Chatham Island shag (Phalacrocorax onslowi)

Also known as: Chatham shag
Synonyms: Leucocarbo onslowi
KingdomAnimalia
PhylumChordata
ClassAves
OrderPelecaniformes
FamilyPhalacrocoracidae
GenusPhalacrocorax (1)
SizeLength: 63 cm (2)

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1).

This large shag species has a short, Mohican-like crest on the top of the head. Its slim body is black with a metallic blue sheen on the upperparts, and white beneath. The wings have patches of white against the black background that appear as bars when the wings are folded against the body. The feet are pink and there is a patch of bare red skin beneath the eye, and a fleshy outgrowth of bare skin on top of the grey bill (2).

The Chatham Island shag is found on four of the Chatham Islands of New Zealand: it breeds on Chatham Island, Star Keys Island and Rabbit Island, and a non-breeding colony is found on North East Reef. It appears to have suffered severe decline in the last ten years, with just 270 pairs remaining in a total area of just one hectare. The reasons for its decline are not fully understood (2).

As a shore bird that does not venture out to the open ocean, the Chatham Island shag inhabits rocky cliffs (2).

The un-waterproofed feathers and large, webbed feet of the Chatham Island shag enable it to dive from the water surface and propel itself efficiently underwater in pursuit of small fish. It returns to shore after fishing where it spreads its wings out to dry the feathers (2).

Shags breed in colonies on rocky shores once a year, the female laying chalky blue eggs in a loose nest while her partner stands guard or fishes. The young are fed by both parents, who regurgitate the contents of their stomach on demand (2).

It is not clear why the Chatham Island shag population is declining so rapidly, but it has been noted with interest and concern that the largest and most successful breeding colonies of this sea bird are found in areas that are not disturbed by the various introduced species living on the Chatham Islands. The colonies of Chatham Island itself are plagued by humans, cattle, pigs, sheep, cats, dogs, weka (Gallirallus australis) and brush-tailed possums (Trichosurus vulpecula). Disturbance is thought to cause the birds to trample on their nests; breaking the eggs before abandoning the site. Breeding sites have also been abandoned following the arrival of the fur seal (Arctocephalus forsteri) on Star Keys Island. Small numbers of birds are shot or caught in crayfish pots, and it is thought that changes in the marine environment may have affected the availability of fish species (2).

A census of the Chatham Island shag was taken in 1997 and a follow-up was done in 2003-2004 as part of the Chatham Island Shag and Pitt Island Shag Recovery Plan that was brought into effect in 2001. It recommends that the population as a whole is surveyed every five years, but that a closer eye is kept on the colonies of Chatham Island, with a census each year. Authorities are hoping to come to an agreement with local land and stock owners that would enable fences to be built around breeding colonies. Dog owners need to be educated as to the effect their pets can have on the Chatham Island shag and eco-tourists must be similarly supervised. It may be necessary to gain legal protection for all colonies (2).

For more information on the Chatham Island shag and its conservation see:

For more information on this and other bird species please see:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk

  1. IUCN Red List (June, 2008)
    http://www.iucnredlist.org
  2. BirdLife International (May, 2006)
    http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3691&m=0