Wader studies in Orkney really got off the ground with the survey of the entire non-cliff shoreline of all inhabited islands of Orkney in the winters of 1982-83 and ...
Wader studiesin Orkney Colin Corse
Reprinted, byagreement withtheeditors,fromthe Shorelines featurein BTONews.
WaderstudiesinOrkneyreallygotoffthegroundwiththe surveyof theentirenon-cliff shoreline of all inhabited islands of Orkneyinthewintersof 1982-83and1983-84,carriedout jointlybymembers oftheTay,Grampian andOrkneyRinging Groups.Priorto this,theonlysurveys carriedouthadbeen theBritish TrustforOrnithology GoldenPloverandRinged Ploversurveys, anda PurpleSandpiper counton Mainland andSouthRonaldsay. Here,the progress overthe past decade is discussed.
Thecomplete survey,an important forerunner ofthe national WinterShorebird Count,showedthecoastline of Orkneyto holdinternationally important numbers offivespeciesof waderandnationally important numbers fora furtherthree (Table1). In total,51,500waderswerecounted, placing the Orkneycoastline alongside majorBritish estuarine sitesin its significance. Thefactthatsuchlargenumbers of wadersare
Figure.1 TheOrkneyIslands.
Table 1.
presenthadnotpreviously beenapparent, as onopen shores,birdsare moreevenlydistributed andin smallerflocks
Important concentrations ofwintering wadersalongtheOrkneycoastline.
Qualifying levelsfor: National International Importance Importance
Population on Orkney Coastline
2,800
9,O00
RingedPlover
230
500
1,600
Sanderling
140
1,000
860
PurpleSandpiper 160
500
Oystercatcher
than on estuaries.
Thisinitialsurveyledto severalquestions beingasked:how didthe numberofwadersusingtheshorevarythroughout the yearandfromyearto year,andwasanyseasonalvariation similarto thatfoundonestuarine sites?To helpanswer thesequestions, monthlycountshavesubsequently been carriedoutat foursiteson MainlandandSouthRonaldsay, providing a suiteof relevant datawhichcannowbeanalysed.
2,8OO
5,7OO
Bar-tailed Godwit
610
1,000
770
Curlew
910
3,500
17,700
Redshank
750
1,500
6,900
Turnstone
450
700
6,000
In addition to theseregularcounts,Sanday,a northern island foundto containhighconcentrations ofwadersinthefirst survey,hasbeencompletely surveyedduringthreemidwinters(January 1983,1984and1987)andthreesprings (lateApril1987,mid-May1988andearlyMay1989).Results fromthe mid-winter studiesrevealedthatRingedPlover, Turnstones andPurpleSandpiper are presentin relatively constantwinternumbers,butthat GoldenPlover,Dunlin,Bar-
37
Table2. Numbers ofwadersonSandayinwinterandinspring. 24-28
26-30
1-5
12-15
Jan1987
Apr1987
May1989 May1988
Oystercatcher
173
785
828
411
RingedPlover
345
193
188
224
Golden Plover
85
0
2
0
GreyPlover
41
81
78
91
0
42
791
117
Knot
Sanderling
212
283
433
353
PurpleSandpiper 1,103
1,055
1,660
509
1,245
135
582
157
Bar-tailed Godwit
601
45
268
219
Curlew
117
121
131
168
Redshank
725
164
204
58
Turnstone
1,242
1,800
3,409
2,591
Dunlin
tailedGodwitandCurlewvaryto a considerably greater extent.
Thespringsurveys onSandayshowed thatbyearlyMay, Turnstone numbers hadnearlytripledfromthesituation in mid-winter (Table2). A similarincreasewasnotrecorded at
anyofthemonthly countsitesonMainland orSouthRonaldsay,indicating thatSandaydiffersfromtheseareasinbeing important as a migration stagingplaceforTurnstones. Purple Sandpipers onSandayalsohadincreased by50%byearly May,withnumbers subsequently dropping sharplybymidMay.Sanderling andKnotalsoclearlypassthroughinMay, the latterspeciesbeingpresentin onlyverysmallnumbers in
cannonnetandhavecontinued to catchwadersfor ringing, concentrating in particular onPurpleSandpipers. TheOrkney wintering birdscomprise mainlythe'long-billed' population, the breedingrangeofwhichisstilluncertain as therehave beennorecoveries fromthe breeding grounds. Studieshave revealedthatalthough Icelandic breeding birdshavelong bills,theyalsohavelongerwingsandtarsithanPurple Sandpipers wintering inOrkney.It isnowsuspected that Orkneywintering PurpleSandpipers mayoriginate fromeither Greenland orCanada,asa birdcolour-dyed onSandayin April1987wassightedinsouth-west Icelandin lateMayof thesameyear,probably en routeto eitherGreenland or Canada.
In an attemptto assessthepopulation turnoveramong OrkneyPurpleSandpipers during the migration period,100 birdswerecolour-dyed inspring1990.NorthRonaldsay was chosenforthisstudyas itsentirecoastlinemeasuresonly18 kmandcouldbe countedeachdaywhilstourteamwasthere, andalsoafterwe leftona weeklybasisbystaffofthe North Ronaldsay BirdObservatory. Theresultsofthisproject are
stillbeingassessed, butwhilstcatching thesebirdswe controlled ourfirsteverPurpleSandpiper fromoutwith Orkney.Anadultcolour-ringed on Helgoland, offtheGerman coast,on 10 March1989andpresenthereagainfromat least 1 Marchto 18 April1990,wascontrolled byus19 dayslater, on7 May.Presumably itwasa birdstopping overinOrkney on itsreturnto itsbreedingground.
Ourlatespringtripsto SandayandNorthRonaldsay have alsoenabledusto collectmuchinformation onfatteningof PurpleSandpipers andTurnstone immediately priortotheir migration. Somestriking results areemerging fromthis,one examplebeingthe muchgreaterweightsreachedby Turnstone in northOrkneyrelative to birdscaughtat thesame timeofyearduringthe1988BTOstudiesonspringmigration inthe Hebrides (BTONews,July-August 1988).Couldit be thatHebrideanbirdssubsequently stagein Icelandwhereas Orkneybirdsflydirectly totheirbreeding grounds in Greenland and Canada?
A separateOrkneyringing studyhadbeenthedazzlingof RingedPlovers, mainlyinAugust andSeptember whenpeak winter. Oystercatcher numbers increase inspring, butbymid- numbersoccur.Althoughnumberscaughthavebeensmall, therehavealreadybeentworecoveries indicating the Mayhavedecreased again,dueto birdspassing throughor breeding andwintering areasoftheseautumnpassagebirds. movinginlandforbreeding andhencenotbeingcountedon the shore. AnadultringedinSeptember 1988wasfoundfreshlydeadin Finnmarkin late-May1989anda first-yearbirdringedin September 1986wascontrolled inTogo,WestAfrica,in Aswellas counting wadersinJanuary1983,theTayand Grampian Groups alsotrapped themusingtheirmin-cannon January1990. nets.In late1983theOrkneyRingingGroupitselfobtained a
