Stewart's scar
| Stewart's scar | ||||||||||||
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Stewart's shard ( Leucocarbo stewarti ) |
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| Leucocarbo stewarti | ||||||||||||
| ( Ogilvie-Grant , 1898) |
The Stewart shear ( Leucocarbo stewarti , synonyms : Phalacrocorax stewarti , Phalacrocorax chalconotus stewarti ) is a species of cormorant that is endemic to Stewart Island / Rakiura and in the Foveaux Strait . By 2016, it was considered conspecific with the Otagoscharbe ( Leucocarbo chalconotus ).
features
The Stewart Shear is a large stocky cormorant that can reach a body length of 68 cm and a weight of 1.8 to 2.9 kg. There are two known plumage morphs, a piebald with dark and white feathers and a bronze-colored. Both morphs can be observed in the breeding colonies.
The Stewart sharks differ from the Otagos shards mainly in their facial skin during the breeding season: They have dark orange-colored papillae on the face, while Otagosshark have both papillae and small bright orange-colored caruncle above the base of the beak.
Systematics
Until 2016, the Stewart's shark and the Otagos shark were classified under the common name Stewart's shark in a single species, Phalacrocorax chalconotus . Using a mitochondrial DNA analysis, however, it was found that the Otagoscharbo is more closely related to the Chatham shear ( Leucocarbo onslowi ). Osteological, morphological, morphometric and genetic differences led to the recognition of Leucocarbo stewarti as an independent species by the International Ornithological Congress in 2017 .
The two taxa probably evolved in the Pleistocene apart, were separated as the populations by the lower sea level and the Chatham Islands were settled by Otagoscharben.
Distribution and way of life
Stewart's shear occurrences are both current, historical, and fossil-based on Foveaux Strait and Stewart Island (based on historical museum skins, modern specimens and subfossil bones). Bone material of this type has been documented from the late Quaternary and archaeological deposits from this region. Rare archaeological and modern finds in Otago come from stranded birds.
From September onwards they breed in colonies by building raised shell nests of organic material and guano on islands and sea cliffs. The colonies are large enough to be conspicuously visible and are used year after year. They forage in coastal waters that are less than 30 m deep and are rarely, if ever, seen inland or far out to sea.
status
The Stewart's Scar is currently not on the IUCN Red List of Endangered Species. The closely related Otagoscharbe is in the "at risk" ( vulnerable ) listed. Fewer than 2500 stewart scars are known. The population seems to be stable compared to the Otagosharbe, where the population continues to decline. Stewart sharks have an advantage because they nest on inaccessible islands just off the coast. Nonetheless, both species are endangered due to their small population sizes, and conservation measures need to be tailored to the genetic variation and limited geographical distribution of each species.
Individual evidence
- ↑ Nicolas J. Rawlence, Charlotte E. Till, R. Paul Scofield, Alan JD Tennyson, Catherine J. Collins, Chris Lalas, Graeme Loh, Elizabeth Matisoo-Smith, Jonathan M. Waters, Hamish G. Spencer, Martyn Kennedy: Strong Phylogeographic Structure in a Sedentary Seabird, the Stewart Island Shag (Leucocarbo chalconotus) PLoS ONE. 9 (3): e90769. doi : 10.1371 / journal.pone.0090769 .
- ↑ a b c d Nicolas J. Rawlence, R. Paul Scofield, Hamish G. Spencer, Chris Lalas, Luke J. Easton, Alan JD Tennyson, Mark Adams, Eric Pasquet, Cody Fraser, Jonathan M. Waters, Martyn Kennedy: Genetic and morphological evidence for two species of Leucocarbo shag (Aves, Pelecaniformes, Phalacrocoracidae) from southern South Island of New Zealand . Zoological Journal of the Linnean Society. 177 (3), 2016, pp. 676-694. doi : 10.1111 / zoj.12376
- ^ IOC World Bird List Version 7.1: Species Updates
- ^ Barrie Heather, Hugh Robertson: The Field Guide to the Birds of New Zealand. Penguin, New Zealand, 2015, p. 290. ISBN 978-0-143-57092-9
- ↑ John R. Platt: Scientists Solve A Shag-adelic Bird Mystery . Audubon, March 25, 2016, National Audubon Society, accessed August 19, 2020