Masked boobies
| Masked boobies | ||||||||
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Masked booby with young bird |
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Sula dactylatra | ||||||||
| Lesson , 1831 |
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The masked booby ( Sula dactylatra ) is a representative of the booby species found on tropical seas .
The population of the masked booby was classified in the IUCN Red List of Threatened Species in 2016 as “ Least Concern (LC) ” = “not endangered”.
Appearance
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The masked booby reaches a body length of 75 to 85 centimeters, the wingspan is 160 to 170 centimeters. Masked boobies weigh between 1.2 and 2.2 kilograms. It is the largest species within the genus Sula .
The masked booby is a white bird with black edges of wings, black tail and dark face mask. The similar looking sexes differ in that the male has a yellow, the female a greenish-yellow beak. The young bird is brownish on the head and underside, and white on the trunk and neck.
Masked boobies fly with powerful, even flaps of their wings, the flight is repeatedly interrupted by gliding phases. They usually fly at altitudes greater than seven meters, the flight is fast and can reach speeds of up to 70 km / h. They are shock divers who hit the sea almost vertically. They rest and swim at sea while lying high in the water. Occasionally they also rest on buoys and other structures in the sea, such as oil platforms. At sea they are not very happy to shout, but in the breeding colonies the shrill, whistling greetings of the males and the trumpeting sounds of the females can be heard.
In the distribution area of the masked booby there are several other types of booby with which the masked booby can be confused. The Australian booby and the cape booby differ from the masked booby by their yellowish head. The gray-footed booby has darker wings that are also darker. He is also long-tailed and the head looks bigger. The red-footed booby is smaller, the Australasian subspecies has a white tail. The head of this booby species is also yellowish.
distribution
The masked booby occurs on all tropical oceans. The distribution area extends in the south to Australia, South Africa and South America, in the north in the Gulf of Mexico and the southeast of the USA. The spread of the masked booby may be influenced by the spread of flying fish . In Western Europe, the masked booby occurs only as a random visitor.
A total of four subspecies are distinguished:
- S. d. personata - breeds in the central and western Pacific .
- S. d. dactylatra - breeds in the Caribbean and some Atlantic islands, such as Ascension and Tobago .
- S. d. melanops - breeds in the western Indian Ocean .
- Tasman Booby S. d. tasmani (synonyms: Sula tasmani , Sula dactylatra fullagari ) - breeds on Lord Howe Island and the Kermadec Islands .
The breeding colonies of the masked booby are found on tropical islands, atolls and cays , which are usually far off the coast of the mainland. Masked boobies also occasionally use very shallow cays, which are washed over in tropical storms or at very high tides. The southernmost breeding colony is on Lord Howe Island .
Food and subsistence
The masked booby is a spectacular diver who dives into the water at high speed. They drop from an altitude of twelve to 100 meters and can reach a diving depth of at least two to three meters. Masked boobies also use waters with a depth of only 1.5 meters during their foraging. During the breeding season they often look for food far away from their breeding colonies. In the waters off Hawaii, masked boobies are regularly seen more than eighty kilometers from the nearest islands, and in the Indian Ocean masked boobies often forage for food at a distance of 160 to 320 kilometers from their breeding colony. The captured prey is usually swallowed underwater.
It feeds mainly on small fish, including flying fish .
Reproduction
Breeding colony
The masked boobies boobies like all kinds a colony breeders, however, have its colonies not spectacular density, as for example when gannets characteristic or the Cape Gannet. On Raine Island off the Australian coast, for example, four pairs breed on 100 square meters. In other breeding colonies, a nest density was found ranging from one nest per 3.3 square meters to one nest per 201 square meters. Breeding colonies exist for a very long time, and white-bellied gannets occasionally use the same breeding colony.
The nesting site is chosen by males at the beginning of the breeding season. The place chosen by him is defended against other males and neighboring breeding pairs. Once the male has mated, the female also takes part in defending the nesting site. In addition to conspecifics, other species of booby are also attacked, as well as people or turtles approaching the nesting area.
Egg laying
The masked booby lays one or two white eggs on the bare sandy soil. Masked boobies show no pronounced nesting behavior, they do not even scratch a shallow hollow in the ground. At the beginning of the breeding season, the male brings twigs and similar material to the nesting site; this is dropped near the nest, but then removed by the breeding bird. A free, round place with a diameter of 75 centimeters to one meter is therefore typical for nesting sites for masked boobies.
Oviposition is largely synchronized within a colony. On the Kure Atoll , eggs were laid in 85 nests within around six days. Both parent birds incubate the clutch for 45 days by covering the eggs with the webbed feet of their feet and keeping them warm. If two eggs have been laid, only one will usually develop. However, when both eggs develop, one chick often hatches four to five days earlier and forces the other chick out of the nest or even eats it (called kainism ). The parent birds have no active role in this and do not bring back chicks that have been thrown out of the nest. Cases in which both chicks grow up are extremely rare. On Raine Island , a 32 hectare cay off the east coast of Australia, only three times two chicks grew in four breeding seasons with 2000 nests each.
Young birds and breeding success
The chicks are about ten centimeters long when hatched and weigh between 40 and 60 grams. They are guarded by their parents until they are three to four weeks old. Chicks are unable to regulate their body temperature for the first six days of life and are dependent on being fidgeted by their parents. Small chicks die in as little as twenty minutes if left unprotected in the tropical sun. The chicks, on the other hand, can survive longer periods without food.
The chicks are initially naked, in the second week short dunes develop on the back and flanks. By the third week of life, they are completely covered with down, which becomes increasingly thick and fluffy over the next two weeks. They lose their down from the 12th week. They fledge after about 120 days.
The breeding success varies greatly. On the Kure Atoll, fledglings grew up in 50 to 90 percent of the nests within six breeding periods. On Kiritimati , children usually do not grow up in El Niño years because there is insufficient food available. Heavy rains occasionally flood nests or impair breeding behavior. Eggs and young birds were and are collected by humans. Rats are essential predators of eggs and young birds on the islands where they were introduced. The herring-headed gull and the arachnid eat eggs and small chicks. Green turtles occasionally accidentally destroy some nests on Raine Island and Pandora Cay .
supporting documents
literature
- PJ Higgins (Ed.): Handbook of Australian, New Zealand & Antarctic Birds. Volume 1: Ratites to Ducks. Oxford University Press, Oxford 1990, ISBN 0-19-553068-3 .
Web links
- Sula dactylatra in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- Videos, photos and sound recordings of Sula dactylatra in the Internet Bird Collection
- BirdLife Factsheet on the Masked Booby .
Single receipts
- ↑ Sula dactylatra in the endangered Red List species the IUCN 2016 Posted by: BirdLife International, 2016. Accessed November 15, 2017th
- ↑ BirdLife Factsheet on the Masked Booby . Retrieved May 1, 2011.
- ^ Higgins, p. 763.
- ^ Higgins, p. 763.
- ^ Higgins, p. 763.
- ↑ Nigel Redman, Terry Stevenson, John Fanshawe: Birds of the Horn of Africa: Ethiopia, Eritrea, Djibouti, Somalia, and Socotra - Revised and Expanded Edition . Princeton University Press , 2016, ISBN 978-0-691-17289-7 , pp. 44 (English, full text in the Google book search).
- ↑ Higgins, p. 764.
- ^ Higgins, p. 766.
- ^ Higgins, p. 769.
- ^ Higgins, p. 769.
- ^ Higgins, p. 767.
- ^ Higgins, p. 769.
- ^ Higgins, p. 768.
- ^ Higgins, p. 768.
- ^ Higgins, p. 770.
- ^ Higgins, p. 770.
- ^ Higgins, p. 770.
- ^ Higgins, p. 770.