Pied shag

Phalacrocorax varius (Gmelin, 1789)

New Zealand status: Native

Conservation status: Nationally Vulnerable

Other names: pied cormorant, kāruhiruhi, karuhiruhi, kawau, yellow-faced cormorant , large pied shag

Geographical variation: Two subspecies are recognised; New Zealand birds are of the subspecies varius

Pied shag. Adult. Northland, January 2008. Image © Peter Reese by Peter Reese

Pied shag. Adult. Northland, January 2008. Image © Peter Reese by Peter Reese

This large black-and-white shag is often seen individually or in small groups roosting on rocky headlands, trees or artificial structures. In regions where it occurs it can usually be readily seen about harbours and estuaries associated with cities or towns. Unlike most other shag species, the pied shag is reasonably confiding, allowing close approach when roosting or nesting in trees. It generally forages alone, but occasionally in small groups when prey is abundant.

Identification

Pied shags mainly inhabit coastal habitats about much of New Zealand. Adults have the crown, back of the neck, mantle, rump, wings, thighs and tail black, although on close inspection the upper wing coverts are grey-black with a thin black border. The face, throat, sides of neck and underparts are white. The long, hooked beak is grey, the iris is green, and legs and feet black. On breeding adults, the skin in front of the eye is yellow, at the base of beak is pink or pink-red, and the eye-ring is blue. Non-breeding adults have paler skin colours than breeders. The upperparts of juveniles and immatures have dark and pale brown tones. Their underparts are white but with varying amounts of brown mottling, from almost entirely brown to little at all. The skin in front of eye is pale yellow, at the base of the beak is grey - pale pink, and eye-ring is grey. 

Voice: generally silent away from nesting colonies, but quite vocal at colonies during pair formation, nest building and when one of a pair returns to nest during incubation. Females give wheezy haa calls, while males give a variety of loud calls, that may be repeated several times, and that sound like aark, kerlick and whee-eh-eh-eh.

Similar species: the pied morph of the little shag is much smaller and has a short stubby yellow beak. Both the king shag and pied morph of the Stewart Island shag have black heads with white throats, patches of white feathers on the upper wings, and pink feet. Juveniles and immatures of black shag can be difficult to distinguish from the similar-sized juveniles and immatures of pied shag. Both can have underparts from nearly all brown to nearly all white. Juvenile black shags have dark heads and upper throat, and have extensive yellowish facial skin about base of the beak, whereas the yellow is only in front of the eye on the pied shag.

Distribution and habitat

The pied shag has a mainly coastal breeding distribution, occurring in three separate areas of New Zealand. Northern North Island: colonies on the western and eastern coasts of Northland and Auckland, and extending down to East Cape. Central New Zealand: Wellington, Nelson, Marlborough and Canterbury as far south as Banks Peninsula. Southern South Island: Fiordland and Stewart Island. Pied shags mainly forage in coastal marine waters, harbours and estuaries, but occasionally also in freshwater lakes and ponds close to the coast.    

Population

While counts of pied shags, along with other coastal species, have been undertaken in a few areas (Wellington Harbour, Marlborough Sounds), no attempt has been made to carry out a national count of the species or the number of pairs at all colonies. However, the population in 2012 was estimated to number 1000-5000 mature individuals. An examination of numbers of pairs at colonies during three periods (pre 1980, 1980-1999, post 1999), suggests that populations in the northern North Island and southern South Island are in decline, while those in central New Zealand are increasing (M. Bell pers. comm.).

Threats and conservation 

There are a variety of threats to pied shags. They were formerly occasionally shot by fishers who considered that they competed for fish; probably few pied shags are shot these days. Pied shags have drowned in craypots, set-nets and on inshore longlines. Some birds have been affected by oil spills, including following the grounding of the container ship Rena off Tauranga in October 2011. During the recent population expansion in central New Zealand, pied shags have established colonies in trees adjacent to peoples’ homes. The noise and smell of such colonies has resulted in a few nesting trees being felled. It is unknown whether changes in prey abundance as a result of commercial fishing or climate change, has impacted, positively or negatively, on the pied shag.  

Breeding

Pied shags mainly nest in trees along coastal cliffs, with a few colonies in trees in or about freshwater lakes near the coast. There is one inland colony known, on Lake Hakanoa, Huntly. Clutches are laid in all months, with peaks during February-April and August-October. Clutch size is typically 2-5 eggs, and both sexes share incubation and care of young. Chicks start flying at 7-8 weeks of age, and remain at or near the colony to be fed by their parents for a further 10-11 weeks. Nearly 80% of nesting attempts at Makara Beach, Wellington, were successful, with a mean of 1.4 fledglings per nest. 

Behaviour and ecology

Adult pied shags appear to be sedentary, but some juveniles disperse widely. When resting during the day, birds occur on undisturbed beaches, shoreline rocks, trees and artificial structures. During the late afternoon or evening, pied shags return to nesting colonies or favoured roosts in trees near water for the night. They are generally a solitary forager, but occasionally small groups gather where prey is readily available. When swimming slowly at the surface, they use alternate feet, but when foraging underwater they use both feet at the same time for propulsion. Pied shags generally forage in water less than 10 m deep.

Food

No comprehensive studies of diet in New Zealand. Pied shags feed mainly on fish (6-15 cm long), and occasionally on crustaceans. Prey species include flounder, mullet, eel, goldfish, perch, goatfish, kahawai, wrasse and common trevally.

Websites

http://en.wikipedia.org/wiki/Australian_Pied_Cormorant

http://www.nzbirds.com/birds/piedshag.html

References

Heather, B.D.; Robertson, H.A. 2005. The field guide to the birds of New Zealand. Viking, Auckland.

Marchant, S.; Higgins, P.J. (eds.) 1990. Handbook of Australian, New Zealand and Antarctic birds. Vol. 1, ratites to ducks. Oxford University Press, Melbourne.

Powlesland, R.G.; Sharp, S.E.; Smith, A.N.H. 2008. Aspects of the breeding biology of the pied shag (Phalacrocorax varius) at Makara Beach, Wellington, New Zealand. Notornis 55: 69-76.

Robertson, C.J.R.; Hyvonen, P.; Fraser, M.J.; Pickard, C.R. 2007. Atlas of bird distribution in New Zealand, 1999-2004. Ornithological Society of New Zealand, Wellington.

Stonehouse, B. 1967. Feeding behaviour and diving rhythms of some New Zealand shags, Phalacrocoracidae. Ibis 109: 600-605.

Taylor, G.A. 2000. Action plan for seabird conservation in New Zealand. Part B: Non-threatened seabirds. Threatened Species Occasional Publication No. 17. Department of Conservation, Wellington.

Recommended citation

Powlesland, R.G. 2013. Pied shag. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Pied shag

Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun

Pied shag

Social structure
monogamous
Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Nest type
raised platform
Nest description
Built of sticks, twigs and foliage and occasionally human rubbish with the nest bowl lined with soft fibrous material such as seaweed and fine grasses. Most nests are used twice a year and refurbished at the start of each nesting cycle and can become substantial structures.
Maximum number of successful broods
Unknown
Clutch size (mean)
3.3
Clutch size (min)
2
Clutch size (max)
5
Mean egg dimensions (length)
59.00 mm
Mean egg dimensions (width)
38.00 mm
Egg colour
Pale blue-green often with patchy white chalky coating when recently laid which erodes during incubation
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Interval between eggs in a clutch
Approximately 2 days
Incubation behaviour
shared
Incubation length (mean)
Unknown
Incubation length (min)
25days
Incubation length (max)
33days
Nestling type
altricial
Nestling period (mean)
Approximately 28 days
Age at fledging (mean)
53 days
Age at fledging (min)
47days
Age at fledging (max)
60days
Age at independence (mean)
Approximately 133 days
Age at first breeding (typical)
Unknown
Age at first breeding (min)
2years
Maximum longevity
20 plus years (Australia)
Maximum dispersal
Unknown