Red-footed booby

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Red-footed booby
Red-footed Booby (Sula sula), white morph

Red-footed Booby ( Sula sula ), white morph

Systematics
Order : Suliformes
Family : Gannets (Sulidae)
Genre : Sula
Type : Red-footed booby
Scientific name
Sula sula
( Linnaeus , 1766)
Brown morph
Flight image of the red-footed booby
Frigate birds and red-footed boobies in a breeding colony
Red-footed booby dune chicks
Brown morph with downy chicks
Red-footed booby in the Galapagos Islands

The red-footed booby ( Sula sula ) is a bird of the booby family (Sulidae). There are several color morphs , but most red-footed boobies have predominantly white plumage. A few individuals show predominantly brown plumage and numerous individuals are mixed forms of the white and brown morphs.

The IUCN classifies the red-footed booby as not endangered ( least concern ) and estimates the population of sexually mature individuals at one million.

features

With a size of 68 to 77 centimeters, the red-footed booby is the smallest and the fastest species. The wingspan is between 140 and 145 centimeters. Red-footed boobies come in two color variants. Like the masked boobies , they wear white plumage with black wing tips or, similar to the youth dress, a brown plumage with darker wings. The beaks are bluish in color, and the face is tinted pink and light gray. They owe their name to their red feet and their red webbed feet.

The chicks wear a white down dress with a black beak and a bare black face. At this stage they are easy to confuse with masked booby chicks. They can only be distinguished in their behavior.

Red-footed boobies are characterized by their fast flight with long gliding phases, during which they often fly just above the surface of the water. More often than other booby species, they reach marine regions that are far from the mainland. You may occasionally cross land masses, but generally avoid long overland flights. Like many booby species they are shock divers and catch flying fish during their flight phases. Unlike other boobies, they are very capable of raising themselves and are rarely seen on the ground.

distribution

Their breeding colonies are located on atolls and volcanic islands in the tropical seas. On the Galapagos Islands , more precisely on the island of Genovesa, also called Tower Island, and on San Cristóbal, it is the third native species next to the blue-footed booby and the Nazca booby . Other breeding areas are on Hawaii , in the Caribbean Sea, in the Atlantic Ocean , in the Pacific , Indian Ocean, and the seas of Northern and Eastern Australia. Larger colonies exist on Little Tobago and on St. Giles Island off Tobago . There is also a breeding colony on Eastern Island, Midway Islands .

Red-footed boobies stay in the tropical climate zone all year round. You can only reach the western coast of Africa as a random visitor . Red-footed boobies can be seen above all over bodies of water with a surface temperature of over 22 ° C. Their distribution is presumably dependent on the distribution of flying fish , which play an essential role in their food spectrum.

nutrition

The food consists mainly of flying fish and squids , which they prey in a dive. The dive usually occurs from a height of more than seven meters. They only swallow their prey when they have reached the surface of the water again.

When fishing, the red-footed booby is often disturbed by seagulls and frigate birds . These try to steal the food with bills on the back and head of the booby. The robber swoops down on the fishing red-footed booby and uses its beak to make the booby vomit the previously devoured fish.

Reproduction

Egg,
Museum Wiesbaden collection

Detailed investigations into the reproductive behavior of the red-footed booby have been carried out on the Galapagos Islands, Kiritimati and Ascension . Red-footed boobies are monogamous breeding birds, the pair relationship exists for at least one breeding period. Red-footed boobies are not tied to a specific season in their reproduction, but there are increased attempts at breeding at certain times of the year. Red-footed boobies that have successfully reared a young bird begin the next attempt at breeding 12 to 15 months later. In the case of red-footed boobies that have not hatched successfully, the distance is slightly smaller. If the egg of a clutch is already lost, red-footed boobies are able to lay another clutch as early as ten to forty days later.

The red-footed booby is the only type of booby that breeds on trees or bushes. For this he has developed special toes on the feet, which are able to clasp branches despite the webbed feet. Other booby species are not able to do this. It often breeds in breeding colonies with other gannet species. Since all other types of booby breed on the ground, the red-footed booby can share a habitat without competition. Usually several pairs breed in one tree. The territorial behavior is difficult to determine due to the nesting in trees. Red-footed boobies, however, at least defend their immediate nest environment from conspecifics and other bird species. The oviposition within the breeding colonies is not synchronized.

The nests are simple rice nests. The clutch consists of only one egg, which is alternately incubated by one of the two parent birds. Red-footed boobies do not have a brood spot, they cover the egg with their webbed feet. The red-footed booby fishes for food far from land and can be absent from the nest for a long time. Occasionally the brooding partner will leave the egg or hatched young to look for food themselves. Then the chick may starve to death or die from exposure to sunlight. Young chicks up to five days of age are unable to regulate their body temperature on their own. During the first few days of life, they depend on being shaded by their parent birds. Young birds defecate on their legs and feet to regulate their body temperature.

Young hatched chicks are 12 centimeters long and weigh an average of 50 grams. They reach a weight of 950 to 1,240 grams when they are 75 to 100 days old. Then their weight is reduced again until they are fully fledged. At this point, they weigh between 750 and 1,100 grams. Chicks are initially naked, by around three to four weeks they are covered with thick dunes. In the 13th week of life, remnants of the downs are still on the back of the head, the neck and the trunk. On Kiritimati, juveniles fledge at around 100 to 110 days, while on the Galapagos Islands development is much slower. They fledge here at an age of 220 to 320 days of life.

When building their nests, seagulls and frigate birds try to capture the nesting material. If the nest is left unattended, the robbers will quickly dismantle it. The hatching rate varies greatly. On the Kure Atoll , 68 percent of 32 eggs hatched. In the Galapagos Islands, however, the hatching rate was only 30 percent. Similar deviations can be seen in the rate of young birds that survive until they fled. Around 90 percent of the hatched young birds also fledged on the Kure Atoll, compared to only 28 percent on the Galapagos Islands. Clutches are relatively often given up by the parents, and disturbances from frigate birds can play a role here. On Raine Island , a 32-acre cay off the east coast of Australia, the bushes in which the red-footed boobies breed occasionally die and then collapse under the weight of the nests. The herring-headed gull , which eats both eggs and small chicks, is one of the predators of the red-footed booby .

threat

The populations are stable, the red-footed booby is one of the most numerous types of booby. Due to their habit of nesting in trees, they are largely protected from predation by introduced rats and feral domestic pigs. Deforestation and fishing are a threat. As a result, their number has fallen sharply on some Pacific islands. Their eggs are sometimes collected and sold by humans.

swell

literature

  • PJ Higgins (Ed.): Handbook of Australian, New Zealand & Antarctic Birds , Volume 1, Ratites to Ducks, Oxford University Press, Oxford 1990, ISBN 0195530683

Individual evidence

  1. BirdLife factsheet on the red-footed booby , accessed on May 1, 2011
  2. Higgins, p. 773
  3. ^ Higgins, p. 774
  4. Higgins, p. 773
  5. ^ Higgins, p. 774
  6. ^ Higgins, p. 774
  7. Higgins, p. 779
  8. Higgins, p. 777
  9. Higgins, p. 779
  10. Higgins, p. 779
  11. Higgins, p. 779
  12. ^ Higgins, p. 775

Web links

Commons : Red-footed Booby ( Sula sula )  - Collection of images, videos and audio files