Sterna nilotica Gmelin, JF, 1789

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Subspecies and Distribution:

    * nilotica (Gmelin, 1789) - Europe S to Mauritania and Tunisia, and E through Middle East, Kazakhstan and Indian Subcontinent to NW China; winters from tropical Africa through Persian Gulf to India. *vaddenda Mathews, 1912 - Transbaikalia, Manchuria and E China (Fuzhou to Hainan); winters mainly SE Asia. * macrotarsa (Gould, 1837) - Australia. * aranea (Wilson, 1814) - New Jersey (rarely New York) S to Texas, Cuba, Bahamas and Puerto Rico, and sparsely along Mexican coast to Yucatán; winters along Central American coasts and S to Brazil and Peru. * vanrossemi Bancroft, 1929 - California (coastal plain and Salton Sea) to N Baja California and Sinaloa (and probably S to Gulf of Tehuantepec), with isolated breeding recorded in Alaska (Copper R Delta); winters S to Ecuador. * groenvoldi Mathews, 1912 - coast and river valleys from French Guiana (Cayenne) to NE Argentina (Buenos Aires); Ecuador and N Peru breeders may be this race or vanrossemi, or an undescribed race.
Licensehttp://creativecommons.org/licenses/by-nc-sa/3.0/
Rights holder/AuthorKaterina Tvardikova
Sourcehttp://pngbirds.myspecies.info/node/619

Number of Occurrences:

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: This species is represented by a large number of breeding occurrences (subpopulations).

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Rights holder/AuthorNatureServe
Sourcehttp://explorer.natureserve.org/servlet/NatureServe?searchName=Gelochelidon+nilotica

Population:

Population

The global population is estimated to number c.150,000-420,000 individuals (Wetlands International 2006), while national population estimates include: c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in China; c.50-1,000 individuals on migration and < c.50 wintering individuals in Taiwan and < c.1,000 individuals on migration in Japan (Brazil 2009).

Population Trend

Decreasing
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Rights holder/Author© International Union for Conservation of Nature and Natural Resources
Sourcehttp://www.iucnredlist.org/apps/redlist/details/22694505

Length: 36 cm

Weight: 170 grams

Licensehttp://creativecommons.org/licenses/by-nc/3.0/
Rights holder/AuthorHammerson, G., NatureServe
Sourcehttp://explorer.natureserve.org/servlet/NatureServe?searchName=Gelochelidon+nilotica

Global Abundance:

100,000 - 1,000,000 individuals

Comments: Global population was estimated at 79,000-310,000 in 2002 (Wetlands International). National Audubon Society waterbird conservation website (http://web1.audubon.org/waterbirds) reported the global population at 195,000. The European population is fewer than 22,000 pairs (BirdLife International 2004).

The current U.S. population of the eastern subspecies aranea (which breeds along the Atlantic and Gulf of Mexico coasts of the United States and northeastern Mexico) is unlikely to exceed 3,600 pairs, with over 60% of these birds occurring in Texas (Molina and Erwin 2006). As few as 250 pairs of subspecies vanrossemi nest at only two locations in the United States, both in California (Molina and Erwin 2006). Including populations in western Mexico, the entire vanrossemi population totals 600-800 pairs (Molina and Erwin 2006).

Licensehttp://creativecommons.org/licenses/by-nc/3.0/
Rights holder/AuthorNatureServe
Sourcehttp://explorer.natureserve.org/servlet/NatureServe?searchName=Gelochelidon+nilotica

Degree of Threat: Medium

Comments: This species was historically decimated by egg collectors and plume hunters. Via and Duffy (1992) concluded that loss of upland foraging sites and island nesting sites has probably been the greatest threat, although predation and competition with gulls, and human disturbance at colonies have also contributed to declines. Other threats include beach erosion and development.

Main threats to populations in North America include loss of natural nesting islands through beach erosion or perturbations to estuarine functions, development or modification of upland habitats near breeding areas that may be important for foraging, and disturbances to colonies by humans and feral or human-subsidized predators (Molina and Erwin 2006).

HABITAT LOSS: Destruction of marshes and nesting sites has probably been the most important problem in the past for gull-billed terns and other waterbirds (Erwin 1980). The past effects of marsh ditching on nesting and foraging are unknown, as are the historical population levels before market hunting and marsh drainage. Today, however, most northeastern marshes are either publicly owned or subject to laws that, at least in theory, protect them from further damage.

ENVIRONMENTAL CONTAMINATION: At the mouths of major estuaries, terns may be exposed to a wide variety of water-borne contaminants, including crude oil and other petroleum products. Analyses of eggs from South Carolina, however, indicated that levels of hydrocarbons were insufficient to induce eggshell thinning and reproductive failure (Blus and Stafford 1980).

HUMAN DISTURBANCE: Human disturbance may include a wide variety of human activities ranging from walking near nesting colonies to more severe forms of disturbance, such as vehicular traffic and slaughter of waterbirds (Parnell et al. 1988). Disturbance may result in desertion of nesting areas or exposure of eggs and chicks to extreme temperatures, rain, wind, and numerous predators, particularly gulls. Human disturbance has its most disastrous effects following hatching, because chicks may leave the nest prematurely and suffer excessive mortality (Sears 1978). Erwin (1980) compared barrier island nest sites in New Jersey with those in Virginia and found that the New Jersey sites were less frequently used by terns because of human disturbance. While there are no guidelines for the minimum distance at which gull-billed terns will flush, Erwin (1989) has proposed a minimum distance of 200 m for posting colonies of black skimmers and common terns, species with which gull-billed terns often nest. However, because these birds are extremely sensitive to disturbance during the nesting period (Sears 1978), even these distances may be insufficient.

PREDATION/COMPETITION: Both pet and feral dogs may pose a problem. Potential mammalian predators include raccoons, red foxes, and rats (Rattus spp.). Suspected rat predation on the eggs and nests was reported in two studies (Sears 1978, Blus and Stafford 1980). Nocturnal avian predators of common terns that are also likely to prey on gull-billed terns include great horned owls and black-crowned night-herons (Nisbet 1975, Morris and Wiggins 1986). Potential diurnal avian predators in the northeast include, laughing gulls, herring gulls, and great black-backed gulls (Buckley and Buckley 1972). Blus and Stafford (1980) suggested that predation by laughing gulls caused nearly complete nesting failure from 1972-75 in South Carolina. Other avian predators include the fish crow and northern harrier. During a period of population decline in Virginia (1975-90), there was an almost a ten-fold increase in the numbers of herring and great black-backed gulls, species which may usurp nesting sites or prey on gull-billed terns (Williams et al., in press). Nesting common terns have abandoned the barrier islands for a more protected, human-made island in the Chesapeake Bay (Williams et al., in press) and this may have left the remaining gull-billed terns at greater risk from predation.

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Rights holder/AuthorNatureServe
Sourcehttp://explorer.natureserve.org/servlet/NatureServe?searchName=Gelochelidon+nilotica

35-38 cm, 230 g

Licensehttp://creativecommons.org/licenses/by-nc-sa/3.0/
Rights holder/AuthorKaterina Tvardikova
Sourcehttp://pngbirds.myspecies.info/node/619

Descansa o duerme solitaria o en grupos, a veces con otras especies de charranes.

Licensehttp://creativecommons.org/licenses/by-nc-sa/3.0/
Rights holder/AuthorLuis Humberto Elizondo C., The Nature Conservancy, Instituto Nacional de Biodiversidad Costa Rica (INBio)
Sourcehttp://darnis.inbio.ac.cr/ubis/FMPro?-DB=UBIPUB.fp3&-lay=WebAll&-error=norec.html&-Format=detail.html&-Op=eq&-Find=&id=3017

Threats:

Major Threats

The species is threatened by the deterioration and loss of habitat, e.g. through wetland drainage, agricultural intensification, pesticide pollution, fluctuating water levels (del Hoyo et al. 1996), beach erosion and the development or modification of foraging sites (Molina and Erwin 2006). It also suffers from reduced reproductive successes as a result of human disturbance at breeding colonies (del Hoyo et al. 1996, Molina and Erwin 2006).
Licensehttp://creativecommons.org/licenses/by-nc-sa/3.0/
Rights holder/Author© International Union for Conservation of Nature and Natural Resources
Sourcehttp://www.iucnredlist.org/apps/redlist/details/22694505

Lacks the long tail streamers of common terns (STERNA HIRUNDO), Forster's terns (S. FORSTERI), and roseate terns (S. DOUGALLII) terns. It is also longer-legged and broader-winged. It can be told from the sandwich tern (S. SANDVICENSIS) by its shorter beak and tail, shallower wingbeat in flight, and more upright posture while sitting.

Licensehttp://creativecommons.org/licenses/by-nc/3.0/
Rights holder/AuthorHammerson, G., NatureServe
Sourcehttp://explorer.natureserve.org/servlet/NatureServe?searchName=Gelochelidon+nilotica
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith