Shags are long-necked aquatic birds with hooked beaks, long, stiff, wedge-shaped tails, and webbed feet. Eight species (subdivided into 14 races) are found in and about New Zealand. Some species inhabit both fresh and salt water; others are entirely marine, and these two major groups may be distinguished from each other in life by the colour of their feet – those of the purely marine shags are pink or yellow; the others have feet which are black. Some species, such as the black shag, are widely distributed; others (especially some of the purely marine forms) are found only on particular off-shore islands. The name cormorant is rarely used in New Zealand. Identification of the various shags is often made difficult for the amateur because of strong superficial similarities and changes in plumage that occur with age and season. Sexes look alike. The young are naked when hatched, and immature birds are usually brownish and often nearly white underneath. Adults of most species are usually black with a green or purple gloss and sometimes white below. About the breeding season ornamental crests, tufts, or plumes appear and vivid face colours may develop. Shags are community nesters – freshwater species build untidy nests in trees; marine species nest on cliff ledges, low bushes, or even on the ground. Though most breeding occurs in the spring, it may take place at other seasons. A characteristic habit of shags after fishing is the “hanging out” of their wings to dry.
Probably the most familiar and widely distributed shags in New Zealand are the black (Phalacrocorax carbo), white-throated (P. melanoleucos), and pied (P. varius) of shore and inland waters, and the beautiful spotted shag (P. punctatus), of rocky coasts.
Their diet consists primarily of fish of various kinds and crustaceans, and although shags are regarded with disfavour by fishermen, especially trout fishermen, there is no doubt at all that they do no damage whatsoever to marine or estuarinc fisheries in New Zealand. Only in special circumstances is one single species – the black shag -likely to vie with man as a predator of trout, and this is probably because the sportsman is trying to maintain high fish numbers in waters not suitable for such artificially dense populations; black shags then arrive and feed on the population that exceeds the carrying capacity of the water.
by Gordon Roy Williams, B.SC.(HONS.)(SYDNEY), Lecturer in Agricultural Zoology, Lincoln Agricultural College.