Abstract An adult Black Tern Chlidonias niger, initially identified as a ‘European Black Tern’ C. n. niger, was present at a tern colony at Long Nanny, Northumberland, during the summers of 2020 and 2021. At the end of summer 2021, the bird was reidentified as an ‘American Black Tern’ C. n. surinamensis – the first record of a breeding-plumaged adult in Britain. The bird returned again in summer 2022. This paper discusses the bird’s occurrence, its identification and other records of American Black Terns in breeding plumage in Europe.
A Black Tern Chlidonias niger was discovered on 30th May 2020 at the Arctic Sterna paradisaea and Little Tern Sternula albifrons colony at Long Nanny, Northumberland. The bird was regularly seen visiting the tern colony during summer 2020, the last definite sighting being on 25th June. The bird returned in 2021, when it was seen between 19th May and 22nd July, and again in 2022, when it was recorded between 13th May and 29th August. As the bird could often be observed at close range, it proved popular amongst local and visiting birders, and many good photographs were taken (e.g. plates 107 & 108).
During summer 2021, I was undertaking survey work to look at disturbance of birds by recreational activities at Lindisfarne NNR. A colony of Arctic and Little Terns on Black Law fell within the area I was surveying, being viewable from Holy Island and Ross. On 10th July, I was surprised to pick out a breeding-plumaged adult Black Tern roosting on intertidal rocks near this colony. I realised it was likely to be the Black Tern that had been seen at the Long Nanny tern colony. I made a note to check the features of ‘American Black Tern’ C. n. surinamensis after I had returned home from the survey work, motivated by a long-held ambition to find a rare tern in a Northumberland tern colony and a desire to learn what adult American Black Terns looked like in breeding plumage.
As I checked the first few online photos of adult American Black Terns, I was amazed at their similarity to the Northumberland bird. In particular, the striking black underparts of the Northumberland individual matched those of American Black Terns, clearly darker than those of ‘European Black Terns’ C. n. niger. It also quickly became apparent that American Black Terns have darker upperparts than European birds, and this feature was also shown by the Northumberland bird.
I soon learnt of further features for separating American from European birds: American Black Tern shows whiter underwings and a paler leading edge along the wings compared with European Black Tern
I e-mailed photos of the Northumberland bird to various people with relevant experience of American Black Tern. The majority of responses were in favour of American, while the remaining people replied that they had no experience of separating adult American from European.
Klaus Malling Olsen commented: ‘[The Northumberland bird] is as good as it gets for surinamensis. The head and underbody are concolorous (in niger, the head is usually the darkest part, slightly contrasting against the greyer-tinged body), the underwings really look white, the upperparts are slightly darker than in niger, and T6 [the outermost tail feather] is as grey as the rest of the tail (in niger, this is slightly paler).’
Following the bird’s reidentification as an American Black Tern in late July 2021, the news was put out on national bird-news services. However, few people saw the bird in 2021 following its reidentification; it was not seen again that year after 22nd July.
The bird returned once again in 2022 and, this time, many more birders had a chance to see it.
After checking through past records on BirdGuides (www.birdguides.com), it became clear that the bird had also been present at other locations in Northumberland. On 30th June 2021, it was at East Chevington, while sightings of a ‘Black Tern’ at various sites along the Northumberland coast during the summers of 2020 and 2021 may also have related to the same individual. In summer 2022, the bird was also seen on the Farne Islands and Coquet Island.
It was suggested that the bird could have been the juvenile American Black Tern seen briefly at St Mary’s Island, Northumberland, on 7th October 2019 (the first county record; Brit. Birds 113: 608–609). However, since Black Terns – both American and European – show a distinct first-summer plumage, it would have been expected that the Long Nanny bird would have exhibited such a plumage in summer 2020. That it didn’t – it was in full adult breeding plumage – shows that it was a different (older) individual.
The adult American Black Tern was seen bringing fish into the Long Nanny tern colony in 2020 and 2021 (plate 107), and conversations with the National Trust tern wardens on site revealed that it was regularly seen displaying to Arctic Terns in 2022, even into June, when Arctic Terns already had eggs. This behaviour indicated that the bird was a male. Perhaps not surprisingly, it has so far been unsuccessful in attracting a mate.
In certain lights, the bird’s head appears slightly darker than the underparts, which further supports it being a male, as males are reported to have darker heads than females
In 1999, the time of the first British record of American Black Tern, Andrews et al.
Compared to European Black Terns, American Black Terns show: darker underparts; darker upperparts; paler underwings; a more obvious pale leading edge to the wings; and black bleeding down from the back of the neck onto the mantle (see also fig. 1 and plates 110 & 111).
Using the same photos, I also looked at the coloration of the outer web of T6. Again, I found little difference between European (28% showed a paler outer web, 72% showed an outer web the same colour as the rest of the feather) and American (22% showed a paler outer web, 78% showed an outer web the same colour as the rest of the feather). Overall, I found the coloration of the outer tail feather of little use in separating individual American Black Terns from European Black Terns.
Andrews et al.
Andrews et al.
To test the extent to which moult timing could be used to distinguish American and European Black Terns, I checked for photos on the Macaulay Library website of birds beginning to show the first signs of moult into non-breeding plumage (i.e. a small number of white feathers around the bill). I found photos of 65 American and 51 European birds fitting the criterion. The mean date on which the 65 American birds were showing the first signs of moult into winter plumage was 31st July (s.e. ±2.31 days), while the mean date for the 51 European birds was 2nd July (s.e. ±2.52 days). The earliest date on which an American Black Tern showed signs of moult was 3rd July, in contrast to 1st June in European Black Tern. These dates are later than those reported by Andrews et al., but my dates are based on a fairly small sample, plus it is likely that some birds had started moult before the photo was taken. In summary, moult can be useful in separating American and European Black Terns – any Black Tern still in full breeding plumage or showing only the first signs of moult after late June should be checked for American Black Tern.
Andrews et al.
Harrison et al.
The coloration of the crown is a useful feature in separating adult American and European Black Terns that are moulting to non-breeding plumage. In American Black Tern, the crown appears to be grey, whereas in European Black Tern the crown appears to be more solidly blackish (Rich Andrews pers. comm.). This difference in apparent darkness may be caused by a difference in the amount of white mottling in the crown – American Black Tern shows more than European Black Tern. This difference in crown coloration will become apparent as moult of the head nears completion in summer.
Accurately gauging the darkness of the underparts and upperparts is key in the identification of adult American Black Terns. However, light conditions can greatly influence the apparent coloration of the plumage, to the extent that the difference in coloration between photographs of the same individual can appear as great as the difference between subspecies (see plate 113). When foraging, for example, Black Terns are constantly changing their posture and angle relative to sunlight, with different feather tracts shaded and exposed to sunlight in any given moment, which creates a changeable impression of coloration. Assessing coloration of Black Terns is likely to be most straightforward in flat light with high and light cloud cover. In dull and overcast conditions, European Black Terns can look darker, while in strong sunlight American Black Terns can appear paler. In Britain, adult breeding-plumaged Black Terns are often observed in spring in poor weather conditions (dull and overcast with precipitation) when they are forced down to inland waterbodies during their cross-country migration.
The coloration of the surface beneath the bird is also a factor – the underwings of an adult Black Tern will appear paler when the bird is above sand than when it is above water. When checking photographs, an assessment of coloration should be made using a series of photographs rather than just one or two. This is because, in a single photograph, American Black Tern can look pale and European Black Tern can look dark, depending on light conditions and camera settings.
Vocal differences appear to exist between American Black Tern and European Black Tern (Magnus Robb in litt.). The main advertising call of American birds (e.g. https://xeno-canto.org/160707) appears to be much faster than that of European birds (e.g. https://xeno-canto.org/102222). This apparent difference in vocalisations may be limited to adults. However, differences in vocalisations between surinamensis and niger need to be properly tested using an appropriate sample. I could find no recordings of the Northumberland bird.
The behaviour of the Northumberland American Black Tern – returning in multiple years to spend the summer in a coastal Arctic and Little Tern colony – is unusual in Britain. American Black Tern breeds in shallow freshwater marshes in open and forested country
I searched the databases of photos on the BirdGuides and Macaulay Library websites for possible adult American Black Terns that have been misidentified as adult European Black Terns. The search did not find any good Americancandidates; however, it showed how individuals of European birds can occasionally look as dark as American birds in some images while appearing normal in others (plates 114 & 115).
Vagrancy of American terns to Europe
The first record of American Black Tern for the Western Palearctic was a juvenile in Iceland in September 1950. Five more records followed in Iceland between 1956 and 1979, but it was not until 1999 that any were found elsewhere, when juveniles were in Dublin, Co. Dublin, in September and at Weston-super-Mare Water Treatment Works, Somerset, on 3rd–11th October. By the end of 2021, there had been a further seven birds in Britain (all in autumn) and 12 elsewhere in the Western Palearctic. All except five records related to juveniles; records of adults are limited to four records in Iceland and a bird feeding in Funchal harbour, Madeira, on 19th August 2007 (see http://madeira.seawatching.net/species/Chl_nig_sur/index.html). In addition, a first-summer was at Lady’s Island Lake and Carnsore Point, Co. Wexford, in July 2006
Magnus Ullman (pers. comm.) said of the Madeiran bird: ‘We found the bird from a boat going out for a seawatch as it was foraging in Funchal harbour. The bird immediately struck us as “a Black Tern looking like a White-winged Black Tern”, so we asked the skipper to make an extra turn in the harbour for us to take some photos. The bird showed pitch-black underparts, just as black as the head, and we also got the impression of black coloration down the nape/mantle, unlike the grey tone of niger. Moreover, the leading edge of the wing was obviously and contrastingly white. At the time, we also concluded that the full breeding plumage in mid August suited surinamensis better than niger, which starts moulting the head in June. As far as I know, the bird was not seen again.’
Northumberland has a propensity for attracting rare terns owing to the county’s coastal Arctic, Common, Sandwich Thalasseus sandvicensis and Little Tern colonies. To date, an impressive list of vagrant terns has been recorded, most famously the Western Palearctic’s only Aleutian Tern Onychoprion aleuticus, on the Farne Islands on 28th and 29th May 1979, and the female Lesser Crested Tern T. bengalensis, ‘Elsie’, that returned to the Farne Islands each summer between 1984 and 1997. Other vagrant terns recorded in the vicinity of Northumberland’s tern colonies include Gull-billed Tern Gelochelidon nilotica, Caspian Tern Hydroprogne caspia, Bridled Tern O. anaethetus, Sooty Tern O. fuscatus, Whiskered Tern C. hybrida and White-winged Black Tern. However, there are still a number of species as yet unrecorded in the county: American Royal Tern T. maximus, African Royal Tern T. albididorsalis, Cabot’s Tern T. acuflavidus, Elegant Tern T. elegans, Least Tern and Forster’s Tern S. forsteri.
Of the 19 species of tern on the British List, only Sandwich Tern, Lesser Crested Tern, Little Tern, Whiskered Tern and White-winged Black Tern have breeding ranges that do not fall inside the Americas. The breeding ranges of several species fall entirely within the Americas: Royal Tern, Cabot’s Tern, Least Tern and Forster’s Tern. The breeding ranges of the other species listed in table 4, such as Arctic Tern, occur both in the Americas and in other parts of the world. Rare species in Britain, such as Gull-billed Tern, Caspian Tern, Sooty Tern and Bridled Tern, may reach Britain from a variety of compass points including the Americas and ringing recoveries have confirmed that individuals of species such as Cabot’s Tern and Caspian Tern have originated from North America. As the American subspecies/populations of these species differ only slightly, if at all from Western Palearctic populations, it is usually impossible to prove American origin unless the bird carries an American ring. However, as in the case of the Northumberland surinamensis, the dates and locations of occurrences in Britain may offer a clue regarding likely origin. For example, Gull-billed Tern occurs most frequently in Britain along the south coast and in East Anglia between May and August. October and November records of Gull-billed Tern are less frequent (comprising about 5% of the total) but several have occurred in regions where Gull-billed Tern is rare at other times of year, raising the possibility that these individuals could be of American origin. For example, Gull-billed Terns in Northumberland in October 2018, Argyll in September–October 2008 and Dumfries & Galloway in October 1990 may all relate to birds of American origin. That said, Gull-billed Tern is a scarce breeder in eastern North America, where fewer than 800 pairs are present (Ian Nisbet pers. comm.). As with American Black Tern, Forster’s Tern tends to be found at locations where, and at times of year (late autumn and winter) when, other tern species are scarce, and the species is likely to be overlooked in spring and summer given its similarity to Common Tern
European Black Tern has yet to be recorded as a vagrant to the USA, which may be because the subspecies is not on the radar of many birders there (Peter Pyle and Julian Hough pers. comms.). However, there is a record of a European Black Tern ringed in Germany in 1984 that was recovered in Brazil in 1986
Whiskered Tern has occurred in the Americas on three occasions, and White-winged Black Tern is more frequent
It is fascinating to speculate on the point at which the Northumberland American Black Tern joined the Arctic Terns that it generally associates with in Northumberland. The majority of records of American Black Tern in Europe have been of juveniles that have arrived in the autumn, which are assumed to have recently crossed the Atlantic from the Nearctic, and the Northumberland American Black Tern perhaps arrived this same way. However, vagrant American Black Terns in Europe generally arrive here one to two months after the majority of Arctic Terns have departed Britain, and so the Northumberland bird was unlikely to have joined Arctic Terns initially on arrival. The bird may have joined Arctic Terns during their return migration in spring, or it may have migrated north separately and joined the Arctic Terns once in Britain. Alternatively, although Arctic Tern has a more southerly non-breeding distribution (primarily around Antarctica) than European Black Tern (coastal tropical Africa), some Arctic Terns remain off equatorial Africa in the winter
Thanks to the following for reading early drafts of the article: Rich Andrews, Rupert Higgins, Chris Knox, John Martin, Keith Naylor, Ian Nisbet and Andy Stoddart. The following individuals helped with the Northumberland bird’s identification and details of previous records of American Black Tern in Europe: Peter Adriaens, Martin Collinson, Pierre-André Crochet, Kate Goodenough, Julian Hough, Yann Kolbeinsson, Daniel López-Velasco, Klaus Malling Olsen, Doug Pratt, Peter Pyle, Pedro Ramalho, Lars Svensson, Patricia Szczys, Magnus Ullman, Arnoud B. van den Berg and Nils van Duivendijk.
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Ross Ahmed, Northumberland; e-mail [email protected]
Ross Ahmed picked up his first pair of binoculars just short of 30 years ago, when he was 11 years old. He has worked as an ornithologist for most of his adult life. He enjoys the challenge of finding birds in the field, particularly at his adopted patch of Holy Island and Lindisfarne NNR, Northumberland. However, he is equally at home behind a computer, where he savours working with numerical data to gain greater insights into topics such as bird distribution and identification.