||Phalacrocorax onslowi Forbes, 1893
||Chatham Shag, Chatham Island Shag, Chatham Shag
||Cormorán de las Chatham
Leucocarbo onslowi ssp. onslowi (Forbes, 1893) — Turbott (1990)
||Turbott, E.G. 1990. Checklist of the Birds of New Zealand. Ornithological Society of New Zealand, Wellington.
||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.
|Red List Category & Criteria:
||Butchart, S. & Symes, A.
||Bell, B., Bell, B., Bell, M., Debski, I. & Wilson, K.
||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:|
- 2012 – Critically Endangered (CR)
- 2010 – Critically Endangered (CR)
- 2009 – Critically Endangered (CR)
- 2008 – Critically Endangered (CR)
- 2007 – Critically Endangered (CR)
- 2005 – Critically Endangered (CR)
- 2004 – Endangered (EN)
- 2000 – Endangered (EN)
- 1996 – Vulnerable (VU)
- 1994 – Vulnerable (VU)
- 1988 – Lower Risk/least concern (LR/lc)
|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). |
|♦ Estimated area of occupancy (AOO) - km2:||1||♦ Continuing decline in area of occupancy (AOO):||Yes|
|♦ Extreme fluctuations in area of occupancy (AOO):||No||♦ Estimated extent of occurrence (EOO) - km2:||8600|
|♦ Continuing decline in extent of occurrence (EOO):||Unknown||♦ Extreme fluctuations in extent of occurrence (EOO):||No|
|♦ Number of Locations:||2||♦ Continuing 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.|
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).