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Sandwich Tern - BirdForum Opus

Sandwich Tern
Photo © by beakerbaz
Minsmere, Suffolk;16 July 2011

Includes Cabot's Tern and Cayenne Tern

Thalasseus sandvicensis

Sterna sandvicensis

Identification

Sandwich Tern, adult in flight
Photo © by NIGHTJAR1
Farne Islands, Northumberland, UK, July 2006

Length 36–46 cm (14¼-18 in), wingspan 85-97 cm, weight 130-285 g

  • Slender black bill with pale yellow tip
  • Black legs
  • Feet have yellow soles
  • Light grey above with blackish wing tips. The rump and rather short forked tail are white. Underparts white (rarely faintly tinged creamy-pink).

Summer Adult: forehead, crown and nape black. Loose long feathers at the nape form a crest in the wind or when excited.
Winter Adult: black areas on the front and top of the head turn white and speckled black on the crest. This can happen as early as June, more usually from July onward.
Juvenile: scalloped with blackish-brown chevrons on mantle and wings, brown on forehead, crown and nape; white elsewhere. Bill is blackish-yellow to all black.
First-winter: mantle becomes pale grey, and forehead white after post-juvenile moult in a month or two after fledging; some scalloping remains on wing coverts.

Variation

T. s. acuflavidus differs from T. s. sandvicensis most obviously in a shorter, stouter bill; in South American eurygnathus populations the bill contains an increased amount of yellow. There are also differences in timings of wing moult, and in the juvenile plumage having less scaling on the mantle[5].

Similar species

Gull-billed Tern is superficially similar in plumage, but differs structurally, with longer legs, shorter broader wings (more gull-like in flight), shorter, thicker, all-black bill, no crest, and a pale grey rump.
Lesser Crested and Elegant Terns are structurally very similar, but differ in their bright orange bills, and in Lesser Crested, also a pale grey rump, and in Elegant, a longer bill.
Juvenile Roseate Tern has a similar scalloped mantle pattern, but is smaller, has a darker forehead, and a longer tail.

Distribution

Sandwich Tern, fresh juvenile (bill not yet fully grown)
Photo © by Xmor
Farne Islands, Northumberland, UK, July 2014

A breeding summer visitor widely on the coasts of Europe and southwestern Asia (Estonia west to Ireland, and western France, and east through the Mediterranean from northeast Spain to the Black Sea and Caspian Sea), wintering on the west and north coasts of Africa, the Arabian Sea, and locally of western India. A separate [sub]species (see Taxonomy, below) breeds on the Atlantic coasts of North and South America, wintering additionally on the Pacific coast of northern South America.

Taxonomy

Like the other Thalasseus terns, this species was formerly often placed in the genus Sterna.

Subspecies

Cabot's Tern, adult summer
Photo by bobsofpa
South Padre Island, Texas, 8 April 2016; note stout-based bill compared to Sandwich Tern

Three subspecies are recognised by some authorities[1], while others treat it as monotypic, with the other two subspecies treated as separate species[2][3]:

  • Sandwich Tern Thalasseus sandvicensis sensu stricto
    • T. s. sandvicensis breeds on the Atlantic and Mediterranean coasts of Europe and winters mostly in the Mediterranean area and on the west coast of Africa but also some up to western Europe.
  • Cabot's Tern Thalasseus (sandvicensis) acuflavidus
    • T. s. acuflavidus breeds on Atlantic coasts of North America and winters on Caribbean and northern South American coasts.
    • T. s. eurygnathus breeds and winters on the Atlantic coast of South America.

A study of genetic data[4] showed that acuflavidus (including eurygnathus) was more closely related to Elegant Tern than to Sandwich Tern, and should be treated as separate species, Thalasseus acuflavidus. In the past, the populations with all or mostly yellow bills were sometimes treated as a separate species, Cayenne Tern T. eurygnathus, but in genetics these are very close to Cabot's Tern[4]. However, notice that the evidence was evaluated by the AOU NACC in 2013 and that the evidence was found lacking in quality[10].

There are one or two records of transatlantic vagrants of each of T. s. sandvicensis in North America and T. s. acuflavidus in Europe; in both cases including ringed birds which allowed confirmed identification at a time when field identification between them was still poorly researched[6][7].

Habitat

Almost entirely marine. Breeds on shingly, sandy or rocky islands with a high degree of protection from land predators.

Behaviour

Flight

Strong flight, often quite high.

Breeding

Colonial nesters (often with Common, Arctic, or other terns), the nest is a ground scrape and they lay 1-3 eggs.

Diet

Their diet consists mostly of small fish (caught by plunge-diving), including squid and shellfish.

Vocalisation

Gallery

Click on images to see full size

References

  1. Clements, J. F., T. S. Schulenberg, M. J. Iliff, S. M. Billerman, T. A. Fredericks, J. A. Gerbracht, D. Lepage, B. L. Sullivan, and C. L. Wood. 2021. The eBird/Clements checklist of Birds of the World: v2021. Downloaded from https://www.birds.cornell.edu/clementschecklist/download/
  2. Gill, F and D Donsker (Eds). 2016. IOC World Bird Names (version 6.3). Available at http://www.worldbirdnames.org/.
  3. Sangster, G., et al. (2011). Taxonomic recommendations for British birds: seventh report. Ibis 153: 883–892.
  4. 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. Phyl. Evol. 52: 263‑267.
  5. Garner, M., Lewington, I., & Crook., J. (2007). ldentification of American Sandwich Tern. Dutch Birding 29: 273-287.
  6. Neise, G. (2011). North American Birding (blog): Sandwich or Cabot's?
  7. Iliff, M., Grantham, M., & Garner, M. (2013). Birding Frontiers (blog): Eurasian Sandwich Tern in North America
  8. Collins Bird Guide ISBN 0 00 219728 6
  9. Handbook of the Birds of the World Alive (retrieved September 2016)
  10. NACC proposals (2013) including one for splitting this species into two, which failed.

Recommended Citation

External Links

GSearch checked for 2020 platform.

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