47 Changesin populationsof breedingwaders on the machair of North Uist, Scotland, 1983- 1998 R.J. Fuller & D.B. Jackson Fuller,R.J. & Jackson,D.B. 1999. Changesin populationsof breedingwaders on the machairof North Uist, Scotland,1983 - 1998. WaderStudy Group Bull. 90: 47-55. Surveysbetween 1983 and 1987confirmed that habitats close to the westcoasts of the islandsof North Uist, Benbeculaand South Uist supportedthe densestconcentrations of breedingwaders in Britain. An extensive surveyin 1995 revealedthat large declines in numbersof breedingwaders had occurredsince the 1980s, especiallyon SouthUist andBenbecula. Predation by a recentlyestablished population of hedgehogsappears to be a majorfactor contributing to the declinesof somespecies on SouthUist. In 1998, a surveywas undertakento clarify the statusof breedingwaders on threemachair sites on North Uist which are hedgehog-free.This surveyestablished that Ringed Plover and Dunlin haddeclined at two of the sitessince the 1980s;at onesite, the reductions exceeded 50%. The causesare unclear, though several hypotheses are discussed.In contrast,Oystercatcher had remainedstable at one sitebut had increasedat two sites. There was no evidenceof long-termpopulation change at any sitefor Lapwingor Redshank.Variation in detectability with the stageof breedingcan be a majorsource of errorin countsof breedingwaders; implications for measuringpopulation changes are considered.Future monitoring requirements for waderson the Uists are also discussed. R..J. Fuller, British Trustfor Ornithology,The Nunnery, Thetford, Norfolk IP24 2PU, UnitedKingdom. D.B. Jackson,Royal Society for the Protectionof Birds,Dunedin House, 25 RavelstonTerrace, Edinburgh EH4 3TP, United Kingdom. INTRODUCTION waderswere maintainedwithin the studyareas. Land lyingon theAtlantic fringe of the islandsof SouthUist, Benbecula and North Uist in the Outer Hebrides is In 1993 and 1995, surveysof breedingwaders were characterisedby machair,which is a level plain of vegetated undertakenon the machairof the Uistsand B enbecula using calcareoussand. Partsof thismachair plain are cultivated; methodsthat were comparable with thoseof the earlier otherareas are permanentlywaterlogged. A transitionzone of surveys(Whyte & O'Brien 1995). Thesesurveys indicated roughgrazing land, known asblackland, lies betweenthe that overallnumbers of RingedPlover, Dunlin, Redshankand machairand the acidicpeatlands and moorland that occupythe Snipehad declinedsince 1983 but that therewas no clear greaterpart of theseislands. The machairand blackland cover changein Oystercatcherand Lapwing. The patternof decline approximately200 km2. Thesehabitats support the densest was most consistent on South Uist where the reductions since concentrationsof breedingwaders in Britain and form one of 1983 were estimatedas: RingedPlover -58%, Dunlin -65%, the mostimportant wader breeding grounds in westernEurope. Redshank-43% (Whyte & O'Brien 1995). In the 1980s,the northernend of SouthUist, especiallyto the westof LochBee, In 1983 an extensivesurvey of breedingwaders was carded supportedexceptional concentrations of breedingRinged out on the machair and much of the blackland of the Uists and Plover andDunlin (Etheridge1982, Fuller et al. 1986); these Benbecula(Fuller et al. 1986). The followingpopulation arenow greatlyreduced. On NorthUist the overallpattern estimateswere made: OystercatcherHaematopus ostralegus was alsoone of decliningnumbers of RingedPlover and (2700 pairs),Ringed Plover Charadrius hiaticula (2250 pairs), Dunlin,but no clearchange in the otherspecies. LapwingVanellus vanellus (4350 pairs),Dunlin Calidris alpina(3300 pairs,corrected for detectability),Snipe Predationrates on RingedPlover, Dunlin andRedshank nests Gallinagogallinago (750 pairs)and Redshank Tringa totanus in SouthUist weremuch higher in the 1990sthan in themid (2650 pairs). The numbersof Snipewere probably greatly 1980s(Jackson 1998). The mainnest losses of RingedPlovers underestimated(Fuller et al. 1983). Subsequentsurveys were are dueto predationby CommonGulls Larus canus (Jackson undertakenin sampleareas of machairon North Uist and 1998). For Dunlin and Redshank,however, much of the SouthUist in eachyear between 1983 and 1987 (Fuller & increasedpredation on SouthUist wasby an expanding Percival1988). Throughoutthis period,high densitiesof populationof hedgehogsErinaceus europaeus. Hedgehogs 48 populationson threelarge areas of machairon NorthUist and B anadjacent island which he had previously surveyed each year Harris from1983 to 1987.The aims of the1998 survey were (a) to C•k•Soundof clarifythe current status of breedingwaders in theseareas . wherehedgehogs have yet to becomeestablished and (b) to estimatethe size of thewader populations before colonisation by hedgehogs.This paper summarises the results of theseand earlierwader surveys on threeareas of NorthUist. North Uist STUDY AREAS Thelocations of eachstudy area are shown on Figure 1. Detailsof eacharea are given below. Eachof theseareas was freeof hedgehogsin 1998;we canbe surethis is the case becausesearches for hedgehog scats were negative, local Benbecul croftershave not encountered hedgehogs and no road kills werefound in theseareas. Furthermore, studies of wader breedingsuccess on Baleshareand Soilas in 1997 did not find anyevidence of egglosses due to hedgehogs (D.B. Jackson unpublished).There is also concemthat American mink Mustelavison, which have established feral populations on Lewisand Hams, might spread to theUists. At thetime of I Machairsand dunesand writing,we areunaware of anyconfirmed records of minkon NorthUist or Berneray. ;• 150mLand over 10 Baleshare(Grid referenceNF790610) 1 An islandat the southwestcomer of North Uist connectedto km themain island by a causeway.The island contains large samplesof all thetypical machair and blackland habitats (Fuller1981). Waders were surveyed across the entire island (totalarea 8.8 km2). Hedgehogs have colonised adjacent parts of southwestNorth Uist but thereis no evidencethat a Sound of populationhas become established onBaleshare. Grazing Eriskay pressurefrom sheep is currentlyhigher on parts of Baleshare Figure 1 The approximatedistribution of machairand sand dunes on North thanon the other study areas. Cattle are also grazed on parts of the island. Uist,Benbecula and South Uist. Locations of three areas surveyed in 1998 are shown:(A) Baleshare,(B) Soilas,(C) Berneray. Soilas(Grid referenceNF815764) Thissite is formedby thepeninsula of cultivatedand uncultivatedmachair and dunes that projects into the Sound of were introducedinto southernSouth Uist in 1974 and 1975 Hamsfrom Sollas and Middlequarter (study area 4.5 km2). (Angus1993) and have subsequently spread throughout South Thereare only two permanently marshy areas, both on the Uist,Benbecula and into the southern part of NorthUist. At southernboundary. At thetime of thesurvey there were presentall themajor wader breeding areas on North Uist and substantialnumbers of cattlegrazing parts of the machair. adjacentislands remain free of hedgehogs.It is especially important,therefore, to documentcurrent population sizes in Berneray(Grid referenceNF905820) theseareas so that any future impacts of hedgehogson wader The site coversthe entire areaof cultivatedand uncultivated populationscan be measured. machairand dunesthat forms the westernhalf of the island (studyarea 5.5 km2). This is the driest of thethree study areas In 1997,breeding success of waderson hedgehog-free areas withno permanently marshy areas, though there are onNorth Uist wasfar higherthan on SouthUist butwas substantialareas of duneslack which are flooded in winter. At similarto thatduring the mid 1980sfor SouthUist (Jackson thetime of the survey cattle, but no sheep, were grazing the 1998).In viewof thishigh breeding success and the high site uncultivated machair and dunes. fidelityof thesebirds (Jackson 1994), it is surprisingthat the 1993and 1995 surveys recorded a decrease inpopulations of SURVEY METHODS RingedPlover, Dunlin andRedshank on someof theseNorth Thesurvey methods were exactly the same as those employed Uistsites. In 1998one of us(RJF) resurveyed breeding wader in theperiod 1983-87 except that much of Baleshareand 49 Table 1 Timing of surveysundertaken at the threesites 1983-1998. 'Early June'indicates that visits were madeduring the first two weeksof June Baleshare Sollas6 Berneray 1983• earlyJune earlyJune earlyJune 19842 5-6 June 1-2 June 8 June 19852 7-8 June 6 June 10 June 1986: 9-11 June 5 June 4 June 19872 3-7 June 2 June 10 June 19933 31May-3 June earlyJune earlyJune 19954 19-21 June 9 & 16 June 23 June 1998• 3-8 June 4-5 June 9-11 June Notes: JSurveys by NCC/Wader Study group teams of surveyors( Fuller et al. 1986) 2SurveysbyWader Study Group teams. RJF involved in allthese surveys 3Balesharesurveyed byRJF. Soilas and Berneray surveyed byRoyal Air Force Ornithological Society (RAFOS) (Dodds etal. 1995) 4Surveyby RSPB contract surveyors ( Whyte & O'Brien1995) 5SurveybyRJF with Vickie Heaney (Soilas) and Ruth Fuller (Baleshare) 6Thesite boundary usedin 1984-87 and 1998 differed tothat used inthe 1993 and 1995 surveys. The latter surveys included enclosedfields between the machair plain and the A865 road. The 1993 and 1995 counts have been adjusted by reference tothe pairsummary maps to makethem comparable with otheryears Berneraywas surveyedby a singleobserver (RJF) in 1998 thanfactors that influence their absolute accuracy i.e. their rather than by a team of two or three observers.This is not relationshipto real populationsize.