| Stewart Island shag | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Suliformes |
| Family: | Phalacrocoracidae |
| Genus: | Leucocarbo |
| Species: | L. chalconotus |
| Binomial name | |
| Leucocarbo chalconotus (Gray, 1845) | |
| Synonyms | |
Phalacrocorax chalconotus | |
TheStewart Island shag (Leucocarbo chalconotus;Māori:matapo) is a species ofshag found on New Zealand'sSouth Island andStewart Island. The Stewart Island shag has sometimes been split into two species, the Foveaux shag and the Otago shag.
The Stewart Island shag wasformally described and illustrated in 1845 by the English zoologistGeorge Gray based on a specimen collected by Percy Earl in theOtago region of New Zealand'sSouth Island. Gray placed the new species in the genusGracalus and coined thebinomial nameGracalus chalconotus.[2][3] The specific epithet is fromAncient Greek χαλκονωτος/khalkonōtos meaning "bronze-backed".[4] The Stewart Island shag is now one of the 15 shags placed in the genusLeucocarbo, which was introduced in 1856 by the French naturalistCharles Lucien Bonaparte.[5]
Twosubspecies are recognised:[5]
The Stewart Island shag has sometimes been split into two species with the subspeciesL. c. chalconotus known as the Otago shag and the subspeciesL. c. stewarti known as the Foveaux shag. The species was split based on a molecular phylogenetic study published in 2016 but were then re-lumped when a later study by some of the same ornithologists found that the two species were separated by only a shallow genetic divergence.[5][6][7]
The species isdimorphic, with two plumages. Roughly one quarter of the individuals are pied, with dark and white feathers, and the rest, known as bronze shags, are dark all over.[8] Both morphs breed together. These large, chunky birds are about 70 cm long and weigh about 2–3 kg.
Stewart Island shags vary in their facial ornamentation in the breeding season. Roughly half of breeding individuals have dark orange papillae on their face, while the other half have small bright orange caruncles above the base of the bill instead.Gular pouch colour in the breeding season also varies, from bright orange to dark orange to purple.[6]
Archaeological evidence shows that Stewart Island shags were formerly found along the entire east coast of the South Island up toMarlborough, but when humans arrived the population was devastated, reduced by 99 percent within 100 years with a corresponding loss of genetic diversity.[9] It became restricted to the rocky offshore islets off theOtago Peninsula, and has scarcely recovered since that time.[10] There are less than 2500 Otago shags remaining, but they can be seen atOtago Harbour, as far north asOamaru, and as far south as theCatlins.[11] Restricted to a small area, and having little or no genetic variation, they require conservation efforts tailored to these extinction risk factors; this could include reintroduction to part of their former range.[6]
Stewart Island shags breed colonially from May to September, making raised cup nests out of organic material andguano on islands and sea cliffs. Colonies are large enough to be strikingly visible, and are used year after year. One notable colony is on the northern shore ofTaiaroa Head, at the mouth of the Otago Harbour. They feed in coastal waters less than 30 m deep and are rarely if ever seen inland or far out to sea.[12]
