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).