Many North American waders are recorded in Europe each year as transatlantic vagrants, but such vagrancy is much harder to identify in species that are common on both continents.
In May 2018, I was on the west coast of Iceland, which is a major spring staging area for Red Knot Calidris calidris islandica, the subspecies that winters in northwest Europe and breeds in the high Arctic of Canada and Greenland. On 18th May, I noticed a Knot with a lime-coloured coded flag-ring on the left tibia at Akrar lagoon (64.6ºN 22.4ºW); the three-character code (70H) together with the orange ring on the right tibia showed that it was ringed on 28th May 2012 at Hog Island, Virginia, USA (37.4ºN 75.7ºW), on its northward migration. The bird had been resighted just once before, on 27th July 2013 at the well-known staging site of the Mingan Archipelago, in the Gulf of St Lawrence, Canada (50.2ºN 63.8ºW), near the start of its southward migration. The wing and bill lengths (164 mm and 38.5 mm, respectively) were typical of C. c. rufa, whereas islandica is unlikely to have a wing length as short as this accompanied by a bill length as long. This is seemingly only the second Knot colour-ringed in the rufa flyway to be encountered in Europe. The subspecies rufa breeds in the Canadian low-Arctic and passes through east-coast states of the USA to and from wintering grounds on the coasts of south Florida, Texas, northern Brazil and southern South America (BirdLife 2018). A Knot ringed on 21st August 2008 at Mingan was resighted on 26th May 2010 in northeast Iceland (66.5ºN 15.9ºW) (Wilson et al. 2010), although measurements (wing 164 mm, bill 34.1 mm) were not unusual for islandica, so it is possible that this was an islandica temporarily displaced from its normal route. There are examples of islandica colour-ringed in May in Norway and resighted at Mingan (Wilson et al. 2010).
The Virginia bird provides firm evidence that rufa is a transatlantic vagrant. It may have been displaced during an earlier migration by the autumn weather systems that deliver many American vagrants to Europe, or it overshot on northward migration into the Canadian high-Arctic breeding grounds of islandica. Either way, it has now joined an islandica Red Knot flock. At present about one in 10–15 rufa Red Knots carry colour rings and flags, fitted throughout the migratory range from Canada to Chile. If rufa Red Knot is as susceptible to transatlantic vagrancy as American Golden Plover Pluvialis dominica or Buff-breasted Sandpiper C. subruficollis, there is a reasonable chance that scrutiny of Red Knot flocks in Europe, and especially at unusual locations on the Atlantic coast of Britain & Ireland, might also be rewarding.
Acknowledgments Thanks to Richard du Feu, Sarah Karpanty, Ed Keeble, Rose Maciewicz, Lena Usyk (http://bandedbirds.org) and Jim Wilson for their input.
BirdLife International. 2018. Species factsheet: Calidris canutus. (Downloaded from www.birdlife.org on 9th October 2018.)
Wilson, J. et al. 2010. Three records of Red Knots Calidris canutus possibly changing flyways. Wader Study Group Bull. 117: 192–193.
Peter J. Knight, Leeds; e-mail P.J.Knight@leeds.ac.uk