Frigate birds
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Male Magnificent Frigatebird ( Fregata magnificens ) |
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| Lacépède , 1799 |
The frigate birds (Fregatidae, Fregata ) are a family and genus of sea birds from the order Suliformes that is widespread in the tropics and subtropics . They are known for the inflatable red throat pouch of the males and their ability to attack other birds and steal their prey ( kleptoparasitism ). It is from this behavior that they get their name, which is intended to tie in with the attacks by frigates . The genus includes five species.
features
Unlike many other representatives of the Suliformes, who are more adapted to a swimming and diving way of life, frigate birds are very good fliers. They have long, narrow wings, and the flight pattern resembles an elongated "W". The wingspan is between 175 and 244 cm, the body length is between 71 and 114 cm. The bones are built very lightly and to an extreme degree pneumatized (i.e. stabilized by trabeculae and filled with air) so that they only make up 5% of body weight - a record in the bird kingdom. With a weight of 600 to 1600 g, they are also lighter in relation to their height than any other bird. The strong chest muscles make a significant contribution to weight with 15 to 20% . The bones of the shoulder girdle are fused together, which is also a unique feature among birds. The humerus is relatively short, while the ulna and radius are greatly elongated. All these characteristics make frigate birds capable of agile flight maneuvers, which they use when attacking other birds. Even when the wind is low, the birds only have to glide and no longer actively flap their wings; however, they can maneuver even when there is no wind and in storms.
Frigate birds have a slender body and short neck. The head is short and rounded. The tail is forked deeply, but this is usually not visible because the twelve tail feathers are often folded together so that the fork is closed. During the flight maneuvers, the tail serves as a rudder, so that it opens and closes with every change of direction.
The legs are greatly shortened and make it almost impossible for the bird to walk or swim. In flight they are mostly hidden in the plumage. Their main purpose is to provide support when sitting on a branch, for which they are provided with strong claws. Like all four toes are all kinds in order Suliformes webbed connected, but these degenerates strong. Frigate birds have a preen gland , but it has regressed; the secretion for oiling the plumage is produced in such small quantities that it is hardly suitable for keeping the plumage waterproof. The bones of the pelvis are also greatly reduced , as they are neither needed for running nor swimming. The fibula and shin are completely fused together.
The beak is slender and strong. It reaches a length of up to 15 cm and ends in a pointed hook, which is helpful both when holding on to slippery prey and when attacking other birds, where it is used as a weapon.
Frigate birds show a very conspicuous sexual dimorphism . First, females are on average 25% larger and heavier than males. The much clearer difference is the color. Only the males have a greatly enlarged throat pouch, which is bright red in color during the breeding season and which can grow considerably again through balloon-like inflation. The plumage of adult males is almost exclusively black, only the male white-bellied frigate bird has a white underbelly. Females have a white breast, so in the white-bellied frigate bird the white coloring covers the entire underside. The feet of the sexes are also colored differently: brown or black in males, white or red in females.
Deviating from the scheme described above, the eagle frigate bird has a light and a dark morph of females; the dark morph shows a brown chest band but no white.
In the case of frigate birds that have just fledged, the head and large parts of the underside are white. After four to six years, the birds are colored. The constantly changing appearance of young and immature frigate birds contributes significantly to the difficulties of reliably identifying frigate bird species.
distribution and habitat
Frigate birds can be found near the coast and in the open sea, but almost never inland. Preferred breeding areas are small oceanic islands, only a few colonies also exist on the coasts of the mainland. Mangrove forests , which offer trees for breeding in the immediate vicinity of the coast, are an ideal breeding habitat . Other trees and shrubbery are also used, only in the complete absence of vegetation is the ground also brooding.
Two species are island endings : the eagle frigate bird breeds exclusively on Ascension , the white-bellied frigate bird on Christmas Island . The other species have much larger distribution areas. For example, the common and arial frigate birds breed on a number of tropical islands in the Pacific and Indian Oceans , and both species can be found on the Atlantic islands of Trindade and Martim Vaz . The magnificent frigate bird breeds on both coasts in the tropical latitudes of the American double continent; another population on the Cape Verde Islands is almost extinct.
Outside the breeding season, frigate birds can be found over all tropical oceans. Frigate birds rarely fly into temperate zones; however, these rare wanderers have already been sighted on the coasts of Scotland, Ireland and Denmark .
Way of life
activity
As the perfect flyer, frigate birds spend most of their lives in the air. You can stay in the air for weeks without landing, sleep during that time and can cover distances of over 400 km per day. They use the circulating winds within cumulus clouds to ascend and thus reach heights of 1600 to 4000 meters. With cross winds emanating from the cumuli, they then gradually slide down again and cover distances of up to 60 km.
In flight, they sleep no longer than 6 minutes at a time, but rest on land for more than 12 hours a day. If you sleep in a circling flight, only use the eye in the direction of the curve bend.
When resting, they often sit on trees or ship masts with their wings spread out, the underside of the wings pointing upwards. This pose, often misleadingly referred to as "sunbathing", has been interpreted in different ways. The two most widespread theories are, on the one hand, that this posture releases heat into the environment by convection , i.e. the pose serves to maintain the temperature, and on the other hand, that bent flight feathers return to an ideal position.
Frigate birds are sociable. They breed in colonies and outside of the breeding season can be seen flying or resting in groups. Often they are found associated with gannets or cormorants .
nutrition
Frigate birds became known for their attacks on other birds in order to steal their prey. However, this is not their only diet. In fact, most of the food is self-hunted. It is always typical that - somewhat unusual for a sea bird - contact with the water is avoided if possible. A distinction must be made between three important diets: hunting marine animals, looting bird nests and kleptoparasitism .
Hunt for marine animals
For all frigate birds, flying fish are the main prey because they can be captured in the air. The same applies to the squids of the family Ommastrephidae, which are also known as "flying squids". Otherwise, frigate birds look for fish or cephalopods that swim so close to the surface that it is not necessary to submerge more than their beak or head. However, it rarely happens that a frigate bird is completely submerged in the water while pursuing its prey - contrary to what is sometimes claimed, it can then take off without any problems and continue its flight.
When hunting, frigate birds often follow schools of tuna or schools of dolphins . Many fish try to escape from these predators by making long leaps above the surface of the water. They are easy prey for the frigate birds waiting above sea level.
In addition to fish and cephalopods, jellyfish, crustaceans and young sea turtles are also prey of the frigate birds. The latter two are also captured on the beach. All of this prey is eaten on the spot and the hunt resumes immediately.
Looting of bird nests
Eggs and juveniles of other seabirds are also mostly captured from the air. A frigate bird rarely lands to eat them. Among the preferred victims of hunting include gannets , terns , petrels and storm petrels . Very rarely, even nests of other frigate birds are attacked.
On Christmas Island, the effects of the predatory behavior of frigate birds on the sooty tern colonies living there were examined in detail . Every year they lose millions of eggs and young to attacks by frigate birds. In 1967 and 1983 the attacks went so far that not a single tern brood was successful.
Kleptoparasitism
In addition to skuas , frigate birds are the best-known examples of kleptoparasitism (also known as "piracy") in the bird kingdom. Their attacks on other birds earned them their name as they were compared to the raids of the frigates by pirates . In English they have the name frigatebird and the name man-o'-war bird . (A man o 'war was a sailing warship, such as a galleon or a ship of the line .)
Most often, boobies are attacked by frigate birds. Attacks on terns, petrels, petrels, tropical birds , cormorants , pelicans , gulls and even ospreys have also been observed. Frigate birds do not have to stray far from the colony to attack other birds. Sometimes they follow seabirds out to sea and attack them as soon as they emerge, but they are often caught on the return flight or even at the nest while the young are being fed.
With their agile flight maneuvers, the frigate birds are always superior to the victim. They bump down on the bird and snap at its tail and wings. Often times these actions throw the bird off balance and it will drop its prey. The frigate birds then immediately pounce on the prey and break off the attack. If an attacked bird does not let go of its prey, it is attacked with beak blows, which can sometimes lead to serious injuries.
Several studies of kleptoparasitic behavior have been carried out. This means that around 5% of the food is captured by attacks on other birds, so frigate birds gain 95% of their food by hunting on their own. Nevertheless, kleptoparasitism is the most well-known diet of the frigate birds because it is downright spectacular. In addition, kleptoparasitism is more significant in some regions than in others. In most cases, it is mostly the larger and heavier females who carry out such attacks, while males rarely or never engage in kleptoparasitism. On Isla Isabel off the coast of Nayarit , for example, attacks by frigate birds on blue-footed boobies were observed and it was found that 1553 attacks were carried out by females and only eight by males. Numerous other studies came to similar results, but not all. On the Galapagos Islands, for example, it is the males who particularly often hunt prey from other birds.
Reproduction
Frigate birds are colony breeders. The breeding colonies can consist of several thousand animals. Within the colonies, seven to thirty pairs can be found in particularly close breeding groups. The colonies are often associated with other sea birds. This neighborhood is only of benefit to the frigate birds: they seek to be close to the species they attack at sea and on their return to the nest. As tropical birds, frigate birds are usually not tied to any specific breeding season. There are breeding frigate birds in the Galapagos at any time of the year. However, there can be fixed times regionally. The frigate birds on Little Cayman start breeding one month after the red-footed boobies , which are available as potential victims.
The courtship is spectacular. Male frigate birds gather in small groups on the coasts and advertise together. They put their heads back and inflate their scarlet throat pouches. At the same time, they spread their wings and present their silvery white undersides. If a female is in the vicinity, the male begins to shake his head and make drumming and snarling noises. This and the widely visible red color attracts the female, which decides on a partner.
The nest is preferably built in tall trees, in the absence of which also in bushes, and on coasts without vegetation even on the ground. Accordingly, the search for nesting material varies in effort. On rather bare islands, the birds have to fly long distances and sometimes leave their island. Often times, frigate birds in a colony try to steal nesting material from one another. Usually the male goes in search of nesting material while the female defends the breeding site against nest predators. Branches, grasses and algae serve as nesting material. If nothing is available, a nest is not built and a hole is made in the ground instead; this is the rule on Ascension . Mating takes place while the nest is being built. The area around the nesting site now becomes an area that is defended against intruders. The otherwise rather silent frigate birds make screaming noises that can be heard for miles. However, there is almost never a fight.
Only one egg is laid. Two clutches of two eggs each have been observed in Hawaii, but these are extremely rare exceptions. Both partners brood and take turns every one to four days. Meanwhile, the other partner goes in search of food. The young hatch after 40 to 55 days. It is initially naked, but develops a down dress in the first few days. After a few days, it learns to stick its beak into the parent bird's beak or throat pouch, which causes it to choke out food. During the first month the boy is always guarded by a parent, after which he is left alone more and more often. The growth is extremely slow. It takes four and a half to seven months for the young to be able to fly. Even after this, the parent birds look after the young for nine to twelve months, and in exceptional cases even eighteen more months. A similar long-term brood care is otherwise only available in birds with gray-footed boobies . It happens that the parents do not succeed in obtaining enough food for themselves and an almost fully grown cub in such a long time, so that even after several months there is still a high mortality rate for the young. In the case of the magnificent frigate bird this is made even more difficult by the fact that the male has not been involved in caring for the young in the last few months. It is estimated that only 25% of broods are successful.
The elaborate breeding can usually only take place every two years. Often the distances are even larger. On Barbuda , however, it was found that there the males breed annually and the females every two years. This also seems to be the case with other species, but not everywhere. Frigate birds look for new partners for each brood.
The estimated average life expectancy is 25 years. A ringed frigate bird lived to be at least 34 years old.
Enemies, causes of death and parasites
Aside from humans, frigate birds have few natural enemies. It can be assumed that they occasionally fall prey to predatory marine fish such as sharks , but this has only been observed very rarely. Young birds, which often die from starvation, sometimes also from older conspecifics or from the few predators, are particularly at risk. The latter includes, for example, the short-eared owl on the Galapagos, which prey on young frigate birds left alone.
Louse flies and feather mites are often identified as ectoparasites . In Hawaii it was found that half of the young birds, one third of the adult males and one fifth of the females there are infested by Haemoproteus iwa , a single-celled endoparasite from the Plasmodia family . However, it has not been determined that this parasite harms its host in any way.
Tribal history
Frigate birds are a very old group of birds. This became clear in 1977 when the almost complete skeleton of an Eocene frigatebird was found in Wyoming . The species was named Limnofregata azygosternon . Another, larger and more long-beaked species from the same epoch was only recently identified and named Limnofregata hasegawai . Apart from these very old fossils, only very young remains of the recent species from the Pleistocene are known, so that there is a very large gap without fossil evidence.
The Limnofregata frigate birds of the Eocene were apparently quite different from today's frigate birds. They had longer toes that formed a rudder foot that was believed to be more suitable for a swimming and diving lifestyle than for today's perennially flying frigate birds. It is also considered unlikely that the sexual dimorphism that is so characteristic of today has already existed.
Systematics
External system
Traditionally, frigate birds were placed in the old order of the coarse pods because they share the characteristic of four webbed toes with them. The coarse pods also included the boobies , cormorants and darters , which even according to the latest information form a monophyletic taxon . Again and again, however, the affiliation of the frigate birds was questioned.
As early as 1888, Shufeldt thought that frigate birds were probably relatives of the tubular noses . The DNA hybridizations carried out by Hedges and Sibley also showed that frigate birds are all closer to the tube-nosed taxa, loons and penguins than they are to the coarse pods. The bird lice (on birds parasitizing pine lice ) of frigate birds are related to those of the tube lugs, which may be a further indication.
However, the results are not uniform. In 1995, for example, Mikhailov carried out an electron microscopic examination of the eggshell structure. His finding was that this was almost identical in frigate birds and the other oarpods.
Recent studies confirm a relationship between the frigate birds and the gannets, the darters and the cormorants.
The probable family relationships are given by the following cladogram :
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Internal system
Frigate birds were initially led with pelicans in the genus Pelecanus . Gmelin called the frigate bird (a division of frigate birds into individual species was not yet common) Pelecanus minor , the little pelican. For this reason, the banded frigate bird still carries the specific epithet minor today . The genus Fregata was established by Lacépède in 1799 .
The Ariel frigate bird was the first to be recognized as a species in its own right and in 1845 Gray even placed it in its own genus Atagen . The four larger species are so similar in their plumage that they have not been recognized as different for a long time. The species that are common today were named in 1914 by Gregory Mathews , although he still regarded the magnificent and banded frigate birds as subspecies of a species. Today five species are generally recognized:
- Eagle frigate bird , F. aquila
- White-bellied frigate bird , F. andrewsi
- Magnificent frigate bird , F. magnificens
- Great Frigatebird , F. minor
- Ariel frigate bird , F. ariel
Many species are very similar to one another. For example, it is considered impossible to distinguish between the male eagle and the magnificent frigatebird. It is believed that the speciation of the genus Fregata began only 1.5 million years ago; this explains the small deviations. All species were nevertheless confirmed as monophyletic; their relationship to one another is as shown in the following cladogram:
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Humans and frigate birds
Interrelationships
Frigate birds do not shy away from being close to people. They regularly follow fishing boats and grab the fish that are thrown overboard as worthless. In some areas they steal fish from nets and boats. The magnificent frigate birds near the Ecuadorian port town of Playas have learned to attack fishermen as soon as they bring their catch from the boats into the port. Although the fishermen arm themselves with clubs, the birds are always successful.
The oldest surviving description of a frigate bird comes from Christopher Columbus . On September 29, 1492 he noted in his logbook: Vieron un ave que se llama rabiforcado, que haze vomitar a los alcatraces lo que comen para comerlo ella y no se mantiene de otra cosa. Es ave de la mar, pero no posa en la mar ni se aparta de tierra 20 leguas. Hay d'estas muchas en las islas de Cabo Verde. ("You saw a frigate bird that forces the boobies to choke out their prey in order to then eat it themselves, and it never eats anything else. It is a sea bird, but it never lands on the water or moves further than 20 iguanas from There are many of them on the Cape Verde Islands. ”) Columbus saw the bird as a sign that the mainland might not be far away and gave it the false assumption that frigate birds never went far from the coast. While he was wrong here, he obviously already knew about the kleptoparasitic behavior. In addition, it emerges from his report that the magnificent frigate bird is said to have once been frequent on Cape Verde. Occasionally, frigate birds are eaten. Until the 20th century it was common on Aldabra to kill and eat several thousand frigate birds each year. The indigenous population of the Antilles also used to eat frigate birds to enrich their menu.
In some parts of Polynesia it is customary to raise young frigate birds, which then become tame and remain in human care. Like carrier pigeons , they can be used to transmit messages.
The American poet Walt Whitman wrote an admiring poem about frigate birds, which he called To the Man-of-War Bird .
Threat and protection
The IUCN currently lists the white-bellied frigate bird, which is endemic to Christmas Island, as critically endangered . For decades, the population decreased due to phosphate mining , for which a third of the island's trees were felled; In addition, the workers ate eggs and young of the frigate birds. After the Australian government took protective measures, the populations recovered, but have experienced a new dramatic decline since the 1990s, mainly caused by the yellow spinner ant . The colonies of this ant are capable of killing young frigate birds.
The eagle frigate bird is listed as endangered. After being downgraded from critically endangered to endangered status in 2000 , a renewed classification as critically endangered is currently being discussed, as the populations have decreased dramatically in recent years. This species was so decimated on Ascension by domestic cats introduced by settlers who ate the young that broods finally only took place on the offshore rocky island Boatswain Bird Island . The recent decline could be related to overfishing, which is depriving birds of their food sources.
In these two examples, all the important reasons that make frigate birds rarer around the world are already mentioned: habitat destruction, hunting, introduction of land mammals on previously mammal-free islands and overfishing. However, the magnificent frigate, the white frigate and the ariel frigate are not threatened globally. Because of their large distribution areas, they each number several hundred thousand individuals. However, all of these species are regionally threatened: the magnificent frigate bird is almost extinct on Cape Verde (regular hunted by fishermen), the banded frigate bird on Martim Vaz (target practice by the Brazilian Navy) and the ariel frigate bird on Trindade (cats), to name just a few examples.
useful information
- The United States named the Frigate Bird nuclear test after the frigate birds.
Sources and further information
Sources cited
Most of the information in this article has been taken from the sources given under literature; the following sources are also cited:
- ^ Henri Weimerskirch, Charles Bishop, Tiphaine Jeanniard-du-Dot, Aurélien Prudor & Gottfried Sachs: Frigate birds track atmospheric conditions over months-long transoceanic flights. Science 01 Jul 2016: Vol. 353, Issue 6294, pp. 74-78 doi: 10.1126 / science.aaf4374
- ↑ http://science.orf.at/stories/2789072/ Why sleeping birds don't fall, August 3, 2016, accessed August 3, 2016.
- ↑ DC Houston: A possible function for sunning behavior by griffon vultures, Gyps spp. and other large soaring birds . Ibis 122; 1980: pp. 366-369
- ^ DW Au & RL Pitman: Seabird relationships with tropical tunas and dolphins . In: J. Burger (Ed.): Seabirds and other Marine Vertebrates: Competition, Predation and Other Interactions . Columbia University Press 1988, ISBN 0-231-06362-8
- ↑ JA Vickery & M. de L. Brooke: The kleptoparasitic interactions between great frigatebirds and masked boobies on Henderson Island, South Pacific . Condor 96; 1994: pp. 331-340
- ↑ JL Osorno, R. Torres & CM Garcia: Kleptoparasitic behavior of the Magnificent Frigatebird: sex bias and success . Condor 94; 1992: pp. 692-698
- ^ J. Bryan Nelson: The breeding biology of frigatebirds - a comparative review . Living bird 14; 1976: pp. 113-155
- ↑ AW Diamond: Sexual dimorphism in breeding cycles and unequal sex ratio in Magnificent Frigatebirds . Ibis 114; 1972: pp. 395-398
- ↑ Thierry M. Work, Robert A. Rameyer: Haemoproteus iwa n. Sp. in Great Frigatebirds (Fregata minor [Gmelin]) from Hawaii: Parasite Morphology and Prevalence . Journal of Parasitology 82; 1996: pp. 489-491
- ↑ Storrs L. Olson: A Lower Eocene frigatebird from the Green River Formation of Wyoming (Pelecaniformes, Fregatidae) . In: Smithsonian Contributions to Paleobiology 1977, No. 35, pp. 1-33
- ↑ a b Storrs L. Olson & Hiroshige Matsuoka: New specimens of the early Eocene frigatebird Limnofregata (Pelecaniformes: Fregatidae), with the description of a new species . In: Zootaxa 2005, No. 1046, pp. 1-15
- ^ RW Shufeldt: Observations upon the osteology of the order Tubinares and Steganopodes . In: US National Museum, Proceedings II . 1888, pp. 253-315
- ↑ SB Hedges & CG Sibley: Molecules vs morphology in avian evolution. The case of the pelecaniform birds . In: Proceedings of the National Academy of Sciences 1994, No. 9, pp. 9861-9865
- ^ Günter Timmermann: The feather fauna of petrels and the phylogenesis of the procellariiform bird tribe . In: Treatises and negotiations of the Natural Science Association in Hamburg 1965, Vol. 8 (Suppl.)
- ↑ KE Mikhailov: Eggshell structure in the shoebill and pelecaniform birds: comparison with hamerkop, herons, ibises and storks . In: Canadian Journal of Zoology 1995, No. 73, pp. 1754-1770
- ↑ Per GP Ericson et al .: Diversification of Neoaves: integration of molecular sequence data and fossils . Biol. Lett. doi: 10.1098 / rsbl.2006.0523
- ↑ Hackett et al .: A Phylogenomic Study of Birds Reveals Their Evolutionary History . Science 27 June 2008: Vol. 320. no. 5884, pp. 1763–1768 doi: 10.1126 / science.1157704
- ^ Brown, Joseph W. and John Harshman. 2008. Pelecaniformes. Version 27 June 2008 (under construction). http://tolweb.org/Pelecaniformes/57152/2008.06.27 in The Tree of Life Web Project
- ↑ Martyn Kennedy & Hamish G. Spencer: Phylogenies of the Frigatebirds (Fregatidae) and Tropicbirds (Phaethonidae), two divergent groups of the traditional order Pelecaniformes, inferred from mitochondrial DNA sequences . In: Molecular Phylogenetics and Evolution 2004, No. 31, pp. 31-38
- ^ JC Den Hartog: An early note on the occurrence of the magnificent frigate bird, Fregata magnificens Mathews, 1914, in the Cape Verde Islands: Columbus as an ornithologist . In: Zoologische Mededelingen (Leiden) 1993, No. 67, pp. 361-364
- ↑ Walt Whitman: To the Man-of-War Bird; at repeatafterus.com
- ^ Fregata andrewsi in the IUCN Red List of Threatened Species . Retrieved December 15, 2008.
- ↑ Fregata aquila in the IUCN Red List of Threatened Species . Retrieved December 15, 2008.
literature
- Josep del Hoyo et al .: Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, 1992, ISBN 84-87334-10-5 .
- Bryan Nelson : Pelicans, Cormorants and their relatives. Oxford University Press, 2005, ISBN 0-19-857727-3 .
Web links
- Video: Heinz Sielmann: Fregata spec. (Fregatidae) - Courtship . Institute for Scientific Film (IWF) 1964, made available by the Technical Information Library (TIB), doi : 10.3203 / IWF / E-594 .
