Eurasian Sandwich Tern in North America

Amazing Ringing Confirmation

This post is informed by several discussions with Greg Neise about this European Sandwich Tern in Chicago in 2010, arguabley a North American first, and ‘poaches’ (following discussion!) from an eBird post here with Marshall Iliff and a BTO post by Mark Grantham

by Marshall Iliff, Mark Grantham and Martin G.

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Although Sandwich Tern is a primarily southern species in North America, the European subspecies is common north through the British Isles. The nominate form, widespread in the Old World from Europe to South Africa and east to India, was recently split from the two New World subspecies by the British Ornithologists’ Union (Sangster et al. 2011) based on a genetic study by Efe et al. (2009). Cabot’s Tern includes two subspecies: northern T. s. acuflavidus has the typical black bill with a yellow tip (just like Eurasian Sandwich Tern) while the more southerly T. s. eurygnathus–also known as Cayenne Tern–has a yellow or orange bill. Cabot’s Tern (subspecies T. s. acuflavidus) has occurred in the United Kingdom twice (records discussed by Garner et al. 2007). The North American Classification Committee considered a split in Sandwich Tern this past year but elected to await more compelling evidence. Despite this decision, it still seems likely that New World and Old World Sandwich Terns will eventually be universally adopted as a split. On 31 July, a long, thin-billed Sandwich Tern was seen on Cape Cod, Massachusetts at South Beach (see photo-illustrated checklist by Blair Nikula). Also of interest, the bird sported a metal band on its right leg. An unbanded Sandwich Tern was spotted at nearby Coast Guard Beach/Nauset Marsh–about 10 miles north–on 3 Aug (illustrated checklist by Ben LaGasse). On 18 August, the banded Sandwich Tern was seen again, this time at Nauset Marsh. It now had a much whiter crown but otherwise appeared similar, with a very long drooping bill; it was accompanied by a bird (also seen 15 August) that looked similar in size and structure but with a more extensive dark cap (illustrated checklist by Keenan Yakola). Finally, on 21 August, Jeff Spendelow of the U.S. Geological Survey was able to read the band number on the banded Sandwich Tern: the band read “British Trust, London”. 20130821_102714

Mark Grantham (BTO) takes up the story:

For such an important record we were eventually able to confirm the ring number with the finder and this was indeed a bird from Northumberland: DB67406 had been ringed as a chick on Coquet Island in 2002. With just one previous record of a ‘possible’ in Chicago in 2010 (details here), this bird could well turn out to be the first Sandwich Tern record for the USA.

DB67406 was seen by biologist Jeff Spendelow, who studies the use of staging sites by Roseate Terns in the Cape Cod area of southeast Massachusetts. It was first seen on one of his study sites on 31st July, but it wasn’t until 21st August that Jeff was able to read its ring, with it also later seen at nearby Chatham on 7th September (in red on the map below). Several other intrepid American birders managed to paddle out to the islands to see the bird, but it was hardly ‘twitchable’! Photographs of the bird do also show many of the features used to separate Sandwich from Cabot’s Tern, but you can’t argue with a bird ringed as a chick in Europe!

Interestingly, there is an equally unusual record the other way round, with a Cabot’s Tern from the USA being found dead in the UK (in green on the map below). NAW 110386842 was ringed as a chick at Beaufort, in 1984 and was found dead in November 1984 at the rather bizarre location of Newhouse Wood in Herefordshire. It was reported independently (as a tern/gull) by two observers so is genuine, and is the first record of Cabot’s Tern in Europe. There have since been further records in Europe (including a possible Cayenne Tern in Wales), but this remains a most bizarre first.

View Map of ringing recoveries: Sandwich and Cabot’s Terns 

Recent work at several Sandwich Tern colonies in the UK has seen large numbers of chicks being colour-ringed, an even better way of keeping track of their movements. At Coquet, 52 chicks were colour-ringed this year alone, with a further 102 on the Farne Islands. Of the latter, 11 have been seen further north in the autumn, from Musselburgh to Findhorn. Birds have also been colour-ringed in Norfolk, Grampian and The Netherlands, so plenty to keep an eye out for. Eurasian Sandwich and Cabot’s Terns are extremely similar. Garner et al. (2007) point out striking differences in juvenile plumage, with Eurasian birds having strong black chevrons on the scapulars in comparison to much more muted upperparts of juvenile Cabot’s Terns. In adult plumage they are much trickier to identify. Potential field marks include: 1) long, thinner, more drooping bill with less of a gonydeal angle in Eurasian Sandwich; 2) broader white fringe to the fresh primaries in Eurasian Sandwich; 3) typically earlier primary molt in Eurasian Sandwich; 4) more ‘salt and pepper’ speckling on the crown of Eurasian Sandwich, with the speckling extending farther foreword on the crown. The Massachusetts bird has a very white forehead and central crown, more like Cabot’s. However, the very fine speckling towards the rear crown may suggest Eurasian Sandwich. The freshly molted inner primaries visible on the 31 July photos by Blair Nikula could be a point in favor of Eurasian Sandwich and the pale tip, although hard to discern, does seem quite broad on the freshest primary. But overall, identification from plumage and structure may not be diagnostic; whether this individual can be confirmed as North America’s first Eurasian Sandwich Tern may depend on what is learned from the band details. There is just one prior suggestion that Eurasian Sandwich Tern has occurred in North America. Greg Neise, in a blog post discussing Illinois’s second record in September 2010, pointed out the very long, drooping bill of that bird and the molt pattern of the crown, making a case for North America’s first Eurasian Sandwich Tern. Chicago is so far outside the normal range of Cabot’s Tern, that either taxon might be almost equally likely here, so this was an interesting suggestion. Whether or not the ID of the Chicago or Massachusetts birds can be confirmed from the existing photos remains to be seen, but we strongly encourage observers to be aware of the possibility of Eurasian Sandwich Tern in North America and to extensively document any suspected occurrences. Within eBird, carefully identified terns can be entered as Sandwich Tern (Cabot’s), Sandwich Tern (Eurasian), and for the yellow or orange-billed population in the Caribbean, Sandwich Tern (Cayenne). Under all circumstances, we recommend identification at the subspecies level to be based on careful assessment of field characters, rather than assumptions about what subspecies seems more likely. As evidenced by this story, we still have much to learn and a significant proportion of the Sandwich Terns in the Northeastern U.S. and Atlantic Canada may in fact turn out to be trans-Atlantic strays rather than wanderers from further south on the Atlantic coast.

Comments on ID issues from Martin G.

Hi Mark
 
I have picked up the story and found other photos….
 
This is of course an amazing record whichever taxa is involved. Given that acuflavida has reached Europe and that there are instances of Nearctic species reaching Britain and returning to North America (Ring-billed Gull and maybe American Wigeon? spring to mind), I tried not to be swayed and see what identification features I could see on this bird irrespective of any known ‘life history’.
 
First point is that when we did the research which culminated in the Dutch Birding paper, we reckoned that the period in which the photos of this bird are taken (July and August in N America) is the most difficult to separate Sandwich and Cabot’s terns “with the effects of wear and moult at their peak during late summer and autumn, this may be the most difficult period to establish a frim identification”. Broadly speaking I still think this is true.
 
However there are some clues on this bird, at least as I interpret the photos (Blair Nikula’s are especially helpful).
 
1) The head pattern shows quite extensive plain looking white patch on the forehead to mid crown. 9410293319_124e53da19_oThe black rear crown feathers are relatively short and fairly obviously peppered with white tips etc. While the plain white area may suggest acuflavida I think it is OK for some sandvicensis. Sort of equivocal for adults. You would expect more black peppering in white area in 1cy birds. However the black rear crown feathers is for me more typical of sandvicensis than acuflavida. Short and obviously white peppered- versus in the vast majority of cases longer, greasy looking and any white tips very tiny on acuflavida- probably hardly visible on the quality of these images. While it’s not absolute and there may be extreme examples of both taxa that fit this head pattern, by gut would be it favours sandvicensis
 
2) The bill shape is quite deep based but I get the impression of a longish bill, obviously decurved slightly and rather fine over the distal half. Difficult to quantify and I wouldn’t stake the full ID (extremes of both taxa can be more obvious)  on it but on balance I would favour sandvicensis
 
3) Most compelling for me are the tips off the outer primaries. These feathers are all old and worn and the critical width of white on the inner web and feather tip is not longer visible. However in some birds white pigmented parts or feathers wear faster than black ones. This is perhaps more familiar in Two-barred Crossbills, in which worn tertials have no white tips left but the shape of the worn tertials can clearly be traced where the white pattern once was. On this bird in a couple of different photos you can clearly see the feather tip is not neatly rounded or pointed but has little ‘pimple’ for a tip- the inner web stopping short of the tip and leaving extra section of outer web extending on. This is the expected shape of wear for a sandvicensis with its broad white tip and broader white fringed on the inner web. On acuflavida the white fringes and tip is too thin to leave such an obvious wear pattern. You may well know that Greg Neise first flagged this up to me on the (to me obvious sandvicensis) he had in Chicago.
 
In short I think this is a ‘sandvicensis’. I am not sure I would be unequivocal/ 100% as I think that e.g. the Chicago bird is a more obvious example, however re-introducing the ‘ring’ element on this bird, the most parsimonious explanation is this is European Sandwich Tern, ringed in UK and travelling to N. American- based on both plumage/structure and parsimony.
 
For me it breaks through the credibility barrier- European Sandwich Terns can and do reach North American (as well s vice versa!)
 
Hope that helps
 
Cheers Martin

REFERENCES: 

Efe, M.A., Tavares, E.S., Baker, A.J. & Bonatto, S.L. 2009. Multigene phylogeny and DNA barcoding indicate that the Sandwich Tern complex (Thalasseus sandvicensis, Laridae, Sternini) comprises two species. Mol. Phylogenet. Evol. 52: 263–267.

Garner, M., Lewington, I. & Crook, J. 2007. Identification of American Sandwich Tern. Dutch Birding 29: 273–287. [online here]

George Sangster, Martin Collinson, Pierre-Andre Crochet, Alan G. Knox, David T. Parkin, Lars Svensson, Stephen C. Votier. 2011. Taxonomic recommendations for British birds – seventh report. Ibis 153: 883-892. [online here].

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