Wader communities in Dublin Bay

Irish Birds (8) 2008: 459

Stewart Holohan

Wader counts have been made on a weekly basis in Dublin since September 2003. Weather permitting, birds are counted 52 weeks per year, to obtain detailed data on the seasonal distribution of species, plumage/moult details, the presence and numbers of juveniles, and on colour-rings and flags. To date (mid-September 2008) over 300 detailed counts have been made, with particular emphasis on the North Bull Island, (over 200 counts). These are continuing on a weekly basis. The purpose of the study is to compare the pattern of Irish wader migration with that of species using identical or similar ecological niches on the Canadian prairies, because the nesting areas of the two flyway groups are similar. Examples are Red Knot Calidris canutus, Sandering C. alba, Dunlin C. alpina and Ruddy Turnstone Arenaria interpres. The same has been proven to be true in Dublin Bay.

Special emphasis is placed on obtaining counts in the previously neglected period of May to mid-August, when it was assumed not much was happening on Irish estuaries. Papers published by the author of this abstract, and Canadian colleagues, on prairie waders have shown that there is a great deal of movement during this summer period. There is a gap of about ten days between the end of the northwards spring migration in June and the appearance of the first Lapwing Vanellus vanellus. In addition, moulting Oystercatchers Haematopus ostralegus, Bar-tailed Godwits Limosa lapponica and Curlews Numenius arquarta are present through summer.

The distribution curve for waders in Dublin Bay shows that the lowest numbers occur in mid-June, but there are always five species present. From around 24 June wader numbers rise very rapidly as presumed unsuccessful breeding birds return to the bay to moult, or stage on migration further south. Peak numbers occur from 21 November to 24 February. They then decrease very rapidly as mainland European nesting birds depart for eastern staging areas such as The Wash (England) or the Wadden Sea (Germany, Denmark and The Netherlands). This is indicated by the presence of colour-ringed or flagged birds from these well studies wader areas. A considerable number of waders from Iceland and Greenland, and probably Nunavut-bound migrants, also pass through Dublin Bay, as proved by colour-ringing.

Considerable effort has been put into finding colour-ringed or flagged birds in order to identify the origins of waders using Dublin Bay. The general areas of origin have been known for a long time (i.e. Europe and North America), but now this study has clarified the origins of five wader species. The most interesting finding so far is hat Sanderlings in Dublin Bay have come from northeast Greenland and Mauretania. This study is continuing, with emphasis on establishing wider links with the Nunavat-Greenland wader breeding areas.

(Website editor comment: The author of this work died on 18th March 2014. Stewart's research on waders is unique in Irish Ornithology having been carried out continuously over a ten year period (2003-2013). Stewart was a highly experienced and respected ornithologist whose research on birds on a number of continents spanned several decades. His work on the Wader Communities of Dublin Bay provides valuable information on their movements during migration, winter and summer.
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