Phalacrocorax onslowi 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Suliformes Phalacrocoracidae

Scientific Name: Phalacrocorax onslowi Forbes, 1893
Common Name(s):
English Chatham Shag, Chatham Island Shag, Chatham Shag
Spanish Cormorán de las Chatham
Leucocarbo onslowi ssp. onslowi (Forbes, 1893) — Turbott (1990)
Taxonomic Source(s): Turbott, E.G. 1990. Checklist of the Birds of New Zealand. Ornithological Society of New Zealand, Wellington.
Identification information: 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.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2bcde+3bcde+4bcde ver 3.1
Year Published: 2016
Date Assessed: 2016-10-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Bell, B., Bell, B., Bell, M., Debski, I. & Wilson, K.
Facilitator/Compiler(s): Benstead, P., Bird, J., Calvert, R., Harding, M., Lascelles, B., McClellan, R., Moreno, R., Symes, A., Taylor, J.
Surveys in 2003 and 2011 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.

Previously published Red List assessments:

Geographic Range [top]

Range Description: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). In 2011 the total population was estimated by Debski et al. (2012) at 355 pairs, representing a 58% decline since 1997. Methods used by Debski et al. (2012) were directly comparable to the 1997 census, and it was concluded that the particularly low counts in 2003-2004 may in part be due to differences in timing of counts. 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).

Countries occurrence:
New Zealand
Additional data:
Estimated area of occupancy (AOO) - km2:1Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:8600
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:2Continuing decline in number of locations:Yes
Extreme fluctuations in the number of locations:No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:A census carried out in 2011 counted 355 breeding pairs (Debski et al. 2012), presumably equating to 714 mature individuals and c.1,070 individuals in total.

Trend Justification:   Debski et al.(2012) estimated a 58% decline from 2011 to 1997. 

Current Population Trend:Decreasing
Additional data:
Number of mature individuals:710Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:1Continuing decline in subpopulations:Yes
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and Ecology: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).

Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):8.7
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s): 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, Debski et al. 2012). 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 [top]

Conservation Actions: 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 (Bester and Charteris 2005) and another census in 2011 2001 reported by Debski et al. (2012). 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).

Citation: BirdLife International. 2016. Phalacrocorax onslowi. The IUCN Red List of Threatened Species 2016: e.T22696861A93589983. . Downloaded on 20 July 2018.
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