Inaccessible Island rail
Inaccessible Island rail | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Gruiformes |
Family: | Rallidae |
Genus: | Laterallus |
Species: | L. rogersi
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Binomial name | |
Laterallus rogersi (Lowe, 1923)
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Inaccessible Island in the Tristan Archipelago | |
Synonyms[3] | |
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The Inaccessible Island rail (Laterallus rogersi) is a small bird of the rail
The Inaccessible Island rail has brown
Unlike many other oceanic islands, Inaccessible Island has remained free from
Discovery
Although the Inaccessible Island rail may have been known to the Tristan Islanders who visited the island annually to hunt seals, the species first came to the attention of scientists during the Challenger expedition of 1872–1876. When the expedition visited the island in October 1873, Sir Charles Wyville Thomson learned of the species and recorded observations made by two German brothers, the Stoltenhoffs, who had been living on the island for the last two years. Thomson was unable to collect a specimen.[6]
Another attempt was made to collect a specimen by
Evolution and taxonomy
Prior to its collection it had been assumed by Thomson that the species was close to the other "island hens" known in the Atlantic, possibly a
In his 1928 paper on the species, Lowe thought the Inaccessible Island rail was the descendant of flightless ancestors which had reached Inaccessible Island via a
The position of the Inaccessible Island rail in the larger rail family (
Two extinct flightless species of rail were at one time placed in the genus Atlantisia with the Inaccessible Island rail. The
Stervander et al. (2019) resolved the taxonomic affinity and evolutionary history of the Inaccessible Island rail by
Morphology
The Inaccessible Island rail is the smallest living flightless bird in the world, measuring 13 to 15.5 cm (5.1–6.1 in). Males are larger and heavier than females, weighing 35–49 g (1.2–1.7 oz), average 40.5 g (1.43 oz), compared to 34–42 g (1.2–1.5 oz), average 37 g (1.3 oz), in females. It is dark chestnut-brown above and dark grey on the head and below, with degraded white barring on the flanks and belly, and adults have red eyes. The female is similar to the male but with paler grey and a faint brown wash on the underparts. It has a black bill, which is shorter than the head.[7] The feathers of the Inaccessible Island rail are almost hair-like, and in particular the flight feathers are degenerate, as the barbules on many of the feathers (but not all, as has sometimes been reported) fail to interlock, giving the feathers a ragged appearance.[16] The wings are reduced and weak, and smaller than same-sized flying relatives, as is the sternum. The tail is short, 3.5 cm (1.4 in) in length, and the uppertail coverts and undertail coverts are nearly as long as the tail rectrices.[7]
The Inaccessible Island rail has a low basal metabolic rate (BMR), measured in 1989 at around 60–68% the rate expected for a bird of its weight. The scientists responsible for the study speculated that the low BMR was not as a result of flightlessness, which does not have this effect in other bird species, but was instead the result of the rail's island lifestyle. The island lacks predators and other competitors, and as such can be expected to be at full carrying capacity for rails. This in turn would favour energy conservation by the rails, resulting in small body size, low BMR and flightlessness.[17] A comparison of flighted and flightless rails, including the Inaccessible Island rail, found that rails that lose the ability to fly also have low BMRs.[18]
Distribution and habitat
The Inaccessible Island rail is
Behaviour
The Inaccessible Island rail is territorial, and the territories they defend are tiny. The territories in the tussock grass habitats around Blenden Hall, where the population densities are highest, extend to 100–400 m2 (1,100–4,300 sq ft). The small size of the territories makes encounters between families and individuals frequent, and confrontations and territorial calling are common. On meeting, confrontations start with loud trills or twittering, then birds may face off, standing very close to each other and displaying ritually with their heads lowered and their bills pointed towards the ground. They may circle, and continue displaying until one bird slowly retreats or a quick skirmish ensues and one bird is driven off.[21]
Diet and feeding
The foraging method used by the Inaccessible Island rail is slow and deliberate and has been compared to that of a mouse, and the bird occupies a similar ecological niche.[19] They feed on a range of invertebrates, including earthworms, amphipods, isopods, mites and a range of insects such as beetles, flies, moths and caterpillars. Centipedes are taken as well, and an introduced species of centipede forms an important part of their diet. Along with animal prey they will take the berries of Empetrum and Nertera as well as the seeds of the dock Rumex. Unlike the Tristan thrush they do not feed on carrion or dead fish.[19]
Calls
The Inaccessible Island rail is a highly vocal species, calling frequently. This may be because of the dense vegetation in which the species lives, making calls the best way to communicate, and pairs and families contact call frequently while feeding. Calls used include a long trill used when pairs meet and when confronting a rival.[19][21] Rivals also make a long twitter "keekeekeekeekee" which can be long and short and end in a "keekeechitrrrr". After skirmishes between rivals the victorious bird may make a "weechup weechup" call. Birds may make a monotonous "tchik tchik tchok tchik" while hunting for prey, and the alarm call when predators are around is a short and hard "chip". They also make a variety of trilling calls while incubating, particularly when pairs swap places during incubation. Before changing places the incubating bird may make a "chip chip chip", but they fall silent when Tristan thrushes approach the nest.[21]
Breeding
The Inaccessible Island rail is a seasonal breeder, laying between October and January. They are monogamous, forming permanent pair-bonds. The nests are situated at the base of ferns with tussock grass, tussock grass clumps, or in tufts of sedges. The nests are domed and oval or pear shaped, with the entrances near the narrow end of the nest and linked by a track or tunnel that can go up to half a metre away. The nests are typically built entirely of the same material the nest is found in; for example, tussock grass or sedges. Where the construction material is tussock grass, larger leaves are used on the outside and finer material lines the nest. There are a few reports of other material being used as lining, such as the leaves of introduced
The clutch size is two eggs, which is low for such small rails.[18] The eggs are greyish milk white dotted with brown-rufous spots and lavender-mauve spots that are concentrated around the apex of the egg. They are large for the size of the mother compared to other rails, and resemble the eggs of the corn crake.[22]
The incubation period for the species is not known, but both sexes incubate the clutch, although the males incubated for longer in the observations that have been made. Both sexes bring food to their partner that is incubating, which is either consumed on the nest or close to the nest. Changeovers of incubation details are preceded by "chip chip chip" calls, which become louder and more frequent the longer its takes the partner to respond.[21]
The eggs hatch within between 23 and 32 hours of each other and can be preceded by the chick in the egg calling for up to 45 hours before hatching. One hatching was recorded as taking 15 hours to complete. Newly hatched chicks are covered by downy black plumage, the legs, feet and bill are black, and the mouth is silvery.[21]
Ecology
Lowe speculated in his 1927 paper that, in the absence of mammalian predators on the island, the brown skua would be the Inaccessible Island rail's only predator.[7] A study of the diet of brown skuas on Inaccessible Island confirmed this, but found that although skuas do eat adults of this species, the rail and other landbirds formed only a small part of the diet of that seabird, especially compared to their abundance on the island. They noted that the landbirds alarm-called when brown skuas were seen.[23] After hearing another rail make an alarm call, adult Inaccessible Island rails become alert, while chicks fall silent.[21] Adults are rarely preyed upon, but the mortality of chicks is high and predation by Tristan thrushes is a major cause of death.[19]
Two species of chewing lice have been found on Inaccessible Island rails, Pscudomenopon scopulacorne and Rallicola (Parricola) zumpti. R. zumpti has not been described on any other species of bird from Inaccessible Island.[24][25] P. scopulacorne found on the Inaccessible Island rail were originally described as a new species, P. rowani (Keler, 1951),[26] but were later lumped into the widespread species in 1974.[25]
Threats and conservation
The Inaccessible Island rail has a tiny global range with a single population. Though still common within its tiny range, with around 5,600 adult birds in the world,[1] the species is considered to be vulnerable if an invasive species were to reach Inaccessible Island.[27] Insular rails, particularly flightless species, are vulnerable to extinction.[28] House mice, feral cats and brown rats, all of which would be a serious threat to this species, are not present on the island, nor have they ever been, but are present on nearby Tristan da Cunha, and could reach the islands via fishing vessels or other boats visiting the island (mice have been found on boats visiting the neighbouring Nightingale Island).[21] Because of this vulnerability, this species is rated as vulnerable by the IUCN Red List.[1] Fires of tussock grass, which were recorded in 1872 and 1909, are assumed to have killed large numbers of rails, but have not occurred since.[21] In the 1950s, they were highly sought after for scientific collections, but permits to do so were rarely granted.[29]
Several conservation measures have been undertaken or proposed to protect this species. Inaccessible Island was once suggested as a site for agriculture for Tristan Islanders, which would have reduced habitat and risked the introduction of invasive species.
See also
- Wake Island rail (Extinct flightless rail on remote Pacific island)
References
- ^ . Retrieved 19 November 2021.
- ^ a b Lowe, Percy (1923). "Description of a new genus and species of Rail, Atlantisia rogersi, from Inaccessible Island". Bulletin of the British Ornithologists' Club. 43 (280). British Ornithologists' Club: 174–176.
- ^ S2CID 53024581.
- ^ a b c Laskow, Sarah (2 November 2018). "How Did the World's Smallest Flightless Bird Get to Inaccessible Island? The first scientists to describe the animal thought it might have walked". Atlas Obscura. Pocket worthy Stories to fuel your mind. Retrieved 14 June 2020.
On this one tiny island, there is a thriving population of thousands of what we'll now call Laterallus rogersi, but they are considered vulnerable to extinction.
- ISBN 9780919880078.
- ^ a b Thomson, Sir Charles Wyville (1877). The Voyage of the "Challenger.": The Atlantic; a Preliminary Account of the General Results of the Exploring Voyage of H. M. S. "Challenger" During the Year 1873 and the Early Part of the Year 1876, Volume 2. London: Macmillan. pp. 184–185. Retrieved 16 March 2017.
- ^ .
- ^ Lowe (1928) p. 103.
- ^ Jobling, J. A. (2017). "Key to Scientific Names in Ornithology | HBW Alive". Handbook of the Birds of the World. Lynx Edicions, Barcelona. Retrieved 13 March 2017.
- ^ .
- ISBN 978-0-7679-0818-4.
- PMID 18350170.
- ^ Smithsonian Institution Press. pp. 28–29.
- PMC 1692427.
- ^ Bourne, W. R. P.; Ashmole, N. P.; Simmons, K. E. L. (2003). "A New Subfossil Night Heron and A New Genus for the Extinct Rail Ascension Island, Central Tropical Atlantic Ocean" (PDF). Ardea. 91 (1): 45–51.
- .
- JSTOR 1368325.
- ^ PMID 16632395.
- ^ S2CID 243565508. Retrieved 3 June 2017.
- ^ .
- ^ a b c d e f g h i j k l m n Fraser, M. W.; Dean, W. R. J.; Best, I. C. (1992). "Observations on the Inaccessible Island Rail Atlantisia rogersi: the world's smallest flightless bird". Bulletin of the British Ornithologists' Club. 112: 12–22. Retrieved 14 March 2017.
- ^ Rothschild, L. W. (1928). "On the eggs of Atlantisia rogersi". Bulletin of the British Ornithologists' Club. 48. British Ornithologists' Club: 121–124.
- .
- .
- ^ .
- ISSN 0013-8789.
- .
- The University of Chicago Press. p. 298.
- .
- .
External links
- BirdLife species factsheet for Atlantisia rogersi
- "Atlantisia rogersi". Avibase.
- Explore Species: Inaccessible Island Rail at eBird (Cornell Lab of Ornithology)
- Interactive range map of Atlantisia rogersi at IUCN Red List maps
- Lindblad Expeditions (23 May 2012). "Seldom-Visited Nightingale and Inaccessible Islands" (Video). National Geographic. Archived from the original on 14 November 2021 – via YouTube.