Stewart Island shag (Phalacrocorax chalconotus)
|Size||Length: 65 – 71 cm (2)|
|Weight||1.8 – 3.9 kg (2)|
The Swewart Island shag is classified as Vulnerable (VU) on the IUCN Red List (1).
This marine bird has the unusual trait of having two distinct colour forms, or morphs. The pied (meaning patchy or mottled) morphs have black and white plumage; black head and upperparts, and white underparts and a white stripe on the wings when folded. The bronze forms have a brownish-black plumage with a bluish-green metallic gloss. The powerful webbed feet, in both forms, are pink (2) (3). Juveniles are also one of the two colour morphs, but differ from the adults by having dark brown plumage in place of any black parts (2). It is very closely related to, and often confused with, the king shag (Phalacrocorax carunculatus), but can be distinguished by its slightly smaller size, and shorter, thinner bill (2). The name shag originates from the Old Norse word ‘skegg’ meaning beard, and refers to the crest; accordingly, the Stewart Island shag has a short, Mohican-like crest on the top of the head (4). It is therefore strange that the scientific name Phalacrocorax derives from two Greek words meaning 'bald raven'.
The Stewart Island shag is found only in New Zealand; on the south-eastern part of the South Island, and on Stewart Island, which lies 30 kilometres south of the South Island (3).
The Stewart Island shag is a marine species, found in open sea and coastal waters. It breeds in rocky coastal areas, and on small islands or stacks near shore (2).
As a marine bird, the diet of the Stewart Island shag consists primarily of fish but also marine invertebrates, sometimes even octopus, taken from water less than 30 m deep (2) (5). Pursuit-diving is the most common feeding method of the shag, whereby the bird dives from the surface and propels itself underwater using its powerful webbed feet (2). Shags, like penguins, are impressively agile at sea, but appear awkward on land. The behaviour of shags has given rise to many Māori sayings; someone obviously poised to leave is compared to a shag ready for flight, and the dejected air of a sitting shag gave rise to the phrase ‘as miserable as a shag on a rock’ (5).
The Stewart Island shag breeds all year round, and nests on exposed sloping rock in colonies of 10 to 500 nests. The nests are constructed from grass, twigs, peat and seaweed, cemented together with excreta and then lined with grass (2) (3). These can be massive nests, sometimes over one meter deep, into which two or three pale blue eggs are laid (2) (5).
There are a number of threats facing the Stewart Island shag. The activities of humans can disturb breeding colonies, and are thought to have caused the desertion of some colonies in the past. Illegal shooting and predation by introduced mammals such as cats, rodents and mustelids, also threaten shag populations (3).
As shags spend the majority of their time at sea, they are very vulnerable to water pollution, particularly oil spills, and impacts from the fishing industry. Fisheries can affect the shag in two ways; harvesting of one species may alter marine ecology, possibly affecting the availability of food for the shag, or shags can become entangled in fishing nets. Abandoned nets pose a particular threat (5).
At present there are few specific conservation measures in place for this bird, other than counts of individuals at certain colonies. The Stewart Island shag is know to sometimes abandon breeding sites and reoccupy them years later, however, in recent years a large number of breeding sites have been deserted, which may indicate that population numbers are declining. Surveys to locate and census all breeding sites are required to determine whether this is correct.
Currently, there is one marine reserve within the range of the Stewart Island shag, the Ulva Island Marine Reserve, within which nothing can be removed or harmed. Surrounding this marine reserve is the Paterson Inlet Mataitai Reserve, where commercial fishing is prohibited and recreational fisheries are managed to ensure their sustainability (6). These reserves are likely to be greatly beneficial for nearby populations of shags, but if populations are declining, further conservation action may be necessary. This could include erecting fences around colonies to protect them from predators and other disturbances, managing fishing practices so as to minimise the threat to shags (3), and even the establishment of further marine reserves.
For further information on this species see:
Birdlife International - Stewart Island shag:
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- Invertebrates: animals with no backbone.
- Morph: one of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).
- Mustelids: a family of carnivores characteristic of the northern temperate latitudes. Relatively primitive with short, stocky legs and long sharp canine teeth.
IUCN Red List (January, 2007)
- del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Vol. 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
Birdlife International (April, 2007)
- Greenoak, F. (1979) All the Birds of the Air; the Names, Lore and Literature of British Birds. Book Club Associates, London.
Te Ara - The Encylopedia of New Zealand (April, 2007)
Department of Conservation (May, 2007)