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Chatham Shag Phalacrocorax onslowi
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Surveys in 2003 indicated that this species is in decline. This, in combination with the extremely small area occupied by its breeding colonies, which suffer disturbance from agriculture and feral mammals, qualifies the species as Critically Endangered.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.
Turbott, E. G. 1990. Checklist of the birds of New Zealand. Ornithological Society of New Zealand, Wellington.

Leucocarbo onslowi Turbott (1990)

63 cm. Large, black-and-white cormorant. Black head, hind neck, lower back, rump, uppertail-coverts, all with metallic blue sheen. White underparts. Pink feet. White patches on wings appear as bar when folded. Large orange caruncles.

Distribution and population
This species is restricted to the Chatham Islands, New Zealand. Four islands support breeding: Chatham, Star Keys, Rabbit and Pitt (Imber 1994, M. Bell in litt. 2012), with a further population on North East Reef (B. D. and D. Bell verbally 1999). In 1997, a census found a total of 842 pairs at 10 sites (Bell and Bell 2000), with the largest colony on Star Keys which, in 1980, had 358 nests containing eggs or chicks (Imber 1994). However, surveys in 2003-2004 estimated the breeding population to be 271 pairs, distributed at 13 colonies, with the largest colony on Star Keys holding 81 pairs (Bester and Charteris 2005, Wilson 2006). This represents a 67.8% decrease in total breeding pairs since 1997, but a poor breeding season or variability in the timing of breeding within and between seasons may have contributed to this apparent decrease, and further surveys are needed to confirm population trends (Bester and Charteris 2005). Although colonies are spread over three islands, the species's breeding range totals less than 1 ha (Wilson 2006). Its foraging range is assumed to be up to 24 km offshore (cf. New Zealand King Shag P. carunculatus).

Population justification
A census carried out in 2011 counted 357 breeding pairs (M. Bell in litt. 2012), presumably equating to 714 mature individuals and c.1,070 individuals in total.

Trend justification
Surveys in 1997 found 840 pairs, but in 2003 only 270 pairs were counted, a 68% decline in six years. A partial survey in 2007/2008 reported a 30% increase on 2003 numbers (S. Waugh in litt. 2009). As such, a cautious estimate places the percentage decline over three generations at 30-49%. However, it is possible that the low numbers in 2003 may reflect a poor breeding season or variability in the timing of breeding between seasons. Census results from 2011 confirm that a decline is on-going, but not as rapidly as indicated in 2003 (M. Bell in litt. 2012).

It nests in colonies, usually high on exposed rocks on top of headlands or small islands, or on cliff-ledges (Marchant and Higgins 1990). It feeds mainly on small fish (Heather and Robertson 1997).

The largest breeding colonies are found on islands free of introduced predators (Taylor 2000). On Chatham, colonies are disturbed by humans, farm stock, feral cats, agriculture (Wilson 2006), feral pigs (Wilson 2006), Weka Gallirallus australis, brush-tailed possum Trichosurus vulpecula and dogs (Heather and Robertson 1997, Taylor 2000). Birds sometimes stampede from their nests when disturbed, causing egg breakage and subsequent predation by gulls (Taylor 2000), and several breeding colonies have been abandoned (Heather and Robertson 1997). Fur seals Arctocephalus forsteri may disturb the colony on Star Keys, possibly causing rapid declines (B. D. Bell in litt. 1994, Heather and Robertson 1997, Taylor 2000, M. Bell in litt. 2012), and have occupied former colony sites (Taylor 2000). Visits by tourists can cause disturbance to colonies if not supervised carefully (B. D. and D. Bell verbally 1999). Illegal shooting of birds occurs infrequently. Population declines may also reflect changes in the marine environment that affect their food supply (Bester and Charteris 2005). Having a distribution on relatively low-lying islands, this species is potentially susceptible to climate change through sea-level rise and shifts in suitable climatic conditions (BirdLife International unpublished data).

Conservation Actions Underway
The first census of this species was completed in 1997 (Bell and Bell 2000), with a follow-up census carried out in 2003-2004 under the Chatham Islands Shag and Pitt Island Shag recovery plan (published 2001) (Bester and Charteris 2005). As yet no conservation action has been specifically directed towards the species (M. Bell in litt. 2012). Conservation Actions Proposed
Census the entire adult population every five years and monitor a Chatham Island colony yearly to determine trends. Fence colonies from stock and pigs on main Chatham Island if agreement is reached with local owners. Conduct education and awareness-raising activities (M. Bell in litt. 2012), and educate dog owners about the possible impact of dogs on breeding grounds. Conduct research into the species's population dynamics, breeding biology, movements, foraging and diet (K.-J. Wilson in litt. 2008).

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. 1997. The field guide to the birds of New Zealand. Oxford University Press, Oxford, UK.

Imber, M. 1994. Seabirds recorded at the Chatham Islands, 1960 to May 1993. Notornis 41(Supplement): 97-108.

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

Taylor, G. A. 2000. Action plan for seabird conservation in New Zealand. Department of Conservation, Wellington.

Wilson, K.-J. 2007. The state of New Zealand's birds 2006: special report seabirds.

Further web sources of information
Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Click here for more information about the Alliance for Zero Extinction (AZE)

Explore HBW Alive for further information on this species

New Zealand Govt - Dept of Conservation - Recovery Plan

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Benstead, P., Bird, J., Calvert, R., Harding, M., Lascelles, B., McClellan, R., Symes, A., Taylor, J.

Bell, B., Bell, B., Bell, M., Wilson, K.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2016) Species factsheet: Phalacrocorax onslowi. Downloaded from on 22/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 22/10/2016.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Chatham Island shag (Phalacrocorax onslowi) 0

Key facts
Current IUCN Red List category Critically Endangered
Family Phalacrocoracidae (Cormorants)
Species name author Forbes, 1893
Population size 720 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 7,200 km2
Country endemic? Yes
Links to further information
- Additional Information on this species