• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Taxonomic note
Has frequently been considered a subspecies of H. unicolor or of H. ostralegus; differentiation relatively weak, and species status perhaps questionable. Recent study of mtDNA, however, supported treatment as a separate species (Banks and Paterson 2007). Form H. ostralegus finschi has on occasion been associated with present species. Monotypic.

Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.
Turbott, E.G. 1990. Checklist of the Birds of New Zealand. Ornithological Society of New Zealand, Wellington.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	D	D1

Red List history

Year	Category	Criteria
2022	Endangered	D
2016	Endangered	D
2012	Endangered	D
2008	Endangered	D1
2006	Endangered
2004	Endangered
2000	Endangered
1994	Endangered
1988	Threatened

Migratory status	not a migrant	Forest dependency	does not normally occur in forest
Land-mass type		Average mass	-

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	2,800 km2	medium
Area of Occupancy (breeding/resident)	24 km2	medium
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	200-249 mature individuals	good	estimated	2021
Population trend	stable	medium	estimated	-
Generation length	11.46 years	-	-	-
Number of subpopulations	1	-	-	-
Percentage of mature individuals in largest subpopulation	100%	-	-	-

Population justification:

In 2014 a minimum of 309 birds were recorded in a census of the population, including about 110 pairs and overall 237 mature individuals (J.E. Dowding in litt. 2016). There were 228 mature individuals in 2019 and the population is considered to be stable (Robertson et al. 2021), therefore is placed in the band 200-249 mature individuals.

Trend justification: As a result of intensive predator management, stock exclusion and nest protection, the population rapidly increased by the mid-2000s to over 300 birds but is estimated to have remained fairly stable since (Moore and Dowding 2017, Robertson et al. 2021). In 1987-1988, the population was estimated at 100-110 birds, including 44 breeding pairs: eight on South East Island (Rangatira), 25 on Chatham Island, nine on Pitt Island and two on Mangere Island. In 1998, a census indicated 140-150 birds, representing a significant increase since 1987-1988. In 2004, a minimum of 266 birds were counted on most of the coast of these four islands in the Chathams group, representing a population of 310-340 birds (Moore 2005, 2007). The population appears to have levelled off as a result of less intensive management, having reached over 100 pairs and 310-360 individuals in total in 2006 (Moore 2008). A minimum of 309 birds were recorded in both 2010 and 2014, including c.110 pairs (Moore and Dowding 2017). The population has slightly decreased from 241 mature individuals in 2010, and 237 in 2014 to 228 in 2019, but is considered stable overall (Robertson et al. 2021). The population on Rangatira (which is not farmed and has no mammalian predators) has declined steadily from about 12 pairs in the 1970s to 2 pairs in 2016, for reasons that are not understood (Moore and Dowding 2017).

Country/Territory	Presence	Origin	Resident	Breeding visitor	Non-breeding visitor	Passage migrant
New Zealand	extant	native	yes

Country/Territory	IBA Name
New Zealand	Main Chatham
New Zealand	Mangere
New Zealand	Rangatira South East Island
New Zealand	Rangiauria Pitt Island

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Marine Intertidal	Rocky Shoreline	major	resident
Marine Intertidal	Sandy Shoreline and/or Beaches, Sand Bars, Spits, Etc	suitable	resident
Marine Intertidal	Shingle and/or Pebble Shoreline and/or Beaches	suitable	resident
Marine Intertidal	Tidepools	major	resident
Altitude	0 - 200 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Biological resource use	Hunting & trapping terrestrial animals - Intentional use (species is the target)	Timing		Scope		Severity		Impact
		Past, Unlikely to Return		Minority (<50%)		Unknown		Past Impact
		Stresses Species mortality
Climate change & severe weather	Habitat shifting & alteration	Timing		Scope		Severity		Impact
		Future		Whole (>90%)		Unknown		Unknown
		Stresses Indirect ecosystem effects, Ecosystem degradation
Climate change & severe weather	Storms & flooding	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Negligible declines		Low Impact: 5
		Stresses Ecosystem degradation
Human intrusions & disturbance	Work & other activities	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		No decline		Low Impact: 5
		Stresses Species disturbance
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Ammophila arenaria	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		No decline		Low Impact: 4
		Stresses Ecosystem degradation
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Bos taurus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		No decline		Low Impact: 4
		Stresses Ecosystem degradation
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Felis catus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		No decline		Low Impact: 4
		Stresses Reduced reproductive success, Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Ovis aries	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		No decline		Low Impact: 4
		Stresses Ecosystem degradation
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Rattus norvegicus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		No decline		Low Impact: 5
		Stresses Reduced reproductive success
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Rattus rattus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		No decline		Low Impact: 5
		Stresses Reduced reproductive success
Invasive and other problematic species, genes & diseases	Problematic native species/diseases - Gallirallus australis	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		No decline		Low Impact: 5
		Stresses Species mortality

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Recommended citation
BirdLife International (2024) Species factsheet: Chatham Islands Oystercatcher Haematopus chathamensis. Downloaded from https://datazone.birdlife.org/species/factsheet/chatham-islands-oystercatcher-haematopus-chathamensis on 23/11/2024.
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 23/11/2024.