Can we recreate or restore intertidal for shorebirds?

PHILIP W. ATKINSON

British Trust for Ornithology,The Nunnery, Thetford,Norfolk IP24 2PU, UK, e-maih phil.atkinson @bto. org

Atkinson,P.W. 2003. Can we recreateor restoreintertidal habitats for shorebirds? StudyGroup Bull. 100: 67-72.

Lossof intertidalhabitat to developmentcontinues apace. Coupled with the long-termeffects of climatechange therewill be an increasingneed to createnew areasof intertidalhabitats if shorebirdpopulations and flyways areto be effectivelyconserved. restoration and creation efforts in the US, Europeand Japan have shown that creatingsalt marshis often a hit or miss affair as new sitestend to supportdifferent communities and a differentrange of ecologicalfunctions to surroundingareas. Creating often meets with a higherdegree of successif sedimentsupply is sufficientas benthicinvertebrates and shorebirdscolonise relatively quickly. Sitesin higherenergy environments tend to reachequilibrium quicker than lower energyenvironments. Many restorationsites tend to be small and thus factors,such as enclosure,tend to impact on the that use the sites.Not only do thefactors controlling the restoration need to be betterunderstood so that high quality habitats canbe producedbut alsothe impactsof creatingnew habitatson shorebirdsat the populationlevel. This will requirea muchbetter understanding of flyways,migration strategies and other factors controlling populations at a large scale.

INTRODUCTION many countrieswhere this hasbeen an issue,there has been an acceptancethat lossof habitatswill needto be compen- One of the greatestthreats facing shorebirds has been the loss satedfor by the restorationor creationof new habitats. or degradationof breeding,staging and winteringhabitats. Many countriesnow have a policy of compensatingfor This has been global in extent and there is probably not a lost habitats. The compensationwill vary in re- flyway that has not been affected by large-scaleloss and sponseto eachparticular situation, e.g. compensationfor a deterioration of wetland habitat. Total wetland loss world- the lossof an areathrough development will be very differ- wide has .been estimated at 50% of those that have been in ent to the strategyused to mitigatethe widespreadeffects of existencesince 1900 (Dugan 1993, OECD 1996). In north- changingclimatic conditions and accelerating -level rise. em countriesmuch of thisloss took place during the first half Compensationfor loss of a particularsite usually involves of thetwentieth century but during the latter part, tropical and the creation of a new site elsewhere. Solutions to sea-level sub-tropicalwetlands were increasinglybeing degradedor rise will necessarilyinclude a larger scale approachwhich lost, predominantlythrough conversion to agriculturaluse, will include a mix of maintaining sea defences which is the major causeof wetland loss worldwide. By throughsoft or hard engineeringtechniques, abandonment 1985, it was estimated that 56-65% of had been or managedrealignment, i.e. takingback sea walls andcreat- drainedfor intensiveagriculture in Europeand North America, ing intertidalhabitats (Dixon et al. 1998).There is hugepoten- 27% in Asia, 6% in South America and 2% in Africa, a total tial to replace lost areas and create valuable habitat for of 26% lossto agricultureworldwide (OECD 1996). These waterbirds. figures mostly refer to freshwaterhabitats and the global The sciencebehind the restorationand creationof many coastalwetland resourceis generallypoorly known. How- terrestrialhabitats is well advanced.However, intertidal habi- ever, changeswithin thesehabitats (including tidal flats, salt tats posespecial problems for restorationbecause they are ,sea grass beds, , saline , shingle topographicallyand ecologicallycomplex and they support banks and transitional brackish- habitats) have been many speciesof animals, some of which require specific everybit aslarge asfreshwater habitats. In the United King- habitatsand linkagesto other terrestrialor . dom, 23% of and 50% of salt marshes have been Moreoverthey exist and evolve within dynamiccoastal set- drained since Roman times (Davidson et al. 1991, Moser et tings,subject to changingtidal levels, and long term al. 1996). mechanicalprocesses that are associatedwith sea-levelrise Added to this continuinganthropogenic loss will be the andclimate change (Atkinson et al. 2001). Often thesecom- creeping effects of changing environmental conditions plexities are ignored and there is a tendencyfor created throughclimate changeand rising sea levels. As a result, coastalhabitats to lack the diversityseen in naturalareas and managersof estuarineand open shorehabitats, which sup- supportonly generalistspecies. Also, created sites rarely portimportant populations of waterbirds(defined here as any follow expectedpaths and the stablestates that are reached speciesdependent on wetlandhabitats at any time duringits often differ from what was expected,despite multi-million lifecycle),will facenew challengesto mitigatethe effectsof dollar investments(Zedler & Callaway 1999), leadingto the both direct habitat loss and thesechanging environmental conclusionthat the currentstate of restorationtheory applied conditions.The responseto thesechanges will differ, but in to coastalhabitats does not necessarilylead to predictability. 67 Bulletin100April2003 68 Wader Study Group Bulletin

To effectivelymitigate this loss,there is a greatdeal to in the . Although only a fraction of the area learn,not only aboutthe processesunderlying coastal habi- presentabout 2,000 yearsago, theseintertidal habitats are tat restoration or creation, but also those that control the still the largestcontiguous area of salt marshin Europe,and shorebirdpopulations that many of theseareas will be created the Wadden Sea is Europe'slargest cov- for. The purposeof thispaper is to assessthe stateof know- eringsome 8,000 km 2. However,in the50 yearsto 1987, ledgeabout creating or restoringsalt marshes and tidal flats 33% of the areawas lost to embankments(Dugan 1993) and for shorebirds,and to ask what we need to know to be better new marshes formed in front of the new sea walls. Within equippedto predictthe outcomes of creationand restoration The , there are over 17,000 ha of man-made salt effortson shorebirdpopulations. As mostresearch has been marshes,created specifically for defence purposes carded out on thesetwo habitats,this paper concentrateson rather than for any other environmentalbenefit (Esselink them.However, it mustbe acknowledgedthat much needs to 1998).This policyis changingand salt marshes on theNorth be doneto addressthe issuesof creatingand restoring other Seacoasts of ,Belgium, The Netherlandsand Den- intertidal habitatssuch as mangrovesand sea grassbeds mark,which are of high conservationimportance because of whichare alsoimportant for waterbirds(e.g. Field 1968). the large concentrationsof wintering,passage and breeding waterfowl that they support,are now increasinglybeing CURRENT STATE OF COASTAL WETLAND managedfor natureconservation purposes (Esselink 2000). RESTORATION SCIENCE Again little hasbeen published in the peer-reviewedlitera- ture althoughthe createdmarshes at Sieperdain The Neth- The scienceof restoringcoastal habitats has been developed erlandsare a notableexception (Castelijns et al. 1997, Eert- in the for three decades and there is now a mann et al. 2002). substantialand growing body of literaturecovering the ex- Elsewherein the world,Japan has led the way in creating pertisethat has been acquired there on the creationand re- tidal mudflatsand, according to the EnvironmentAgency of storation of wetlands. Of most relevance to this review, are Japan,37 coveringapproximately 900 ha were createdbe- those studies that have focussed on efforts to create and re- tween 1973 and 1998 (WAVE 2001a,b). This is small com- storetidal wetlands(e.g. Broome et al. (1988), Zedleret al. paredto the lossof nearly4,000 ha (42% to reclamation) (1988) & Zedler (1996)), despitethe fact thatmany of them over the sametime period(WAVE 2001a,b).The total area have concentratedon physicalfeatures with only limited of tidal flats in Japanis 51,443 ha (EnvironmentAgency of monitoringof , andinvertebrates. This has culmi- Japan1997). Six of thenewly created mudflats were directed natedin the productionof practicalhandbooks for the re- towardscreating areas for birds,but there are few accessi- storationof tidal wetlands(e.g. Zedler 2001). A recentspe- ble data with which to assess success. cial issueof WetlandsEcology and Managementfocused Researchhas therefore been geographically rather limited uponthe beneficial use of dredgematerial for therestoration andfocussed on particularhabitats or .One of the of US salt marshesand mudflats (Streever 2000). Unvege- largestissues, rarely tackled in moststudies, has been a de- tated mudflats are not classed as wetlands under S.404 of the tailed assessmentof the physical,temporal and biological US and thus intertidal habitat creation work factorsthat determinethe resultinghabitats and communi- in the US has focussed on the creation of salt marshes. As a ties and how theserelate to the rangeof variationfound in consequence, creation schemes in theUS haveusu- naturalareas. Most studieshave simply describedthe bio- ally beenmotivated by a desireto disposeof dredgedmater- logicalcommunities and the changeswithin them.Restora- ial ratherthan by natureconservation concerns. tion schemesare also generally small (both in extent and In NW Europethe experienceof creatingnew habitat, number)compared with surrounding"natural" areas. Where especiallymudflats, is fairly limitedand the useof dredge comparisonsare made, the high variability exhibited by natu- material or managedrealignment to createor restoreareas ral areasoften hides differencesin the sampledattributes hasoften been haphazard with little or no monitoring.Again, between createdand restoredsites and surroundingnatural few studieshave monitored the impacton shorebirdsthough areas.This meansthat results from many studiesmay notbe therehave been some. In particular,a createdmudflat on the applicableat a larger(i.e. regionalrather than site) scale. Teesestuary, NE ,has been monitored intensively This makes the definition of a "successful" restoration andthis has provided valuable information on benthic inver- quitedifficult, given that natural habitats are very varied and tebratesand shorebirdusage (Evans et al. 1997, 2001). In restorationsites tend to be small.It may be thatwe canonly addition,managed realignment sites at Toilesburyand Orp- createa subsetof naturalhabitats and thus any wetlandhabi- landson the Blackwaterestuary, SE England,have been tat createdcould be thoughtof as a success.Therefore to be monitoredfor plants, and birds (Reading et al. able to restoreor createhabitats for shorebirdssuccessfully, 2000, Atkinsonet al. in pressb). they shouldexhibit the functionsand processeswithin the Themajority of papersabout managed realignment in the variationfound in surroundingnatural habitats at a rangeof UK have concernednon-biological processes such as - spatialscales. In manycases, this will meanallowing dynamic chemicalchanges, tidal exchange,persistence of saltmarsh changeto takeplace, e.g. allowinghabitats to shiftupshore in unmanagedretreat sites and policy related to managed in relation to . In estuaries,it meanstaking a realignment(see Atkinson et al. 2001 for list). It is perhaps strategicapproach at the level, using the whole not surprisingthat little has been publishedin the peer- estuaryas a functionalunit rather than concentratingon reviewedliterature on thebiological aspects, as sites at which particularvulnerable areas within the .This type of habitatcreation or restorationhas been practised in the UK approachhas the advantage of allowephemeral habitats such are generallyless than five yearsold. assaline lagoons and fresh/ transitional habi- Largeareas of man-mademarshes and flats are found tats,which are importantfor shorebirds,to remain.

Bufferin 100 April 2003 Atkinson. Can we recreate or restore •nterhdal habitats for shoreb•rds? 69

WHAT DO STUDIES TELL US SPECIFICALLY al. (1995) showedthat the higher length of openwater/ ABOUT SHOREBIRDS? interfacein restoredsites caused a higherusage by shorebirds whereasthe lack of a maturesalt bush (Ivafrutes- Are created/restoredsalt marshesequivalent to natural certsand Baccharishalmifolia) led to a lower usageof the marshes?Despite waterbirds, and shorebirdsin particular, restoredmarsh by passerines. being an importantcomponent of coastalecosystems, few In Galveston,Texas, speciesrichness and diversitywas intertidal habitatrestoration schemes have specificallytar- higherin the naturalmarshes due to the presenceof migra- getedthis group,unless specialist or endangeredspecies are tory waterfowl,wintering shorebirds and salt marshspecial- involved(e.g. Light-footedClapper Ralluslongirostris istssuch as rails andmarsh sparrows (Melvin & Webb 1998). in the United States).The resultsof the few studiesin the US The assemblageon constructedsites was dominated by that haveassessed usageon restoredor createdSpartina and , which nested on the surroundingunvegetated dominated marshes are mixed. Both natural and restored .The main conclusionfrom thisstudy was that created marshesprovide habitats for birds,but not necessarily for the saltmarshes provided bird habitat,but not necessarilyfor the same communities.For example in GalvestonBay, Texas, samespecies assemblage as natural salt marshes. The reasons shorebirdusage and diversity was higher on naturalmarshes for the differenceswere thoughtto be dueto the natureof the dueto a greaterdiversity of habitatsin naturalareas (Melvin sites.All of the createdmarshes were on smooth,gently slop- & Webb 1998). However, Havens et al. (1995) found that, ing shorelinesexposed to wave action and containedflat althoughwaterbird was higher in restoredareas, monoculturesof Spartinawith few openings. and tidal they did not hold populationsof Willet Catoptrophorus flats were rare. Natural marshes tended to have more marsh semipalmatus,a marshspecialist, whereas Brawley et al. edgeand open water. Melvin andWebb postulated that created (1998) found that restorationof tidal flow to an impound- marshessupported fewer shorebirdsand rails becausethey ment led to reinstatementof breedingWillet. In a study of were at overallhigher elevation, had lessedge habitat, deep ditched and unditchedmarshes, Reinert et al. (1981) found and steep-sidedchannels and taller and denserSpartina. thatmore open water led to a greaterdiversity of shorebirds. Peaksand troughsin bird abundanceon naturalsalt marshes Overall, the few US studieshave concludedthat, in terms were strongly related to seasonalmigration chronology, of bird usage,functional equivalence of man-mademarshes whereas those in restored areas did not. This indicated that with naturalmarshes may or may not occurand much of this natural marshesprovided habitat that was not available in is due to differencesin habitatbetween the two typesof site. nearbycreated salt marshes. In mostcases, macrofauna (including birds) colonise quickly Salt marshesin the UK and US show very different andthe assemblagereaches maturity in a shortspace of time, characteristics,ones in the US tendingto be peatrather then often lessthan threeyears, e.g. at the Gog-le-hi-tewetland sedimentbased. One frequentdifference between restored (Simenstad& Thom 1996). At this site, the taxa richnessof and natural marshes in both the UK and US, is the consoli- epibenthicorganisms, and densityof fishesall ap- dated of the in restored and created salt proachedasymptotic trajectories (i.e. stability)within three marshes(due to re-wettingwith salt water), as well as their to five years of restoration,but the numbersof birds using lack of naturalcreek systems, smooth topography and poor the sitecontinued to increaseover the sevenyear durationof . Re-wetted sedimentsin the UK tend to be ex- the study.Despite these rapid responses by fish,invertebrates tremely hard and tabularin form and thus,if sedimentdoes and birds, the restoration, creation and enhancementof the not come in from the surroundingarea and settle,these hard estuarinemarshes appears to havebeen problematic (Zedler mudhabitats are inhospitable environments for invertebrates 1988, Moy & Levin 1991), as measurementsof other eco- andplants. This haslead to reducedstructural diversity and logical functionsindicated that this particularwetland was differencesin vegetationcommunities on someof the natu- in an early stageof maturity.Few predictabletrajectories of rally-regeneratedmarshes in SE England. communitydevelopment were evident and few indicated Althoughnot a shorebird,the Englishpopulation of Twite systemmaturity. For example,the organiccontent, chloro- Carduelisfiavirostriswinters exclusively on saltmarshes and phyll/phaeophytinpigments and the infaunataxa richness feeds on some restoredsalt marshes.Atkinson (1998) com- and density increased slowly or remained relatively de- paredusage of naturallyrestored salt marshes by Twite with pressedover the samethree to five yearsof monitoring,but surroundingareas. Twite feedon the seedsof Salicorniaspp. productionshowed a gradualprogression towards andthe pioneer communities dominated by thisspecies were referencemarsh levels. Simenstad & Thom (1996) alsopoint absentfrom many of the restoredmarshes. The sitestended outthat many "functional trajectories" are unpredictable and, to be , highlydissected and poorly drained, except around due to the short-termnature of monitoringprojects, it is creekedges. Consequently, the vegetationcommunities were impossibleto understandwhy trajectorieseither converge, dominatedby a rank mix of grassPuccinellia diverge,fluctuate or achievean alternativestable state to ref- maritima and Sea PurslaneHalimione portulacoides and erence areas. lacked the diversity found on surrounding"natural" areas Differencesin habitatare oftencited asreasons why bird even thoughsome of the restoredsites were more than 100 assemblagesare not the same in restored and reference yearsold. It is thereforeunlikely that they will ever reacha marshes. Havens et al. (1995) showed that a constructed statewhere they will be colonisedby Twite. This studyin- marsh in Sarah's Creek in Virginia supportedfar fewer dicatesthat, becausecreated marshes in SE Englandtend to Marsh Wrens Cistothoruspalustris than natural marshes be different from natural marshes, other such as becausethe band of Spartina on the restoredmarsh was too RedshankTringa totanus,which breed extensivelyon salt thin. The stem densityand height of Spartina on somere- marshesin NW Europe,may well use createdareas in dif- stored marshes in southern California was unsuitable for ferent ways to natural areas. Light-footedClapper Rails (Zedler 1993). Also, Havenset

Bulletin 100 April 2003 70 Wader Study Group Bulletin

DO CREATED MUDFLATS FUNCTION IN A SIMILAR waterbirds.For example,Dunlin Calidrisalpina gather near MANNER TO "NATURAL" ONES? the water'sedge, Red-necked Stints Calidris ruficollisare found"where the waterhas drained to a thin film" andspe- Althoughmudflat creation is mosthighly developed in Japan cies suchas Grey-tailedTattler Heteroscelusbrevipes and (WAVE 2001), thereare few accessiblereports of bird usage GreenshankTringa nebularia are found where there are from there and success has to be inferred from studies of small pools. KentishPlover Charadriusalexandrinus and benthic invertebrates.The best examplesof how birds use LesserSand Plover C. mongolusare found in drier areas. areas of created or restored mudflats are from UK studies. This highlightsthe fact that a diversity of habitats,even At two of the mostintensively studied managed realign- withinwhat might seem homogeneous mudflats, is important mentsites in theUK (Toilesburyand Orplands on theBlack- for shorebirds.Restored sites often lack this range of micro- water estuaryin SE England),the sedimentstypically be- habitatsand tend not to showsuch habitat diversity at a fine- came consolidatedas re-wetting with saltwateroccurred. scale. However, accretionof soft sedimentswas quite rapid and benthicinvertebrates colonized relatively quickly and - HOW CAN NEW HABITAT CREATION SCHEMES birds and wildfowl soon began to use the site. Shelduck MAXIMISE BENEFITS TO SHOREBIRDS? Tadorna tadorna, Dunlin Calidris alpina, Grey Plover Pluvialis squatarola and Redshankprobably exploitedthe Coastalhabitats can be createdor restored.The majorityof polychaetesand Hydrobia that initially colonisedthe sites studiesreviewed by Atkinson et al. (2002) involved coastal (Atkinsonet al. in pressb, Readinget al. 2000). In threeto sitesthat were created for reasonsother than supporting wild- four yearsMacoma balthica colonisedand particularly at life andsuccess, however it wasmeasured, was often a very Toilesburythis coincided with increasingusage by hit or miss affair. Most sites supportedpopulations of Calidris canutus.Other speciessuch as EurasianOyster~ waterbirds,but oftenfailed to capturethe diversity observed catcherHaematopus ostralegus, which feed mainly on larger on natural areas. bivalves,tended to showvery low usageof the site. Most studieslooking at the processesunderlying restora- At the created mudflat at Teesmouth, both shorebirdsand tion/creation have been carried out at small scales in com- their invertebrateprey colonisedin the first winter (Evanset parisonwith surroundingareas and often fail to capturethe al. 1998, 2001) and man-madewetlands surroundingthe rangeof naturalvariation found at the largerscales (Neckles almostcompletely reclaimed estuary provided extra feeding et al. 2002) at which migratoryshore birds usually operate. time for shorebirds,especially during severe and windy Successfulrestoration/creation may take time but, oncethe (Davidson & Evans 1986). It was found, however, generalroles of hydrodynamics, dynamics and that successfulrecolonisation by three of the main inverte- other forcing factors are understood,then wetland habitats brate prey species,Corophium, Nereis and Hydrobia, re- canbe created.The currentresults are oftenunpredictable quireda leadin time of aboutthree years (Evans 1998). Even and it is unclearwhether the salt marshcreation process is after abundantprey populationshad becomeestablished, essentiallychaotic (i.e. small differencesin startingstates or somewader species, such as Grey Plover,Bar-tailed Godwit management leading to very different stable states) or Limosa lapponica, Dunlin, Red Knot and Ringed Plover whetherit is just a caseof "gettingthe reciperight". What- Charadriushiaticula, were still rare or absent.The degreeof everthe case,to maximisethe likelihoodof creatinga fully enclosureof thesite was thought to be responsible,highlight- functioningwetland encompassingthat rangeof variation ing the importancethat perceived risk canplay in foundin naturalareas, it is likely that larger-scaleprojects determiningwhere birds feed. This has importantimplica- aremore likely to be successful.At present,our knowledge tionsfor the sitingand designof futuremitigation sites as is limitedand it is essentialthat new projects adopt an experi- birdsmay only usesuch unsafe sims when food resources are mentalapproach and ensure that adequate monitoring is car- low elsewhereor during severeweather. Creating "poor ried out at appropriatetimescales. quality"sites to replace"high quality" ones is likely to lead Generally,once habitats are created,benthic fauna and to populationdeclines or at leasta reductionin the capacity birdsrespond fairly quicklyif conditionsare suitable.This of the habitatsto supportbirds. is becausecoastal wetlands are often high-energyenviron- Many more studieslook at changesin invertebratenum- ments,at low elevations,and with high soil-watertables. As bers.The speedwith whichinvertebrates colonise these sites such,they are likely to resemblethe surroundingnatural tendsto be in line with what canbe predictedthrough know- environmentin a relativelyshort time-frame, i.e. yearsrather ledgeof life historytraits. Mobile species,and those that have than centuries(Warren et al. 2002). For example,created a planktoniclarval phase,such as Nereis and otherpoly- marshesin the high energysandy environments of the Sev- chaetes, and Hydrobia colonise in the first year or two. ern Estuaryare virtually indistinguishablefrom surrounding Bivalves and other speciesthat have no planktoniclarval marshes.However, marshesin the muddy, lower-energy phaseor take time to grow to a suitablesize, suchas oligo- environmentsof someestuaries in SE Englandare often of chaetesand larger bivalves, either fail to coloniseor take a very different structureand supportdifferent severalyears to appear(Atkinson et al. 2002). This hasim- types than surroundingnatural marshes(Atkinson 1998, plications for the rates of colonisationby birds, so that Atkinson et al. 2001). speciesthat feed on smallpolychaetes are likely to colonise before thosethat feed on large bivalves,a featureobserved HOW WILL SHOREBIRDS RESPOND? at variousUK realignmentsites (Atkinson et al. in pressb). The Waterfront Vitalization and Environment Research As recognitionof the needfor mitigatingindustrial develop- Center (WAVE) handbook (WAVE 2001a,b) details the mentincreases, one of the greatestchallenges may not be the mechanismsby whichmudflats can be createdand highlights creation of suitable sites with sufficient food and shelter, but the importanceof creatingsmall-scale habitat diversity for a good knowledge of shorebirdecology. Given the inter- • Bulletin100April2003 Atk•nson: Can we recreate or restore •nterhdal habitats for shoreb•rds? 71 dependenceof sites,changes in one sitemay haveknock on know whereto targetthem in the bestway thatwill maintain effectson populationsin others.Therefore it is necessaryto andshore up the inevitablegaps that will appearalong the maintaina completenetwork of sitesin eachflyway in order flyways. to preserveviable shorebird populations. These must include To answerthe questionin the title of thispaper: yes, we wintering, stagingand breedingareas as well as other key can createintertidal habitats, but if the questionis "can we sitessuch as cold-weatherrefuges and or "drop out" zones createdhabitats to order",the answeris probablyno. The for migrants during adverseweather conditions.In most trackrecord in creatinggood quality habitats has been poor years,such additional sites may not be importantfor main- and,especially where salt marshis involved,restoration has tainingsurvival rates, but in a few, they might be crucial. tended to be a very hit or miss affair. This is becausewe Very few studieshave evaluatedthe impactof creating knowfar toolittle aboutwhat constrains the restoration pro- new habitatson birds.However, the generalprinciples found cess.In the longterm, a partnershipis neededbetween ecol- in the large literatureon habitatloss can be applied,as this ogists,conservation bodies, governments and engineers. is theconverse situation. Migratory shorebirds rely on whole Only in thisway will it bepossible to setup the kind of large networksof sitesso, to understandthe impactsof habitat capitalprojects required to takethe science forward and reach creation on thesepopulations, research needs to be carried an understanding,not only of how to createcoastal habitats, out at large scalesencompassing whole migratory ranges but alsothe impactthey will haveon shorebirdpopulations. (Haig et al. 1998). It is fine to createhabitats that birds use but a more relevant questionto ask is what are the conse- ACKNOWLEDGEMENTS quencesfor the populationas a whole?Sites vary in quality andif, for example,a site createdfor winteringshorebirds I wouldlike to thankJenny Gill, Rob Robinsonand Jennifer runsout of food,it may haveled to an increasein mortality Smartfor usefulcomments on draftsof thismanuscript and ratesand not have improvedthe capacityof the networkto Steve Crooks, Alistair Grant and Mark Rehfisch for useful supportthe species.Similarly, if the food supplyis insuffi- discussionof thetopics within this paper. Much of thethink- cientat a stagingsite, birds may fail to refuelwith sufficient ing behindthis paper was carried out for a projectfunded by speedand thus fail to reachthe breedinggrounds in time to English Nature. breedsuccessfully. For the vastmajority of species,we do not know the con- REFERENCES sequencesof habitatcreation or losson the populationas a whole. Given the interdependenceof sites,changes in one Atkinson, P.W. 1998. The wintering ecologyof the Twite Carduelis flavirostrisand the consequencesof habitat loss.PhD thesis,Univer- areawill affectthe populationsin otherareas. The choiceof sity of East Anglia. winteringor stagingareas can have important implications Atkinson, P.W., Clark, N.A., Clark, J.A., Bell, M.C., Dare, P.J. & Ire- for survivaland possibly the productionof youngin shore- land, P.L. in pressa. Changesin commerciallyfished shellfish stocks birds (Clark & Butler 1999, Gill et al. 2001). The effectsof and shorebirdpopulations in the Wash, England.Biol. Cons. climatechange may alterthe qualityof currentlyused sites Atkinson, P.W., Crooks, S., Drewitt, A., Grant, A., Rehfisch,M.M., andthus impact on shorebirdpopulations sometime in the Sharpe,J. & Tyas, C. in pressb. ManagedRealignment in the UK - the first five yearsof colonisationby birds.Ibis. future.At present,however, it canbe arguedthat few clear Atkinson,P.W., Crooks,S., Grant, A. & Rehfisch,M.M. 2001. Thesuccess impactsof climate changeat a populationlevel have been of creation and restoration schemesin producing intertidal habitat seen in shorebirds (Norris & Atkinson 2001, Piersma & suitablefor waterbirds.English Nature Research Report 425. English Lindstromin press)and that changesin populationshave Nature, Peterborough. beendue to impactsby man(e.g. Evans 1997, Piersma et al. Brawley, A.H., Warren, A.S. & Askins, R.A. 1998. Bird use of restora- 2001, Atkinsonet al. in press). tion and referencemarshes within the Barn IslandWildlife Manage- ment Area, Stonington,Connecticut, USA. Environ. Management22: 625-633. HOW DO WE PROCEED IN THE FUTURE? Broome, S.W., Seneca, E.D. & Woodhouse, W.W. 1988. Tidal salt marshrestoration. Aquatic Botany 32: 1-22. To understandthe impactof habitatcreation we needa better Burchett, M.D., Pulkownik, A., Grant, C. & MacFarlane, G. 1999. understandingof theconsequences of wintering, staging and Rehabilitationof salinewetlands, Olympics 2000 site,Sydney, Aus- breedingin particularsites. The availableevidence is thatthe tralia. I: Managementstrategies based on ecologicalneeds assessment. Mar. Poll. Bull. 37:515-525 "quality"of a siteis important,but for the majorityof spe- Castelijns,H., van Kerkhoven, W. & Maebe, J. 1997. VogelsVan Her ciesthis conceptis not fully understood.We are beginning Sieperdaschor, Over Een Niet Voorziene Dijkdoorbraak En De to achievean appreciation of thisthrough detailed large-scale OnverwachtGunstige Gevolgen Die Dat Voor VogelsHad. Natuur- studiesof birdsand their food supplies (e.g. Gill et al. 2001), beschermingsverenigingde Steltkluut in samenwerkingmet het RIKZ throughinvestigating the role of density-dependencein ed. Terneuzenen Middelburg. breedingand wintering areas (Sutherland 1996) and through Clark, C.W. & Butler, R.W. 1999.Fitness components of avianmigra- tion: a dynamicmodel of WesternSandpiper migration. Evol. Ecol. theuse of process-basedmodels that predict mortality under Res. 1: 443-457. differentscenarios (e.g. Stillmanet al. 2000, Stillmanet al. Davidson,N.C. & Evans,P.R. 1986.The role and potential of man-made in press,Stillman, this volume). However, we still needmore and man modified wetlands in the enhancement of the survival of detailed studies that relate environmental factors to demo- overwinteringshorebirds. Col. Waterbirds9: 176-188. graphicrates. Davidson,N.C.D., d'A Laffoley, D., Doody, J.P., Way, L.S., Gordon, With anincreasingly developed world, the capacity of the J., Key, R., Drake, C.M., Pienkowski,M.W., Mitchell, R. & Duff, networkof sitesupon which shorebirds depend will become K.L. 1991 Nature conservation and estuaries in Great Britain. 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