Chathamrail
| Chathamrail | ||||||||||||
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Chathamralle ( Gallirallus modestus ) |
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| Systematics | ||||||||||||
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| Gallirallus modestus | ||||||||||||
| ( Hutton , 1872) |
The extinct Chatham Rail ( Gallirallus modestus ) was completely or nearly flightless and lived at least three islands to New Zealand belonging Chatham group simultaneously with the Dieffenbach's Rail ( Gallirallus dieffenbachii ).
Physique and plumage
The top of the rail was olive brown. The chin was gray, the throat, the underside of the body and the tail wore gray-brown feathers with faint whitish banding. The wings were brown and their outermost hand wings were banded yellowish white. The eyes, beak and barrel were light brown. The young animals were monochrome brown-black.
The rail was 22.5 centimeters long and thus smaller than the Dieffenbach rail, but both have beaks that are almost the same length. The beak of the chathamrail was slightly curved, longer than the head, and had a recess in the beak that protruded beyond the center of the beak. The oval nostril was in the middle of this depression.
The wings were very short, rounded with soft arm and hand wings. The thumb had a short claw. All the bones of the wing, shoulder girdle and sternum were significantly smaller than the cortex compared to the body size. The tail feathers were very short and soft and were hidden by the tail covers. The rest of the plumage was also very soft.
The metatarsal bones were shorter than the middle toe and were scaly. The front toes were long, thin, and all about the same length. The back toe was short and very thin and pointed inward. The claws were short and blunt.
The Chathamralle exhibited a strong dimorphism, presumably a sexual dimorphism, although it is unknown whether males or females were larger.
The creamy white eggs were 37 * 28 mm in size and had slightly reddish and purple spots. The eggs of the chatham rail were almost as large as the largest known eggs of the much larger cortex rail, whose eggs are between 32 x 24 mm and 37 x 29 mm in size.
Way of life
The nocturnal rail lived in dry forests and with its long beak, the relatively far forward nostrils and the nocturnal activity reminded a little of a very small kiwi . This suggests that it ate like this one by poking its beak in the ground for food. Since the original species, the bandage rail, hardly consumed any vegetable food, it can be assumed that the chatham rail, unlike the kiwi, consumed no or almost no vegetable food. This also corresponds to the only historical information about its diet, in which it was said that the railroad mainly fed on insects and small crustaceans.
The chatham rail nested in burrows. After hatching, the young are said to have hidden in fallen hollow trees.
Spread and extinction
The species was discovered by Travers on Mangere in 1871 and first described by Hutton as Rallus modestus in 1872 . Other specimen copies of the species were collected, but it became extinct between 1896 and 1900. It existed on at least three islands in the Chatham group, namely Chatham, Mangere and Pitt.
Goats and rabbits grazed large parts of the original vegetation on the Chatham Island in the range of the Chathamralle and largely destroyed their habitat. As a result, less suitable habitats were available for the railroad and rats and cats could catch them more easily without the cover of the plants.
Systematic classification
This rail was described scientifically for the first time in 1872, but because its plumage is reminiscent of the youthful dress of Gallirallus phillipinensis, it was mistaken for a Dieffenbach rail in youthful dress. Only when more of this type of bellows were collected was this refuted by the fact that the plumage of adolescents and adults looked the same. Hutton placed them in their own genus (Cabalus) in 1874 due to skeletal differences in the flying apparatus. Today, the Chathamrale, like the Dieffenbachrale, is a descendant of the banded rail (Gallirallus philippensis). The regression of the wing skeleton is interpreted as neoteny (retention of youthful characteristics in the adult animal), which also explains the plumage, which is reminiscent of the youthful dress of the Dieffenbachrale.
Genetically, the Dieffenbach rail and the Chatham rail differ approximately equally from the bandage rail. There are basically four possibilities, compatible with the result of the DNA examination, how the two closely related species could have originated.
The species could have developed simultaneously on the same island from the same ancestor capable of flying. This is contradicted by the fact that no mechanism is known that could explain a split of the species into two species under these conditions and that such a thing has not yet been clearly demonstrated.
The species splitting could have come about because each species developed on a different Chatham island and that after splitting into several species they reached the other islands of the archipelago by swimming.
The species could have developed independently of one another from different ancestors capable of flying, one of which was also the ancestor of the Schnepfenrale ( Capellirallus karamu ). What speaks against this theory is that neither fossils nor living birds know of a second possible species of origin and that it is also not clear why this species should then have disappeared.
The skeleton of the Chathamrail is more regressive than that of the Dieffenbachrale, that is, the neoteny is more pronounced and it is therefore assumed by many authors that the Ralle developed from a trunk that reached the Chatham Islands at an earlier point in time than the one from which the Dieffenbachrail arose.
On islands where only one flightless descendant of the union rail is known, a form has always emerged that uses more different habitats and consumes more different food than the union rail. It is also larger than the original species and has receded wings. Examples of such species are the Dieffenbachralle, the Wekaralle and the Waldrale . Large, flightless species that were very similar to one another and were less specialized than the serpentine rail emerged through parallel evolution on the most diverse islands.
The Chathamralle differs from this regularly occurring type in that it is considerably smaller and has a noticeably long beak, which indicates greater specialization. A similarly specialized species, which presumably also descends from the Union rail, is the Schnepfenrale ( Capellirallus karamu ) from New Zealand, where the Weka was also a less specialized descendant of the Union Rail. It therefore seems logical to assume that highly specialized species will only emerge when the ecological niche of the generalist has already been occupied. This is also supported by the fact that the genetic drift causes faster changes in small populations than in a large established population and that a large established population can exert more evolutionary pressure on a small founding population than vice versa.
However, it has been doubted that two colonizations in close proximity to one another on the island could actually lead to the emergence of two species, as it was assumed that the two species could not have separated far enough from each other to favor the emergence of new ones.
Web links
Individual evidence
- ↑ a b c d e f g h i j k l m Steven A. Trewick: Sympatric flightless rails Gallirallus dieffenbachii and G. modestus on the Chatham Islands, New Zealand; morphometrics and alternative evolutionary scenarios. Journal of The Royal Society of New Zealand Volume 27 Number 4 December 1997 pp 451-464
- ↑ a b c d e f g h i j k Dieter Luther: The extinct birds of the world. 4th edition, unchanged reprint of the edition from 1986. Magdeburg: Westkarp-Wiss and Heidelberg: Spektrum Akad. Verlag. 1995
- ^ A b c d e Walter Lawry Buller (1838-1906): A History of the Birds of New Zealand. 1888
- ↑ a b c d e Rothschild, Lionel Walter (1868-1937): Extinct birds: an attempt to unite in one volume a short account of those birds which have become extinct in historical times: that is, within the last six or seven hundred years: to which are added a few which still exist, but are on the verge of extinction (1907). London: Hutchinson
- ↑ a b Cabalus modestus in the IUCN Red List of Threatened Species 2009.2. Listed by: BirdLife International, 2008. Retrieved November 9, 2009.
- ↑ a b STORRS L. OLSON: A CLASSIFICATION OF THE RALLIDAE. THE WILSON BULLETIN December 1973 Vol. 85, No. 4th
- ^ A b c Richard N. Holdaway, Trevor H. Worthy, Alan JT Tennyson: A working list of breeding bird species of the New Zealand region at first human contact. New Zealand Journal of Zoology, 2001, Vol. 28: 119-187
- ^ A b c Jerry A. Coyne , Trevor D. Price: Little evidence for sympatric speciation in island birds. Evolution Volume 54 Issue 6, Pages 2166 - 2171 doi : 10.1111 / j.0014-3820.2000.tb01260.x