Pitt Island shag

Stictocarbo featherstoni (Buller, 1873)

New Zealand status: Endemic

Conservation status: Nationally Critical

Other names: Pitt Island cormorant, Pitt shag

Geographical variation: Nil

Pitt Island shag. Adult in breeding plumage with Mangere Island in background. Little Mangere Island, Chatham Islands, October 1976. Image © Department of Conservation (image ref: 10035243) by Rod Morris, Department of Conservation Courtesy of Department of Conservation

Pitt Island shag. Adult in breeding plumage with Mangere Island in background. Little Mangere Island, Chatham Islands, October 1976. Image © Department of Conservation (image ref: 10035243) by Rod Morris, Department of Conservation Courtesy of Department of Conservation

The Pitt Island shag is a critically endangered shag restricted to the Chatham Islands. As the only small slender grey shag with yellow feet in the islands, it is easily recognised. Despite its declining population, it can readily be found breeding and roosting in small groups along the rocky coast line throughout the group. It is a marine species that breeds and roosts on rocky headlands and offshore islets and within parts of the brackish Te Whanga Lagoon. A recent DNA study proposes placing spotted shag and Pitt Island shag in the genus Phalacrocorax rather than Stictocarbo, closest to pied shag, black-faced shag (P. fuscescens) and little black shag.

Identification

The Pitt Island shag is a small, slender marine shag commonly seen roosting on rocky shorelines or feeding close offshore. It is the only yellow-footed shag in the Chatham Islands, and is slender and grey, with a very slender bill (all characters unlike the two other resident shag species: Chatham Island shag and black shag). Pitt Island shags have a dark brown-grey back with a small black spot on each feather, and a pale grey breast. The head is blackish when breeding and has a prominent double crest on the forehead and nape. In flight, Pitt Island shags appear slim and dark-bodied, and hold the head and neck horizontally. Before the breeding season, adults have dense white filoplumes on the hindneck and their facial skin is bright green. During breeding this fades to pale green, the filoplumes are shed, and the crests become less prominent.

Voice: during breeding, male Pitt Island shags are noisy at colonies, with range of grunting, gargling and ticking calls, however females are silent. Birds are largely silent when away from colonies.

Similar species: Pitt Island shags are unmistakeable in the Chatham Islands, being the only small slender grey shag with yellow feet. Birds in flight can be separated from other shag species present in the Chatham Islands by their slender profile and the way they hold their head and neck horizontally.

Distribution and habitat

The Pitt Island shag is endemic to the Chatham Islands group, with birds breeding on Chatham Island, Pitt Island (including offshore islets such as Rabbit Islands and Murumuru Rocks), Rangatira Island, Mangere Island, Little Mangere Island, Western Reef, The Castle, Star Keys, Sisters and Forty Fours. Colonies are situated on eroded pockets, cracks and ledges on coastal cliffs, with birds commonly roosting on headlands and offshore rock stacks. The Pitt Island shag is an exclusively marine feeder, foraging throughout inshore coastal waters. One small colony is found within the brackish Te Whanga Lagoon where birds also forage within the deeper, southern portion of the lagoon.

Population

The Pitt Island shag population has undergone significant decline in the past 15 years. In 1997 the breeding population was 729 pairs, but had declined to an estimated 434 pairs in 2011.

Threats and conservation

Populations of Pitt Island shag are threatened by loss of breeding habitat, disturbance from stock, human persecution, introduced predators, gull predation and fisheries bycatch. However given that population declines have been recorded at colonies on remote predator free off shore islands it is likely that some at-sea effects are impacting on the population.

There has been no direct conservation management action to benefit Pitt Island shag other than co-ordinated island wide population censuses. The recent increase in fencing coastal habitats on the Chatham Islands will prevent stock from gaining access to some colonies, thereby reducing disturbance. The conservation status of this species was changed from nationally endangered to nationally critical in 2013.

Breeding

Pitt Island shags breed in loose colonies of 5-40 pairs. Nests are built in eroded pockets, cracks and ledges on coastal cliffs. The 2-4 eggs are laid August – September, sometimes as late as December. Adults share incubation, which takes around 30 days. Chicks are initially guarded by one parent, then are left alone in the nest when approximately two weeks old. Chicks are fed by regurgitation by both parents and probably fledge at about 6-8 weeks. It is likely that birds start breeding when 2-3 years old.

Behaviour and ecology

Pitt Island shags roost in small flocks, but usually feed solitary. Birds feed close to shore along rocky coasts, and in the brackish Te Whanga Lagoon, where they swim on surface, diving to forage underwater for small fish. They are sedentary, remaining solely within coastal Chatham Island waters.

Food

Pitt Island shags catch and eat small fish, especially bullies, and marine invertebrates such as snails and polychaete worms.

Weblinks

http://www.birdlife.org/datazone/speciesfactsheet.php?id=3691

References

Aikman, H.; Miskelly, C. 2004. Birds of the Chatham Islands. Department of Conservation, Wellington.

Bell, M.; Bell, D. 2000: Census of the three shag species in the Chatham Islands. Notornis 47: 148-153.

Bester, A.J.; Charteris, M. 2005: The second census of Chatham Island shag and Pitt Island shag – are numbers declining? Notornis 52: 6-10.

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.

Robertson, H. A; Dowding, J. E; Elliott, G. P; Hitchmough, R. A; Miskelly, C. M; O’Donnell, C. F. J; Powlesland, R. G; Sagar, P. M; Scofield, R. P; Taylor, G. A. 2013. Conservation status of New Zealand birds, 2012. NZ Threat Classification Series 4. Department of Conservation. Wellington.

Recommended citation

Bell, M. 2013 [updated 2015]. Pitt Island shag. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Pitt Island shag

Social structure
monogamous
Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Nest type
ground-level platform
Nest description
A roughly constructed platform of twigs, ice plant and seaweed about 50 cm in diameter.
Nest height (mean)
0 m
Nest height (min)
0 m
Nest height (max)
0 m
Maximum number of successful broods
1
Clutch size (mean)
2-3
Clutch size (min)
1
Clutch size (max)
4
Mean egg dimensions (length)
61 mm
Mean egg dimensions (width)
39 mm
Egg colour
Pale blue with white chalky coating
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Interval between eggs in a clutch
Unknown but probably 2-3 days days
Incubation behaviour
shared
Incubation length (mean)
Unknown probably 28-32 days
Nestling type
altricial
Nestling period (mean)
Unknown
Age at fledging (mean)
Unknown
Age at independence (mean)
Unknown
Age at first breeding (typical)
Unknonw probably 3 years
Maximum longevity
Unknown
Maximum dispersal
15 km