Data Zone
Justification of Red List category
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.
Population justification
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 1997 to 2012.
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 2007). 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 2007). Its foraging range is assumed to be up to 24 km offshore (cf. New Zealand King Shag P. carunculatus).
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 species is restricted to the Chatham Archipelago, but the largest breeding colonies occur at predator-free islets. Some colonies are still present on the main island (Chatham Island) and suffer risk from invasive, non-native predators including feral cats, weka and possums. In addition, disturbance by sheep, cattle, pigs and people can lead to birds stampeding from nests with subsequent breakage of eggs or nest predation by gulls (Heather and Robertson 1997, Taylor et al. 2000, Wilson 2006, Croxall et al. 2012). Entire colonies have been deserted as a result of disturbance by stock and people (Bell and Bell 2000). Occasional illegal shooting of shags is also reported (Bell pers. comm. 1998 in Taylor 2000). Invasive fur seals Arctocephalus forsteri disturb birds nesting at Star Keys and have occupied former colony sites there, representing a source of competition for breeding sites (Taylor 2000).
Direct mortality from capture in lobster pots caused a low level of mortality when free bait was used, which attracted Chatham Shags, but since switching to covered bait, this mortality has effectively ceased (Bell 2012). There is still potential for a level of mortality caused by gill-nets (Rowe 2010), but this threat has not been examined in detail.
Sea level rise and other weather anomalies associated with climate change is a factor potentially threatening the whole population. Estimates specific to New Zealand calculated a rate of sea-level rise of 2.8 ± 0.5 mm yr-1 during the 20th century (supported by time-gauge records of 2.1 ± 0.1 mm yr-1 between 1924 and 2001) which is significantly faster than the rates reconstructed for the preceding four centuries (Gehrels et al. 2008). With a greatly restricted range, covering relatively low-lying islands, this species is particularly susceptible to climate change through sea-level rise and climatic shifts.
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).
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.
Text account compilers
McClellan, R., Miller, E., Moreno, R., Symes, A., Taylor, J., Calvert, R., Bird, J., Fjagesund, T., Harding, M., Hermes, C., Benstead, P., Lascelles, B., Martin, R.
Contributors
Wilson, K., Debski, I., Bell, B., Bell, M.
Recommended citation
BirdLife International (2024) Species factsheet: Chatham Islands Shag Leucocarbo onslowi. Downloaded from
https://datazone.birdlife.org/species/factsheet/chatham-islands-shag-leucocarbo-onslowi on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/12/2024.