that may not greatlyhelp in buildinggeneral modelsof waterfowl use of estuaries with which to compare the effects of a disturbance(see Cayford 1993 for further 98 conclusionsabout the intensityof disturbanceare not drawn from only part of the time or area, since observationscan be concentratedin those placesand duringthose times when disturbanceis greatest (Goss-Custard& Verboven 1993) Davidson& Rothwell:Humandisturbanceto waterfowlon estuaries:conservationand coastalmanagementimplications of currentknowledge Comprehensiveunderstandingof the significanceof disturbance to estuarine waterfowl thus depends on understandingwhether(and by how much)the birds have a bufferingcapacityremainingbefore facing reduced energy balance and so potentiallyreduced survival.This in turn relies in part on an understanding of such features as the carryingcapacityof an area, the nutritionalstate and requirementsof the birds and actual feeding rates in relationto potentialmaxima Since this detailed information pressure is often not available (and is very hard to establish), assessments must be based on more limited available information Local effect e.g stop feeding move within estuary Another lesson to be learnt from using waterfowl ecology and population dynamics to underpin analyses of disturbanceis the need to distinguish between effect and impact, and between whether it is individuals or populationsthat are affected This is summarised in Figure Many studies, for example most of those in this volume, report local (i.e within an estuary or part of an estuary) effects on at least some individuals.Examples include cessation of feeding, changing feeding locationsand moving roostingsites In some cases there is evidence that total numbers 'Estua effe e.g.decrease in •, estuary population '[Estuary impa e.g birds die ct of birds using an estuary decreased in response to human disturbance (Townshend & O'Connor 1993; Kirby et al 1993) However, it is much harder to detect whether such changes have an impact on individual birds (e.g by reducingtheir fitness to survive), or on a waterfowl populationsuch that a biogeographical population declines First this is because it is difficult to control for the many other factors that could affect fitness and populationdynamics (see Cayford 1993) Second, waterfowl are highly migratory so that any effect of disturbance (e.g leaving on migration in a poorer nutritionalcondition)could have its impact many thousandsof kilometresaway e.g on migratory staging areas or arctic breedinggrounds(see Evans et al 1991; Davidson & Morrison 1992) Large-scale changes in the use of sites by certain species, apparently linked to changes in intensityof disturbance have been noted Changes in the habits of species such as Wigeon and Brent Geese Branta bernicla in response to disturbanceassociated with Popula impact ,g, population decline• Figure Stages in detectingeffectsand impactsof disturbanceto waterfowl WHO IS MOST DISTURBED, BY WHOM, WHERE AND WHEN? When during the annual cycle? We have pointedout that human disturbanceon estuaries adds to a baseline of disturbance from natural causes suchas birdsof prey or the risingof the tide forcingbirds to abandonfeedinggrounds.The effectsof such shootingare well documented(Madsen 1993) Such changes in habit can be of a scale detectable across additional disturbance flyways even under natural, undisturbed, conditions, i.e when Nevertheless, this volume includesmany examples of studiesshowingat least localor short-termeffectsof disturbance, and there is evidence in at least some cases that such disturbance can and does lead to a substantialdecrease in energy balance (e.g Belanger & Bedard 1990) Furthermore,despitethe very great variation in scale and pattern of observed disturbance responsesthere are some commonfeatures that emerge whichcan indicatethe locations,times and circumstancesof highvulnerabilityto disturbance These are discussed below will be most serious at times when birdshave difficultyfindingsufficientfoodfor their needs they are at or closeto the thresholdof meetingtheir energy balance Such conditionscan arise when either food is difficultto find and/orwhen demandsfor energy are high(Pienkowskiet al 1984) Problemsof balancing the budgetoccurnotjust when birdsfind difficultyin meetingtheir daily existenceneeds Wildfowlaccumulate storesof fat and proteinin advance of periodsof high demand.At suchtimesthe dailyfood intakemustgreatly exceed that needed to supplyshort-termneeds There are several circumstancesand times of year when waterfowlare close to their energy balance 99 Dawdson& RothwelhHuman disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge threshold and so are vulnerable to additional disturbance.One is duringperiodsof cold winter weather At such times food becomes harder to find whilstenergydemandfor thermoregulationincreases, so that food intake has to be increased When severe weather lastsfor a few days or more waterfowlregularly draw on fat and protein stores accumulated earlier in the winter Even withoutadditionalproblemscaused by disturbancesome waterfowl species regularlyhave increasedmortalityduringcold weather (e.g Davidson 1981, Davidson & Evans 1982) Such mortalitycan occur within about one week of the onset of cold weather It usuallyseems to occurafter birdshave exhausted the fat stores that providetheir major energy source during periodsof insufficientfood intake Additional disturbance of waterfowl at such times, particularlyif it involvesflight, accelerates the rate of nutrientstore use and so increases mortalityrisks Recognitionof this has led since the mid-1980s to the impositionin the UK and some other European countriesof statutorybans on wildfowlingduring prolongedsevere weather, a major objectivebeing to reduce disturbanceto non-quarryspecies In northerntemperate regions most waterfowl accumulateenergy reservesduringthe early part of the winter, with a peak in late December - late January (depending on species) broadly coincidingwith the time when severe weather occurs most often Waterfowl For waders the periodin autumn when they undergoa major moult may also be one when the direct and indirecteffects of disturbanceare high Moult is a time when energy demandsare high, because birdsneed to acquire nutrientsfor the growthof new feathers However, as moult takes place at the end of summer when food is abundant and weather mild, waders generallyseem to have littledifficultyin meetingenergy needs Even so, waders seem to concentrateon large estuarieswhen moulting,and this is consideredto be an adaptationto avoidanceof disturbance(Prater 1981) Certainlyflyingwhen in activewing moultis less energeticallyefficient,and moultingbirds may be less manoeuvrableand so more vulnerable to predators Hence additionaldisturbancecausingextra periodsof flightduringmoultwill increasevulnerabilityat this time of year which is oftenwhen largestnumbersof people visit estuaries (see below) Some waterfowl become flightlessduringtheir autumn moult Such birdsseek seclusionand are particularlyvulnerableto human disturbance that causes them to move from safe refuges to areas where depredation risk is greater are thereforeparticularlyvulnerableto severe spellsoutside this midwinterperiod, either in early winter whilst stores are still being laid down or in late winter/earlyspring when stores are declining.In early winterfood intake must exceed daily needs for stores to be accumulated, so althoughdisturbancemay have no obvious impact at the time it may delay the timingof energy store gain, so increasingvulnerabilityto later periodsof severe weather In spring and autumn many waterfowl are gaining large stores of fat and proteinin preparationfor their major migrationsbetween Arctic breeding groundsand their winteringgroundsin Europe and Africa Duringthese periodsdaily food requirementsare high and some evidence indicatesthat birds are feeding at or near their maximum attainable intake (Ens et al 1990) These problemsof achieving high food intakes appear particularlyacute in springwhen birds are migratingon very tight schedules so as to reach breeding groundsat the righttime Hence in spring(especiallyfrom late April to late May) disturbancethat reduces net energy gain could lead to birdsmigratingto their breedinggrounds with reducedenergy stores In some years, arctic wadersneed to draw heavilyon theirstoressoonafter arrivingon breedinggrounds.If springsnow-meltis late and weather conditionsare bad, reduced energy stores may affect breedingsuccessand even adult survival (see Boyd 1992; Davidson & Morrison 1992) Several studiesof disturbanceduringmigratorystaginghave lOO indeed shown populationeffects includingreductionsin numbersof birdsusingstagingareas (e.g Pfisteret al 1992) and substantialincreasesin daily energy expenditurethat exceeded the compensatorycapacity of the birds (Belanger& Bedard 1990) It is also possible that a disturbance-influenced redistributionin early autumn may influencebird distributionlater in autumn and in winter Knowingabout such movementsis importantin interpretingeffectsof disturbance.Observedbirddistributionslater in the year may reflect the past historyof human disturbance, especiallyif such redistribution involvesmovingto a differentestuary, ratherthan disturbanceobservedat the time (see also Smit & Visser 1993) Which species are most vulnerable? The type and scale of responseby differentwaterfowlto disturbance is very variable Even the same species of bird can react in differentways at differenttimes and on differentestuaries- for example sometimesby habituatingto repeated disturbance and at others becomingincreasinglynervods.For example Redshanks Tringa totanusfeeding in narrowtidal creeks with frequentpassers-byon the shore may tolerate people within20 m, yet Redshankson some large estuariesfly off when a person is stillover 100 m away It is not clear which circumstances lead to habituationand which to disturbance.Amongstfactors implicatedin such variabilityare time of year, time of tide, weather conditions,flock size, feeding success, type of disturbingagent and past historyof disturbance Some general patternsare, however, emerging from all this variability.Some bird species (e.g Brent Goose, Redshank, Bar-tailedGodwit Limosa lapponicaand Davidson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge Curlew Numenius arquata) are more 'nervous'than others (e.g Oystercatcher,TurnstoneArenaria interpres and Dunlin Calidrisalpina) The presenceof just one person on a tidal flat can create a surprisinglylarge cordonsanitairein which birdsstop feeding or fly off, in one study rangingfrom about for gulls and 13 for Dunlinsup to 50 for Curlews (Smit & Visser 1993) So a few people evenly scatteredover the tidal flats can preventbirdsfeeding in a large area of many estuaries (see below) However, in extreme cases, for example Wigeon on parts of the Exe Estuary, it can even be just one disturbanceincidentat the wrong time that deters birdsfrom feeding untilthe next tidal cycle (Fox et al 1993) What is most disturbing? There are also general patterns about who and what causes most serious disturbance Several to estuarine waterfowl widespread and long-lastingdisturbance often comes ,'rom aircraft, and that the slower the aircraft the worse the disturbance- helicopters,microlights,and light aircraft (even when not low-flying)disturbmore than jets (Smit & Visser 1993; Stock 1993) Fast (jet) planes also cause disturbancewhen flying low over feeding grounds and roosts(Koolhaas et al 1993) although it is not clear whether the disturbanceis induced more by the sudden loud noise or the planes' movement On the tidal flats, moving people and animals (especiallydogs) generallycreate worse disturbance than people who stay in one place for some time However, note that even these static types of use can cause major disturbanceif they are intensiveand/or widespread From water, close approach to roostingflocks on or causes serious disturbance there too On many Britishestuariesmany differenttypes of recreational activitytake place, so the potential for synergisticeffects and impacts is considerable For example Table shows that out of the 155 British estuarieshalf or more of 18 categoriesof aquatic-based recreationoccurredon 52 estuaries (34% of British estuaries)and that only six estuaries, mostlyin northern Scotland, had no aquatic recreation recorded Diverse aquatic recreationaluse is particularlycommon in Table The frequenceof occurrenceof some widespread recreational activities on the British estuarine resource Data on the 155 Britishestuaries gives known occurrence in 1989 and studies have now found that the most near the shoreline of the estuaries in Great Britain (Table 1) So birds movingto a differentestuary as a disturbanceavoidance responseare very likelyto find many activitiescapable of causingdisturbanceoccurring In additionsince for many waders feeding is best on the tidal flats close to the water's edge, close approachesto muddyshores both by sailed craft (especially sail-boards)and high-speedpowered craft create major disturbancealso to feeding birds Approachesfrom the water seem generally to disturbbirds more than from land: e.g in one study Curlews flew from a sail-board at 400 m away compared with about 100 m from a walker (Smit & Visser 1993) comesfromJNCC's EstuariesReviewdatabasebeing developedfrom the work of the NCC EstuariesReview (Davidsonet al 1991) Activity No % 75 125 88 66 76 106 132 116 140 44 69 48 81 57 43 49 68 85 75 90 28 45 Golf-courses 47 30 Light aircraftflying 43 28 Power-boating Sailing Sail-boarding Water-skiing Canoeing Bathing/generalbeach use Angling Walking/dogwalking Bird-watching Motor-cycling Horse-riding Table Examplesof the diversityof differentaquatic-based recreational activities on British estuaries Data on the 155 Britishestuaries gives known occurrence in 1989 and comes fromJNCC's EstuariesReviewdatabasebeingdevelopedfrom the workof the NCC EstuariesReview(Davidsonetal 1991) Country Where? A widespread view of human disturbance to waterfowl suggeststhat conflictis not a major issue because as birds are mobile they can readily fly elsewhere to avoid the disturbance.Ecologicaltheory (see above) shows that the solutionis not usually so simple Furthermore, activitieswith disturbance potential not occur in isolationfrom each other, nor in only one place Surveys compiledin 1989 by the Nature ConservancyCouncil's Estuaries Review found, for example, that many recreationalactivitieswere taking place on half or more Britishestuaries Total no of estuaries* No with > 50% % with > 50% of activitytypes activitytypes England 81 35 43 Scotland Wales 50 28 14 50 155 52 34 Great Britain 12 * total for each countryincludesthose estuariesshared between two countries,e.g Severn, Dee, Solway 101 Dawdson & Rothwell: Human disturbanceto waterfowl on estuaries:conservationand coastal management implicationsof current knowledge 5OO I i I for feeding will tend to exacerbatesuch disturbance problemssince some shy species generallyavoid feedingon narrowshores(e.g Bryant1979) I 4OO Dunlin ß No ß of people 300 200 Redshank 100 1,000 • ••' 2,000 Curlew • 3,000 4,000 5,000 Area of tidal flats (ha) F•gure2 The numbersof mobilepeoplewho, if evenlyspaced,would d•sturbthree differentwader species(Redshank,Curlewand Dunlin) from different areas of tidal flats, derived from data in Smit & Visser (1993) Wales and parts of England,with few Scottishestuaries beingusedfor morethan eightaquaticactivities.A similarpatternof multiple-purpose use of estuaries occurs for land-based recreation Furthermore there tendsto be a greaterdiversityof recreationalactivityon estuariesthat form part of the Ramsar/SPA networkof internationallyimportantsites: internationally-important estuariesaverage 6.7 activities/estuary; other estuaries average5.1 activities/estuary So in Britainthere is at least potentialrecreationaldisturbanceto waterfowlin many places,and from many differentactivitiesin any one place,withestuariesin Wales and southernand eastern England having most potentialpressure The size of the area available to birds may also affect levels of disturbance:on small estuaries there may be few alternative locationsavailable for birds moving away from a disturbance,and it takes only a few activitiesin differentplaces to make much of such an area untenable to birds of some species A hypothetical example is shown in Figure 2, which showsthe cumulative size of a minimum cordon sanitaire created for differentwader species disturbedby increasing numbersof mobile people This impliesthat for some shy speciessuchas the Curlewas few as 20 evenly distributedpeople could preventbirdsfrom feeding on over 1,000 of estuary, an area of tidal flats equivalent to estuaries such as Hamford Water or Southampton Water Of course it is highlyunlikelysuch a 'worst-case' situationwould ever occur, not least since many parts of the tidal flats of estuaries are too soft for people to move on them (e.g.Goss-Custard& Verboven1993) Nevertheless,such figuresdo give an indicationof the considerablepotentialfor disturbancefrom intensificationof human activityeven where it involves quitesmallnumbersof people.Land-claimwhich narrows the width of intertidal shore available to birds 102 Like the presence of birds on estuaries many recreationalactivitiesshow marked seasonalityand many are restrictedto a few of the suite of habitats on coasts and estuaries This means there are complex patternsof both geographicaland temporal overlap between birds and people This is illustratedin Figure Differentwaterfowl are present on estuaries throughout the year, but their habitat usage differsseasonally Most species breed chiefly on the upper parts of sandy beaches,shingleridgesand saltmarshes,as well as on coastalgrazing marshesand other grasslands,and relativelysmall numbersuse tidal flats for feeding In contrast,when arctic and boreal breeding populations return in autumn and early winter they utiliseall habitats (exceptfor generallylittleuse of maturesand-dunes)for feedingand for roosting,this usage continuinguntillate spring(Davidson& Stroudin press).However,many recreational activities occur chiefly in late summer and early autumn, leadingto littleoverlapwith periodsof main bird usage of some habitats.Activitiesthat occur throughoutthe year, or largelyin winter,can carry a high riskof causingdisturbance.However,it is probably the late summer/early autumn period (and sometimes also in spring)when most recreationalactivitiestake place, intensityof use is greatest,and waterfowlare most vulnerable This period coincideswith the latter part of the breeding period for local breeders and particularlywith the arrivaland moultingof the more northerlybreeding populations Interestinglyit seems that sand-dunes(in winter)and saltmarshes,particularlythose with well developed creek systems restrictingaccess, may be the habitats where waterfowl are least vulnerableto anthropogenic disturbance Even so there are places where bird use even of saltmarshesdoes appear to be restrictedby recreationaluse, for example of parts of the Wadden Sea by spring-stagingBrentGeese (Stock1993) However, it is firm, sandy flats, sand beaches and shingleridgesthat oftenseem to be amongstthe most widelyand intensivelyused by both peopleand birds, and where conflictsmay be most common (see e.g Pfister eta/ 1992) InevitablyFigure is a generalisationand masks what can be major differencesbetween differentestuariesin the patternof uses and the overlapsof birdsand people.Suchvariationcan oftenarisethrough differences of ease of access to the shoreline NeverthelessFigure3 does give some pointersto where conflictof use is most likelyto arise It also showsthat some activities,notablylow-flyingby light aircraftand micro-lights,affectthe wholeestuarine resourcerather than just some habitats.This, coupled with the relativelywide-scaleand long-lastingeffectson Davidson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge Season Spring Habitat Summer Autumn Winter * GR SD SB SH SM MF SF SL ()W A Birds Breeding * o * ß * o o o o * * * * * o * * o * * * * o ß ß ß ß ß ß ß Migratory staging Wintering B People Bathing Bird-watching Walking Bait-digging Wildfowling * Sailing Sail-boarding Light aircraft flying ß ß 0 ß ß ß ß Key: majorseasons andhabitatsof use minor seasons and habitats of use * Habitattypesare: GR grasslands; SD sanddunes;SB sandbeaches; SH shingle;SM saltmarsh; MF mudflats;SF sandflats;SL shoreline;OW openwater Figure3 Seasonaloccurrenceof birdsand selectedrecreationalactivities,and theirusageof estuarinehabitats waterfowlinducedby low-flyingaircraft,place this activityamongstthe mostcapableof creating widespreadand seriousdisturbanceto waterfowl.It may also be amongstthe mostdifficultto controllocally without zonation with little or no damaging effects, there are widespread examples where effects and impacts of varyingseverityhave been described,despite the complexityof unravellingsuch multifactorial phenomena Clearly people's recreationaland other uses of estuaries MANAGING FOR WATERFOWL DISTURBING ACTIVITIES AND POTENTIALLY Althoughthere are many instancesin whichwaterfowl and people appear to co-existon estuarieswith or can and lead to disturbance to waterfowlwith often uncertainconsequences,so the guidingprincipleof managingfor human activitiesin areas that supportimportantwaterfowl populations needs to be one of avoidanceor limitationof overlap throughtemporal and Iocationalzoning Unlike some 103 Davidson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge other estuarine activities there is often considerable potentialfor flexibilityin the pursuitof recreationaluses of estuaries The potentialeffects and impactsof disturbancehave been widely recognisedin wildlifeconservation legislationand agreements, as has the need to develop conservationmeasures for birds whilsttaking into account human uses For example Article 4.4 of the EC Directiveon the Conservationof Wild Birds requires Member States to 'take appropriate steps to avoid any disturbancesaffectingthe birds, in so far as these wouldbe significanthavingregardto the objectivesof this Article'.These objectivesare the takingof special conservationmeasuresconcerningthe habitatof Annex I species (includingmigratorywatedowl) in order to ensure their survivaland reproductionin their area of distribution.In its judgementon the recent LeybuchtBay (Germany)case the EuropeanCourtfoundthat the significanceof the disturbancerelated to the level at a single site rather than at the populationlevel e.g involvinga populationdecline Other internationalagreementsincludethe recognition of the need to manage disturbingactivities.The forthcomingAfrican/Eurasianand Asian/Australasian Waterfowl Agreements have a series of action plans which include the need for range states to take measures to reduce the levels of disturbance to migratorywatedowl caused by human activities includinghunting,fishingand other outdoorrecreation The actionplans identifyappropriatemeasuressuch as the establishment of disturbance-free zones in protected areas where no human access is permitted, and the establishmentof core sanctuaryareas withinmajor watedowl huntingareas (IWRB 1993) International conservationplans for individualwatedowl species currentlyunderdevelopmentalso recognisethe impodanceof managingfor recreationaland other disturbance(e.g Stroud in press) They also identifythe need for informationon the pattern and distributionof potentiallydisturbingactivitiesand populationson a watedowl flyway scale, usingcompatiblemethodologies (Davidson et al 1991; in press) Organisationsinvolvedin developingstrategiesfor coastal and estuarine conservation FUTURE There has already been considerablework on the integrationof recreationwith other estuarine uses, and and other estuarine wildlife DIRECTIONS Continuingto developways of integratingthe many different recreational uses on an estuary, both with each other and with migratorywatedowl populationsso as to avoid continuingor increasingpressureon this internationallyimportantpart of our wildlifeheritageis one of the keysto achievingsuccessfulintegrated coastalzone management.The impodanceof achieving such integrationis increasinglyrecognisedas an essentialplank in establishingsustainableuse of estuaries for the future Such integrationcan be achieved in a variety of ways: througheducationand the provisionof information,and throughvoluntaryand statutoryagreements and zonations Implementingthe best approachto minimising disturbanceto watedowl in each locationdependson a good understandingof the behaviour and needs of both birds and people Otherwise there are risksof exacerbatingratherthan reducinga problem,for example by establishingzones in incorrectplaces in relationto bird usage However, for the reasonswe have describedabove such informationis not always available nor easy to acquire A recent workshop (Doody 1993) has identifiedkey topics requiringfurther research on coastal recreation in the UK These include: ß reviewingof currentliteratureand researchon the relationshipbetween ecologicaland recreational within Great Britain also recogniserecreationaland other disturbanceto watedowlas a key issuethat needs addressingin the preparationof integratedcoastal zone management (e.g Rothwell& Housden 1990; EnglishNature 1992) EnglishNature'sinitiativefor the promotionof estuary managementplans based on sustainableestuarineuse includesobjectivesaimed at identifyingand resolving multi-useconflictsso as to avoid damage to estuarine wildlife(Grabrovaz1993) 104 with the needs of waterfowl There are numerousexamples of the developmentof refuge areas and use of zonation (both temporal and Iocational),especiallyin relationto wildfowling(e.g Hirons & Thomas 1993; Madsen 1993; Owen 1993; Townshend& O'Connor1993) as well as attemptsto manage more general leisure and recreationalusage (e.g Kirbyet al 1993) In addition,types of conflict between individualsports and nature conservationhave been assessed by Sidaway (1988) and good practice examples of coastal recreationmanagement,including those aimed specificallyat reducingdisturbanceto waterfowl,are beingwidelypublicised(e.g Sports Council 1992) issues; ß establishingstandardisedmethodsfor assessing recreational impact; ß experimentalwork on habitat and speciesfeatures to establishwhen changes occur in relationto the level and timingof activityand in relationto zoning; ß reviewingpeople's attitudesto recreational disturbanceof ecologicalfeatures; and ß assessingthe vulnerabilityof habitats,speciesand sites in relation to recreational These recommendations uses for research on broader recreational issues than just disturbanceto watedowl Davidson& Rothwell:Humandisturbance to waterfowlon estuaries:conservation andcoastalmanagementimplications of currentknowledge link closely with Cayford's (1993) view that much of the future research should be experimental Much of the research on the topics listed by Doody (1993) would contributevaluably to our understandingof how disturbance affects waterfowl in order to understand Coastal Marine Science 9: 369-385 Burd,F 1992 Erosionand vegetationalchangeon saltmarshesof Essex and north Kent between This current volume helps to increase the availabilityand variety of the existinginformationbase In doing so it clearly reveals the need for further research Bryant,D.M 1979 Effectsof prey densityand site characteristicson estuary usage by overwinteringwaders (Charadrii).Estuanne & the ways in which a wide variety of factors influencethe extent, effect and impactof disturbanceto estuarine waterfowl 1973 and 1988 Research & surveyin natureconservationNo 42 Nature Conservancy Council, Peterborough Cayford, J 1993 Wader disturbance:a theoretical overview Wader Study Group Buff.68 (Special Issue) Davidson,N.C 1981 Survivalof shorebirds(Charadrii)duringsevere weather: the role of nutritionalreserves Pp 231-249 in N.V Jones& W.J Wolff(eds.),Feedingand survivalstrategiesof Additionally,we believe that much more effort is requiredto achieve an understandingof fluctuationsin populationsizes of speciessite by site, regionby region and flyway by flyway The opportunitiesto examine impactsof permanenthabitat losscaused by developmentor coastalsqueeze shouldbe exploited They could tell us much about the behaviourof individualsand populationsin responseto major perturbations.We would also encouragethe increasein the use of major experimentationon populations.The massive impactson distributionand populationsize caused by removingor imposingreserve statusor on the commencementor cessationof a disturbingactivity such as shooting,mud walkingor militaryuse deserves greater attention Such work has to be on a truly internationalscale Only by examiningthe full geographicalrange of a species and the factors influencingits distributionand survivalwill we be able to begin to answer some of the questionssurrounding sustainabilityand maintenanceof biodiversity to waterfowl and REFERENCES Belanger, L & Bedard, J 1990 Energeticcost of man-induced disturbance to stagingSnow Geese J Wildl.Management 54: 36-41 Bell, D.V & Fox, A.D 1991 Shootingdisturbance:an assessment of its impact and effects on overwinteringwaterfowl populationsand their distributionin the United Kingdom Report to Nature Conservancy Council by Wildfowl & Wetlands Trust and BritishAssociationfor Shooting& Conservation Boyd, H 1992 Arcticsummerconditionsand BritishKnot numbers: an exploratoryanalysis Wader Study GroupBuff.64, Suppl.: 144-152 man-made and man-modified wetlands in the enhancement of the survivalof overwinteringshorebirds.Colonial Waterbirds9' 176-188 Davidson,N.C., Laffoley,D d'A., Doody,J.P., Way, L.S., Gordon,J, Key, R., Drake, C.M., Pienkowski,M.W., Mitchell, R & Duff, K.L 1991 Nature conservation and estuaries in Great Britain Nature ConservancyCouncil,Peterborough Davidson,N.C & Morrison,R.I.G 1992.Time-budgetsof prebreedingKnotson EllesmereIsland,Canada WaderStudy Group Buff.64, Suppl.: 137-143 Davidson,N.C & Rothwell,P.I (eds.) 1993 Disturbanceto waterfowl on estuaries.Wader StudyGroupBuff.68 (Special Issue) Davidson,N.C., Rothwell,P.I & Pienkowski,M.W In press.Towards a flywayconservationstrategyfor waders Proc 1992 WSG Odessa Conference.Wader StudyGroupBuff.,Special Issue Greece, April 1993 Doody,J.P 1993 Workshopon "Coastalrecreationecologyresearch needs" Coastal News 2/93: in press We thank also David Stroudand Ken Norrisfor providinginformation and helpfulcommentson earlier versionsof this paper, and AphroditeNiggebruggefor preparingthe data used in Tables Davidson,N.C & Evans,P.R 1986 The roleand potentialof conservation: conservingcoastalhabitatnetworkson migratory waterfowlflyways.Proc.4th EUCC Congress,Marathon, The synthesisin this paper could not have been made withoutthe contributionsto the presentationsand discussionsat the originalNCC/RSPB workshopon disturbance Davidson,N.C & Evans, P.R 1982 Mortalityof Redshanksand Oystercatchersfrom starvationduringsevere weather Bird Study 29: 183-189 Davidson, N.C & Stroud, D.A in press Internationalcoastal ACKNOWLEDGEMENTS recreational estuarineorganisms.Plenum Press, New York EnglishNature 1992 Caringfor England'sestuaries.An agenda for action EnglishNature, Peterborough Ens, B.J., Piersma,T., Wolff,W.J & Zwarts,L (eds.) 1990 Homewardbound:problemswadersface when migratingfrom the Bancd'Arguin,Mauritania,to theirnorthernbreeding groundsin spring.Ardea 78(1/2) Evans, P.R., Davidson, N.C., Piersma, T & Pienkowski, M.W 1991 Implicationsof habitatlossat migrationstagingpostsfor shorebirdpopulations.Acta XX Int Orn Congr.:2228-2235 Fox, A.D., Bell, D.V & Mudge,G.P 1993 A preliminarystudyof the effectsof disturbanceon feedingWigeon grazingon Eel-grassZostera Wader StudyGroupBull.68 (Special Issue) Grabrovaz,M 1993 Strategyfor the sustainableuse of England's estuaries.ConsultationDocument.EnglishNature, Peterborough Goss-Custard, J.D & Verboven,N 1993 Disturbance andfeeding shorebirdson the Exe estuary.WaderStudyGroupBull.68 (Special Issue) 105 Dawdson & Rothwell: Human disturbanceto waterfowl on estuaries:conservationand coastal management implicationsof current knowledge H•rons, G & Thomas, G 1993 Disturbance on estuaries: RSPB nature reserve experience Wader Study Group Buff.68 (Special Issue) International Waterfowl & Wetlands Research Bureau 1993 The African/Eurasian WaterfowlAgreement and the Asian/AustralasianWaterfowlAgreement.Two Agreements under the Bonn Convention Action Plans, Proposed Structure IWRB, Slimbridge K•rby,J.S., Clee, C & Seager, V 1993 Impactand extentof recreationaldisturbanceto wader roostson the Dee estuary: some preliminaryresults WaderStudyGroupBuff.68 (Special Issue) Koolhaas,A., Dekinga,A & Piersma,T 1993 Disturbanceof foraging Knotsby aircraftin the DutchWadden Sea in August-October 1992 Wader Study Group Buff.68 (Special Issue) Madsen, J 1993 Experimentalwildlifereservesin Denmark:a summaryof results.WaderStudyGroupBuff.68 (SpecialIssue) Prater, A.J 1981 Estuary birds of Britain and Ireland T & A.D Poyser, Berkhamsted Rothwell, P.I & Housden, S.D 1990 Turning the Tide A Future for Estuaries.The Royal Society for the Protectionof Birds, Sandy Schultz, R & Stock, M 1993 Kentish Plovers and tourists:competitors on sandycoasts?WaderStudy GroupBuff.68 (SpecialIssue) Sidaway, R 1988 Sport, recreationand nature conservation.Sports Council and Countryside Commission, London Smit, C J & Visser, G.J.M 1993 Effects of disturbance on shorebirds:a summaryof existingknowledgefrom the Dutch Wadden Sea and Delta area Wader Study Group Buff.68 (Special Issue) Sports Council 1992 Heritage Coasts.Good practicein the Planning, Managementand SustainableDevelopmentof Sportand Active Recreation Factfile Countrysideand Water Recreation Sports Council, London Owen, M 1993 The UK shootingdisturbanceproject.Wader Study Group Buff.68 (Special Issue) Pfister,C., Harrington,B.A & Levine,M 1992 The impactof human disturbanceon shorebirdsat a migrationstagingarea Biol Cons 60:115-126 P•enkowski, M.W., Ferns, P.N., Davidson, N.C & Worrall, D.H 1984 Balancingthe budget:measuringthe energyintakeand requirementsof shorebirdsin the field Pp 29-56 in P.R Evans, J.D Goss-Custard& W.G Hale (eds.), Coastal waders and wildfowlin winter Cambridge University Press, Stock, M 1993 Studies on the effects of disturbanceson staging Brent Geese: a progressreport Wader Study GroupBuff.68 (Special Issue) Stroud, D.A in press The developmentof an international conservationplan for the Greenland White-frontedGoose IWRB Special Publ Swennen, C., Leopold, M.F & de Bruijn, L.LM 1989 Time-stressed oystercatchers,Haematopusostralegus,can increaseintake rate Anim Behav 38: 8-22 Cambridge Townshend, D.J & O'Connor, D.A 1993 Some effects of disturbance P•enkowski,M.W 1993 The impactof tourismon coastal breeding waders in western and southernEurope:an overview Wader Study Group Buff.68 (Special Issue) to waterfowlfrom bait-diggingand wildfowlingat Lindisfarne National Nature Reserve, north-east England Wader Study Group Buff.68 (Special Issue) * 'Effects'and 'impact'are usedin the biologicalsense:i.e effect=observed response;impact=implies reductionin survivalat individual or populationlevel 106 ... Hale (eds.), Coastal waders and wildfowlin winter Cambridge University Press, Stock, M 1993 Studies on the effects of disturbanceson staging Brent Geese: a progressreport Wader Study GroupBuff.68... meeting and this volume would not have happened Copyright¸ 1993 by the Wader StudyGroup(WSG) Publishedby the RSPB and the Wader Study Group, w•th financial assistance Committee of the U.K Joint... the end of summer when food is abundant and weather mild, waders generallyseem to have littledifficultyin meetingenergy needs Even so, waders seem to concentrateon large estuarieswhen moulting,and