Damara tern

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Damara tern
Damara Tern (8077271589) .jpg

Damara tern ( Sternula balaenarum )

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Terns (Sternidae)
Genre : Sternula
Type : Damara tern
Scientific name
Sternula balaenarum
Strickland , 1853

The Damara tern ( Sternula balaenarum ) is a species of sea bird from the family of the tern (Sternidae). It was originally part of the genus Sterna , after a revision of the tern family, it was transferred to the genus Sternula in 2005 . The type epithet balaenarum (Greek: φαλαινα (phalaina) for whale) refers to the Walvis Bay in Namibia , formerly Damaraland .

features

The Damara tern reaches a body length of 23 cm, a wingspan of 51 cm and a weight of 46 g. The forehead, the slightly curved beak and the reins are black. The coat, the top, the rump and the upper tail are light gray. Throat and underside are gray-white. The white component continues to the nape of the neck. The edges of the outer tail feathers are white. The legs are dark. The non-breeding adult birds have a white forehead and a gray and black speckled skull. The juvenile birds have a gray-brown skull, a dark band through the eye and above the neck, gray wing feathers and brown wing-covers with dark borders. The first winter plumage resembles the plumage of the non-breeding adult birds. However, the hand wings are darker and the arm wing leading edge is weak.

Vocalizations

The call consists of a sharp, high-pitched tsit tsit and a rough, quick kid-ick or rrreekikkik

Spreading and migrations

The breeding area extends from Cabinda in northern Angola, over southern Angola, along the coast over Namibia to the Cape Province of South Africa. Outside the breeding season, the Damara tern migrates north to Benin, Cameroon, People's Republic of Congo, Democratic Republic of the Congo, Ivory Coast, Gabon, Ghana, Liberia, Nigeria and Togo.

habitat

The Damara tern breeds on gravel as well as on stony plains and dunes up to three kilometers inland. It avoids outside beaches, which are often visited by predators. They look for their food in coastal waters of bays, estuaries, lagoons, salt pans and in the surf zone.

Eating behavior

The diet consists mainly of small fish and squid. During a study of the diets of Seeschwalbenjungen in Namibia, which was published in 2011, were Atherina breviceps , Liza richardsonii , Engraulis and fish from the family of blennies (Blenniidae) the most common prey species. The young birds ate fish that were 1.5 to 12 cm long and weighed 30 g. The Damara tern spies its prey while shaking flight and snatches it when diving into the water. The same study came to the conclusion that the Damara tern has the greatest hunting success at high tide and the least at low tide. The hunting successes increased, while the overall diving rate decreased with increasing wind speed.

Reproductive behavior

The breeding season is between late October and mid-November, but new clutches can be found until February. The Damara tern form groups of one to ten breeding pairs, occasionally up to 50. The nests are at an average distance of 57 to 185 m apart. No territorial interference was observed. As a nesting place, depressions without vegetation with scattered shells and stones between dunes are preferred. Only one pair breeds per well. The clutch consists of one egg, rarely two.

The adult birds show only weak attack behavior towards intruders. The breeding season is 18 to 22 days. The chick is white on the underside and fawn brown with fine black flecks on the top. It leaves the nest after two days and crouches motionless on the ground. The young are fully fledged after 20 days. After that they are dependent on the adults for another two to five months. The Damara tern breeds for the first time when it is three to four years old.

status

A total of 70 breeding colonies are known in the entire breeding area, of which 56 (with 87 percent to 93 percent of the breeding population) occur on the coast off the Namib between the Kunene and Oranje rivers . 65 to 148 pairs breed in the southern Cape Province of South Africa. The easternmost subpopulation breeds on the coast of the Indian Ocean in the Eastern Cape Province and consists of 25 to 29 pairs, which is due to a small increase in the population during the 1990s. There are fewer than 190 breeding pairs north of Cabinda in Angola. In a study published in 2010, the population between Tombua and the mouth of the Kunene in Angola was estimated at 573 individuals, with a breeding colony of six pairs located 30 km north of the Kunene. Between 2004 and 2015, the Damara Tern was on the IUCN's early warning list ( near threatened ) because of the moderately small population of 13,500 individuals estimated in 1998. A number that was nevertheless significantly higher than in previous surveys. A more recent, more comprehensive survey found a total population of less than 5730 breeding birds. Therefore, the IUCN status in 2016 was to "endangered" ( vulnerable ) changed. The Damara tern is a protected species in both Namibia and South Africa. But a large part of their breeding areas is not protected and therefore particularly vulnerable to human disturbance. A restricted area on the Diamond Coast between Swakopmund and Oranjemund offers protection from human disturbance, but only a few pairs breed in this area. The diamond mining near the breeding areas can also endanger them. A release of sediments into the foraging grounds as a result of the diamond mining was not found, but the feeding success in a colony of Damara shells in Elizabeth Bay in southern Namibia was considerably impaired. Motorized beach vehicles put some colonies at risk, resulting in a low reproductive rate. Coastal development is causing colonies to wipe out. Anthropogenic activity on the beaches can lead to an increased increase in predators. For example, the fish entrails that are disposed of by fishermen in the breeding areas attract black-backed jackals that hunt the young terns. Another source of danger arises from the consequences of climate change. These include increased tidal flooding in the large low-lying colonies such as Hottentots Bay, the world's largest breeding colony, increasing fluctuations in food availability as a result of reduced upwelling and an increased surface temperature of the sea. There are also reports that the Damara tern is caught as a food source in Angola and West African countries.

In November 2000, the disruption of the breeding colony at Caution Reef was successfully prevented with the help of information boards and barriers. This led to a slight increase in nest density and made it possible to increase the hatching rate from 56 to 80 percent. The ban on off-road vehicles on the South African beaches in 2001 also reduced disruption along the breeding beaches and increased breeding success. There were similar trends in Namibia after the use of vehicles on the beach was also restricted over two breeding seasons.

literature

  • David A. Bannerman: Larger Birds of West Africa. Penguin, London 1958.
  • RK Brooke: South African Red Data Book: Birds. (= South African National Scientific Programs Report. 97). Council for Scientific and Industrial Research, Pretoria, South Africa, 1984.
  • EK Urban, CH Fry, S. Keith (Ed.): The Birds of Africa. Vol. 2, Academic Press, London / New York 1986.
  • RJ Braby, A. Shapira, RE Simmons: Successful conservation measures and new breeding records for Damara Terns Sterna balaenarum in Namibia. In: Marine Ornithology 29, 2001, pp. 81-84.
  • Robert E. Simmons: First breeding records for Damara Terns and density of other shorebirds along Angola's Namib Desert coast. In: Ostrich. Journal of African Ornithology. 81, 1, 2010, pp. 19-23.
  • Justin Braby: New migration records for the Damara Tern Sterna balaenarum. In: Ornithological Observations. 1, 2010, pp. 38-41.
  • Justin Braby: The conservation and biology of the Damara Tern in Namibia . PhD thesis. University of Cape Town, South Africa, 2011.
  • Justin Braby, Sigrid J. Braby, Rodney J. Braby, Res Altwegg: Immature Survival and Age at First Breeding of Damara Terns: Conservation from a Non-Breeding Perspective. In: Ardea. 99 (2), 2011, pp. 185-190.
  • Justin Braby, Lesley Gordon Underhill, Robert E. Simmons: Prey capture success and chick diet of Damara terns Sterna balaenarum in Namibia. In: African Journal of Marine Science. 33 (2), 2011, pp. 247-254.
  • Philip A Whittington, Anthony J Tree, Maëlle Connan, Elizabeth G Watkins: The status of the Damara Tern in the Eastern Cape, South Africa. In: Ostrich. 86 (1 & 2), 2015, pp. 65–73.
  • M. Gochfeld, J. Burger, E. de Juana, EFJ Garcia, CJ Sharpe: Damara Tern (Sternula balaenarum). In: J. del Hoyo, A. Elliott, J. Sargatal, DA Christie, E. de Juana (Eds.): Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona 2017. (accessed from HBW Alive on September 11, 2017).

Web links

Commons : Damara Tern  - Collection of images, videos, and audio files

Individual evidence

  1. ↑ ES Bridge, AW Jones, AJ Baker: A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution. In: Molecular Phylogenetics and Evolution. 35, 2005, pp. 459-469. PDF full text ( memento from July 20, 2006 in the Internet Archive ).
  2. ↑ a b Justin Braby, Lesley Gordon Underhill, Robert E. Simmons: Prey capture success and chick diet of Damara terns Sterna balaenarum in Namibia. In: African Journal of Marine Science. 33 (2), 2011, pp. 247-254.
  3. ↑ a b c Justin Braby: The conservation and biology of the Damara Tern in Namibia . PhD thesis. University of Cape Town, South Africa, 2011.
  4. ↑ RJ Braby, A. Shapira, RE Simmons: Successful conservation measures and new breeding records for Damara Terns Sterna balaenarum in Namibia. In: Marine Ornithology. 29, 2001, pp. 81-84.
  5. ^ Philip A Whittington, Anthony J Tree, Maëlle Connan and Elizabeth G Watkins: The status of the Damara Tern in the Eastern Cape, South Africa. In: Ostrich. 86 (1 & 2), 2015, pp. 65–73.
  6. ^ A b Robert E. Simmons: First breeding records for Damara Terns and density of other shorebirds along Angola's Namib Desert coast. In: Ostrich: Journal of African Ornithology. 81, 1, 2010, pp. 19-23.
  7. ^ RE Simmons, I. Cordes, R. Braby: Latitudinal trends, population size and habitat preferences of the Damara Tern Sterna balaenarum on Namibia's desert coast. In: Ibis. 140 (3), 1998, pp. 439-445.