Whiskered Tern Chlidonias hybrida Scientific name definitions

23–29 cm; 60–101 g (mean 84 g); wingspan 64–70 cm. Slender, medium-small tern, with wings more rounded than in Sterna; shortish tail with only slight fork; forehead to nape black, with contrasting white cheeks; upperparts, including rump and tail, mid-grey; underparts grey, darker on belly, with ­contrasting pale grey underwing and white undertail-coverts; iris dark brown; bill dark reddish, legs red. Superficially resembles Sterna paradisaea and S. repressa, but darker below, with much shorter tail. Non-breeding adult very pale above and below, with dark-flecked pale crown, black patch behind eye merging into dark band across nape, and black bill; crown pattern less contrasting than in C. niger, but more complete than in C. leucopterus. Female significantly smaller than male in all dimensions, to a greater extent than in most terns (1 Ledwoń, M. (2011). Sexual size dimorphism, assortative mating and sex identification in the Whiskered Tern Chlidonias hybrida. Ardea. 99(2): 191–198. Close ). Juvenile has head pattern similar to non-breeding adult, but face washed buff and hindneck tipped dark grey; mantle , scapulars and tertials contrastingly darker, with buff tips. Races differ somewhat in coloration of breeding plumage, but only slightly in size; delalandii darkest, with white cheek stripe narrower.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Breeds on vegetated inland lakes, marshes and rivers, mainly in lowlands, but up to 2000 m in Armenia; in Italy prefers artificial fish ponds and drainage ponds covered with water-lilies; in Africa opportunistically seeks pans after heavy rains. In Australia mainly coastal, breeding in arid interior in very wet years. Feeds over lakes, marshes , and rice fields, but also over sprouted farm fields, and coastal lagoons, tidal mudflats and estuaries.

W Europe birds migrate to W Africa, wintering at freshwater wetlands inland and on coasts (3 Borrow, N., and R. Demey (2001). Birds of Western Africa. Christopher Helm, London, UK. Close ). Small numbers, a few hundred in total, now winter regularly in Camargue, S France, and at coastal wetlands of Iberian Peninsula (4 de Juana, E., and E. Garcia (2015). The Birds of the Iberian Peninsula. Bloomsbury, London, UK. Close ). E European birds winter mostly in E Africa, with a few in S Middle East. Those from the Caspian and Turkestan zones winter from Iran to Pakistan and Sri Lanka, and possibly also E Africa. Wintering birds are also numerous in S & SE Asia, including the Greater Sundas, Sulawesi and Philippines. Australian birds mainly nomadic, but those from S Australia migrate to N parts of Australia and N to Greater Sundas, Philippines and S New Guinea. Passage in the Philippines peaks in May and Sept (5 Kennedy, R. S., P. C. Gonzales, E. C. Dickinson, H. C. Miranda, and T. H. Fisher (2000). A Guide to the Birds of the Philippines. Oxford University Press, Oxford and New York. Close ). Occasional transatlantic vagrancy has been recorded: to Iceland, Azores, USA (Delaware and New Jersey) (6 Howell, S. N. G., I. Lewington, and W. Russell (2014). Rare Birds of North America. Princeton University Press, Princeton, NJ, USA. Close ) and even more exceptionally Paraguay (Jan 2016) (7 Williams, R. (2016). Neotropical notebook. Neotropical Birding. 18: 45–52. Close ). 

Terrestrial and aquatic insects, e.g. water beetles (Dytiscidae), Odonata and their larvae, grasshoppers, flying ants, spiders; also tadpoles and frogs, small crabs, small fish. In N Australia, examination of 55 stomachs revealed c. 32% Coleoptera, 18% Odonata, 9% Hemiptera and 9% spiders; fish made up 13% of items but 45% of weight, and frogs 2% of items and 6% of weight; males took more fish and fewer insects, and had more diverse diet. In general, males take larger prey and a higher proportion of vertebrate prey than females, which are smaller (1 Ledwoń, M. (2011). Sexual size dimorphism, assortative mating and sex identification in the Whiskered Tern Chlidonias hybrida. Ardea. 99(2): 191–198. Close ). Flies back and forth or flutters 2–6 m above water, then swoops (aerial-dipping) or drops (hover-dipping) to pick up small surface items; infrequently engages in plunge-diving. Often hawks insects over fields and lake margins; sometimes feeds behind plough in Spain. In Gulf of Thailand, recorded feeding at sea in association with Bryde’s whale (Balaenoptera brydei). Generally forages within 1 km of colony, occasionally up to 9 km.

Harsher than in other Palearctic Chlidonias spp.; advertising call is a rasping “kyick” or “cherk”; alarm call a more rasping loud “kerch”, often repeated; young very vocal when soliciting food, giving a loud “chee chee” call (8 Cramp, S., Editor (1985). The Birds of the Western Palearctic. Volume 4. Oxford University Press, Oxford, UK. Close ).

May–Jun in Europe, Nov–Dec in Australia, Dec in Tanzania. Forms synchronous subcolonies , usually in monospecific colonies of 10–100 pairs. Broad but flimsy nest of stems or decaying rushes, placed on floating or emergent vegetation over water , usually 60–80 cm deep; in very shallow water, nest may rest on bottom; alternatively nest of dry grass on water-lily leaves ; may usurp grebe nest. Nests 1–5 m apart. Clutch 2–3 eggs; incubation 18–20 days; chick black-spotted buff, with black forehead , creamy breast, black bill and pink legs; can leave nest within one day and swim to vegetation; fledging 23 days; fed for few weeks after. Hatching success 66% in Australia. Many breed first at two years.

Not globally threatened (Least Concern). The global population has not been estimated precisely recently but is within the range of 300,000–1,500,000 individuals, and is thought to be fluctuating overall (9 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ). The largest breeding populations are those of the nominate form in E Europe and across C Asia to China, and of javanicus in SE Asia and Australia. The total European population is estimated at 66,300–108,000 pairs. However, breeding in much of W and C Europe is typically local, occasional and irregular and here the species was locally far more abundant in the past. The Spanish breeding population is the largest in W Europe and fluctuates between 5000 and 8000 pairs, as nesting conditions permit; it was much larger in the 19th century and the first half of the 20th century, numbering several tens of thousands of pairs (4 de Juana, E., and E. Garcia (2015). The Birds of the Iberian Peninsula. Bloomsbury, London, UK. Close ). Elsewhere in W Europe the only sizable colonies are in western and central France where the population has fluctuated from 2200 to 3900 pairs post-2000 (10 Dubois, P. J., P. Le Maréchal, G. Olioso, and P. Yésou (2008). Nouvel Inventaire des Oiseaux de France. Delachaux et Niestlé, Paris, France. Close ). Some E European populations have shown substantial increases and associated colonization of new areas in recent decades; in Romania, Ukraine, Belarus, C Russia, Lithuania, Latvia, Germany, the Netherlands, Poland, Slovakia and Hungary; in Poland, for example, the population has rapidly increased from 40 breeding pairs in 1990 to more than 1600 pairs in 2007 (11 Ledwoń, M., Betleja, J., Stawarczyk, T. and Neubauer, G. (2014). The Whiskered Tern Chlidonias hybrida expansion in Poland: the role of immigration. Journal of Ornithology. 155(2): 459–470. Close ). Recorded nesting in NW Africa, from Morocco to Tunisia, irregularly and perhaps opportunistically but sometimes in large numbers, e.g. 1000 pairs at Iriki, S. Morocco in 1966 (12 Robin, P. (1968). L’avifaune de l’Iriki (Sud-Marocain) Alauda. 36(4): 237–253. Close ); recent breeding records from the region have involved only a few pairs (13 Thévenot, M., R. Vernon, and P. Bergier (2003). The Birds of Morocco: An Annotated Check-list. British Ornithologists’ Union Check-list 20. British Ornithologists’ Union, Tring, UK. Close , 14 Isenmann, P., Gaultier, T., Hili, A.E., Azafzaf, H.D. and Smart, M. (2005). Oiseaux de Tunisie. [Birds of Tunisia]. SEOF, Paris. Close ). In sub-Saharan Africa, breeds in small, scattered, often non-permanent colonies; the breeding subspecies delalandii is estimated at 15,000–30,000 pairs in total (9 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ). Breeding populations are subject to a diversity of threats notably including habitat loss from wetland drainage and a seasonal lack of nesting habitat; nesting lagoons are often ephemeral and may disappear in dry years. The habit of nesting in concentrated colonies makes the nests vulnerable to predation, including by human egg collectors. In India, large quantities of eggs are collected for sale and for local consumption, causing population decline in certain areas of Kashmir. In Ukraine, fishermen collect eggs. Many nests lost to adverse weather, e.g. high winds and waves.