Large foot fowl
| Large foot fowl | ||||||||||||
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Grouse ( Alectura lathami ) |
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| Megapodiidae | ||||||||||||
| Lesson , 1831 |
The megapodes (Megapodiidae) are in the Australasian common room family of Fowls . The 22 species form a clearly defined taxon , which is characterized by morphological similarities such as the eponymous enlarged toes, but above all by the extraordinary breeding behavior. Some species build huge brood mounds, others bury their eggs in the ground.
features
Big footed fowl, like almost all hen birds, are clumsy ground-dwellers who rarely fly. Their size ranges from 28 to 70 cm, their weight from 500 to 2450 g. The smallest member of the family is the Lapérouse chicken, the largest is the bush chicken. The large and strong legs and feet were not only eponymous in German, but also in the scientific name (Megapodiidae). Since they are used in connection with the breeding behavior for digging and filling nesting mounds, the size is an advantage. The rear toe is fully developed and level with the front toe - a feature that large footed hens have in common with the Hokkos and that ensures that both are often thought to be related.
The beak , which is typically short and unspecialized, but is equipped with a sensitive temperature sense with which the temperature of the nesting mound is controlled, is also related to the breeding behavior .
In the plumage, brown, black and gray tones predominate. This inconspicuous color ensures camouflage in the undergrowth. The bare skin on the face is more colorful and in some species it extends over the entire head and neck. Based on this, some species have paired skin flaps under the chin or noticeable throat pouches. The hammer chicken wears a bony helmet structure on its head that is reminiscent of a cassowary .
The sexual dimorphism is when it exists, is not particularly striking. Males are often slightly larger, the bare skin areas are a bit more colorful, and the skin flaps and bone ridges are larger and more noticeable. However, these differences are so small that they can hardly be used in field ornithological terms.
The wings of the big foot fowl are large and rounded. They enable a flight over short distances. Mostly, the ability to fly is only used in case of danger. Larger species often only manage distances of a few meters.
The tail is very different depending on the species. The "real" big foot fowl of the genus Megapodius have a very short, angular tail. In contrast, the tails of the grouse and talegallas are long and rounded and can be unfolded or set up during courtship.
distribution and habitat
The main area of distribution of the large foot fowl is in Australia , New Guinea and Indonesia east of the Wallace Line . One way the Philippines chicken, also lives in the Philippines and the western Wallace Line island of Borneo , another that Nikobarenhuhn, on to India belonging Nicobar Islands . In addition, several species live scattered on the Melanesian and Polynesian islands.
In the Pacific the range is very scattered. The pritchard hen lives exclusively in the caldera of the Niuafoʻou island , which belongs to Tonga , while there are no large foot fowl on the surrounding islands. However, it appears that the extremely patchy range was caused by humans. Reports by seafarers of the 18th and 19th centuries indicate that New Caledonia , the Kermadec Islands , Samoa and Ha'apai were also home to large foot fowl. Subfossil finds document former occurrences of large foot fowl in Fiji . Accordingly, it was most likely Polynesian, Melanesian, or European hunters who wiped out large foot fowl on most of the oceanic islands.
However, the question remains why the large foot fowl did not spread further west. There are two theories about this: According to the first, it is the competition of the pheasant-like species , which are widespread in Asia , that did not allow large footed fowl to cross the Wallace line. After the other, it is the extensive lack of predatory mammals that makes Oceania an ideal habitat for the big foot fowl; this advantage does not exist west of the Wallace Line.
The preferred habitat of almost all species is the bottom of the tropical rainforest . On some islands, large foot fowl have adapted to open bushland due to habitat restrictions. The thermometer chicken in Australia is the only species that lives in semi-arid habitats characterized by mallee and acacias .
Way of life
activity
Most big foot fowl lead an inconspicuous life in the dense underbrush, which makes them difficult to observe. In particular , little is known about the way of life of many island endemics .
Diurnal species predominate, but there are also crepuscular and mostly nocturnal large foot fowl. They are mostly met individually or in pairs. The surroundings of a nest are bitterly defended against other conspecifics. Only the hammer grouse and the molucca grouse are more sociable and tolerate further nests nearby. Outside the breeding season, representatives of some species can be seen resting in small groups in the trees.
nutrition
Big footed chickens are omnivores. Their vegetable diet includes seeds, buds, flowers, leaves and fruits; animals eat insects, spiders, millipedes, worms and snails. In the thermometer chicken, the best-researched species, the vegetable portion of the diet is 87%, the animal portion 13%.
Like many other birds, big foot fowl often swallow gravel and sand, which are used to mechanically break up food in the gizzard ( gastroliths ).
Since large foot elk paws for food in the forest floor and stirs up the leaves, smaller birds occasionally follow them to prey on frightened small animals. This behavior has been observed in some panther birds, for example .
Reproduction
In the entire bird world, cattle-footed fowls are unique because they do not warm their eggs through body temperature, but through other systems - for example by piling up a brood mound or burying the eggs. Large foot fowl have developed five different breeding systems. The most common is the construction of a breeding mound, as well as the use of the heat of volcanic soil, the heat of the sun and the heat produced by the rotting of tree roots. The fifth method is brood parasitism .
Brood mound
The breeding mounds of the foot-fowl are built from plant material and soil. In most cases, moist material is first stacked and then covered by dry material. Most of the time, the male is solely responsible for building the mound, with some species the female assists. The preferred location for a brood mound is shady under trees, where it is not exposed to large temperature fluctuations. An exception is the thermometer chicken, which breeds in arid regions.
The exact composition of a brood mound varies from species to species. The shape also differs even within a species. However, the abundance of shapes described in some species often seems to be related to the fact that the observers saw hills at different stages of construction. Usually a conical hill is built up first, the top of which is then later flattened to form a plateau.
The purpose of a brood mound is to provide the eggs with warmth and moisture. The heat is generated by microorganisms that break down the organic material. The temperature in the hill is 32 to 38 ° C for the thermometer chicken, 33 to 39 ° C for the Reinward chicken, and apparently in similar temperature ranges for the other species. It is important for the development of the eggs that the temperature in the brood mound remains constant. A hill as large as possible and the use of a lot of fresh material are conducive to this consistency. Long droughts and persistent rainfall can still cause the temperature to fluctuate. The fowl's embryo is surprisingly tolerant of such disturbances; it can react to unfavorable temperature conditions through slower growth and late hatching. The thermometer chicken alone has to constantly look after the hill in order to keep the temperature in the open regions of Australia constant. So it is regularly covered with sand to prevent overheating, or even opened.
In order to produce the necessary heat, a brood mound must be at least 2 m wide and 75 cm high. Most big foot fowls, however, build larger mounds. Especially since some species are rebuilding or expanding old hills, these constructions can take on gigantic proportions. The record is held by the hill of a Reinward chicken, which was 12 m wide and 5 m high. Some hills have been used over a period of forty years. The structures then permanently change the landscape. In Australia, for example, there are some breeding mounds that have not been used for 1500 years, but which are still recognizable.
Bury the eggs
Eight species are known to bury their eggs in the sand or in the ground. To do this, they use special points that guarantee an exceptional supply of heat. Three species use this method exclusively, the other five use it in addition to building brood mounds.
The chickens dig a passage that is 90 to 200 cm long and 15 to 40 cm wide - such a passage is usually shorter in the sand than in solid earth. At the end of this aisle, the eggs are laid and then left to their own devices. Apart from brood parasites, these large foot fowl are the only birds that do not care for the brood after they have laid their eggs .
Geothermal energy is mainly used as a heat source by the Bismarck grouse, the Pritchard grouse, the Lapérouse grouse and the hammer grouse. An example is the pritchard hen, endemic to the volcanic island of Niuafoʻou , which lays its eggs in the volcanic soil. Since places with the necessary warmth (here, too, it is in the range of over 30 ° C) are rare, in some places there are collections of many large foot fowl in a very confined space. In the Pokili region on the island of New Britain , up to 53,000 Bismarck chickens can be found at the same time and lay their eggs there.
The use of solar heat, on the other hand, is the breeding principle of the hammer and Moluccan grouse. The eggs are buried in the sand and exposed to the heat of the sun. This procedure is only used during the dry season.
Little research has been done on the use of the heat from rotting tree roots. This appears to be the normal practice for the Layard chicken of the Vanuatu Islands.
Brood Parasitism
Brood parasitism has also been little researched, but seems to occur quite often. It has been proven that in New Guinea the New Guinea hen lays its eggs in the brood mounds of the Kamm- und Halsbandtalegalla. Clutches of different species in one hill have also been found on other mounds, although it was ultimately unclear which species parasitized which. Large footed fowl who use this method save the energy-sapping building of a brood mound, but their young, like those of other large footed fowl, do not need brood care either. This distinguishes the brood parasitism of the big foot fowl from that of the cuckoo , for example , in which a benefit is drawn from the parasitic behavior far beyond the oviposition.
Pair formation
As a rule, large foot fowl are monogamous. However, polygyny is the rule in the bush chicken and has also been demonstrated in the thermometer chicken. In this case, several females lay their eggs in a mound. Usually, however, a couple looks after a brood mound.
A female usually inspects several breeding mounds before deciding on one and thus on a partner. The perfection of the hill is more important than its size or shape. So mounds are rarely chosen that contain many large twigs and other bulky objects that make it just as difficult to open the mound to lay eggs as it is to free the young later.
The mating takes place on the hill.
Egg laying
Before laying the eggs , the female carries out “test digs” in the mound, in which she looks for places with a suitable temperature. With the well-developed temperature sense of the beak, the heat is checked again and again and ultimately a place is chosen.
Large footed chickens have extremely large clutches. A hammer chicken lays eight to twelve eggs, a thermometer chicken 15 to 24, and a bush chicken even up to 30 eggs. Eggs can be laid over a period of several months.
While the grouse, comb talegalla, and brown-breasted talegalla have pure white eggs, the eggs of the other species are reddish brown in color. The eggs weigh 75 to 230 g, depending on the species, and are exceptionally large and heavy at 10 to 20% of the body weight of the female.
In addition, the eggs have a number of other remarkable properties. Their yolk content is always over 50%, in many species even over 60%. In birds, including other fowl, a proportion of less than 50% is normal. Similar high values are only found for kiwis . But the water content in the eggs is lower. The shell of the eggs is very thin - namely 31% thinner than an egg from another chicken. There are two reasons for this: On the one hand, the thin shell facilitates the oxygen supply to the interior, so that even the little air that arrives underground is sufficient; on the other hand, it is easier for the boy to break open the shell because he does not have an egg tooth .
Brood and hatching
The number of days between oviposition and hatching can vary extremely depending on the environmental conditions. In bad climatic conditions, the embryo slows down its growth and hatches considerably later. Thermometer chickens hatch after fifty days under ideal conditions, and only after 96 days under difficult conditions. Since the eggs are not laid at the same time, but over a period of several months, the young also hatch at very different times.
Since there is no air chamber in the egg as in most other birds' eggs, it must hatch very quickly. Like all avian embryos, the embryo was supplied with oxygen via the allantochorion . As soon as this breaks, the air supply is cut off and the young bird has to leave the egg as quickly as possible. The young bird lacks an egg tooth - strictly speaking, an egg tooth initially forms in the embryo, but it has already receded at the crucial moment of hatching. The shell is therefore burst open by kicking it with the feet - this is where the small thickness of the shell benefits. The boy then struggles independently through the hill or through the earth upwards. With a large breeding mound, this walk can take a full day.
Young big foot fowl are more developed when hatching than any other bird - a result of the high proportion of yolk in the eggs and the long incubation time. A Bismarck grouse that has just hatched from the egg measures 11 cm, which is a third of the length of the adult bird. The hatched big-footed chicken has no down coat and is able to fly and regulate its body temperature from day one. Brood care no longer takes place. If the youngster encounters the parent birds on the hill, they take no notice of him or shoo him away. It is therefore immediately on its own.
In addition to poor climatic conditions in the region indoaustralischen especially lizards breeding responsible for the failure. On the Australian mainland there are also foxes and martens that did not originally exist there. After being introduced by humans, they are to a large extent responsible in some regions for failure of the breeding of large footed chickens.
Tribal history
Fossil foot fowl
Representatives of the genus Quercymegapodius , which were widespread in Europe in the Eocene and Oligocene , used to be the oldest representatives of the large foot fowl . Today, however, one no longer believes that it was a question of large foot fowl or even just their relatives, and puts them either in a separate family Quercymegapodiidae or in the fossil Gallinuloididae.
Although subfossil finds from the Holocene are common, especially from oceanic islands, older finds are rare. The oldest known large foot fowl is Ngawupodius minya from the late Oligocene of Australia. From the Pleistocene of Australia, Progura gallinacea, a large foot fowl up to 7 kg is known, which was two to three times the size of a bush hen, the largest of the recent large foot fowl.
Evolution of breeding behavior
In connection with the large foot fowl, it is also interesting to consider how the remarkable breeding methods came about. At first glance, these are more reminiscent of crocodiles and other reptiles . From this, the Swiss zoologist Adolf Portmann concluded in 1938 that large foot fowl were particularly primitive birds that had not yet developed nest-building and still had the procedures of their reptilian ancestors. Doubts about this theory arose in the 1960s when it was discovered that the embryo of the big foot fowl does develop an egg tooth , but it regresses again - a sign that big footed chickens in their tribal history must have had breeding behavior like all other birds ( biogenetic Basic rule ). Today Portmann's theory is no longer tenable. The similarities to the breeding behavior of reptiles arose in convergent evolution .
A long unanswered question was which breeding strategy is older: building nesting mounds or burying the eggs in heated areas. The answer is made more difficult by the fact that no systematic separation can be drawn between “hill builders” and “graves”. Thus, within the genus Megapodius there are both mound builders and graves, and some species practice one method on one island and the other on a neighboring island. Burying seems to be the simpler method, so that ornithologists at the beginning of the 20th century suspected it must be the older one. Clark contradicted this, who said that a guarded brood hill is a transition between the typical bird's nest and a hole in the earth that is left after the eggs have been laid. Clark's view is supported by new phylogenetic studies, which show that the lowest branches in the large footed cladogram all lead to hill-builders and only the youngest branches lead to graves (see below).
However, the question of why the hill-building method was developed remains unanswered. It is true that the big foot fowl save themselves the breeding and rearing of young, but the construction of a brood mound and its care is an enormous effort that is likely to exceed the effort of a conventional bird brood. For example, a male thermometer chicken spends eleven months at a stretch building and maintaining its brood mound. The development of the behavior was probably favored by the extensive absence of carnivorous mammals in their area of distribution.
Systematics
External system
Traditionally, the big foot fowls are settled at the base of the chicken birds . Zoologists of bygone centuries also placed them in the vicinity of plover-like birds , pigeons , lyre tails , cocktails or even birds of prey . Their position on chickens, like their monophyly, is no longer in doubt today.
A distant relationship to the South American Hokkos was very often assumed within the chicken family . Both are then led in a common subordination Craci (or Cracides, Cracoidea). This assumption, which was initially based on anatomical similarities, was also confirmed by biochemical studies of the eggs and by DNA hybridization . Most significant of the competing views is that which sees large foot fowls as sister groups to all other chicken birds. This is supported by analyzes of the spring structure.
Internal system
A subdivision of the large foot fowl into two subgroups “large” (Alecturini) and “real” (Megapodiini) large foot fowl goes back to George Clark, who tried a classification in 1964. Today this subdivision is no longer tenable. According to a morphological analysis from 1992, the genera Megapodius , Eulipoa and Macrocephalon form a monophyletic taxon, the genera Aepypodius and Alectura another. The latter two are therefore the sister group of all other large foot fowl.
The following division into seven genera with 22 species follows Jones, Dekker and Roselaar 1995.
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Alectura
- Bush Chicken , Alectura lathami , Eastern Australia
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Aepypodius
- Comb bush chicken , Aepypodius arfakianus , Guinea , Misool
- Brown breasted grouse , Aepypodius bruijnii , Waigeo
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Talegalla
- Red-billed Talegalla , Talegalla cuvieri , western New Guinea and offshore islands
- Black- billed Talegalla , Talegalla fuscirostris , southern New Guinea, Aru Islands
- Collared Talegalla , Talegalla jobiensis , northern New Guinea and offshore islands
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Leipoa
- Thermometer chicken , Leipoa ocellata , southern Australia
- Macrocephalon
- Eulipoa
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Megapodius
- Pritchardhuhn , Megapodius pritchardii , Niuafoʻou
- Lapérouse chicken , Megapodius laperouse , Palau , Northern Mariana Islands
- Nicobar Grouse , Megapodius nicobariensis , Nicobaren
- Philippines chicken , Megapodius cumingii , Philippines , Sulawesi, northern Borneo
- Sulahuhn , Megapodius bernsteinii , Banggai and Sula Islands
- Tanimbar Chicken , Megapodius tenimberensis , Tanimbar Islands
- Moluccan big foot chicken , Megapodius freycinet , Northern Moluccas
- Geelvink foot fowl , Megapodius geelvinkianus , Schouten Islands
- Megapodius forstenii , Southern Moluccas
- Bismarck Grouse , Megapodius eremita , Bismarck Archipelago , Solomon Islands
- Layard chicken , Megapodius layardi , Vanuatu
- New Guinea Chicken , Megapodius decollatus , northern New Guinea and offshore islands
- Reinward chicken , Megapodius reinwardt , Lesser Sunda Islands , west and south New Guinea, northern Australia, islands off the aforementioned areas
Humans and large foot fowl
For centuries, large foot fowl have been used by the human inhabitants of the islands on which they are native. As mentioned under distribution , this has led to their extinction on several oceanic islands.
The eggs with their high proportion of yolk are particularly popular, so that some island populations may have died out because all of their brood mounds were opened to get to the eggs. Indeed, since the breeding mounds are easy to spot, it is easy to wipe out a population completely. The meat of the birds is also eaten in some places.
But such ruthless extermination was not carried out everywhere. Eggs have been dug up for centuries in the southern Moluccas or New Britain , but most of them are left untouched so as not to endanger the population of the birds. Today, however, the rules no longer apply, and egg collecting in New Britain soon got so out of control that nearly 5 million eggs were stolen a year in the 1970s.
Excessive egg-collecting has resulted in numerous species being classified by the IUCN as endangered (Moluccan grouse, biak grouse, Layard grouse, Nicobar grouse) or critically endangered (hammer grouse, Lapérouse grouse, pritchard grouse). The brown-breasted talegalla, which is endemic to the island of Waigeo , was thought to be extinct before it was discovered in 2002 that it is still quite common in mountainous regions of the island; because of its small distribution area, this species is also considered endangered.
The thermometer chicken, which is native to Australia and is probably the best-known of all large foot fowl, is now classified as endangered. There has been a dramatic decline in stocks in recent years, but this has other causes. These include free-roaming foxes, martens and dogs, urban sprawl, disruption from sheep, cattle and goats, and sterility from pesticides . In the Northern Territory , the thermometer chicken is already extinct, in other regions a catalog of immediate measures is now intended to halt the decline.
By contrast, the other well-known species of Australia, the bush chicken, has become even more common in recent years. Since it is now also building its hills in parks and gardens in Brisbane , it is often perceived as a nuisance, especially since it uses materials from flower beds and compost heaps. Sometimes an existing compost heap is also accepted as a breeding mound.
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:
- ^ Rene Dekker: Distribution and Speciation of Megapodes (Megapodiidae) and Subsequent Development of their Breeding . In: Willem Renema: Biogeography, Time, and Place: Distributions, Barriers, and Islands . Springer, 2007. ISBN 978-1-4020-6373-2
- ^ A. Portmann: Contributions to the knowledge of the postembryonic development of birds . In: Revue Suisse de Zoologie et Annales du Musee d'Histoire Naturelle de Genève 1938, No. 45, pp. 273–348
- ↑ a b G.A. Clark: Notes on the embryology and evolution of the megapodes (Aves: Galliformes) . In: Postilla 1960, No. 45, pp. 1-7
- ↑ RWRJ Dekker: Predation and the western limits of Megapode distribution . In: Journal of Biogeography 1989, No. 16, pp. 317-321
- ^ M. Laskowski & WM Fitch: Evolution of avian ovomucoids and of birds . In: B. Fernholm, K. Bremer & H. Jörnvall: The hierarchy of life: molecules and morphology in phylogenetic analysis . Amsterdam: Excerpta Medica, 1989
- ↑ CG Sibley, JE Ahlquist & BL Monroe: A classification of the living birds of the world based on DNA-DNA hybridization studies. In: Auk 1985, No. 105, pp. 409-423
- ^ TG Brom: Variability and phylogenetic significance of detachable nodes in feathers of tinamous, galliforms and turacos. In: Journal of Zoology 1991, No. 225, pp. 589-604
- ↑ Bernhard Grzimek (Ed.): Grzimeks Tierleben , Volume 7 ( Birds 1 ). dtv, 1980. ISBN 3-423-03205-7
- ^ GA Clark: Ontogeny and evolution in the megapodes (Aves: Galliformes) . In: Postilla 1964, No. 78, pp. 1-37
- ^ IUCN Red List , February 3, 2008
- ↑ Aepypodius bruijnii in the endangered Red List species the IUCN 2011. Posted by: BirdLife International, 2008. Accessed November 13, 2011th
- ↑ Leipoa ocellata in the endangered Red List species the IUCN 2011. Posted by: BirdLife International, 2008. Accessed November 13, 2011th
literature
- Darryl N. Jones, René Dekker & Cees S. Roselaar: The Megapodes . Oxford University Press, 1995, ISBN 0-19-854651-3 .
- Josep del Hoyo et al .: Handbook of the Birds of the World. Volume 2: New World Vultures to Guinea Fowl. Lynx Edicions, 1994, ISBN 84-87334-15-6 .
