Ornamental tern
| Ornamental tern | ||||||||||
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Ornamental tern ( Thalasseus elegans ) |
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| Scientific name | ||||||||||
| Thalasseus elegans | ||||||||||
| ( Gambel , 1849) |
The ornamental tern ( Thalasseus elegans ) is a species of bird from the family of the tern (Sternidae). Their brood distribution is limited to a small part of the North American Pacific coast in southern California and northern Lower California . In 1999 there were only five known colonies, with 90–97% of the total population on Isla Rasa in the Marino Archipiélago de San Lorenzo National Park in Mexico . The species almost always joins large colonies of other seabirds such as the black-headed gull and the predatory tern in particular .
Due to its limited distribution, the species is listed by the IUCN as 
(= Near Threatened ) on the warning list .
description
With a body length of 39 to 43 cm, a wingspan of 76 to 81 cm and a weight of about 260 g, the ornamental tern is a medium-sized tern. The feathers at the back of the head are elongated into a shaggy hood - the longest in all terns. The beak is about 53–69 mm long, often longer than the head, as well as narrow and pointed. Due to the slightly curved ridge of the beak, the tip looks slightly bent down. In flight, the ornamental tern looks very slender and elegant and flies with powerful, balanced wing beats. The tail is forked deep. The legs and feet are usually black with yellowish or orange discolouration, rarely completely light red. The genders do not differ externally.
In adult birds in the breeding plumage, the beak is light yellow to red-orange or orange-red, with the tip usually more yellow and the base often red. The top of the head and the hood are black. The back, shoulder feathers and upper wings are bluish light gray, from which the somewhat darker, inner hand wings stand out . The rest of the plumage including the lower wing, the rump and the tail feathers is white. The underside can have a slightly pink tint.
In the plain dress, the forehead and reins are white. The remaining black mask appears triangular, begins around the eye and widens sharply towards the elongated neck plumage. The beak is more dull red in color than in the splendid dress.
The youth dress is similar to the plain dress, but the back and shoulder feathers are tinted brown. Most of the upper wing coverts appear scale-like due to the darker grayish or brownish gray centers, the middle arm coverts are light gray. The control feathers are dark gray with darker tips and white ends. The tips of the inner hand and arm wings are clearly lightened. The beak, which is shorter than that of adult birds, looks light yellowish to reddish orange with blackish markings on the edges of the upper beak. The legs are mostly black, the feet often a little greenish.
Distribution and existence
The brood distribution is limited to southern California and Baja California . In the course of the last century at least twelve breeding colonies existed simultaneously; the distribution area was still extended to the Bay of San Francisco and further over the Gulf of California . At the turn of the millennium, only five breeding colonies were known:
- Isla Rasa in the Gulf of California, Baja California (Mexico) - 1994: 22,500 breeding pairs, 90–97% of the total population
- Western Salt Company in the south of San Diego Bay (California) - 1996: 1870 breeding pairs, 1998: fewer than 15 pairs
- Bolsa Chica Ecological Reserve , Orange County (California) - 1995: 5000 breeding pairs, 1998: only a few pairs left
- Isla Montague , mouth of the Colorado River , Baja California (Mexico) - 1992: 275 breeding pairs
- Los Angeles Harbor (California) - 1998: about 3000 breeding pairs
hikes
The ornamental tern is a medium to long-distance migrant that overwinters mainly on the South American Pacific coast. After the breeding season, dismigrations take place northwards along the coast to northern California, and more rarely to British Columbia . In autumn, most of the birds have left the breeding grounds by the end of November. In spring they return to the colonies from mid-March.
The wintering areas on the Pacific coast extend from Nayarit in Mexico south to Puerto Montt in Chile . However, the species is only more frequent overwinterers south of Ecuador; further north it is rare in winter, but sometimes appears regularly as a winter guest.
The species has been identified as an odd visitor in Texas and Arizona. A bird ringed in San Diego in 1966 was found on Johnston Atoll in the North Pacific in 1969 . In 1974 and 1984 the ornamental tern appeared in Arcachon in France as a breeding guest in a colony of the sandwich tern . In 1974 one specimen was observed there, in 1984 there were two. All of them were paired with sandwich terns. There were also random visitors in Northern Ireland and Ireland (1982), Belgium (1988) and Germany (2004).
nutrition
The Ornamental Tern feeds on smaller fish that appear in large schools. Crustaceans are only rarely added. The most common prey fish is the American anchovy ( Engraulis mordax ). Other frequently captured species come from the families of the anchovies , herrings , earfish , gobies and mackerel .
The foraging for food usually takes place individually or in groups of two to three individuals. Here shake the birds over the water and come down into the water occasionally. During the breeding season, smaller groups often set out from the colony together to fly to the feeding grounds on the usual routes. Swarms of several hundred specimens sometimes gather in places with cheap food. Ornamental terns have been observed to hunt near shags or mullets , which round up smaller fish.
literature
- Gary P. Burness, Kara Lefevre, Charles T. Collins: Elegant Tern (Thalasseus elegans) , in A. Poole (Eds.): The Birds of North America Online , Cornell Lab of Ornithology, Ithaca 1999, doi : 10.2173 / bna. 404
- Klaus Malling Olsen, Hans Larsson: Terns of Europe and North America , Princeton University Press, Princeton / New Jersey 1995, ISBN 0-691-04387-6
- Gerald S. Tuck, Hermann Heinzel : The sea birds of the world. Paul Parey Publishing House, Hamburg / Berlin 1980, ISBN 3-490-07818-7 .
Individual evidence
- ↑ a b c d Burness et al. (1999), section Distinguishing Characteristics , see literature
- ↑ a b Olsen / Larsson (1995), p. 63f, see literature
- ↑ a b c Burness et al. (1999), section Distribution , see literature
- ↑ Burness et al. (1999), section Demography and Populations , see literature
- ↑ Burness et al. (1999), Migration section , see literature
- ↑ a b Burness et al. (1999), Food Habits section , see literature
Web links
- Thalasseus elegans in the endangered Red List species the IUCN 2012. Posted by: BirdLife International, 2010. Accessed March 25, 2013.
- Videos, photos and sound recordings of Thalasseus elegans in the Internet Bird Collection