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Staging duration and passage population size of Sanderlings in the western Dutch Wadden Sea
Loonstra, A.H.J.; Piersma, T,; Reneerkens, J. (2016). Staging duration and passage population size of Sanderlings in the western Dutch Wadden Sea. Ardea 104(1): 49-62. dx.doi.org/10.5253/arde.v104i1.a4
In: Ardea. Nederlandse Ornithologische Unie: Arnhem; Leiden. ISSN 0373-2266, more
Peer reviewed article  

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Keyword
    Calidris alba (Pallas, 1764) [WoRMS]
Author keywords
    Calidris alba; staging ecology; capture-recapture models; colour-ringing; staging duration; site fidelity; population estimation; Wadden Sea; primary moult; migration

Authors  Top 
  • Loonstra, A.H.J., more
  • Piersma, T,, more
  • Reneerkens, J.

Abstract
    The population of Sanderlings Calidris alba along the East Atlantic flyway hasgrown considerably during the last decades. Perhaps reflecting this augmentedpopulation size, increasing numbers of Sanderling have been reported to stagein the Wadden Sea during spring and autumn migration. Estimates of thenumbers of Sanderlings in the Wadden Sea have previously been based on alimited number of counts that were not corrected for the turnover of individuals.In this study, we accounted for turnover using estimates of the probability thatindividually colour-ringed Sanderlings are still present two days after a sighting.In combination with daily counts during high tide, we estimated the total numberof Sanderlings that used the island Griend and surrounding mudflats, in thewestern Dutch Wadden Sea, during southward passage in 2013 and 2014. Wealso estimated minimal staging durations of Sanderlings at Griend. Nonmoultingbirds were significantly heavier upon capture, which suggests thatthey were refuelling for long non-stop migratory flights. Winter sightingsconfirmed that the non-moulting Sanderlings winter in sub-Saharan Africa andthat the moulting Sanderlings spent the winter in Europe or northern Africa.With an average minimal stay in the western Dutch Wadden Sea of 9 days in2013 and 12 in 2014, non-moulting Sanderlings stayed for a much shorter timethan moulting Sanderlings, which stayed for 32 days in 2013 and 36 days in2014. Non-moulting individuals were less likely to be resighted between years.Estimates of minimal staging duration are likely underestimates of the truestaging duration, and we propose that moulting Sanderlings probably completetheir wing moult in the Wadden Sea. We estimated that the total number ofSanderlings using the western Dutch Wadden Sea before migration to Euro -pean or African wintering areas were 27,546 (95% CI 22,739–41,449) in 2013and 22,574 (95% CI 16,436–46,114) in 2014. This would amount to 11–14% ofa total flyway population of 200,000 individuals, representing an amazingdegree of concentration for what is regarded as a rather widely and thinlyspread shorebird species.

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