Schulz & Stock: Kentish Plovers and tounsts

Kentish Plovers and tourists: competitors on sandy coasts?

Rainer Schulz & Martin Stock

Schulz, R. & Stock, M. 1993. Kentishplovers and tourists:competitors on sandy coasts? Wader Study Group Bull. 68: 83-91.

The effects of human-relateddisturbances in a breedingcolony of Kentishplovers were investigated.Nest searchesrevealed a maximumof nearly 200 nests in the forelandof St Peter in Schleswig-Holstein.The breedingcolony thus accountsfor 10% of the entire north-west Europeanbreeding population and containsnearly 50% of the German population.Large parts of the potentialbreeding habitat could not be colonisedbecause they were occupiedby tourists sun-bathingand restingin the primarydunes. Furthermore,the birdsshowed reduced hatching success. Nest failuresfrom various causes amounted to 52.1% on average. A strong relationshipbetween the disturbanceintensity and the rate of clutch losseswas found. Habitat characteristicssuch as vegetation cover and the vegetation structurearound the nests, expressed as the view obstruction,can reduce these losses. Possible disturbance-related and disturbance-independentreasons for nest failuresare discussed.

R. Schulz, WWF-Wattenmeerschelle,Schleswig-Holstein, Norderstrasse 3, D-2250 Hdsum, Germany

M. Stock,Landesamt fur den NationalparkAm-Halen 40 a, 2253 Tdnning,Germany

INTRODUCTION Schleswig-Holsteinpart of the Wadden Sea we studied the effects of tourism on colonisation, distribution and The Kentish Plover Charadrius alexandrinus is one of hatchingsuccess of Kentishplovers. The natural the most widespreadwaders in the world. Different breedingareas of the species, such as primarydunes, subspeciesare foundon five continents. The Kentish sandy coastal areas and exposed washed-up shell Plover was once widely distributedalong most fragment areas are simultaneouslythe preferred Europeancoasts, from Scandinaviato southernIberia, habitatsof touristsduring the summer months. Tourist on the coasts of southern England as well as in the activitiesare a major source of disturbanceto large Mediterranean and the Black Sea areas. Formerly large portions of these areas. inlandbreeding areas also existed in Spain and in the Pannonicregion in south-eastEurope. The northern- This investigationis part of an applied ecosystem most populationsbreed along the coastsof the Wadden researchproject in the Wadden Sea area of Schleswig- Sea and the south-west Baltic Sea (Glutz et al. 1975; Holstein and deals with the effects of human Cramp & Simmons1983). disturbances to birds. Aims, content and the structure of the interdisciplinaryproject are describedby At presentthe nominateform (EuropeanKentish Plover) Leuschner (1988) and Leuschner & Scherer (1989). appearsto be amongof the most rapidlydisappearing waders in Europe. Breedingpopulations have declined in many regions,e.g. in Sweden, Hungaryand the Wadden Sea, or have disappeared from many areas in STUDY AREA recentyears, e.g. from breedinghabitats in Norway, Great Britain, Denmark, Hungary and the Baltic area. The westernmostparts of the Eiderstedtpeninsula, the Increasingtourism and the destructionof natural sandy shores of St Peter-Ording(Figure 1), form an habitats are considered the main reasons for the decline exceptionto the geomorphologyof the west coast of (Bauer & Thielcke1982), despitethe fact that the Schleswig-Holstein.The peninsulais the only area speciesis often regardedas adaptableand insensitive between Bl•tvandshuk in Denmark and Den Helder in to human disturbance. An internationalworking group the Netherlandswhere the sandy barriercoast lines the establishedin responseto this rapid decline hopes to mainland. This coastal stretchis dominatedby a large enlightenquestions concerning the ecologyand status systemof barrierbeaches of differentages, composing of Kentish Plovers and to find evidence supportingthe a mosaicof pleistocenedunes, saltmarshes,tidal sand need for species conservation(J6nsson et al. 1990). As flats and highersand flats. On some restrictedsites a partof the EcosystemResearch Project in the primarydunes have built up. Elongatedlagoons have

83 Schulz & Stock: Kentish Plovers and tourists

[-• sand bordercore zone nationalpark • sparsevegetation • saltmarshes •...... primarydunes • tidalflats, gullies

Figure1. Habitatmap of thestudy area inthe foreland of St Peter-B0hl.The potentialbreeding habitat is shadedmedium-grey (beach chair dunes and large primarydunes). The borderof the core zone of the nationalpark is indicated. developed behind the barriers. The total area is Park 'Schleswig-HolsteinischesWattenmeer' as well as traversed by an extensive natural gullysystem (Ehlers the primarydunes on the youngestsea-wall. The 1988). potentialbreeding habitat is thuscharacterised mainly by the primarydune area (Figure 1). The total area In the south-eastpart of the coast - at St Peter-B•Shl- the comprises 90 ha, of which 12 ha are not accessible to oldestand thusinnermost barrier beach supports a most the public. The entirearea - exceptthe well-protected remarkable naturalsandy saltmarsh. A successionof core zone - is heavilydisturbed by walkingtourists. differentvegetation communities from a Puccinellion Pads of the primarydunes are used by nudists. rnaritimae to an Arrnerion rnaritimae can be found. This vegetationis protectedby a youngerbarrier covered with a mixtureof differentplant species characteristicof salt- METHODS marshesas well as primarydunes. The outermost barrierforms an extendedsea-wall covered by an Preliminaryinvestigations began in 1989, when 113 Elymo-Agropyretumjuncei with Agropyron junceum KentishPlovers were individuallymarked with predominating.The vegetationcover reaches a height colour-rings.Since the beginningof the studya set of of nearly 50 cm and is denser on the seaward side of the parametersoutlined below were investigatedas part of barrier beach than on the lee side. The sea-wall is 1.5 a long-termstudy on the populationecology of Kentish km longand nearly250 m wide. The dunesvary in Plovers. Resultspresented here reflectonly data heightbetween 0.5 and 1.5 m and are notflooded during concerningthe effects of disturbanceson colonisation, '-normalhigh tides. Only the gulliesand an extended distributionand hatchingsuccess of the 1990 season. lagoonregularly flood. The studyarea (Figure1) includespads of the more open saltmarshvegetation Breedingbird numberswere assessedusing the within the totallyprotected core zone of the National methoddescribed by Brunckhorstet aL (1988), by

84 Schulz & Stock: Kentish Plovers and tourists searching for nests, by calculatingthe proportionof RESULTS ringed to unringed birds, and by determiningthe percentage of birds ringed the previousyear and by Total bird numbers birds caught on the nest this season. Every nest was Followingthe standard procedure described by mapped on an infra-red photographof the area; the Brunckhorstet al. (1988) a total of 70 breeding pairs exact positionwas described by triangulation. were counted in the study area in 1990 (H•lterlein, unpubl.). This number is quite low in comparisonwith To describe nest habitat characteristics, we measured the corrected actual number of breeding pairs. the vegetationcover (in steps of 10%) within a circle of 50 cm and 200 cm aroundthe nests after hatching. The vegetation height was measured within the smaller A maximum of 236 to 239 Kentish Plovers present at circle. the same time was examined in the middle of June by means of two different methods. Nest searches Kentish Plovers often select nest sites in close proximity revealed a total of 130 clutches with 77 nests present at either to individualplants or to clumps of loose the same time at the end of May. ApplyingMayfield's vegetation. We quantifiedthe degree of view correctionfactor to these numbers implies a total of 178 obstructionfrom the perspectiveof the incubatingbirds breeding attempts in the 1990 season. This can be by measuringthe width of tufts of vegetationhigher than translated to a total number of 120 pairs. 15 cm within a radius of 100 cm around the nest. This translated easily to an angle describingthe view from The course of the breeding season is given in Figure 2. the nest: a view angle of 0 ø was characteristicof nests The graph shows the start of the laying period with a located within plant groups - total obstruction- and an median laying date of 18 May, a maximum number of angle of 360 ø described nest sites with an unobstructed nests simultaneouslypresent on 29 May and a median view. hatching date of 16 June.

The relativedensity of the nestswas establishedby countingthe numberof nests in an area of 1 ha Overall hatching success surroundinga certainnestcup. This was only appliedto Table 1 presents the overall hatchingsuccess for the nests under active incubationat the end of May after most 1990 season with and without the Mayfield correction of the eggs had been laid. The age of newlyfound eggs factor. A total of 130 nests was found; the fate of 101 of was estimatedby measuringtheir floating characteristics these nests is known: 65% were successful and 35% followingthe proceduredescribed by Hays & LeCroy (1971) and Van Paassen et aL (1984). Assumingan The breedingseason 1990 (in weeks) incubationperiod of 30 days (Rittinghaus,1961; pers. median: 18.5 obs.) the layingdate for successfulnests can be calculatedfrom the hatchingdate. The hatchingsuccess was correctedusing the formulaof Mayfield(1961, 1975). The fate of the clutcheswas examined by visual observationsand by readingtracks and footprints. A lO I-l 3o200 tI 'l I I [ i I I i starti ofIlaying I clutchwas assumedto be successfulif hatchingchicks were heard in the egg or if at least one chick hatched. A 80 max:29.5 clutchwas presumedlost to predationif yolkand/or egg- 70, numberof nests shell fragmentswere found. In some cases clutcheswere 60 present collectedby humansor floodedby extremelyhigh tides. 5O

The disturbance intensityin the study area was 4O measured by countingand mappingthe number of tourists(walking and restingpeople were considered 2O separately) on 50 days from April to July. Tourist counts were made during times of peak activity in the area, between 15.00 and 16.00 hours as well as on 0 r .,1-'-I...... FI I--II-1 individualdays throughoutthe whole day in intervalsof median: 16-6 30 minutes. To assess the influence of disturbance 2O intensityon hatchingsuccess an index (person- hours/10ha/day) was calculated by multiplyingthe 10 number of people in the surroundingarea of a certain 300 t ¾hatching nest with the mean length of stay of the people in each Figure2. The courseof the breedingseason in the studyarea of St spot, summed over the entire breeding period. Peter-B6hl.

85 Schulz & Stock: Kentish Plovers and tourists

Table 1. Overall hatchingsuccess of Kentish Plovers, 1990, with and without Mayfield correctionfactor. 12-

Parameter found calculated 10_ fate known (n) 101 138 successfulnests (n) 66 66 losses (n) 35 72 rate of losses (%) 34.7 52.1 number of nests (n) 130 178

were lost due to various causes (7% destroyed by high t•des, 9% taken by egg collectors,the remaining19% were taken by predators or were lost due to unknown causes). No significantcorrelations could be found 1 between weather data and the amount or the percentageof clutchlosses. The maximumnumber of pentadafter stad of laying losses occurswithin the first 10 days after laying Figure 3. Number of clutch losses - due to various causes - in (Figure 3). 78.8% of clutch losses occurredwithin the pentadsafter the stad of laying. first 15 days. not colonised,as these potentialbreeding habitats were occupied by restingtourists. The birds were only able Spatial distribution of nests in relation to tourist to settle in the remainingundisturbed areas. Most of activities the successful nests were found in remote areas which Kentish Plovers prefer to breed in areas with sparse lie off the placesof maintouristic activities and walking vegetation on primary dunes. The spatial distributionof routes or within the well-protected core zone of the the nests, the fate of the nests and the use of the area nationalpark. Even on a small scale, e.g. on the by humans are shown in Figure 4. The upper part of westernmosttip of the large primarydune (Figure4) it is the map shows the first two parameters in relationto obviousthat potentialbreeding places are pre-empted sun-bathingand restingpeople, the lower part in here mainlyby sun-bathersand restingpeople. As may relationto beach-walkers. Sun-bathingand resting be derivedfrom our distributionmaps (Figure4), their people were concentratedon the westernmost,the influenceseems to be more importantthan the influence so-called 'beach-chair'dune and at the tip of the large of walkingpeople. The latter mostlyfollow the high-tide pnmary dune in the east. The more plant-coveredsalt- line and were rarely seen within the breeding area. marshes were less regularlyoccupied. Walking people concentratedat the parking lot and along the high-tide I•ne, with most of the people walking to the tip of the The effect of human disturbance on hatching sea-wall at the end of the study area. success There was a clear relationshipbetween the disturbance Most of the nests were found in the eastern part of the intensityand the numberof clutcheslost - excluding potentialbreeding habitat. Heavily disturbedareas, losses due to egg-collectorsand flooding- duringthe which includethe westernmostpart of the large primary breeding season (Table 2). The rate of losses dune and the smaller 'beach-chair' dune next to it, were increasedwith increasingdisturbance intensity in the

Table 2. Relationshipbetween the disturbanceintensity and the numberof clutcheslost.

Parameter disturbanceintensity (person-hours/10ha/day) 0-2 2-4 4-10 >10 number of nests * 20 21 22 22 clutch losses * 10.0 13.6 28.6 36.4 number of nests 1 22 24 30 25 clutch losses found 1 18.2 25.0 46.7 44.0 clutch losses calculated 1 27.6 43.4 68.0 59.0

* excludingcollected and floodedeggs • all nests.

86 Schulz & Stock: Kentish Plovers and tourists

1 Intensityof disturbance

2 [people/50counts]

3-4

5-7 square size: 50x50 rn

8-14

15

restingpeople

j :

• hatched ß clutchdepredated ß clutchdeserted

A clutch flooded

• eggs collected

0 fate unknown

. ©:

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walkingpeople .... .

;

Figure4. The distributionand the fate of KentishPlover nests within the studyarea in relationto the touristuse of the area: a) restingand sun- bathingpeople, b) walkingpeople. The grid indicatesthe intensityof touristusage of the respectivesquares.

87 Schulz & Stock: Kentish Plovers and tourists

vegetation cover lowers clutch losses toward 0%. This Rates of number clutch loss relationshipis little influenced by the fact that less of club,'hes vegetated dunes are more often used by resting and

-30 sun-bathingpeople than the more heavily vegetated 60% - ones. The log disturbanceintensity is in fact only slightlynegatively correlated with the vegetation cover -20 40% _ (r2 = -0.09; df - 129; p = 0.006).

-10 2O% Combined effects To determine both the effect of disturbanceintensity and the influenceof the vegetation cover on hatching 0-19 20-39 40-59 60-79 80-100 success we divided all clutches into four classes. This Vegetationcover (%) was done usingthe disturbanceintensity (> or < 180ø) F•gure5. Numberof clutchesfound (columns)and the rate of clutch of the nestcupsas the criteria for the division(Figure 6). losses in relationto extent of vegetation cover. Thirty-fourper cent of all nests were hidden (view angle < 180ø). In less disturbedareas all these birds were nest surroundings(person-hours/10 ha/day). Clutch successful. Even in more disturbed places the losses in losses were lowest (10.0%) in areas with little hidden nests were low (14.3%). But 50% of the disturbance but increased steadily with increasing clutches were lost at high levels of disturbance and disturbancelevel up to 36.4% in heavily disturbed where nests were situated on open ground. Losses areas. The differences in clutch losses between a low were thus lower in areas with dense vegetation and low disturbanceintensity (< 4person-hours/10ha/day)and a levelsof disturbance(p > 0.05, X2- test). This clearly highdisturbance intensity (> 4 person-hours/10ha/day) indicates that hatching success in highly disturbed were significant (Chi-Square = 4.71, p < 0.05). In the areas even with optimal habitat is as low as in poor correcteddata (after Mayfield1975) clutchlosses habitat with a low level of disturbance. account for 27.6% of nests in low disturbance areas and increase to 59% under a high disturbancelevel. Figure 7 summarises the effects of different parameters on the fate of the nests. Differences were tested with the Mann-Whinney U-test. Nests were Clutch losses in relation to vegetation cover more often successful in places with a higher Kentish Plovers are not equally distributedwithin the vegetation cover, on less open sites and on spots with studyarea. Touristuse of partsof the primarydune is a low disturbance intensity. No differences between one of the reasons. In general, plovers mainly colonise successful and failed nests could be detected in areas with sparsevegetation. Most of the nests are different vegetation heights and different relative found in zones with a vegetation cover of less than 40% abundances of nests per 10 ha. (Figure 5). Hatchingfailure in such areas is 22.6% on average. The rate of clutchloss in open habitatis the highestvalue foundaccounting for 63.6%. Increased nestparameters and • successfulnests

clutchlosses (% for each class) ofslgmficance the mean level(u-test)for the d•fference D fafiednests p n 10 20 30 40 50 60 70 I I I I I I i

vegetationover 1me(%) .07 66 19

66 vegetationcover 4mo(%) .07 19

vegetationheight (cm) n5 66 19 !

nestlocation: .05 64 locationofthe ./- n=28 • opemng angle (ø) 10 19 I ope 56 I abundance (nest 10ha) n5 nesthidden•,,•n12 14•• 6:=16. 7 disturbanceintensity -05 66 (absolute numbers) 19 I '<4level of disturbance>4 Figure6. Clutchlosses (% for eachclass) in relationto the locationof Figure7. Differencesof the mean of certainparameters between the nest and the level of disturbance. See text for explanation. successful and failed nests.

88 Schulz & Stock: Kentish Plovers and tourists

DISCUSSION populationsare decreasing. The overall loss rate in our study area accounted for 52.1% and is thus comparably The study in the forelandof the whole coastlinein St high. Furthermore,plovers are very sensitive to Peter revealeda breedingpopulation of nearly200 pairs disturbancesduring rearing. Yalden & Yalden (1990) in 1990. This area thus holdsthe largestconcentration could show that the time juvenile Golden Plovers of Kentish Plovers in north-western Europe. The Pluvialisapricaria spent feeding was significantly populationaccounts for nearly 10% of the N W reduced under disturbedconditions. Flemming's et al. Europeanand for nearly 50% of the German breeding (1988) study yielded similar results in Piping Plovers population(H•.lterlein unpubl.). Similar numbers were Charadrius melodus. Disturbances resulted in a lower also reportedin the 1970s for this specificarea (Glutz et survival rate of chicks up to an age of 17 days. By al. 1975). In the 1980s H•.lterlein(1986) and Kempf et altering chick behaviour, disturbancesled to a 50% al. (1989) reportedless than 50 pairs.These low reductionin the rearing success. Whether this affects numbersare partlydue to differentmethods. the long-term populationlevel is not yet known but Rittinghaus'data were based on nest countswhereas currentlyunder investigation. the more recent data were gained by countingterritorial birdsfollowing the methoddescribed by Brunckhorstet al. (1988). Despitethese difficultiesthere is evidence WHAT ARE THE REASONS FOR CLUTCH LOSSES? that an enormous reduction in numbers has occurred. Between 1970 and 1990 the German Kentish Plover In additionto collecting,flooding and crushing,the populationhas droppedfrom 900 to 412 pairs.As reason for losses in some circumstances was recentlystressed by Smit & Visser(1990), Kentish discovered. Losses directly attributedto human Ploversand LittleTerns belongto the most threatened activitiesare in general low, e.g. Pienkowski(1984) for breedingspecies in the Wadden Sea area. Their Ringed Plovers Charadriushiaticula. Indirect effects are populationshave decreaseddramatically during the last more often responsible,often through an increase in decades. The authors concluded that this decline of the predation pressure. The fact that open nests fail more breedingpopulation is due to lossof suitablebreeding often than hidden ones is an indication that aerial, sites and to disturbances from tourists. visually-searchingavian predators are more likely to cause losses than nocturnal mammalian predators. To The distributionof Kentish Plovers within the study area what extent dogs are predators of plovers' eggs in the is stronglyinfluenced by touristuse of the area. The study area is unclear, but dogs are well known as potentialbreeding habitat in the westernmostpart of the predatorsof eggs and young of various plover species, area, the so-called 'beach-chairdune', and other parts e.g. KilldeerCharadrius vociferus, Ringed and Kentish of the area cannot be used by the birds. It can be Plovers (Nol & Brooks 1982, Pienkowski 1984, Szbkely concluded that disturbances reduce the size and the unpubl.). value of the foreland area in St Peter-B0hl. Resting peopleand sun-bathershave a greaterinfluence than It is very likely that avian predators, mostly gulls, less do beach-walkers.This may be attributableto habitation often crows, are responsiblefor many losses. Although to beach-walkers as recently found by HSppop & Hagen we do not know exactly what role mammalian predators (1990) in breedingOystercatchers but is surelyalso play, there is a fox den near the colonyand many traces affectedby habitatfeatures like vegetation cover and/or have been found. An increase in predator density due to opennessof the nest-site. an elevated tourist use of an area is a well-known effect (Watson1982, Pienkowski 1984). G0tmark & Ahlund When studyingthe effects of disturbances,one of the (1984) found that human-relateddisturbances in an major questionsto be answered is whether or not a Eider colony Somateria mollissima led to increased disturbanceis significantto a bird. In populationterms predationshortly after the disturbancecompared with this means whether or not the populationcan withstand the predationrate before. This may explain why clutch a certain reductionin productivityto secure a certain losses in our study area seem to occur more often on population level or not. days with a very high disturbancepressure. Avian predatorslike gulls can probablyfind disturbednests Rittinghaus(1961) reporteda very low rate of egg more easily through the movements of disturbed losses(6%, only data for one year published)for the plovers.Other circumstances,such as an increase in populationhe studiedon the undisturbedisland of ploverfootprints in a sandy area as a consequenceof Oldeoog, Niedersachsen.Unfortunately, he did not repeated disturbances,are likely to attract gulls. comment on the populationdevelopment. In recent Similarly,Pienkowski (1984) considersboth disturbed years Szbkely (1991) found a clutchloss rate of movements of parents and footprintsreasonable marks between 56.7 and 79.3% for a small breeding for predatorygulls. Furthermoreif the predatorstolerate populationin Hungary,and J0nsson(1991) reported a closer approach of touriststhan do plovers, the losses lossesup to 60% for KentishPlovers in S-Sweden. Both can be very high as found by Anderson& Keith (1980)

89 Schulz & Stock: Kentish Plovers and tourists

•n a seabird colony.Specialisation of individualbirds on D. Fr0hlich kindlycorrected our English.The 'Wetteramt certain cues can increase their predatory effectiveness Schleswig'allowed us to make use of unpublisheddata considerably.As well as gulls, Oystercatchersare also from a nearby weather station. known as predatorsof plover and tern nests (pers. obs., Haddon & Knight1983.) Haddon & Knight(1983) This work was financiallysupported by the Federal observed an individualOystercatcher depredating 12 EnvironmentAgency and the Umweltbundesamtas part nests of Little Terns within 30 minutes. of the project:'Ecosystem Research Wadden Sea. This is contribution no. 13. Nol & Brooks(1982) proposea relationshipbetween clutch losses in a Killdeercolony and the numberof roostinggulls nearby. Althoughwe have only little REFERENCES evidence supportingthis assertion,it is very likelythat gullsflying to their roost searchfor nests as we Anderson, D.W. & Keith, J.D. 1980. The human influence on seabird observed in the same area in the case of Little Terns. breeding success:conservation implications.BioL Conserv. 18: 65-80.

Bauer, S. & Thielcke, G. 1982. Gef•,hrdete Brutvogelartenin der DISTURBANCE-INDEPENDENT FACTORS BundesrepublikDeutschland und im Land Berlin: Bestandsentwicklung,Gef•,hrdungsursachen und Schutzmal•nahmen. Vogelwarte31: 183-391. Gulls foragingalong a hightide waterlinecould be responsiblefor the largeramount of clutchlosses at the Brunckhorst, H., H•.lterlein, B., Hoffmann, H., Petersen W., & R0sner, outer ridge of the sea-wall, as found in our study. A H. U. 1988. Empfehlungenzur Brutbestandserfassungvon larger numberof lossesin such areas is thus the direct K0stenv0gelman der deutschenNordseek0ste. SeevSgel 9: 1-8. consequenceof the nest site location. Cramp, S. & Simmons,K.E.L. 1983. The Birds of the Western A high density of breeding birds in a colonycan Palearctic.Vol III University Press, Oxford. subsequently increase the predator density and thus lead to a higher predation pressure. However, it is also Ehlers, J. 1988. The morphodynamicsof the Wadden Sea. Balkema, Rotterdam. possiblethat a commonantipredator behaviour of the nesting birds serves as a precautionfor the whole Flemming,S.P., Chiasson, R.D., Smith, P.C., Austin-Smith,P.J. & colony (G0ransson et al. 1975). A density-dependent Bancroft, R.P. 1988. Piping plover status in Nova Scotia related higher rate of clutch losses as found by Page et al. to its reproductiveand behavioural responsesto human disturbance. J Field OrnithoL 59:321-330. (1983) in Snowy Plovers Charadriusalexandrinus could not be observed in our study area. The highest Glutz von Blotzheim, U.N., Bauer, K.M. & Bezzel, E. 1975. Handbuch plover density in our study plot was found in an area der VSgelMitteleuropas. Akademische Verlagsgesellschaft, with high Agropyronjunceum vegetation and most of Wiesbaden Bd.6. the nests were hidden. Habitat factors can thus G0ransson, G., Karlsson, J., Nilsson, S.G. & Ulfstrand, S. 1975. •nhibitthe negative effects of a higher breeding Predationon birds'nests in relationto antipredatoraggression density. and nest density:an experimental study. Oikos 26:117-120.

We can conclude that tourist-induced disturbances G0tmark,F. & Ahlund,M. 1984.Do fieldobservers attract nest reduce the effective size and the value of the potential predatorsand influencenesting success of commoneiders? J Wildl.Manage. 48:381-387. breeding habitat in our study area. Large areas are not colonizedor breeding success in such areas is very low. Haddon,P.C. & Knight,R.C. 1983 A guide to little tern conservation. Plovers and tourists are indeed competitorsfor rare RSPB, Sandy. resources.This already has led to conservationefforts H•,lterlein,B. 1986. Laro-Limikolen-Brutbest•ndean der schleswig- as suggestedby Schulz & Stock (1991). Largeparts of holsteinischen NordseekfJste 1983-1985. Corax 11: 332-398. the entire breedingarea are now protectedduring the breedingseason. The effectsof these measureson the Hays, H. & LeCroy, M. 1971. Field criteriafor determiningincubation breedingsuccess of Kentish Ploversand LittleTerns stage in eggs of the commontern. WilsonBull 83: 425-429. are currentlyunder investigation. H0ppop, O. & Hagen, K. 1990. Der Einflu13von St0rungenauf Wildtiere am Beispiel der Herzschlagrate br0tender Austernfischer.Vogelwarte 35:301-310. ACKNOWLEDGEMENTS J0nsson, P.E. 1991. The Kentish Plover Charadrius alexandrinus in We would like to thank H. H0tker, P. E. J0nsson, P. Scania, South Sweden, 1990 - a report from a conservation project.Anser30: 41-50. Meininger,H. U. R0snerand T. Sz6kelyfor valuable discussionsduring the courseof the project.We thank J0nsson, P.E., Maininger,P.L. Schulz, R. & Sz•kely, T. 1990. Tye T. Sz6kely for allowingus to use his unpublisheddata. WSG Kentishplover project. WSG Bull 60: 1-3.

90 Schulz & Stock: Kentish Plovers and tourists

Kempf, N., Fleet, D.M., R0sner, H-U. & Prokosch, P. 1989. Brut-und Spacingout at Mono Lake:breeding success, nest density,and Rastvogelz•hlungenim Schleswig-HolstemischenWattenmeer predation in the Snowy Plover. Auk 100: 12-23. 1987/1988 - Landesamt ffir den Nationalpark Schl.- HolsteinischesWattenmeer, T0nning. Pienkowski,M.W. 1984. Breedingbiology and populationdynamics of Ringed Plovers Charadrius hiaticula in Britain and Greenland: Leuschner,C. 1988.(•kosystemforschung Wattenmeer- Hauptphase nest populationas a possiblefactor limitingdistribution and 1: Erarbeitungder Konzeptionsowie Organisationdes timingof breeding. J. Zool, Lond. 202:83-114. Gesamtvorhabens(Forschungsverbund). Forsch. Ber. Umweltbundesamt Berlin: 1-155. Rittinghaus,H. 1961. Der Seeregenpfeifer-NBB 282, Ziemsen Verlag, WittenbergLutherstadt, 126 pp. LeuschnerC. & Scherer, B. 1989. Fundamentalsof an applied ecosystem reasearch project in the Wadden Sea of Schulz, R. & Stock, M. 1991. Kentishplovers and tourists- conflictsin Schleswig-Holstein.Helgol•nder Meeresunters43: a highlysensitive but unprotectedarea in the Wadden Sea 565-574. National Park of Schleswig-Holstein.Wadden Sea Newsletter 1/91: 20-24. Mayfield, H.F. 1961. Nestingsuccess calculated from exposure. Wilson Bull 73: 255-261. Smit, C.J. & Visser, G.J.M. 1991. Developmentin breedingand non- breeding bird populationsin the Wadden Sea area - Talk at the Mayfield, H.F. 1975. Suggestionsfor calculatingnest success. Wilson Int. Wadden Sea Symposium, Ameland, Oct 1990. Bull 87: 456-466. Sz•kely, T. 1991: Habitat selection of Kentish Plovers Charadrius Nol, E.A. & Brooks, R.J. 1982. Effectsof predatorexclosures on alexandrinusthe male assessmenthyphothesis. nestingsuccess of Killdeer.J Field OrnithoL53: 263-268. Watson,A. 1982. Effectsof humanimpact on Ptarmiganand Red Paassen, A.G. van, Veldman, D.H. & Beintema, A.J. 1984. A simple Grouse near ski lifts in Scot/and - Ann. Rep. ITE 1981' 51. device for determinationof incubationstages in eggs. Wildfowl 35: 173-178. Yalden, P.E. & Yalden, D.W. 1990. Recreational disturbance of breedingGolden Plovers Pluvialisapricarius. Biol. Consen/. 51: Page, G.W., Stenzel, L.E., Winkler, D.W. & Swarth, C.W. 1983. 243-262.

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91