Thegull-billed tern (Gelochelidon nilotica) is atern in the familyLaridae. It is widely distributed and breeds in scattered localities in Europe, Asia, northwest Africa, and the Americas. TheAustralian gull-billed tern was previously considered a subspecies.
The gull-billed tern wasformally described in 1789 by the German naturalistJohann Friedrich Gmelin in his revised and expanded edition ofCarl Linnaeus'sSystema Naturae. He placed it with terns in thegenusSterna and coined thebinomial nameSterna nilotica.[2] Gmelin based his description on the "Egyptian tern" that had been described in 1785 by the English ornithologistJohn Latham in his bookA General Synopsis of Birds.[3] Latham had in turn based his own account on that by the Swedish naturalistFredrik Hasselquist that was published in 1757.[4] The gull-billed tern was moved to the resurrected genusGelochelidon based on amolecular phylogenetic study published in 2005.[5][6][7] The genus had been introduced in 1830 by the German zoologistAlfred Brehm.[8] The genus name combines theAncient Greekgelaō meaning "to laugh" withkhelidōn meaning "swallow". The specific epithetnilotica is fromLatinniloticus meaning "of the River Nile".[9]
This is a fairly large and powerful tern, similar in size and general appearance to aSandwich tern, but the short thickgull-likebill, broad wings, long legs and robust body are distinctive. The summer adult has grey upperparts, white underparts, a black cap, strong black bill and black legs. The call is a characteristicker-wik. It is 33–42 cm (13–17 in) in length and 76–91 cm (30–36 in) in wingspan.[10][11] Body mass ranges from 150–292 g (5.3–10.3 oz).[12]
In winter, the cap is lost, and there is a dark patch through the eye like aForster's tern or aMediterranean gull. Juvenile gull-billed terns have a fainter mask, but otherwise look much like winter adults.
Juvenile Sandwich terns have a short bill, and are frequently mistaken for gull-billed tern where the latter species is uncommon, such asNorth Sea coasts.
It breeds in warmer parts of the world in southernEurope, temperate and easternAsia, both coasts ofNorth America, easternSouth America. Thisbird has a number of geographical races, differing mainly in size and minor plumage details.
All forms show a post-breeding dispersal, but the northern breeders are mostmigratory, wintering south toAfrica, theCaribbean and northern South America, southern Asia and New Zealand.
The gull-billed tern is one of the species to which theAgreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.
The gull-billed tern breeds in colonies on lakes, marshes and coasts (including bays and earthen levees). It nests in a ground scrape and lays two to five eggs. While widely distributed in freshwater areas in Eurasia, it is associated almost solely with saltwater, coastal areas in North America.[10]
This is a somewhat atypical tern, in appearance like aSterna tern, but with feeding habits more like theChlidonias marsh terns,black tern andwhite-winged tern. It does not normally plunge dive forfish like the other white terns, and has a broader diet than most other terns. It largely feeds on insects taken in flight, and also often hunts over wet fields and even in brushy areas, to take amphibians and small mammals.[10] It is also an opportunistic feeder, and has been observed to pick up and feed on dead dragonflies from the road.[13]
^Bridge, E.S.; Jones, A.W.; Baker, A.J. (2005). "A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution".Molecular Phylogenetics and Evolution.35 (2):459–469.Bibcode:2005MolPE..35..459B.doi:10.1016/j.ympev.2004.12.010.PMID15804415.
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