Spotted green pigeon

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Spotted green pigeon
The only specimen in existence today

Extinct (1820s)  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Columbiformes
Family: Columbidae
Genus: Caloenas
Species:
†C. maculata
Binomial name
†Caloenas maculata
(Gmelin, 1789)
Synonyms
  • Columba maculata Gmelin, 1789

The spotted green pigeon or Liverpool pigeon (Caloenas maculata) is a

Tahitian islanders was this bird. In 2014, a genetic study confirmed it as a distinct species related to the Nicobar pigeon, and showed that the two were the closest relatives of the extinct dodo and Rodrigues solitaire
.

The surviving specimen is 32 cm (13 in) long, and has very dark, brownish

arboreal, and fed on fruits. The spotted green pigeon may have been close to extinction by the time Europeans arrived in its native area, and may have disappeared due to over-hunting and predation by introduced animals
around the 1820s.

Taxonomy

Illustration by John Latham, from A General History of Birds, 1823

The spotted green pigeon was first mentioned and

study skin. This museum later became World Museum, where the specimen is housed today, but Banks' specimen is now lost. Latham also mentioned a drawing of a spotted green pigeon in the collection of the British antiquarian Ashton Lever, but it is unknown which specimen this was based on; it could have been either, or a third individual. Latham included an illustration of the spotted green pigeon in his 1823 work A General History of Birds, and though the basis for his illustration is unknown, it differs from Davies' specimen in some details. It is possible that it was based on the drawing in the Leverian collection, since Latham stated that this drawing showed the end of the tail as "deep ferruginous" (rust-coloured), a feature also depicted in his own illustration.[3][4][5]

The spotted green pigeon was

Ptilinopus in 1826, and the German ornithologist Johann Georg Wagler instead suggested that it was a juvenile Nicobar pigeon (Caloenas nicobarica) in 1827.[3] The Italian zoologist Tommaso Salvadori listed the bird in an appendix about "doubtful species of pigeons, which have not yet been identified" in 1893.[6] In 1898, the Scottish ornithologist Henry Ogg Forbes supported the validity of the species, after examining Nicobar pigeon specimens and concluding that none resembled the spotted green pigeon at any stage of development. He therefore considered it a distinct species of the same genus as the Nicobar pigeon, Caloenas.[7] In 1901, the British zoologist Walter Rothschild and the German ornithologist Ernst Hartert agreed that the pigeon belonged to Caloenas, but suggested that it was probably an "abnormity", though more than one specimen had been recorded.[8]

World Museum in Liverpool, where the only specimen is kept

The spotted green pigeon was only sporadically mentioned in the literature throughout the 20th century; little new information was published, and the bird remained an enigma.

onomatopoeic word (resembling the sound of the bird) used especially for shearwaters (members of Procellariidae) in east Polynesia.[12] The English ornithologists Julian P. Hume and Michael Walters, writing in 2012, agreed with Gibbs that the bird warranted generic status.[13]

In 2020, after examining historical texts to clarify the origin and extinction date of the spotted green pigeon, the French ornithologist Philippe Raust pointed out that the information in Henry's 1928 book Ancient Tahiti was not gathered by her, but by her grandfather, the English reverend John Muggridge Orsmond, who collected ancient Tahitian traditions during the first half of the 19th century. The book devotes several pages to birds of Tahiti and its surroundings, including extinct ones, and the entry that Gibbs had linked to the spotted green pigeon reads: "The titi, which cried “titi”, now extinct in Tahiti, was speckled green and white and it was the shadow of the mountain gods". The titi was included in the paragraph relating to pigeons, which suggests it was well recognised as such, and Raust found it consistent with the spotted green pigeon. Though Steadman had dismissed the idea based on the name titi also being used for shearwaters, Raust pointed out that this name was used for a wider variety of birds with vocalisations that sound like "titi". Raust also noted that an 1851 Tahitian dictionary compiled by the Welsh reverend

long-tailed koel (Urodynamis taitensis), which is called "tītī oroveo", and which is somewhat similar to Latham's illustration of the spotted green pigeon, being dark brown with paler spots and underparts. Raust believed that the study of these texts reinforced the Tahitian origin of the spotted green pigeon, and suggested this could be confirmed if possible bones of this species were one day found on Tahiti and analysed for DNA. So far, few paleontological sites on Tahiti have been studied, and fossils found there have not yet revealed unknown species.[14]

The only specimen is today catalogued as NML-VZ D3538 at World Museum, Liverpool, where it is locked under environmentally-controlled conditions outside public view. It is kept in a cabinet in the museum's basement with other particularly important bird specimens, such as other extinct birds and

type specimens. The store room is monitored for pests, and the temperature and humidity is kept stable to avoid infestations and damp. The specimen is handled with gloves when examined by researchers, and exposure to light is limited.[15][3]

Evolution

The Nicobar pigeon belongs to the same genus, and is mainly terrestrial.

In 2014, an

phylogenetic trees (or cladograms) is shown below:[16]

Didunculus strigirostris
(Tooth-billed pigeon)

Goura

Goura victoria
(Victoria crowned pigeon)

Goura cristata
(Western crowned pigeon)

Raphinae

Raphus cucullatus
(Dodo)

Pezophaps solitarius
(Rodrigues solitaire)

Caloenas

Caloenas maculata (Spotted green pigeon)

Caloenas nicobarica
(Nicobar pigeon)

Raphines, such as the dodo, are the closest relatives of the genus Caloenas.

The spotted green pigeon was shown to be closest to the Nicobar pigeon. The

mitochondrial genomes from eleven pigeon species, including the spotted green pigeon.[18]

The distribution of the Nicobar pigeon and the Kanaka pigeon (which does not appear to have had diminished flight abilities) suggests

island hopping and an origin for the spotted green pigeon in Oceania or southeast Asia. The fact that the closest relatives of Caloenas were the extinct subfamily Raphinae (first demonstrated in a 2002 study), which consists of the dodo from Mauritius and the Rodrigues solitaire from Rodrigues, indicates that the spotted green pigeon could also have originated somewhere in the Indian Ocean. In any case, it seems most likely that the bird inhabited an island location, like its relatives. That the Caloenas pigeons were grouped in a clade at the base of the lineage leading to Raphinae indicates that the ancestors of the flightless dodo and Rodrigues solitaire were able to fly, and reached the Mascarene Islands by island hopping from south Asia.[16][19]

Description

Alternate version of Latham's 1823 illustration; note the long wings.

Latham's 1823 description of the spotted green pigeon from A General History of Birds (expanded from the one in A General Synopsis of Birds) reads as follows:

Length twelve inches. Bill black, tipped with pale yellow; round the eye somewhat naked; general colour of the plumage dark green, and glossy; the head and neck are darker than the rest, and of one plain colour; the feathers of the neck long and narrow, like the hackles of a Cock; every feather of the wings and scapulars tipped with a spot of very pale cinereous white, with a point running upwards, somewhat triangular: quills and tail black; the feathers of the first tipped with cinereous white, those of the last with ferruginous white, and even at the end: belly, thighs, and vent, dusky black: the legs are brown, and the shins covered half way with downy feathers; claws black. We have only seen two specimens; one in the collection of Gen. Davies, the other in possession of Sir Joseph Banks. In a drawing of one at Sir Ashton Lever's, the end of the tail is deep ferruginous.[4]

Most literature addressing the spotted green pigeon simply repeated Latham's descriptions, adding little new information, until Gibbs published a more detailed description in 2001, followed by the museum curator Hein van Grouw in 2014. The surviving specimen measures 32 cm (12.6 in) in length, though study specimens are often stretched or compressed during taxidermy, and may therefore not reflect the length of a living bird. The weight has not been recorded. The spotted green pigeon appears to have been smaller and slenderer than the Nicobar pigeon, which reaches 40 cm (15.7 in), and the Kanaka pigeon appears to have been 25% larger than the latter. At 126 mm (5 in) in length, the tail is longer than that of the Nicobar pigeon, but the head is smaller in relation. The bill is 20 mm (0.8 in), and the

primary feathers have been pulled out of each wing, and suggested that the wings would therefore had been about 50 mm (2 in) longer in life, around 225 mm (9 in) in total. This is in accordance with Latham's 1823 illustration, which shows a bird with longer wings.[3][11][16]

Side view of the only specimen

The bill of the specimen is black with a yellowish tip, and the

scapular feathers, vague and dark on the primary feathers. The underside of the wings is black with browner flight feathers, which have a pale spot or band at the tips. The breast is brownish-black with a faint green sheen. The tail is blackish with a dark green sheen, brownish-black on the underside, with a narrow, cinnamon-coloured band at the end. This differs from the rust-coloured tail-tip apparently shown in the drawing owned by Lever, and Latham's own illustration. The legs are small and slender, have long toes, large claws, and a comparatively short tarsus, whereas the Nicobar pigeon has shorter claws and a longer tarsus.[3][11]

1898 illustration by Joseph Smit, incorrectly depicting the bird with a knob on its bill and legs in reverse positions

When examining the specimen, van Grouw noticed that the legs had at one point been detached and are now attached opposite their natural positions. The short feathering of the legs would therefore have been attached to the inner side of the upper tarsus in life, not the outer. The plate accompanying Forbes' 1898 article shows the feathers on the outer side, and depicts the legs as pinkish, whereas they are yellow in the skin. The spotted green pigeon has at times been described as having a knob at the base of its bill, similar to that of the Nicobar pigeon. This idea seems to have originated with Forbes, who had the bird depicted with this feature, perhaps due to his conviction that it was a species of Caloenas; it was depicted with a knob as late as 2002. This is despite the fact that the surviving specimen does not possess a knob, and Latham did not mention or depict this feature, so such depictions are probably incorrect. The artificial eyes of the specimen were removed when it was prepared into a study skin, but red paint around the right eye-socket suggests that it was originally intended to have red eyes. It is unknown whether this represents the natural eye colour of the bird, yet the eyes were also depicted as red in Latham's illustration, which does not appear to have been based on the existing specimen. Forbes had the iris depicted as orange and the skin around the eye as green, though this was probably guesswork.[3][11]

The triangular spots of the spotted green pigeon are not unique among pigeons, but are also seen in the spot-winged pigeon (Columba maculosa) and the speckled pigeon (C. guinea), and are the result of lack of melanin deposition during development. The yellow-buff coloured spots are very worn, while less worn feathers have white tips; this indicates that the former were stained during life or represent a different stage of plumage, and that the latter were fresher. The plumage of the spotted green pigeon was distinct in being very soft compared to that of other pigeons, perhaps due to the body feathers being proportionally long. The hackles were not as elongated as those of the Nicobar pigeon, and the feathers did not differ from those of other pigeons in their microstructure. The plumage was also distinct in being very pigmented, except for the tips of the feathers, and even the down was dark, unlike that of most other birds (a feature otherwise seen in aberrant plumage).[3]

Though the plumage of the spotted green pigeon resembles that of the Nicobar pigeon in some respects, it is also similar to that of species in the imperial pigeon genus Ducula. The metallic-green colouration is commonly found among them, and similar hackles can be seen in the

moult. Therefore, van Grouw found it possible that the dull, brownish-black underparts of the surviving spotted green pigeon specimen represents the plumage of an immature bird, as the adults of similar birds have stronger and more glossy iridescence. He suggested that the brighter bird with paler underparts and whiter wing tips seen in Latham's illustration may represent the adult plumage.[3]

Behaviour and ecology

Ducula pigeons, like the goliath imperial pigeon
, may be ecologically comparable.

The behaviour of the spotted green pigeon was not recorded, but theories have been proposed based on its physical features. Gibbs found the delicate, part-feathered legs and long tail indicative of at least partially arboreal habits. After noting that the wings were not short after all, van Grouw stated that the bird would not have been terrestrial, unlike the related Nicobar pigeon. He pointed out that the overall proportions and shape of the bird (longer tail, shorter legs, primary feathers probably reaching the middle of the tail) was more similar to the pigeons of the genus Ducula. It may therefore have been ecologically similar to those birds, have likewise been strongly arboreal, and kept to the dense canopy of forests. By contrast, the mainly terrestrial Nicobar pigeon forages on the forest floor. The dark eyes of the Nicobar pigeon are typical of species that forage on forest floors, whereas the coloured bill and presumably coloured eyes of the spotted green pigeon are similar to those of frugivorous (fruit-eating) pigeons. The feet of the spotted green pigeon are also similar to those of pigeons that forage in trees. The slender bill indicates that it fed on soft fruits.[3][11]

Believing that the wings were short and round, Gibbs thought the bird was not a strong flyer, and therefore not nomadic (periodically moving from place to place). In spite of the evidently longer wings which might have made it a strong flyer, van Grouw also thought it would have been a sedentary (mostly staying at the same location) bird, that preferred not to fly across open water, similar to species in Ducula. It may have had a limited distribution on a small, remote island, which may explain why its provenance remains unknown.[3][11] Raust pointed out that the fact that Polynesians considered the titi to emanate from mountain gods suggests that it lived in remote, high-altitude forests.[14]

Extinction

The spotted green pigeon is most likely extinct, and may already have been close to extinction by the time Europeans arrived in its native area.[11] The species may have disappeared due to being over-hunted and being preyed upon by introduced animals. Hume suggested that the bird may have survived until the 1820s.[13] Raust agreed that the bird's extinction occurred during the 1820s, pointing out that the entry of the titi in Henry's 1928 book was based on much older accounts.[14]

References

  1. ^
    doi:10.2305/IUCN.UK.2016-3.RLTS.T22734732A95095848.en
    . Retrieved 12 November 2021.
  2. doi:10.5962/bhl.title.49894
    .
  3. ^ a b c d e f g h i j k l van Grouw, H. (2014). "The Spotted Green Pigeon Caloenas maculata: as dead as a Dodo, but what else do we know about it?". Bulletin of the British Ornithologists' Club. 134 (4): 291–301.
  4. ^
    doi:10.5962/bhl.title.62572
    .
  5. doi:10.1111/j.1474-919X.1949.tb02264.x
    .
  6. ^ Salvadori, T. (1893). Catalogue of the Birds in the British Museum. Vol. 21. London: Natural History Museum. p. 641.
  7. ^ Forbes, H. O. (1898). "On the type of the Spotted Green Pigeon, of Latham, in the Derby Museum". Bulletin of the Liverpool Museums. 1 (3–4): 83.
  8. doi:10.5962/bhl.part.22170
    .
  9. ISBN 978-0-8014-3954-4
    .
  10. ^ BirdLife International (2014). "Species factsheet: Caloenas maculata". BirdLife International. Retrieved 9 September 2014.
  11. ^
    ISBN 978-1-4081-3556-3
    .
  12. S2CID 85810953
    .
  13. ^
    ISBN 978-1-4081-5725-1
    .
  14. ^
    doi:10.25226/bboc.v140i1.2020.a2
    .
  15. ^ Holmes, Wesley (202). "'Liverpool pigeon' sealed away in a locked cabinet". Liverpool Echo. Retrieved 2023-06-21.
  16. ^
    PMID 25027719
    .
  17. doi:10.1038/511387a
    .
  18. PMID 27782796
    .
  19. PMID 11872833
    .
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