Inca tern

03 10 2007 Club Regatas 063

The uniquely coloured Inca tern, Larosterna inca, is a seabird being endemic to the Humboldt Current area. Larosterna inca is found along the Pacific coast from northern Peru south to central Chile. The Inca tern belongs to the family Sternidae and is the only member of the genus Larosterna. Inca terns are  listed as Near Threatened because its population has apparently experienced a moderately rapid decline.

Join Mundo Azul and become a conservation volunteer, participating in research projects on Inca terns and other marine species.

You can also observe Inca terns during the coastal-marine birding tours, as well as dolphin watching tours of our associated travel operator Nature Expeditions.

Zarcillo

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Family: Laridae (Gulls and terns)
Species name: Larosterna inca (Lesson, 1827)

Common names:
Engl: Inca tern
Fr : Sterne Inca
German : Inkaseeschwalbe
Esp : Zarcillo

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Description of Inca terns

The Inca Tern is a large tern, 41cm long. Both sexes are similar. This uniquely-plumaged tern can be identified by its dark grey body, with white restricted to the trailing edges of the wings. Incaterns have  a white moustache and yellow wattle on the both sides of its head, as well as red-orange beak and feet. The moustaches of Inca terns consist of tufts of white feathers on either side of the head running from in front of the eyes to the back of the cheeks, where they are prolonged by the plumes of the feathers. The ornaments seem to provide a good indication of individual quality among adult Inca terns. Adult Inca terns with longer moustaches were the most productive and their chicks were heavier and had better immune responses.

Zarcillo 2 juvenil

The juvenile Inca tern has blackish plumage, bill and legs. We can see small grey tufts at bill base.

The subadult Inca tern is browner. The bill turns dark horn-coloured, and becomes redder little by little. It shows some dull brown curling feathers at gape.

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Page author: Stefan Austermühle

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Distribution of Inca terns

Pacific Coasts and coastal islands of South America from the Gulf of Guayaquil, Ecuador south to Valdivia, Chile.

The Inca tern is resident in its range. Only the non-breeding Inca terns may move according to the food resources. The range estimate for Inca terns (breeding/resident) is 477,000 km2

Join Mundo Azul and become a conservation volunteer, participating in research projects on Inca terns and other marine species.

You can also observe Inca terns during the coastal-marine birding tours, as well as dolphin watching tours of our associated travel operator Nature Expeditions.

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Zarcillo 5

Conservation of Inca terns

The Inca tern is listed by the IUCN as Near Threatened because its population has apparently experienced a moderately rapid decline. Prior to the guano industry (c.1850) there were millions of Inca terns in Peru (according to accounts from Coker 1919, Hutchison 1950). Current numbers are much lower than two centuries ago, being estimated at more than 150,000. Nevertheless they are common and breed in some localities.

Mass dispersal and breeding failures have resulted periodically from El Niño Southern Oscillation (ENSO) events. However, both fish-stocks and the populations of seabirds that depend upon them, are adapted to these fluctuations. Population declines are usually promptly reversed, suggesting that food shortages trigger rapid dispersal not high mortality in Inca tern adults and high reproduction rates (up to two successful broods in a year). Constant massive fishing of anchovies for fishmeal production however creates a permanent artificial El-Niño-like food shortage inhibiting the Inca terns population to grow to original numbers.

Other threats for Inca terns are:

Reduction of nesting habitat for Inca terns as a result of guano harvesting may affect population dynamics. Gulls, owls, turkey vultures, peregrine falcon, cats and rats are reported to prey on Inca terns. The presence of rats and cats on some islands can also prevent nesting or reduce breeding success of Inca terns.

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Conservation measures for Inca terns:

In december 2009 – after nine years of lobbying from Mundo Azul and other NGOs – the Peruvian government created the protected area National Reserve Guano Islands, protecting the bird and sea lion breeding colonies on 28 guano islands and cliffs, being distributed along two thirds of the Peruvian coastline.

Conservation measures proposed for Inca terns are:

  • Identify those breeding sites where introduced predators are a problem for Inca terns and control/remove them from these sites.
  • Determine effects of Inca tern interactions with fisheries.
  • Monitor Inca tern population levels at key sites.
  • Establish key locations as Marine Protected Areas.

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Breeding of Inca terns

The Inca tern is gregarious, living and nesting in huge colonies of several thousands of birds, often close to the gulls’ colonies.  The Inca tern breeds twice a year, between April and July and between October and December.

Courtship is an elaborate ritual in Inca terns, especially in birds seeking a mate for the first time. The first stage is “high flight”, in which the Inca tern male ascends at speed, as if to demonstrate his prowess, to often several hundred meters, while the female pursues him. Courtship feeding and zigzag dancing in the sky has great symbolic value: it helps the female Inca tern gauge the fishing skills of her partner. The male Inca tern also pursues her in the air with gifts of fish until she finally accepts him. The pair then chooses a nest site. Ground courtship of Inca terns occurs near the nest site, and involved much strutting around and pirouetting with raised tail and drooped wings. This is usually a prelude to copulation.

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Unlike most terns, which tend to nest on open ground, Inca terns select sheltered nest sites. The Inca tern breeds on rocky cliffs. It nests in a hollow or burrow or sometimes the old nest of a Humboldt Penguin, and lays one to three eggs.

Inca terns often return to the same nest site years in a row. Male and female Inca terns incubate the eggs for three to four weeks. Both parents feed the greyish chicks. The young Inca terns fledge about 4 weeks after hatching, and reach their independence one month later. Young chicks are then able to fly after 7 weeks.

Inca terns are monogamous. They have a 2-3 year adolescent period before they breed. The life expectancy of Inca terns is 12-14 years. Inca terns can live into their 20’s.

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Feeding of Inca terns

The Inca tern feeds by plunge-diving from the air, after brief flight above the prey, and also by surface-dipping. The Inca tern swims or sits on the water and picks-up prey from the surface.

Inca terns feed, often in large flocks, on schooling anchoveta (Engraulis ringens), mote sculpins (Normanychtic crokeri) and silversides (Odothestes regia regia) found in the cold water of the Humboldt Current. Additionally, Inca terns scavenge offal and scraps from sea-lions, dolphins and fishing boats. They actully plunge down onto sea lions and dolphins taking the chewed-up food from between their teeth.

The Inca tern is a graceful flier but is not a strong swimmer, its webbed feet are too small to propel it through the water effectively. It is, however, able to float on the surface.

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Behaviour of Inca terns

Inca terns often gather in the thousands. They roost on sandy beaches with flocks of Grey and Franklin’s gulls and share breeding islands with Guanay, cormorants and pelicans. Inca terns often accompany fishing cormorants, sea lions and cetaceans. They are quarrelsome and steal from other birds and try to snatch food from between the teeth of the sea lions. Graceful and agile, Inca terns fly on steady wing beats with the head pointed down scanning the ocean’s surface for fish. They hover before swooping low to snatch their food from the water’s surface. Occasionally, Inca terns will dive into the water and immediately fly out with their catch. Rarely do Inca terns land on the water. Molting occurs in the spring and autumn.

Join Mundo Azul and become a conservation volunteer, participating in research projects on Inca terns and other marine species.

You can also observe Inca terns during the coastal-marine birding tours, as well as dolphin watching tours of our associated travel operator Nature Expeditions.

Stay in touch with Mundo Azul! Sign up to our google group “Mundo Azul International” and receive news about our work and nature conservation in Peru, Web site updates, action alerts, suggestions on how you can participate or help, volunteer opportunities, internship and job openings and much more.

Follow us on Twitter

Become a member of our Facebook group “Mundo Azul International

Page author: Stefan Austermühle

 

 

 

Sources:

BirdLife International (2010) Species factsheet: Larosterna inca. Downloaded from http://www.birdlife.org on 15/12/2010.

Alberto Velando and José C. Márquez: “Predation risk and nest-site selection in the Inca tern”

A. Velando, C. M. Lessells and J. C. Ma´rquez: “The function of female and male ornaments in the Inca Tern: evidence for links between ornament expression and both adult condition and reproductive performance”, JOURNAL OF AVIAN BIOLOGY 32: 311–318. Copenhagen 2001

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